Front. Plant Sci.Frontiers in Plant ScienceFront. Plant Sci.1664-462XFrontiers Media S.A.10.3389/fpls.2022.754232Plant ScienceOriginal ResearchNitrogen and Chemical Control Management Improve Yield and Quality in High-Density Planting of Maize by Promoting Root-Bleeding Sap and Nutrient AbsorptionLiuXiaoming1ZhangLiguo2YuYang3QianChunrong3LiCongfeng4WeiShi1LiCaifeng1*GuWanrong1*1College of Agriculture, Northeast Agricultural University, Harbin, China2Institute of Maize Research, Heilongjiang Academy of Agricultural Sciences, Harbin, China3Institute of Crop Cultivation and Tillage, Heilongjiang Academy of Agricultural Sciences, Harbin, China4Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing, China
Edited by: Ioannis Tokatlidis, Democritus University of Thrace, Greece
Reviewed by: Mingcai Zhang, China Agricultural University, China; Dalei Lu, Yangzhou University, China
*Correspondence: Caifeng Li licaifeng@neau.edu.cnWanrong Gu wanronggu@neau.edu.cn
This article was submitted to Crop and Product Physiology, a section of the journal Frontiers in Plant Science
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High-density planting aggravates competition among plants and has a negative impact on plant growth and productivity. Nitrogen application and chemical control can improve plant growth and increase grain yield in high-density planting. Our experiment explored the effects of nitrogen fertilizer and plant growth regulators on maize root-bleeding sap, phosphorus (P) and potassium (K) accumulation and translocation, and grain yield and quality in high-density planting. We established a field study during the 2017 and 2018 growing seasons, with three nitrogen levels of N100 (100 kg ha−1), N200 (200 kg ha−1), and N300 (300 kg ha−1) at high-density planting (90,000 plants ha−1), and applied Yuhuangjin (a plant growth regulator mixture of 3% DTA-6 and 27% ethephon) at the 7th leaf. Our results showed that N200 application combined with chemical control could regulate amino acid and mineral nutrient concentration delivery rates in root-bleeding sap and improve its sap rate. Also, the treated plant exhibited higher P and K uptake and translocation ability. Furthermore, chemical control and N200 treatment maintained a high level of ribulose-1,5-bisphosphate carboxylase (RuBPCase), phosphoenolpyruvate carboxylase (PEPCase), nitrate reductase (NR), and glutamine synthetase (GS) enzymatic activities in leaves. In addition, plant growth regulator and nitrogen application improved the enzymatic activities of GS, glutamate dehydrogenase (GDH), and glutamic pyruvic transaminase (GPT) and the contents of crude protein, lysine, sucrose, and soluble sugar in grain and ultimately increased maize yield. This study suggests that N200 application in combination with chemical control promotes root vitality and nutrient accumulation and could improve grain yield and quality in high-density planting.
nitrogen fertilizerchemical controlroot bleeding sapnutrient absorptionmaize2016YFD0300103CARS-02-12National Key Research and Development Program of China10.13039/501100012166National Modern Agriculture Industry Technology System10.13039/501100015336Introduction
The root is an essential absorption system, and its function is to maintain the supply of nutrients and soil moisture for crop growth and development (Xu et al., 2009; Fan et al., 2021). The root system of crops greatly influences the above-ground growth and biomass yield, which play an important role in yield formation (Yang et al., 2004; Chen et al., 2022). The capacity for nutrient and soil moisture uptake by crops is directly influenced by root development and root activity strength (Li et al., 2019). Well-developed root systems are always accompanied by vigorous above-ground growth and high yields. Root-bleeding sap is a sign of root pressure, and its change is consistent with root activity (Xu et al., 2016). The root-bleeding sap is directly correlated to the uptake of nutrients and water and reflects the root system's potential for plant growth and root activity (Ansari et al., 2004; Noguchi et al., 2005). The concentration of nutrients in root-bleeding sap represents the nutritional status and reflects root absorption and translocation rates in crops (Noguchi et al., 2005; Nishanth and Biswas, 2008). Hence, an appropriate rate of root-bleeding sap is vital to optimizing maize yield and directly influencing maize growth and development.
Nutrient absorption and translocation in crops are the physiological basis for dry matter accumulation and yield formation, influencing crop growth and development (Wu et al., 2018; Li et al., 2021). The difference in biomass yield is closely correlated to the plant's nutrient uptake and utilization characteristics. It is generally believed that obtaining a higher yield requires crops to absorb a large amount of nutrients from the soil (Wu et al., 2015; Zhan et al., 2016). Phosphorus promotes carbohydrate and starch synthesis in stems and leaves and increases the nutrient transport to the grains, thereby improving grain weight and quality (Wang and Ning, 2019). Potassium can stimulate the synthesis and transport of carbohydrates and promote the growth of maize ear (Shahzad et al., 2017). Phosphorus and potassium are nutrient elements in great demand for maize. Adequate P and K supply promotes root development and dry matter accumulation and enhances maize's resistance to stress (Xie et al., 2011; Iqbal et al., 2020). Furthermore, maize's adequate P and K contents promote the grain development process and help in obtaining a relatively high grain number per ear and weight (Liu et al., 2011). Therefore, the absorption and translocation of P and K play an important role in maize growth and yield potential in the process of yield formation.
Maize (Zea mays L.) is one of the most essential cereal feeds worldwide and occupies a prominent place in global food security and sustainable development (Palacios-Rojas et al., 2020). Since the mid-1990s, with the improvement of the economy and dietary structure in China, the consumption of animal-derived foods, such as meat, milk, and eggs, has increased, which rapidly increased the demand for maize. Maize is the most widely cultivated crop in China, and its production reflects people's need (Liu S. Q. et al., 2021). Northeast China is a major maize producing region, and its planting area and yield account for 31 and 34%, respectively, of the total maize production in China (Liu and Ye, 2020). The current maize planting density in Northeast China is relatively low, resulting in fewer grain yields (Luo et al., 2020). Maize yield in this region has only reached 50% of its yield potential, which offers an excellent opportunity for increasing yield. It is generally accepted that relying on high-density planting to enhance population productivity is one of the most important measures to increase yield potential (Tang et al., 2018). However, high-density planting increases resource competition among maize plants, leading to a decline in individual plant productivity and negatively affecting yield potential (Rossini et al., 2011). This inevitably intensifies the competition betwen the root systems as it is an important organ for maize to obtain environmental resources. Increased planting density leads to decreased row spacing, resulting in increased nutrients, water, and space competition between maize plants. It also severely limits the spatial distribution of the root system and restricts the capacity of nutrient absorption and utilization, ultimately leading to a decline in root quality and grain yield (Gao et al., 2021). According to Shao et al. (2018), root length and root number per plant decrease significantly as planting density increases. The increase in planting density not only inhibits the growth, quantity, and quality of maize roots but also reduces nutrient absorption and translocation in maize (Li et al., 2020; Gao et al., 2021). Therefore, enhancing root physiological characteristics and nutrient absorption capacity in high-density planting for optimal maize growth and high yield has become a significant problem in maize production.
A sufficient supply of nutrients has become essential to achieving high crop yield under high-density planting. Nitrogen, one of the most critical nutrient elements during the maize growing period, greatly affects the root morphological characteristics and physiological activities (Li et al., 2019). It is reported that nitrogen application could significantly increase the total length, volume, and effective absorption area of roots, thereby improving root nutrient absorption capacity (Liu et al., 2017). Furthermore, nitrogen fertilizer plays an important role in the crop's nutrient accumulation and transport activity. Appropriate nitrogen application can increase the grain yield by increasing nutrient accumulation post-anthesis and nutrient translocation to grains (Zhang et al., 2021). Chemical control is one of the efficient cultivation measures, which regulates plant growth and development process, enhances nutrient utilization capacity and environment adaptability, and improves grain yield and quality (Hutsch and Schubert, 2017; Stutts et al., 2018). The application of plant growth regulators can enhance the capacity of crops to absorb nutrients and soil moisture by improving their root growth characteristics (Lin et al., 2019; Nawaz et al., 2020). Yuhuangjin is a type of plant growth regulator that is widely used in maize production in China. The main component is ethephon and diethyl aminoethyl hexanoate DTA-6, which improves plant growth, enhances lodging resistance, optimizes yield component, and increases yield (Zhang et al., 2014). Therefore, we hypothesized that chemical control and nitrogen fertilizer could improve root growth, increase nutrient absorption, and promote yield formation in maize. To prove this hypothesis, this study investigated the effects of chemical control and nitrogen fertilizers on root-bleeding sap characteristics, P and K accumulation and translocation, and grain yield and quality in high plant density. This study aimed to provide a theoretical basis for increasing maize yield and quality in future high-density planting management practices.
Materials and MethodsSite Description
The experiment was conducted from April to September in 2017 and 2018 at the experimental station of Northeast Agricultural University, Harbin, Heilongjiang Province, China (126°54′E, 45°46′N). The region has a typical warm temperate monsoon climate with an annual mean temperature of 4.5°C and annual mean precipitation of 569 mm. The crop rotation system is continuous maize cropping, and the soil type at the experimental site is chernozem. The physical and chemical characteristics of tillage layer soil were pH 6.85; organic matter 25.25 g kg−1; total nitrogen 1.70 g kg−1; available phosphorus 65.34 mg kg−1; and available potassium 179.35 mg kg−1. Temperature and rainfall during the growth stage of spring maize in 2017 and 2018 are shown in Figure 1.
Monthly rainfall distribution and mean temperature during spring maize growing stage in 2017 and 2018.
Experimental Design and Field Management
The experiment was laid out as a split-plot design with three replicates. Two chemical treatments (Y, Yuhuangjin; Control (CK), water) were used as the main plots, and three nitrogen fertilizer levels were used as the subplots: 100 kg ha−1 (N100), 200 kg ha−1 (N200), and 300 kg ha−1 (N300). The plant growth regulator Yuhuangjin (the mixture of 3% DTA-6 and 27% ethephon) was provided by Haolun Co., Ltd., Fujian, China. About 0.83 mL L−1 of Yuhuangjin solution was sprayed on the foliar surface at the seven-leaf stage in the afternoons between 16:00 and 18:00 h. Yuhuangjin was applied at 450 L ha−1, and the same volume of water was applied to the control plants. Spring maize Longyu 365, a high-yielding variety in Heilongjiang province, was sown manually at 90,000 plants ha−1 on 30 April and harvested on 25 September in 2017 and 2018. The size of each plot was 5.2 × 8 m with 0.65 m row spacing. All plots were supplied with 100 kg ha−1 P2O5 and 100 kg ha−1 K2O. The total phosphorus and potassium and half of the nitrogen (urea, 46% N) were applied at the sowing. The balance half of the nitrogen was applied at the jointing stage. No irrigation was applied during the maize growing season. Pests, weeds, and diseases were controlled in a timely manner, and tillage management was conducted according to local farmer management.
Collection of Root-Bleeding Sap
Three representative plants were sampled from each plot at jointing, tasseling, early grain filling, and milking stages. The plants were cut at the third basal internode using lopping shears at 19:00 h. The incision was washed with distilled water, covered with a centrifuge tube containing degreasing cotton (≈2/3 of the centrifugal tube volume), and secured with plastic wrap to collect the root-bleeding sap. The centrifuge tubes were collected at 6:00 h the next day, and the weight was measured (Wang H. et al., 2019). The bleeding sap rate was calculated as the weight increase of the centrifuge tube per hour per plant (g h−1 plant−1).
Analysis of Root-Bleeding Sap Components
Concentrations of serine (Ser), glutamic acid (Glu), glycine (Gly), alanine (Ala), valine (Val), lysine (Lys), methionine (Met), arginine (Arg), and leucine (Leu) in the root-bleeding sap were measured using high-performance liquid chromatography with pre-column derivatization (Li H. W. et al., 2012). Concentrations of P, K, Ca, Mg, Fe and Zn were measured using inductively coupled plasma optical emission spectroscopy (ICP-AES, OPTIMA 3300 DV, Perkin-Elmer, USA).
Determination of Photosynthesis and N Metabolism Enzyme Activities in Ear Leaf
Approximately 0.5 g of fresh ear leaf was homogenized with an extraction medium (pH 8.4, 0.1 mmol L−1 Tricine-HCl, 10 mmol L−1 MgCl2, 1 mmol L−1 EDTA, 7 mmol L−1 β-mercaptoethanol, 5% glycerol (v/v) and 1% PVP) in an ice-cold mortar with a pestle. The homogenate was centrifuged at 15,000 × g for 10 min at 4°C. The supernatant was used for the RuBPCase and PEPCase assays following the methods of Lilley and Walker (1974) and Arnozis et al. (1988), respectively.
Approximately 1 g of fresh ear leaf was homogenized with the extraction medium (pH 7.5, 0.1 mol L−1 Tris-NaOH, 5 mmol L−1 MgCl2 and 1 mmol L−1 DTT) precooled in ice, followed by centrifugation at 20,000 × g for 15 min at 4°C. The supernatant was used for enzyme assays. Nitrate reductase (NR) activity was determined by the method of Lewis et al. (1982), and glutamine synthetase (GS) activity was determined by the method of Canovas et al. (1991).
Determination of N Metabolism Enzyme Activity in Grain
Three ears per plot were randomly sampled at 10, 15, 20, 25, and 30 days after silking. Approximately 100 grains in the middle of the ear were collected and frozen in liquid N2 and stored at −80°C for enzyme assays. About 0.5 g of frozen grain was homogenized with phosphate buffer (pH 7.2), followed by centrifugation at 10,000 × g for 20 min. The supernatant was used for enzyme assays of GS and glutamate dehydrogenase (NADH-GDH and NAD-GDH) activities following the method of Wang et al. (2016).
About 0.2 g of frozen grain was homogenized with Tris-HCl extraction buffer (pH 7.2, 50 mmol L−1 trihydroxymethyl aminomethane) precooled in ice, followed by centrifugation at 20,000 × g for 20 min at 4°C. The supernatant was used for the glutamic-pyruvic transaminase (GPT) assay following the method of Wang et al. (2016).
Analysis of Nutrients Concentration in Grain
The grains were sampled and oven-dried at 40°C for 24 h and ground to powder at harvest. The resulting grain powder was passed through a 0.25 mm mesh and stored at 4°C for analysis. Crude protein in grain was assayed by the micro-Kjeldahl method described by the Association of Official Agricultural Chemists AOAC (1975). Crude fat was assayed following the method of AOAC (1984). Starch was assayed by the colorimetric method described by Boros et al. (2004). Lysine was assayed using the colorimetric method described by Reddy et al. (2013).
Approximately 1 g of fresh grain was ground in a mortar with liquid nitrogen, and 10 ml of distilled water was added to the sample and incubated in boiling water for 60 min. The mixture was centrifuged at 12,000 × g for 20 min at 4°C. The supernatant was used for soluble sugar and sucrose measures. Soluble sugar was measured by the anthrone colorimetric method described by Liu et al. (2007). Sucrose was measured by the anthrone method described by Van (1968).
Determination of P and K Accumulation and Translocation
Three plants were sampled from each plot and separated into stems, leaves, and grains during harvest. The samples were dried in an oven at 105°C for 30 min and afterward at 80°C to a constant weight. Dried samples were weighed and ground to pass through a 1-mm sieve and digested by an H2SO4-H2O2 mixture (Wolf, 1982). The P concentration was determined by the ammonium molybdate ascorbic acid reduction method (Murphy and Riley, 1962). The K concentration was determined by the flame photometer method. Nutrient (P or K) accumulation was calculated based on the sum of the dry matter and P or K concentration in plant parts.
Nutrient (P or K) translocation amount of pre-silking (TAE, kg ha−1) = vegetative organ nutrient (P or K) content at silking—vegetative organ nutrient (P or K) content at maturity.
Nutrient (P or K) translocation rate of pre-silking (TRE, %) = TAE/vegetative organ nutrient (P or K) content at silking × 100.
Contribution rate of nutrient (P or K) translocation amount of pre-silking (CTAE, %) = TAE/grain nutrient (P or K) content at maturity × 100.
Nutrient (P or K) accumulation amount of post-silking (AAT, kg ha−1) = plant nutrient (P or K) content at maturity – plant nutrient (P or K) content at silking.
Contribution rate of nutrient (P or K) accumulation amount of post-silking (CAAT, %) = AAT/grain nutrient (P or K) content at maturity × 100.
Statistical Analysis
The data were summarized to calculate the mean value and standard error (SE). The mean value was compared by the analysis of variance (ANOVA) to analyze the significant differences between samples with different treatments (P < 0.05). All statistical analyses were performed by SPSS 19.0 procedures (SPSS Inc., Chicago, IL, USA). Microsoft Excel 2010 was used to draw tables.
ResultsRoot-Bleeding Sap and Nutrients Composition Delivery Rate
The chemical control and nitrogen fertilization exhibited a significant influence on the rate of root-bleeding sap during the maize growing period in 2017 and 2018 (Table 1). At the same N levels, chemical control increased root-bleeding sap rate with an average augment of 12.26, 15.99, 14.21, 8.97, and 18.46% from the jointing stage to the maturing stage compared with water treatment. Root-bleeding sap rate first increased and then decreased with the increase of nitrogen application under the same chemical treatment, and the highest value was measured under N200 treatment. The results show that a high N level inhibited the increase of root-bleeding. An analysis of the synthetic effect revealed that the highest root-bleeding sap rate was obtained from N200 application under chemical control.
Effects of chemical control and nitrogen fertilizers on root-bleeding sap rate (μg h−1 plant−1) during the maize growing period in 2017 and 2018.
Year
Treatment
Jointing stage
Tasseling stage
Early filling stage
Milk stage
Maturing stage
2017
N100+CK
1.42d
1.75d
1.99d
2.75cd
0.76d
N200+CK
1.56c
1.96c
2.17c
2.79c
0.86c
N300+CK
1.47d
1.85cd
2.08cd
2.71d
0.82c
N100+Y
1.58c
2.07b
2.31b
2.99b
0.92b
N200+Y
1.77a
2.26a
2.49a
3.10a
1.03a
N300+Y
1.67b
2.20a
2.38b
2.98b
0.98a
2018
N100+CK
1.36c
1.65c
2.03d
2.50c
0.70c
N200+CK
1.49b
1.87b
2.24bc
2.64b
0.80b
N300+CK
1.47b
1.75c
2.15c
2.56c
0.77b
N100+Y
1.53b
1.95b
2.32b
2.70b
0.82b
N200+Y
1.67a
2.10a
2.50a
2.85a
0.91a
N300+Y
1.61ab
1.98b
2.45a
2.77ab
0.90a
N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under chemical control, respectively. Means within a column for the same year followed by the different letters indicate a significant difference at P < 0.05.
The delivery rate of free amino acids in root-bleeding sap was influenced by chemical control and nitrogen fertilizer, which decreased after the jointing stage in maize (Table 2). At the same N levels, chemical control increased the delivery rate of Ser, Glu, Gly, Ala, Val, Lys, Met, Arg, and Leu with an average augment of ≈11.45–19.04% than water treatment at the tasseling stage in both years, which was consistent at different growth stages. Under the same chemical treatment, the free amino acid delivery rate obtained the highest value under N200 treatment, which showed an average augment of 6.54–15.04% and of 4.15–6.97% compared with N100 and N300 nitrogen rates in both years. From the analysis of synthetic effect, the delivery rate of free amino acids in root-bleeding sap was optimal in N200 application under chemical control.
Effects of chemical control and nitrogen fertilizers on amino acids concentrations (μg h−1 plant−1) in root-bleeding sap during the maize growing period in 2017 and 2018.
Growth stage
Treatment
2017
2018
Ser
Glu
Gly
Ala
Val
Lys
Met
Arg
Leu
Ser
Glu
Gly
Ala
Val
Lys
Met
Arg
Leu
Jointing stage
N100+CK
479.35d
284.97d
1.34d
13.91d
57.59d
92.92e
5.46c
85.15d
17.88e
468.15d
279.68d
1.27d
13.39d
54.58d
89.06d
4.95d
83.29d
16.63d
N200+CK
506.23c
310.99c
1.44c
15.38c
62.68bc
101.63cd
5.87b
95.36b
19.47cd
495.77bc
303.61c
1.38c
14.56bc
59.63bc
96.43c
5.26c
90.14c
18.15c
N300+CK
496.70cd
307.06c
1.40cd
14.26d
59.52cd
96.61de
5.30c
89.93c
18.36de
482.89cd
295.27c
1.31d
14.07c
57.71c
91.45d
5.13cd
87.15cd
17.36cd
N100+Y
539.22b
334.64b
1.56b
16.01bc
66.32b
105.60bc
6.00b
99.17b
20.86bc
516.74b
327.46b
1.45b
15.22b
62.46b
101.54b
5.59b
94.82b
19.43b
N200+Y
568.89a
359.67a
1.65a
17.53a
71.86a
116.71a
6.48a
105.17a
22.92a
543.23a
346.84a
1.57a
16.24a
66.87a
109.18a
6.11a
100.48a
21.32a
N300+Y
544.89ab
339.95b
1.56b
16.51ab
67.04ab
108.43b
6.17ab
99.18b
21.74ab
525.28ab
335.29ab
1.49b
15.48ab
63.52b
104.77ab
5.78b
96.57ab
20.08b
Tasseling stage
N100+CK
377.14d
227.46d
1.13d
11.69d
49.83d
73.17d
4.37d
74.47e
13.91c
365.26d
212.76d
1.04d
11.24d
45.62d
70.33d
4.05d
69.02d
13.34d
N200+CK
403.18c
242.68c
1.22c
12.64c
53.64cd
82.09c
4.72c
80.27cd
15.97b
386.53c
230.53c
1.12c
12.29c
50.57c
78.05c
4.48bc
75.24bc
15.36b
N300+CK
383.42d
226.22d
1.13d
11.74d
49.96d
73.17d
4.28d
76.75de
14.39c
370.72cd
218.42d
1.07cd
11.73cd
47.45d
72.48d
4.29c
72.65c
14.21c
N100+Y
424.42b
255.84b
1.26bc
13.55b
55.78bc
86.38b
5.07b
83.34bc
17.40a
409.58b
245.84b
1.19b
13.26b
52.63c
82.09b
4.66b
78.73b
16.02b
N200+Y
453.42a
278.94a
1.36a
14.70a
61.24a
94.45a
5.33a
89.53a
18.28a
435.21a
264.39a
1.30a
14.02a
59.29a
88.84a
5.03a
85.82a
17.27a
N300+Y
438.67ab
265.77b
1.31ab
14.05ab
58.21ab
89.34b
4.97b
85.13b
17.02ab
422.47ab
254.56ab
1.23b
13.68ab
56.34b
84.27b
4.83ab
80.56b
16.29b
Early filling stage
N100+CK
318.24c
173.80c
0.71c
9.88e
44.29c
61.05e
3.99d
66.60c
7.71c
302.85c
169.82d
0.69d
9.43d
40.03d
60.61d
3.68d
62.14d
7.06d
N200+CK
342.15bc
197.32b
0.77b
11.05cd
48.62b
69.74c
4.31c
72.01b
9.14b
333.52b
185.35c
0.74c
10.24c
44.67c
66.44c
4.04bc
70.47b
8.23c
N300+CK
329.59bc
184.54c
0.71c
10.36de
44.05c
65.30d
4.01d
66.90c
7.75c
315.62c
177.47cd
0.70d
9.77cd
42.98c
63.25d
3.89c
66.44c
7.32d
N100+Y
367.79ab
209.01b
0.88a
11.59bc
51.53a
72.88c
4.42bc
74.67b
9.47b
345.07b
198.09b
0.83b
10.88b
47.44b
72.96b
4.21b
73.92ab
8.98b
N200+Y
383.05a
230.34a
0.90a
12.86a
54.37a
83.57a
4.90a
79.70a
10.80a
367.26a
221.53a
0.88a
12.02a
51.85a
78.37a
4.65a
77.25a
9.75a
N300+Y
365.08ab
222.42a
0.87a
12.25ab
52.57a
77.77b
4.61b
78.99a
9.84ab
351.63ab
207.04b
0.85ab
11.34b
48.62b
76.72a
4.36b
75.34a
9.52a
Milk stage
N100+CK
147.14d
108.01e
0.50e
6.00d
23.39d
39.69d
2.02cd
29.19c
3.86c
148.53d
110.84d
0.55e
5.89d
22.08e
39.82d
1.78d
27.14e
4.14e
N200+CK
169.19c
123.96cd
0.69c
7.08c
29.31b
47.88c
2.17c
36.59b
4.99b
163.29c
120.06c
0.64c
6.78c
25.31c
45.47c
1.92c
32.19c
5.05c
N300+CK
162.04c
119.80de
0.63d
6.68c
26.81c
44.55c
1.95d
31.15c
4.25c
157.24c
114.26d
0.59d
6.14d
23.86d
41.19d
1.83cd
30.18d
4.63d
N100+Y
183.75b
134.16bc
0.71bc
8.04b
30.24b
52.28b
2.51b
39.02b
5.33b
179.08b
130.32b
0.70b
7.66b
28.75b
50.95b
2.27b
34.63b
5.51b
N200+Y
209.35a
148.63a
0.82a
8.89a
33.84a
60.34a
2.77a
45.58a
6.46a
192.41a
142.89a
0.76a
8.25a
31.87a
56.21a
2.49a
40.52a
6.11a
N300+Y
190.15b
144.44ab
0.75b
8.14b
32.59a
55.58b
2.46b
39.37b
6.07a
184.47ab
136.93a
0.72b
7.62b
29.24b
53.02b
2.35b
35.79b
5.78b
N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under chemical control, respectively. Means within a column for the same growth stage followed by the different letters indicate a significant difference at P < 0.05.
A similar change trend was observed in the mineral nutrient concentrations in bleeding sap during the maize growing period in 2017 and 2018 (Table 3). The mineral nutrient concentrations were significantly affected by chemical control and nitrogen fertilizer. The delivery rate of mineral nutrients first increased and then decreased with the increase of nitrogen application under the same chemical treatment. At the same N levels, chemical control obviously increased the delivery rate of mineral nutrients at different growth stages. From the analysis of synthetic effect, the delivery rate of mineral nutrients in root-bleeding sap was optimal in N200 application under chemical control.
Effects of chemical control and nitrogen fertilizers on mineral nutrients concentrations (μg h−1 plant−1) in root-bleeding sap during the maize growing period in 2017 and 2018.
Growth period
Treatment
2017
2018
Fe
Mn
Cu
Zn
Ca
Mg
Mo
K
P
B
Si
Fe
Mn
Cu
Zn
Ca
Mg
Mo
K
P
B
Si
Jointing stage
N100+CK
1.62d
4.37d
0.046c
10.93c
318.23c
299.46cd
0.057d
1747.53e
113.76c
1.14cd
50.45c
1.55d
4.15d
0.043d
10.08d
302.98d
259.46d
0.051d
1682.49d
104.07d
1.01d
44.37d
N200+CK
1.80c
4.75c
0.050bc
11.55bc
347.74b
314.76bc
0.064c
1920.50cd
123.26bc
1.21c
53.66b
1.79c
4.62c
0.049c
11.39bc
332.63bc
290.56c
0.058c
1801.37c
115.48c
1.11c
48.62c
N300+CK
1.87c
4.80c
0.051bc
11.66b
339.26b
284.37d
0.055d
1833.47de
118.52c
1.07d
53.96b
1.77c
4.51c
0.047c
10.92c
320.06c
278.85c
0.056c
1754.88cd
110.75c
1.04d
45.89d
N100+Y
2.06b
5.22b
0.056ab
12.43a
350.32b
332.33ab
0.070b
1998.30bc
134.01ab
1.37b
55.22b
1.96b
5.07b
0.053b
11.85b
346.45b
307.82b
0.064b
1895.03b
122.62b
1.26b
51.84b
N200+Y
2.17a
5.50ab
0.060a
12.82a
383.02a
345.53a
0.075a
2124.70a
142.78a
1.49a
58.39a
2.12a
5.43a
0.058a
12.77a
370.82a
333.13a
0.071a
2093.27a
136.59a
1.39a
56.25a
N300+Y
2.20a
5.57a
0.062a
13.05a
374.64a
328.45ab
0.068b
2087.37ab
138.60a
1.37b
58.97a
2.08a
5.39a
0.057a
12.64a
362.17ab
316.28b
0.066b
1956.36b
127.94b
1.28b
53.08b
Tasseling stage
N100+CK
0.49d
4.29d
0.063e
9.26d
300.46e
292.80d
0.062d
1538.44d
110.49c
1.09d
44.41d
0.52e
4.05d
0.58d
8.98d
282.94d
267.25d
0.059d
1496.05d
98.72c
1.00d
42.67d
N200+CK
0.65c
4.73c
0.069d
9.97c
320.38cd
310.57bc
0.075c
1671.27c
118.37bc
1.18c
46.93c
0.62c
4.52bc
0.64c
9.53c
303.39c
285.03bc
0.069c
1602.88c
109.46b
1.10c
45.42c
N300+CK
0.71c
4.90c
0.071cd
9.92c
307.73de
297.60cd
0.071c
1608.97cd
110.54c
1.09d
45.82cd
0.58d
4.37c
0.62c
9.39cd
287.33d
276.29cd
0.066c
1579.14c
102.78c
1.06c
44.68cd
N100+Y
0.77b
5.04bc
0.074bc
10.93b
344.16ab
328.07a
0.086b
1760.22b
123.53b
1.28b
49.99b
0.74b
4.68b
0.69b
10.21b
320.17b
297.42b
0.077b
1693.49b
112.53b
1.17b
48.39b
N200+Y
0.90a
5.40ab
0.078ab
11.48a
359.44a
335.49a
0.094a
1874.43a
135.76a
1.39a
53.39a
0.86a
5.23a
0.76a
11.15a
343.48a
325.28a
0.086a
1819.53a
125.85a
1.31a
52.05a
N300+Y
0.92a
5.55a
0.079a
11.74a
335.66bc
323.83ab
0.088b
1822.54ab
126.88ab
1.29b
54.78a
0.83a
5.06a
0.74a
10.92a
325.84b
316.17a
0.084a
1786.67a
117.09b
1.22b
50.83a
Early filling stage
N100+CK
1.55c
5.87d
0.039c
4.85d
456.81c
361.88d
0.095e
1036.46c
143.64c
0.96d
25.91d
1.47d
5.79d
0.34d
5.17d
450.24e
333.92d
0.088d
1087.65d
128.95d
0.90d
22.07e
N200+CK
1.68b
6.65c
0.045bc
5.83c
486.52b
377.28c
0.103cd
1251.03b
155.73bc
1.07c
28.92c
1.63c
6.27c
0.38c
5.59c
477.91cd
354.38c
0.096c
1174.59c
141.63c
0.99c
28.58c
N300+CK
1.73b
6.75c
0.044bc
5.95c
475.80b
358.97d
0.098de
1167.03b
151.38bc
1.03c
30.43c
1.59c
6.05cd
0.37c
5.42cd
468.17de
340.03cd
0.093c
1106.27d
134.07d
0.93d
24.94d
N100+Y
1.77b
7.30b
0.044bc
6.73b
524.52a
392.79b
0.109bc
1248.27b
163.15ab
1.16b
34.17b
1.75b
6.91b
0.41b
6.58b
496.87bc
377.49b
0.104b
1256.76b
152.19b
1.06b
32.31b
N200+Y
1.94a
7.98a
0.050ab
7.12a
537.46a
411.63a
0.122a
1396.47a
173.51a
1.22a
37.13a
1.85a
7.64a
0.46a
6.94a
525.75a
403.67a
0.115a
1362.09a
169.72a
1.14a
35.85a
N300+Y
1.98a
7.91a
0.051a
7.28a
525.22a
399.12ab
0.113b
1380.29a
165.35ab
1.16b
37.88a
1.81ab
7.38a
0.45a
6.85ab
520.33ab
396.54a
0.108b
1283.15b
157.94b
1.12a
33.67b
Milk stage
N100+CK
0.37d
1.26d
0.021c
2.64d
117.79c
20.18d
0.067d
481.15d
41.52d
0.17d
15.89c
0.35d
1.31d
0.23d
3.42d
113.06d
24.31e
0.065d
493.17d
42.35d
0.20d
13.77d
N200+CK
0.46c
1.66c
0.026bc
3.26c
130.83b
30.82c
0.076c
560.38c
48.58c
0.25c
16.56c
0.43c
1.62c
0.26c
3.89c
126.74c
31.38d
0.073c
545.39c
46.88c
0.24c
15.85c
N300+CK
0.48c
1.80bc
0.028bc
3.54c
129.95b
32.04c
0.069d
539.03c
46.93cd
0.25c
17.03c
0.41c
1.57c
0.24d
3.57d
118.38d
25.47e
0.068d
516.28d
44.27d
0.21d
14.42d
N100+Y
0.59b
1.92b
0.026b
4.31b
155.06a
38.73b
0.085b
622.59b
57.07b
033a
20.97b
0.56b
1.85b
0.30b
4.36b
139.02b
36.79c
0.079b
603.05b
52.53b
0.29b
20.51b
N200+Y
0.68a
2.33a
0.031ab
4.65ab
167.65a
49.55a
0.091a
712.55a
64.38a
0.35a
24.25a
0.64a
2.26a
0.33a
4.73a
158.85a
45.32a
0.088a
684.91a
57.96a
0.32a
22.69a
N300+Y
0.69a
2.44a
0.034a
4.97a
162.60a
46.57a
0.089ab
676.37a
58.75ab
0.27b
25.50a
0.62a
2.18a
0.31b
4.48b
152.37a
42.68b
0.085a
627.56b
54.19b
0.30b
21.18b
N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under chemical control, respectively. Means within a column for the same growth stage followed by the different letters indicate a significant difference at P < 0.05.
P and K Accumulation and Translocation
Changes between the P and K accumulation in maize plants followed similar trends; both P and K increased gradually from the jointing stage to thewe maturing stage (Table 4). Chemical control and N fertilization level exhibited a marked influence on P and K accumulation amount during the maize growing period in both years. At the same N levels, chemical control increased P accumulation amount with an average augment of 4.48, 15.34, 22.07, 23.52, and 24.32% and K accumulation amount with an average augment of 6.30, 14.43, 17.60, 18.94, and 19.55% from the jointing stage to the maturing stage in 2017 and 2018. Under both water and chemical control conditions, P and K accumulation amount increased by increasing the N level from N100 to N300, but there was no significant difference between N200 and N300 treatments in both years. Compared with N100, N200 and N300 treatments increased P and K accumulation amount with an average augment of 22.41 and 24.26%, respectively.
Effects of chemical control and nitrogen fertilizers on P and K accumulation (kg ha−1) during the maize growing period in 2017 and 2018.
Nutrient
Treatment
2017
2018
Jointing stage
Tasseling stage
Early filling stage
Milk stage
Maturing stage
Jointing stage
Tasseling stage
Early filling stage
Milk stage
Maturing stage
P
N100+CK
9.88c
22.02c
26.96c
29.08d
30.31d
9.55c
20.78c
25.81c
27.82c
28.95c
N200+CK
10.26bc
25.55b
32.52b
36.78bc
39.09bc
10.02bc
23.74b
30.64b
34.35b
36.37b
N300+CK
10.45b
26.32b
33.57b
37.83b
39.85b
10.38b
24.66b
31.89b
35.77b
37.81b
N100+Y
10.20b
25.48b
32.78b
36.03c
38.01c
10.04b
23.62b
31.16b
34.29b
36.13b
N200+Y
10.76a
29.85a
40.08a
45.65a
48.64a
10.61a
27.81a
38.27a
43.43a
46.18a
N300+Y
10.96a
30.10a
40.37a
45.86a
48.65a
10.68a
28.17a
38.75a
43.77a
46.38a
K
N100+CK
37.0.88c
72.56c
93.49c
105.01d
114.71d
37.49c
70.15c
89.64c
100.87c
109.61c
N200+CK
39.53bc
81.61b
107.64b
123.89bc
137.60bc
39.36bc
77.42b
101.27b
114.92b
125.88b
N300+CK
41.21b
85.18b
112.92b
129.75c
143.62c
39.91b
78.79b
103.25b
117.38b
128.53b
N100+Y
39.95b
82.01b
107.51b
122.60b
134.81b
38.67bc
76.04b
99.21b
112.45b
123.04b
N200+Y
42.89a
96.47a
130.70a
152.04a
169.10a
42.52a
89.88a
120.96a
139.24a
153.72a
N300+Y
43.05a
97.22a
133.48a
154.80a
172.73a
43.13a
91.37a
123.52a
141.91a
156.29a
N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under chemical control, respectively. Means within a column for the same nutrient followed by the different letters indicate a significant difference at P < 0.05.
Changes in the proportion of P and K accumulation in maize plants during various growth stages seemed to follow similar trends (Table 5). Proportions of P and K accumulation had a higher value at emerging (VE) —jointing (JT) and JT—tasseling (TS) stages and decreased gradually from TS—early-filling (EF) to milk (MK)—maturing (MT) stage. The proportions of P and K accumulation were significantly affected by chemical control and N fertilization level. At the same N levels, chemical control increased the proportions of P and K accumulation at TS-EF, EF-MK, and MK-MT stages, while the proportions decreased at the VE-JT stage and remained relatively constant at the JT-TS stage in 2017 and 2018. Under both water and chemical control conditions, N supply significantly increased the proportions of P and K accumulation. However, there was no significant difference between N200 and N300 treatments, and the highest proportions were obtained under N200 treatment at EF-MK and MK-MT stages in both years.
Effects of chemical control and nitrogen fertilizers on the proportion of P and K accumulation (%) at different maize growing stages in 2017 and 2018.
Nutrient
Treatment
2017
2018
VE-JT
JT-TS
TS-EF
EF-MK
MK-MT
VE-JT
JT-TS
TS-EF
EF-MK
MK-MT
P
N100+CK
32.60a
40.04a
16.31d
6.98d
4.07d
32.99a
38.79a
17.37d
6.94d
3.90d
N200+CK
26.25b
39.12a
17.82c
10.91b
5.90b
27.55b
37.72a
18.97c
10.20b
5.55b
N300+CK
26.23b
39.83a
18.19c
10.69b
5.05c
27.45b
37.77a
19.12c
10.26b
5.40b
N100+Y
26.85b
40.19a
19.21b
8.55c
5.21c
27.79b
37.59a
20.87b
8.66c
5.09c
N200+Y
22.12c
39.26a
21.02a
11.46a
6.14a
22.98c
37.25a
22.65a
11.17a
5.96a
N300+Y
22.54c
39.34a
21.11a
11.28a
5.73b
23.03c
37.71a
22.81a
10.82a
5.63b
K
N100+CK
33.02a
30.23a
18.25d
10.04c
8.46d
34.20a
29.80a
17.78c
10.25c
7.97c
N200+CK
28.73b
30.58a
18.92cd
11.81b
9.96c
31.27b
30.24a
18.95b
10.84b
8.71b
N300+CK
28.69b
30.62a
19.31bc
11.72b
9.66c
31.05b
30.25a
19.03b
10.99b
8.68b
N100+Y
29.63b
31.20a
18.92cd
11.19b
9.06b
31.43b
30.37a
18.83b
10.76b
8.61b
N200+Y
25.36c
31.69a
20.24ab
12.62a
10.09a
27.66c
30.81a
20.22a
11.89a
9.42a
N300+Y
25.07c
31.54a
21.12a
12.41a
9.86a
27.60c
30.87a
20.57a
11.77a
9.20a
VE, emerging stage; JT, jointing stage; TS, tasseling stage; EF, Early filling stage; MK, milk stage; MT, maturing stage. N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under chemical control, respectively. Means within a column for the same nutrient followed by the different letters indicate a significant difference at P < 0.05.
Chemical control and nitrogen fertilizer significantly influenced the nutrient (P and K) translocation and contribution, including the vegetative organ nutrient content at the silking stage (VCS), the vegetative organ nutrient content at the maturing stage (VCM), and the grain nutrient content at the maturing stage (GCM), the nutrient translocation amount of pre-silking (TAE), the nutrient translocation rate of pre-silking (TRE), the contribution rate of nutrient translocation amount of pre-silking (CTAE), the nutrient accumulation amount of post-silking (AAT), and the contribution rate of nutrient accumulation amount of post-silking (CAAT) (Table 6). At the same N levels, VCS, VCM, GCM, TAE, AAT, and CAAT of P and K in maize plants under chemical control were markedly higher than those under water treatment. In contrast, TRE and CTAE of P and K in maize plants under chemical control were markedly lower than those under water treatment. Under both water and chemical control conditions, VCS, VCM, GCM, and TAE of P and K in maize plants were significantly increased by increasing N levels; however, TRE and CTAE were decreased. While N supply in general significantly increased AAT and CAAT of P and K in maize plants, there is no significant difference between N200 and N300 treatments, and the highest values were obtained under N200 treatment in both years.
Effects of chemical control and nitrogen fertilizers on maize nutrient (P and K) translocation and contribution during the maize growing period 2017 and 2018.
Nutrient
Treatment
2017
2018
VCS (kg ha−1)
VCM (kg ha−1)
GCM (kg ha−1)
TAE (kg ha−1)
TRE (%)
CTAE (%)
AAT (kg ha−1)
CAAT (%)
VCS (kg ha−1)
VCM (kg ha−1)
GCM (kg ha−1)
TAE (kg ha−1)
TRE (%)
CTAE (%)
AAT (kg ha−1)
CAAT (%)
P
N100+CK
21.19d
7.54e
22.27c
13.64d
64.40a
61.27a
8.62c
38.73d
20.37c
7.03d
21.02c
13.35d
65.51a
63.49a
7.68c
36.51c
N200+CK
26.33c
10.26c
28.63b
16.07c
61.04b
56.13c
12.56b
43.87b
24.60b
9.52bc
25.73b
15.09c
61.32b
58.63b
10.65b
41.37b
N300+CK
27.82b
11.05b
28.80b
16.77b
60.27b
58.24b
12.03b
41.76c
25.49b
9.97b
26.01b
15.52bc
60.90b
59.69b
10.48b
40.31b
N100+Y
26.08c
9.17d
29.13b
16.91b
64.84a
58.05b
12.22b
41.95c
25.10b
9.07c
26.83b
16.03b
63.87a
59.77b
10.79b
40.23b
N200+Y
32.16a
13.50a
34.94a
18.66a
58.01c
53.39d
16.29a
46.61a
31.29a
12.92a
33.24a
18.38a
58.73b
55.29c
14.86a
44.71a
N300+Y
32.24a
13.72a
34.11a
18.52a
57.43c
54.29d
15.59a
45.71a
31.46a
12.89a
33.35a
18.58a
59.04b
55.69c
14.78a
44.31a
K
N100+CK
82.58e
35.07d
78.64e
47.51e
57.53b
60.41a
31.13d
39.59d
79.59d
30.88d
76.73c
48.70c
61.20a
63.48a
28.02d
36.52d
N200+CK
96.39c
44.87b
94.73d
51.51d
53.44d
54.38c
43.21c
45.62b
89.70bc
39.76b
88.12b
49.94bc
55.67b
56.68c
38.18b
43.32b
N300+CK
100.76b
44.26b
103.36b
56.50b
56.08c
54.67bc
46.86b
45.33bc
92.03b
40.56b
89.97b
51.47b
55.93b
57.21c
38.50b
42.79b
N100+Y
91.77d
37.38c
97.43c
54.39c
59.27a
55.82b
43.04c
44.18c
87.11c
35.31c
86.13b
51.80b
59.46a
60.14b
34.33c
39.86c
N200+Y
111.62a
52.11a
118.51a
59.51a
53.31d
50.22d
59.00a
49.78a
103.24a
46.12a
107.60a
57.12a
55.33b
53.08d
50.48a
46.92a
N300+Y
112.83a
51.85a
121.03a
60.98a
54.05c
50.38d
60.05a
49.62a
105.96a
46.89a
109.40a
59.08a
55.75b
54.00d
50.33a
46.00a
VCS, vegetative organ nutrient (P or K) content at silking stage; VCM, vegetative organ nutrient (P or K) content at maturing stage; GCM, grain nutrient (P or K) content at maturing stage; TAE, nutrient (P or K) translocation amount of pre-silking; TRE, nutrient (P or K) translocation rate of pre-silking; CTAE, contribution rate of nutrient (P or K) translocation amount of pre-silking; AAT, nutrient (P or K) accumulation amount of post-silking; and CAAT, contribution rate of nutrient (P or K) accumulation amount of post-silking. N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under Yuhuangjin treatment, respectively. Means within a column for the same nutrient followed by the different letters indicate a significant difference at P < 0.05.
RuBPCase and PEPCase Activities in Leaf
Chemical control and N fertilization level exhibited a marked influence on RuBPCase activity in leaves during the maize growing period in 2017 and 2018 (Figure 2). At the same N levels, chemical control increased RuBPCase activity with an average augment of 12.45, 12.91, 11.03, and 13.02% from the jointing stage to the milk stage in 2017 and 2018, respectively. Under both water and chemical control conditions, RuBPCase activity increased with an average augment of 6.78% by increasing the N supply level from N100 to N200 in both years, but further increasing the N supply level from N200 to N300 decreased RuBPCase activity at different stages. From the analysis of synthetic effect, RuBPCase activity in maize leaf was optimal in N200 application under chemical control.
Effects of chemical control and nitrogen fertilizers on RuBPCase and PEPCase activities in ear leaf during the maize growing period in 2017 and 2018. N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under chemical control, respectively. Error bars indicate the value of standard error. Different letters within a growth stage indicate a significant difference at P < 0.05.
A similar trend was also observed for PEPCase activity in maize leaf, and the activity was significantly affected by chemical control and N fertilization levels (Figure 2). At the same N levels, chemical control increased PEPCase activity with an average augment of 15.46, 11.98, 15.13, and 17.43% from the jointing stage to the milk stage in 2017 and 2018, respectively. Under both water and chemical control conditions, PEPCase activity under N200 treatment was higher than those under N100 and N300 treatments, with an average augment of 7.87 and 4.46% at different stages, respectively. From the analysis of synthetic effect, PEPCase activity in maize leaf was optimal in N200 application under chemical control.
NR and GS Activities in Leaf
Chemical control and N fertilization level exhibited a marked influence on NR and GS activities in leaves during the maize growing period in 2017 and 2018 (Figure 3). At the same N levels, chemical control increased NR activity with an average augment of 18.23, 17.11, 14.32, and 14.71% and increased GS activity with an average augment of 20.28, 24.12, 17.41, and 25.69% from the jointing stage to the milk stage in both years, respectively. Under water and chemical control conditions, NR and GS activities were significantly increased by increasing the N level from N100 to N200, but further increasing the N supply level from N200 to N300 caused a decrease in NR and GS activities at different stages. From the analysis of synthetical effect, NR and GS activities in maize leaf were optimal in N200 application under chemical control.
Effects of chemical control and nitrogen fertilizers on NR and GS activities in ear leaf during the maize growing period in 2017 and 2018. N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under chemical control, respectively. Error bars indicate the value of standard error. Different letters within a growth stage indicate a significant difference at P < 0.05.
N Metabolism Enzyme Activity in Grain
Chemical control and N fertilization level exerted a marked effect on grain GS, GDH, and GPT activities from 10 to 30 days after silking in 2017 and 2018 (Figure 4). Of these, GS and GDH activities increased between 10 and 20 days after silking and then decreased until 30 days after silking. However, GPT activity fluctuated with grain growth, which was highest and lowest at 25 and 30 days after silking, respectively. At the same N levels, chemical control increased GS, GDH, and GPT activities with an average augment of 15.22, 12.76, and 14.21% from 10 to 30 days after silking in both years, respectively. Under both water and chemical control conditions, GS, GDH, and GPT activities in grain were significantly increased by increasing the N supply level from N100 to N200 in both years, but further increasing the N supply level from N200 to N300 caused a slight decrease in grain N metabolism enzyme activities. From the analysis of synthetic effect, N metabolism enzyme activities in grain were optimal in N200 application under chemical control.
Effects of chemical control and nitrogen fertilizers on GS, GDH, and GPT activities in grain from 10 to 30 days after silking in 2017 and 2018. N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under chemical control, respectively. Error bars indicate the value of standard error. Different letters within a growth stage indicate a significant difference at P < 0.05.
Nutrients Concentrations in Grain
At the same N levels, chemical control significantly increased crude protein, lysine, sucrose, and soluble sugar concentrations of maize compared with water treatment in 2017 and 2018 (Table 7). Crude protein and lysine concentrations were significantly increased by increasing the N supply level from N100 to N200, but further increasing the N supply level from N200 to N300 caused a significant decrease in 2017 and a slight decrease in 2018. Similar trends were also observed for sucrose and soluble sugar concentrations of maize grain. Crude fat and starch concentrations were unaffected by chemical control and N fertilization level. The results show that nutrient concentrations in maize grain were optimal in N200 application under chemical control.
Effects of chemical control and nitrogen fertilizers on grain nutrients concentrations (%) of maize during maize growing period 2017 and 2018.
Year
Treatment
Crude protein
Crude fat
Starch
Lysine
Sucrose
Soluble sugar
2017
N100+CK
9.53e
5.16a
71.81a
0.43d
1.02e
1.68d
N200+CK
10.67c
5.20a
73.14a
0.47b
1.11b
1.78b
N300+CK
10.06d
5.16a
72.56a
0.45c
1.07d
1.72cd
N100+Y
10.78c
5.14a
71.69a
0.45c
1.09c
1.74bc
N200+Y
11.78a
5.26a
73.18a
0.49a
1.15a
1.85a
N300+Y
11.33b
5.22a
72.97a
0.47b
1.12b
1.82a
2018
N100+CK
9.05e
5.21a
71.63a
0.42c
1.02c
1.67c
N200+CK
10.12cd
5.28a
73.57a
0.45b
1.14b
1.80b
N300+CK
9.67d
5.23a
72.35a
0.45b
1.09b
1.75bc
N100+Y
10.29bc
5.24a
72.06a
0.45b
1.10b
1.79b
N200+Y
11.18a
5.34a
73.94a
0.49a
1.17a
1.93a
N300+Y
10.74ab
5.29a
72.68a
0.48a
1.11ab
1.88ab
N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under chemical control, respectively. Means within a column for the same year followed by the different letters indicate a significant difference at P < 0.05.
Yield and Yield Components
Chemical control and N fertilization level exhibited a marked influence on yield and yield components of maize in 2017 and 2018 (Table 8). Chemical control significantly increased the number of grains per ear and 1,000-grain weight compared with maize under water treatment in 2017 and 2018. Grain number per ear and 1,000-grain weight significantly increased by increasing the N supply level from N100 to N200, but further increasing the N supply level from N200 to N300 caused a slight decrease in 2017 and 2018. The highest grain yields were obtained from the N200 application under chemical control in 2017 and 2018.
Effects of chemical control and nitrogen fertilizers on yield and yield components of maize during the maize growing period 2017 and 2018.
Year
Treatment
Ears number per ha
Grains number per ear
1,000-grain weight (g)
Yield (kg ha−1)
2017
N100+CK
81,078a
541c
332b
10511c
N200+CK
81,654a
568b
327b
11548b
N300+CK
81,782a
560b
316c
11053bc
N100+Y
81,657a
571b
340ab
11427b
N200+Y
81,683a
591a
351a
12646a
N300+Y
82,150a
570b
339ab
11921b
2018
N100+CK
80,325a
531c
294c
9840bc
N200+CK
80,793a
550bc
298bc
10430b
N300+CK
78,685b
533c
298bc
9204c
N100+Y
81,052a
556abc
306bc
9990bc
N200+Y
81,184a
581a
327a
11704a
N300+Y
81,167a
566ab
314ab
10732ab
N100+CK, N200+CK, and N300+CK indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under water treatment, respectively; N100+Y, N200+Y, and N300+Y indicate nitrogen applied levels at 100, 200, and 300 kg ha−1 under chemical control, respectively. Means within a column for the same year followed by the different letters indicate a significant difference at P < 0.05.
Correlation Analysis
As shown in Figure 5, correlation analysis indicated that grain yield was positively correlated with the rate of root-bleeding sap, the delivery rate of amino acids and mineral nutrients in the bleeding sap, and CAAT of P and K. Besides, the CAAT of P and K were positively correlated with the rate of root-bleeding sap.
Correlation analysis of root-bleeding sap, nutrient contribution, and grain yield (values are the average in both years). CAAT, contribution rate of nutrient (P or K) accumulation amount post-silking.
Discussion
The root system is an essential source for uptake of water and nutrients, and its physiological activity is closely correlated to the development of the plant's parts above ground and the yield formation of crops (Yang et al., 2004; Fan et al., 2021). Root-bleeding sap reflects the capacity of roots to uptake water and nutrients, and it represents the physiological activity of the root system (Ansari et al., 2004; Wang P. et al., 2019). It has been found that root growth is closely associated with root-bleeding sap rate. The reduction of root quality in high-density planting seriously affects yield formation (Yu et al., 2019; Liu Z. et al., 2021). A balanced application of nitrogen can enhance root activity by supplying nutrients to form a robust root system (Wang H. et al., 2019). Equally, chemical control can optimize root morphological construction and improve the absorption ability of the root system (Lin et al., 2019).
In this study, N200 application in combination with chemical control significantly enhanced the rate of root-bleeding sap to enhance the strength of root activity. The nutrient concentrations in root-bleeding sap are closely associated with the absorption and transformation capacity of the root system, and its variation reflects the interaction intensity of nutrients in the aboveground and underground plant parts (Nishanth and Biswas, 2008). The xylem sap can transport nutrients upward to the aboveground tissues. The nutrient concentrations in root-bleeding sap are generally recognized as indicators of the plant's nutrient status (Ansari et al., 2004). Amino acids are essential for maintaining plant growth and, when contained in root-bleeding sap, promote root growth (Zheng et al., 2020). Mineral nutrient concentration is considered a primary factor for plant growth and grain yield. The delivery rate of mineral nutrients primarily depends on the root physiological activity and the nutrient concentrations across the root zone (Liang et al., 2020). High-density planting reduces root physiological activity and intensifies the depletion of nutrients in the root zone, resulting in the reduction of free amino acids and mineral nutrient concentrations (Yu et al., 2012; Liang et al., 2020). The content of free amino acids varied significantly with different nitrogen nutrient levels. It is believed that the delivery rate of free amino acids in root-bleeding sap increases with an increasing rate of nitrogen application (Li et al., 2009). In the present study, we found that N200 application combined with chemical control increased the delivery rate of amino acids and mineral nutrients in root-bleeding sap. The proper cultivation measure can improve the capacity of roots to absorb, synthesize, and transport carbohydrates, auxin, and other substances, thereby promoting root activity and root growth (Wang H. et al., 2019). The increase in root activity and its capacity for water and nutrients could lay the foundation for the increase in maize yield under high-density planting.
Nutrient absorption and accumulation are the basis of crop yield formation, and it directly affects the growth process of crops (Wu et al., 2018; Gorlach et al., 2021). Nutrient absorption in maize increases with plant growth. Sufficient nutrient supply during the growth period is the key to obtaining a high maize yield (Ray et al., 2020). Phosphorus and potassium are essential macronutrient elements for maize growth, which play an important role in the yield potential (Wu et al., 2015; Zhan et al., 2016). Nitrogen fertilizer is recognized to be an important factor affecting nutrient accumulation and transportation in addition to chemical control, which also impacts plant nutrient absorption capability (Van Oosten et al., 2019; Ray et al., 2020). In the present study, chemical control increased P and K accumulation amounts at different N levels. P and K accumulation amount increased with increasing level of N application, but the differences between N200 and N300 treatments were not significant. The nutrient accumulation by plants during different growth stages may impact crop yield. It is believed that the high nutrient absorption of N, P, and K in the middle growth stage of crops can promote pre-anthesis non-structural carbohydrate (NSC) reserves in the stem and accordingly enhance grain sink strength during grain filling (Fu et al., 2011; Li W. H. et al., 2012). Liu et al. (2019) considered that the P and K nutrient absorption in the late growth stage played an important role in improving maize production. In the present study, chemical control and nitrogen fertilizer greatly influenced the proportion of P and K accumulation during different growth stages in maize plants. Similarly, chemical control significantly increased the proportion of P and K accumulation during different growth stages except for the VE-JT and JT-TS stages. The proportion of P and K accumulation after the tasseling stage was obviously increased with increasing levels of N application. Chemical control and nitrogen fertilizer application substantially improved the CAAT of P and K in maize plants, and the highest CAAT of P and K were recorded under N200 application in combination with chemical control. The above results indicate that chemical control and nitrogen fertilizers can improve nutrient accumulation in maize after tasseling and increase the transfer of nutrients from vegetative organs to grains, consequently providing a material basis for yield formation. This result is similar to the study by Ray et al. (2020), which found that appropriate nutrient accumulation and translocation after silking created good conditions for maintaining the supply of nutrients to the grains, resulting in increased yields.
Carbon and nitrogen metabolism determines the level of crop production and function to provide the main energy and basic nutrients for plants (Cui et al., 2019). RuBPCase, PEPCase, NR, and GS are key enzymes involved in carbon and nitrogen metabolism in plants. In the present study, chemical control combined with N200 treatment increased RuBPCase, PEPCase, NR, and GS activities, leading to more assimilate accumulation and higher grain yield (Cheng et al., 2019; Yang et al., 2020). The plants maintained a high carbon and nitrogen metabolism and nutrient accumulation, which was the basis for assimilate accumulation in the grains. Main enzymes such as GS, GPT, and GDH are involved in the nitrogen metabolism in grains, and their activities directly affect the synthesis of amino acids and protein in grains (Wang et al., 2016). The N200 application, in combination with chemical control, significantly increased amino acid and protein content in grains, which in turn increased GS, GPT, and GDH activities. Chemical control and N200 treatments also increased the sucrose and soluble sugar contents of grains. This may be due to its association with higher sucrose metabolism and key enzyme activities (Kaur et al., 2018).
Increasing planting density is one of the important practices to increase maize yield per unit area in agricultural production (Tang et al., 2018). However, high-density planting intensifies the competition for light, nutrients, moisture, and space between maize plants, which restricts the growth of shoot and root systems, resulting in reduced crop yield (Rossini et al., 2011). The root system is the crop organ responsible for the uptake of nutrients, and a higher root activity enhances the nutrient absorption capacity in the root system (Yang et al., 2004). In the present study, the rate of root-bleeding sap was positively correlated with the contribution rate of nutrient (P or K) accumulation amount post-silking. It showed that the enhancement of root activity might be an effective method to develop the absorption and utilization capacity of P and K. Maintaining a relatively high level of root activity is an important approach to improving maize production. Niu et al. (2020) showed that increased root activity ensured the availability of soil nutrients and boosted photosynthetic capacity and biomass production, which are critical for grain filling and yield formation. In the present study, the grain yield was positively correlated with the rate of root-bleeding sap, the delivery rate of amino acids and mineral nutrients in bleeding sap, and the CAAT of P and K. It further confirmed that maintaining higher root activity and absorption and utilization capacity of P and K are the important approaches to obtaining high yields. Establishing a well-developed root system and efficient plant population can promote photosynthate production and nutrient accumulation and improve phosphorus and potassium distribution ratios after silking. Excessive nutrient transfer after silking usually affects the photosynthesis in leaves at a later growth stage, resulting in acceleration of leaf and root senescence and limiting yield improvement. However, deficient nutrient transfer after silking is harmful to grain filling, making it difficult to achieve a high yield. Therefore, appropriate cultivation methods can coordinate nutrient transfer and nutrient accumulation after silking and optimize the source-sink relationship, which plays an important role in improving yield. Our study on maize cultivation in Northeast China indicated that N200 combined with chemical control could optimize P and K absorption and translocation in the later growth stage by increasing root activity, thereby improving grain yield and quality.
Conclusion
N200 application in combination with chemical control significantly increased the root-bleeding sap rate, amino acid delivery rate, and mineral nutrient delivery rate. It promoted the accumulation and translocation of P and K nutrients after the tasseling stage, and as a result, it provided a material basis for yield formation. Moreover, N200 combined with chemical control obviously enhanced enzyme activities of carbon and nitrogen metabolism in leaves, increased nitrogen metabolism enzyme activities in grains during the early and middle grain filling stage, and improved amino acid and protein content in grains, thereby increasing the grain yield and quality of maize in high-density planting. The schematic representation indicates that nitrogen fertilizers and chemical control increased the grain yield and quality by optimizing root-bleeding sap, nutrient accumulation and transport, photosynthesis, and N metabolism in maize under high-density planting (Figure 6). Therefore, attention should be paid to promoting nitrogen fertilizer and chemical control management in high-density planting of maize in future agricultural production in Northeast China as it plays a crucial role in improving maize yield and quality.
The schematic representation of nitrogen fertilizers and chemical control regulated maize yield. The red arrows (↑) and the blue arrows (↓) represent the positive and passive roles of treatment, respectively.
Data Availability Statement
The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.
Author Contributions
XL and LZ collected and analyzed the samples and wrote the manuscript. YY, CQ, and CoL contributed to the writing and editing of the manuscript. SW, CaL, and WG contributed to the design of the work and analysis and revised the manuscript. All authors read and approved the article.
Funding
This study was financially supported by the National Key Research and Development Program of China (2016YFD0300103) and the National Modern Agriculture Industry Technology System (CARS-02-12).
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Publisher's Note
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ReferencesAnsariT. H.YamamotoY.YoshidaT.SakagamiK.MiyazakiA. (2004). Relation between bleeding rate during panicle formation stage and sink size in rice plant. Soil Sci. Plant Nutr.50, 57–66. 10.1080/00380768.2004.10408452AOAC (1975). Official Methods of Analysis, 12th Edn. Washington, DC: Association of Official Agricultural Chemists.AOAC (1984). Official Methods of Analysis, 14th Edn. Arlington, VA: Association of Official Analytical Chemists.ArnozisP. A.NelemansJ. A.FindeneggG. R. (1988). Phosphoenolpyruvate carboxylase activity in plants grown with either NO3- or NH4+ as inorganic nitrogen source. J. Plant Physiol.132, 23–27. 10.1016/S0176-1617(88)80177-9BorosD.SlominskiB. A.GuenterW.CampbellL. D.JonesO. (2004). Wheat by-products in poultry nutrition. Part II. Nutritive value of wheat screenings, bakery by-products and wheat mill run and their improved utilization by enzyme supplementation. Can. J. Anim. Sci. 84, 429–435. 10.4141/A03-113CanovasF. M.CantonF. R.GallardoF.GarciagutierrezA.DevicenteA. (1991). Accumulation of glutamine-synthetase during early development of maritime pine (Pinus pinaster) seedlings. Planta185, 372–378. 10.1007/BF0020105924186421ChenP. P.GuX. B.LiY. N.QiaoL. R.LiY. P.FangH.. (2022). Effects of residual film on maize root distribution, yield and water use efficiency in Northwest China. Agric. Water Manag.260, 107289. 10.1016/j.agwat.2021.107289ChengY. Y.WangY.HanY. L.LiD. Y.ZhangZ. K.ZhuX. Q.. (2019). The stimulatory effects of nanochitin whisker on carbon and nitrogen metabolism and on the enhancement of grain yield and crude protein of winter wheat. Molecules24, 1752. 10.3390/molecules2409175231064118CuiG. C.ZhangY.ZhangW. J.LangD. Y.ZhangX. J.LiZ. X.. (2019). Response of carbon and nitrogen metabolism and secondary metabolites to drought stress and salt stress in plants. J. Plant Biol. 62, 387–399. 10.1007/s12374-019-0257-1FanY. F.GaoJ. L.SunJ. Y.LiuJ.SuZ. J.WangZ. G.. (2021). Effects of straw returning and potassium fertilizer application on root characteristics and yield of spring maize in China inner Mongolia. Agron. J.113, 4369–4385. 10.1002/agj2.20742FuJ.HuangZ. H.WangZ. Q.YangJ. C.ZhangJ. H. (2011). Pre-anthesis non-structural carbohydrate reserve in the stem enhances the sink strength of inferior spikelets during grain filling of rice. Field Crops Res. 123, 170–182. 10.1016/j.fcr.2011.05.015GaoJ.LeiM.YangL. J.WangP.TaoH. B.HuangS. B. (2021). Reduced row spacing improved yield by optimizing root distribution in maize. Eur. J. Agron.127, 126291. 10.1016/j.eja.2021.126291GorlachB. M.HenningsenJ. N.MackensJ. T.MuhlingK. H. (2021). Evaluation of maize growth following early season foliar P supply of various fertilizer formulations and in relation to nutritional status. Agronomy11, 727. 10.3390/agronomy11040727HutschB. W.SchubertS. (2017). Maize harvest index and water use efficiency can be improved by inhibition of gibberellin biosynthesis. J. Agron. Crop Sci.204, 209–218. 10.1111/jac.12250IqbalS.AkhtarJ.NazT.RiazU.HussainS.MazharZ.. (2020). Root morphological adjustments of crops to improve nutrient use efficiency in limited environments. Commun. Soil Sci. Plan.51, 2452–2465. 10.1080/00103624.2020.1836199KaurM.SharmaS.SinghD. (2018). Influence of selenium on carbohydrate accumulation in developing wheat grains. Commun. Soil Sci. Plan.49, 1650–1659. 10.1080/00103624.2018.1474903LewisO. A. M.WatsonE. F.HewittE. J. (1982). Determination of nitrate reductase activity in barley leaves and roots. Ann. Bot.49, 31–37. 10.1093/oxfordjournals.aob.a086227LiG. H.ChengQ.LiL.LuD. L.LuW. P. (2021). N, P and K use efficiency and maize yield responses to fertilization modes and densities. J. Integr. Agric.20, 78–86. 10.1016/S2095-3119(20)63214-2LiG. H.WangL. F.LiL.LuD. L.LuW. P. (2020). Effects of fertilizer management strategies on maize yield and nitrogen use efficiencies under different densities. Agron. J.112, 368–381. 10.1002/agj2.20075LiG. H.ZhaoB.DongS. T.ZhangJ. W.LiuP.RenB. Z.. (2019). Morphological and physiological characteristics of maize roots in response to controlled-release urea under different soil moisture conditions. Agron. J.111, 1849–1864. 10.2134/agronj2018.08.0508LiH. W.LiuL. J.WangZ. Q.YangJ. C.ZhangJ. H. (2012). Agronomic and physiological performance of high-yielding wheat and rice in the lower reaches of Yangtze River of China. Field Crops Res.133, 119–129. 10.1016/j.fcr.2012.04.005LiS. X.WangZ. H.MalhiS. S.LiS. Q.GaoY. J.TianX. H. (2009). Nutrient and water management effects on crop production: and nutrient and water use efficiency in dryland areas of China. Adv. Agron.102, 223–265. 10.1016/S0065-2113(09)01007-4LiW. H.HouM. J.CaoY. S.SongH.ShiT. Y.GaoX. W.. (2012). Determination of 20 free amino acids in asparagus tin by high-performance liquid chromatographic method after pre-column derivatization. Food Anal. Methods5, 62–68. 10.1007/s12161-011-9197-1LiangX. Y.GuoF.FengY.ZhangJ. L.YangS.MengJ. J.. (2020). Single-seed sowing increased pod yield at a reduced seeding rate by improving root physiological state of Arachis hypogaea. J. Integr. Agric.19, 1019–1032. 10.1016/S2095-3119(19)62712-7LilleyR. M.WalkerD. A. (1974). An improved spectrophotometric assay for ribulosebisphosphate carboxylase. BBA-Enzymology358, 226–229. 10.1016/0005-2744(74)90274-54368401LinY. R.WattsD. B.KloepperJ. W.FengY. C.TorbertH. A. (2019). Influence of plant growth-promoting rhizobacteria on corn growth under drought stress. Commun. Soil Sci. Plan.51, 250–264. 10.1080/00103624.2019.170532933083600LiuA. H.YeZ. C. (2020). “China Agriculture Yearbook” in China Statistical Yearbook (Beijing: China Agriculture Press), 373–402. (in Chinese).LiuH. R.SongH. X.LiuD. P.GuanC. Y.LiuQ.ChenS. Y. (2007). Dynamics changes of soluble sugar and free amino acid contents in stem and leaf of different oilseed rape varieties (in Chinese with English abstract). Acta Agri Boreali-occidentalis Sin. 16, 123–126. 10.3969/j.issn.1004-1389.2007.01.029LiuK.MaB. L.LuanL. M.LiC. H. (2011). Nitrogen, phosphorus, and potassium nutrient effects on grain filling and yield of high-yielding summer corn. J. Plant Nutr.34, 1516–1531. 10.1080/01904167.2011.585208LiuM. L.WangC.WangF. Y.XieY. J. (2019). Maize (Zea mays) growth and nutrient uptake following integrated improvement of vermicompost and humic acid fertilizer on coastal saline soil. Appl. Soil Ecol.142, 147–154. 10.1016/j.apsoil.2019.04.024LiuS. Q.JianS. L.LiX. N.WangY. (2021). Wide-narrow row planting pattern increases root lodging resistance by adjusting root architecture and root physiological activity in maize (Zea mays L.) in Northeast China. Agriculture11, 517. 10.3390/agriculture11060517LiuZ.YingH.ChenM.LiuZ. T.YingH.ChenM. Y.. (2021). Optimization of China's maize and soy production can ensure feed sufficiency at lower nitrogen and carbon footprints. Nat. Food2, 426–433. 10.1038/s43016-021-00300-1LiuZ.ZhuK. L.DongS. T.LiuP.ZhaoB.ZhangJ. W. (2017). Effects of integrated agronomic practices management on root growth and development of summer maize. Eur. J. Agron.84, 140–151. 10.1016/j.eja.2016.12.006LuoN.WangX. Y.HouJ. M.WangY. Y.WangP.MengQ. F. (2020). Agronomic optimal plant density for yield improvement in the major maize regions of China. Crop Sci.60, 1580–1590. 10.1002/csc2.20000MurphyJ.RileyJ. P. (1962). A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta27, 31–36. 10.1016/S0003-2670(00)88444-5NawazM.IshaqS.IshaqH.KhanN.IqbalN.AliS.. (2020). Salicylic acid improves boron toxicity tolerance by modulating the physio-biochemical characteristics of maize (Zea mays L.) at an early growth stage. Agronomy10, 2013. 10.3390/agronomy10122013NishanthD.BiswasD. R. (2008). Kinetics of phosphorus and potassium release from rock phosphate and waste mica enriched compost and their effect on yield and nutrient uptake by wheat (Triticum aestivum). Bioresour. Technol.99, 3342–3353. 10.1016/j.biortech.2007.08.02517905580NiuL.YanY. Y.HouP.BaiW. B.ZhaoR. L.WangY. H.. (2020). Influence of plastic film mulching and planting density on yield, leaf anatomy, and root characteristics of maize on the Loess Plateau. Crop J.8, 548–564. 10.1016/j.cj.2019.12.002NoguchiA.KageyamaM.ShinmachiF.SchmidhalterU.HasegawaI. (2005). Potential for using plant xylem sap to evaluate inorganic nutrient availability in soil—I. Influence of inorganic nutrients present in the rhizosphere on those in the xylem sap of Luffa cylindrica Roem. Soil Sci. Plant Nutr.51, 333–341. 10.1111/j.1747-0765.2005.tb00038.xPalacios-RojasN.McCulleyL.KaepplerM.TitcombT. J.GunaratnaN. S.Lopez-RidauraS.. (2020). Mining maize diversity and improving its nutritional aspects within agro-food systems. Compr. Rev. Food Sci. Food Sci. Food Saf.19, 1809–1834. 10.1111/1541-4337.1255233337075RayK.BanerjeeH.DuttaS.SarkarS.MurrellT. S.SinghV. K.. (2020). Macronutrient management effects on nutrient accumulation, partitioning, remobilization, and yield of hybrid maize cultivars. Front. Plant Sci.11:1307. 10.3389/fpls.2020.0130732983197ReddyY. R.RaviD.ReddyC. R.PrasadK. V. S. V.ZaidiP. H.VinayanM. T.. (2013). A note on the correlations between maize grain and maize stover quantitative and qualitative traits and the implications for whole maize plant optimization. Field Crops Res.153, 63–69. 10.1016/j.fcr.2013.06.013RossiniM. A.MaddonniG. A.OteguiM. E. (2011). Inter-plant competition for resources in maize crops grown under contrasting nitrogen supply and density: variability in plant and ear growth. Field Crops Res.121, 373–380. 10.1016/j.fcr.2011.01.003ShahzadA. N.FatimaA.SarwarN.BashirS.RizwanM.QayyumM. F.. (2017). Foliar application of potassium sulfate partially alleviates pre-anthesis drought-induced kernel abortion in maize. Int. J. Agric. Biol.19, 495–501. 10.17957/IJAB/15.0317ShaoH.XiaT. T.WuD. L.ChenF. J.MiG. H. (2018). Root growth and root system architecture of field-grown maize in response to high planting density. Plant Soil430, 395–411. 10.1007/s11104-018-3720-8StuttsL.WangY.StapletonA. E. (2018). Plant growth regulators ameliorate or exacerbate abiotic, biotic and combined stress interaction effects on Zea mays kernel weight with inbred-specific patterns. Environ. Exp. Bot.147, 179–188. 10.1016/j.envexpbot.2017.12.012TangL. Y.MaW.NoorM. A.LiL. L.HouH. P.ZhangX. Y.. (2018). Density resistance evaluation of maize varieties through new “Density-Yield Model” and quantification of varietal response to gradual planting density pressure. Sci. Rep.8:17281. 10.1038/s41598-018-35275-w30470761Van OostenM. J.Dell'AversanaE.RuggieroA.CirilloV.GibonY.WoodrowP.. (2019). Omeprazole treatment enhances nitrogen use efficiency through increased nitrogen uptake and assimilation in corn. Front. Plant Sci.10:1507. 10.3389/fpls.2019.0150731867024VanH. E. (1968). Direct microdetermination of sucrose. Anal. Biochem.22, 280–283. 10.1016/0003-2697(68)90317-55641848WangC.NingP. (2019). Post-silking phosphorus recycling and carbon partitioning in maize under low to high phosphorus inputs and their effects on grain yield. Front. Plant Sci.10:784. 10.3389/fpls.2019.0078431249585WangF.GaoJ. W.LiuY.TianZ. W.MuhammadA.ZhangY. X.. (2016). Higher ammonium transamination capacity can alleviate glutamate inhibition on winter wheat (Triticum aestivum L.) root growth under high ammonium stress. PLoS ONE11:e0160997. 10.1371/journal.pone.016099727512992WangH.XuR. R.LiY.YangL. Y.ShiW.LiuY. J.. (2019). Enhance root-bleeding sap flow and root lodging resistance of maize under a combination of nitrogen strategies and farming practices. Agric. Water Manag.224, 105742. 10.1016/j.agwat.2019.105742WangP.WangZ. K.PanQ. C.SunX. C.ChenH.ChenF. J.. (2019). Increased biomass accumulation in maize grown in mixed nitrogen supply is mediated by auxin synthesis. J. Exp. Bot.70, 1859–1873. 10.1093/jxb/erz04730759246WolfB. (1982). A comprehensive systems of leaf analysis and its use for diagnosing crop nutrients status. Commun. Soil Sci. Plant.13, 1035–1059. 10.1080/00103628209367332WuH.XiangJ.ZhangY. P.ZhangY. K.PengS. B.ChenH. Z.. (2018). Effects ofpost-anthesis nitrogen uptake and translocation on photosynthetic production and rice yield. Sci. Rep.8, 12891. 10.1038/s41598-018-31267-y30150736WuL. Q.CuiZ. L.ChenX. P.YueS. C.SunY. X.ZhaoR. F.. (2015). Change in phosphorus requirement with increasing grain yield for Chinese maize production. Field Crops Res.180, 216–220. 10.1016/j.fcr.2015.06.001XieW. J.WangH. Y.XiaJ. B.YaoZ. G. (2011). Influence of N, P, and K application on Zea mays L. growth and Cu and Pb accumulation. Plant Soil Environ.57, 128–134. 10.17221/225/2010-PSEXuC. L.TaoH. B.TianB. J.GaoY. B.RenJ. H.WangP. (2016). Limited-irrigation improves water use efficiency and soil reservoir capacity through regulating root and canopy growth of winter wheat. Field Crops Res. 196, 268–275. 10.1016/j.fcr.2016.07.009XuL. Z.NiuJ. F.LiC. J.ZhangF. S. (2009). Growth, nitrogen uptake and flow in maize plants affected by root growth restriction. J. Integr. Plant Biol.51, 689–697. 10.1111/j.1744-7909.2009.00843.x19566647YangC. M.YangL. Z.YangY. X.ZhuO. Y. (2004). Rice root growth and nutrient uptake as influenced by organic manure in continuously and alternately flooded paddy soils. Agric. Water Manag.70, 67–81. 10.1016/j.agwat.2004.05.003YangH.GuX. T.DingM. Q.LuW. P.LuD. L. (2020). Weakened carbon and nitrogen metabolisms under post-silking heat stress reduce the yield and dry matter accumulation in waxy maize. J. Integr. Agric.19, 78–88. 10.1016/S2095-3119(19)62622-5YuX. F.ZhangQ.GaoJ. L.WangZ. G.BorjiginQ.HuS. P.. (2019). Planting density tolerance of high-yielding maize and the mechanisms underlying yield improvement with subsoiling and increased planting density. Agronomy9, 370. 10.3390/agronomy9070370YuX. M.WangB.ZhangC. X.XuW. P.HeJ. J. (2012). Effect of root restriction on nitrogen levels and glutamine synthetase activity in “Kyoho” grapevines. Sci. Hortic.137, 156–163. 10.1016/j.scienta.2012.01.025ZhanA.ZouC. Q.YeY. L.LiuZ. H.CuiZ. L.ChenX. P. (2016). Estimating on-farm wheat yield response to potassium and potassium uptake requirement in China. Field Crops Res.191, 13–19. 10.1016/j.fcr.2016.04.001ZhangQ.ZhangL. Z.EversJ.WerfW. V. D.ZhangW. Q.DuanL. S. (2014). Maize yield and quality in response to plant density and application of a novel plant growth regulator. Field Crops Res.164, 82–89. 10.1016/j.fcr.2014.06.006ZhangZ.YuZ. W.ZhangY. L.ShiY. (2021). Optimized nitrogen fertilizer application strategies under supplementary irrigation improved winter wheat (Triticum aestivum L.) yield and grain protein yield. PeerJ9, e11467. 10.7717/peerj.1146734141470ZhengT.HaiderM. S.ZhangK. K.JiaH. F.FangJ. G. (2020). Biological and functional properties of xylem sap extracted from grapevine (cv. Rosario Bianco). Sci. Hortic.272, 109563. 10.1016/j.scienta.2020.109563