Cotton is an economically important crop worldwide and represents a significant source of income for farmers in many countries. China, India, the United States, Pakistan, and Brazil are the top cotton-producing countries globally, accounting for more than 75% of the world’s cotton production (STATISTA, 2022). China ranks first globally, with 5.99 million tons of cotton production (Arshad et al., 2021). In 2020, Xinjiang’s cotton planting area was 25019 km², and the total output was 5.2 million tons, accounting for 78.9% and 87.3% of the total cotton planting area and total output of China, respectively, and 8.82% and 22.3% of the total cotton planting area and total output of the world, respectively (National Bureau of Statistics, 2020). In the northwest inland cotton production region, the average amounts of applied N, P₂O₅ and K₂O are 296 kg ha⁻¹, 141 kg ha⁻¹ and 87 kg ha⁻¹ in the high-yield cotton region (7466 kg ha⁻¹), while the average amounts of applied N, P₂O₅ and K₂O are 278 kg ha⁻¹, 116 kg ha⁻¹ and 75 kg ha⁻¹ in the low-yield cotton production region (5904 kg ha⁻¹) (Li et al., 2019). The statistics above show that Xinjiang cotton production is characterized by a “high input, high yield and high risk” development status (Lou et al., 2021). Recently, there has been a shift toward more sustainable cotton production methods, such as organic and fair-trade cotton, in response to concerns about the environmental and social impacts of conventional cotton farming, especially the excessive use of conventional chemical inputs.

Excessive application of chemical fertilizer (CF) can increase cotton production costs and a decline in soil organic matter and soil fertility with no crop yield increment (Yan et al., 2007; Khan et al., 2017b). Therefore, it is necessary to develop efficient fertilizer management options to ensure high cotton yield with improved photosynthetic performance. The application of organic fertilizer can improve soil nutrients, soil physical and chemical properties, and crop yield while also promoting crop nutrient absorption (Agbede et al., 2010). Increasing organic fertilizer is beneficial for increasing crop yield and improving crop quality (Liu et al., 2017; Liang et al., 2021; Mousavi et al., 2022). The combined application of organic fertilizer and chemical fertilizer in an integrated manner can promote the absorption and utilization of chemical fertilizer (Kautz et al., 2004), enable efficient utilization of resources (Wright et al., 2004; Jagadamma et al., 2007). With the development of the chemical fertilizer industry, the amount of chemical fertilizer application in China has increased each year, while the proportion of organic fertilizer applied has decreased (Pan, 2014). The proportion of organic fertilizer relative to total fertilizer input decreased from 99.9% in 1949 to 37.4% in 1990 and 25.0% in 2003 (Xiao et al., 2017). Continuous, single and excessive applications of chemical fertilizer have resulted in low soil organic matter (SOM) contents and fertilizer utilization rates (Roelcke et al., 2004). However, most organic liquid fertilizers (OFs) are solid or biogas slurries with low efficiency that cannot meet the requirements of high crop yields or that contain heavy metals, resulting in environmental pollution (Yoder and Davis, 2020).

A new type of OF that is water-soluble and can activate soil nutrients has been shown to achieve efficient management of nutrient resources, resulting in high crop yields with less damage to the environment (Maintang et al., 2021). Coupling OF with CF has been shown to effectively improve the CF utilization rate, thereby significantly improving soil fertility and crop yield (Mooy et al., 2019; Puteri et al., 2021). OFs can boost soil texture, improve the crop growth environment, and enhance the accumulation of photosynthetic products, thus leading to an increase in cotton yield (Tian et al., 2014). Hence, understanding the effects of the application of OF combined with CF throughout the whole growth period on crop growth and yield formation is important to boost yield, particularly in arid regions. However, the interactions between OF with CF and the effect on cotton photosynthesis remain poorly known.

Photosynthesis is a prerequisite for cotton yield (Tissue et al., 2010; Wu et al., 2019). Previous research has mainly focused on the effects of photosynthetic physiology in cotton plants (Hu et al., 2016; Shah et al., 2021), winter wheat (Jiang et al., 2004), maize (Wang et al., 2021) and other crops. However, there are few studies on the effects of the combined application of OF and CF on cotton leaf photosynthetic physiology and yield under mulch drip irrigation. This study hypothesized that a new strategy of OF application combined with reduced CF could improve photosynthetic performance and thus increase cotton yield. The main objectives of this study were to 1) investigate dynamic changes in leaf photosynthetic traits and the spatial and temporal distribution of soil organic matter content; 2) determine the relationship between cotton yield, photosynthetic performance, and soil organic matter content; and 3) determine how application of organic liquid fertilizer with reduced application of chemical fertilizer improves cotton yield. The tested hypothesis was that OF combined with reduced CF would improve cotton yield through leaf physiological functioning. Our study is significant for validating the performance of integrated nutrient management through organic and chemical fertilization in cotton, thereby helping farmers optimize cotton production while significantly minimizing conventional fertilizer requirements.

Long−term and excessive use of CF may not sustain high crop yields and lead to environmental pollution, such as greenhouse gas emissions to the atmosphere (Khan et al., 2017a). In this study, compared with the CF treatment, higher biological yields, seed yield (OF_0.8) and economic coefficient (OF_0.8) might have been achieved because of the combined effect of OF and CF application, enhancing soil nutrient availability and improving nutrient absorption and utilization by cotton plants (Saikia et al., 2015). This result may also have occurred because the reduced CF amount promoted leaf functioning, i.e., photosynthetic characteristics, which further increased aboveground biomass formation and its transition to reproductive organs, resulting in a higher cotton yield (Khan et al., 2017b; Ahangera et al., 2021; Shi et al., 2021). This suggests that under mulch drip irrigation systems, the application of OF can ensure a high cotton seed yield and economic coefficient due to enhanced cotton biomass accumulation.

Moreover, SOM is essential for maintaining ecosystem function and agricultural sustainability (Raiesi, 2021). In this study, SOM significantly increased under OF application compared with the CF treatment. This finding suggests that OF can improve soil quality and increase crop yield (Urra et al., 2020). In this study, OF (OF_0.8, OF_1.0 and OF_1.2) resulted in a higher SOM content at the 0−60 cm soil depth. Previous studies showed that the SOM content reached 22.84 g kg⁻¹ after the long-term application of traditional organic fertilizer from 1992 to 2016 (Chen et al., 2022). However, OF was supplied in both years, which resulted in SOM values of 22.7−25.8 g kg⁻¹ possibly due to the following reasons: 1) Under OF, the water−soluble organic matter content was up to 20.8%. The decomposition rate of organic matter in the organic waste liquid was fast, which was beneficial for rapidly increasing SOM (Mooy et al., 2019); 2) Small amounts of organic waste liquid and CF were applied several times throughout the whole cotton growth period to avoid soil loss and volatilization of nutrients. This application scheme further favored the accumulation of organic matter in the soil as well as an enhancement in plant nutrients (Agbede et al., 2010). Hence, under mulch drip irrigation systems, the application of OF can induce a suitable soil nutrient environment for the efficient production of cotton.

Furthermore, crop yield formation is also regulated by photosynthetic performance, Chl content and photosynthetic area (Santos et al., 2013; Wang et al., 2015; Wang et al., 2016; Shah et al., 2021). In this study, compared with the CF treatment, the OF_0.8 treatment resulted in a higher Chl content, P _n, G _s and E. The increases in these parameters resulted from the application of OF, which released more soil carbon dioxide, which regulates stomatal opening and consequently leads to a high photosynthetic rate (Dębska et al., 2016). Second, the use of OF can increase the nitrogen content of plant functional leaves, which in turn improves the activities of photosynthetic carbon assimilation enzymes (Rubisco), leading to a higher photosynthetic rate and cotton yield (Grassi et al., 2010; Sepehri and Sanavy, 2003). In this study, LA increased with increasing ratios of OF, possibly because the combination of OF with excessive CF resulted in a larger LA. This further results in severe canopy shading, greatly reducing the ability of the canopy to intercept light energy and thus inhibiting the net photosynthetic performance of cotton plants (Hueso et al., 2021). The photosynthetic performance of the cotton leaves did not increase as the ratio of OF combined with CF increased, suggesting that an appropriate proportion of OF combined with CF can create a good light environment by maintaining a reasonable LA, high Chl content and high photosynthetic performance.

Additionally, Chl fluorescence plays a unique role in measuring photosynthesis and in the absorption, transmission, dissipation and distribution of light energy by the photosystem (Sinsawat et al., 2004; Dorta-Santos et al., 2020). The maximum photochemical efficiency (F _v/F _m) is an important indicator of whether plants are under stress; a value above 0.8 indicates that the plants are not under stress, and a slight decline in the value of this parameter may correspond to a light protection mechanism (Narayan et al., 2020). At IF in 2020, the F _v/F _m values of the CF, OF_0.6, OF_1.2, and OF_1.4 treatments began to decline to less than 0.8, indicating that cotton leaves in these four treatments experienced photoinhibition, and the activity of the PSII reaction center was significantly reduced.

However, the F _v/F _m values of OF_0.8 and OF_1.0 remained at approximately 0.8, which indicates that these OF treatments better promote the PSII primary light energy conversion efficiency of cotton plant leaves; that is, the captured light energy is converted into chemical energy, which is conducive to improving the photosynthetic capacity of cotton (Zhang et al., 2013). This suggests that the combination of OF and CF (OF_0.8, OF_1.0 and OF_1.2 treatments) could improve the drought resistance of cotton. Compared with the CF treatment, the OF treatments improved the Y(II), ETR and qP of the cotton. In addition, the OF_0.8 and OF_1.0 treatments significantly increased Y(II), ETR and qP in this study. This indicates that the application of CF alone and the OF_1.4 treatment may decrease the PSII quantum yield, blocking electron transfer in the PSII reaction and decreasing the photochemical activity of the PSII reaction center. An appropriate application of OF and CF can delay cotton plant senescence, which results in increased light energy utilization efficiency in crop leaves (Ikeuchi et al., 2014).

Improving the photosynthetic capacity (photosynthetic rate) can increase seed cotton yield under limited drip irrigation systems (Gao et al., 2021). In addition, a higher leaf F _v/F _m can promote the photosynthetic capacity of reproductive organs and ultimately build high-yield cotton with optimum fruiting nodes (Zhen et al., 2020). It has been shown that improving the leaf photosynthetic capacity in the later stage can guarantee a high seed cotton yield (Li et al., 2006), as evidenced in this study as well. Photosynthetic performance and soil nutrients are the key indicators for evaluating irrigation and fertilization management benefits (Luo et al., 2023). The result of PCA principal component analysis showed that multiple correlations between yield and PSII parameters, photosynthetic performance parameters are the main factor responsible for differences among treatments (Rodríguez et al., 2023). In addition, previous studies have also demonstrated that photosynthetic parameters such as F _v/F _m, F _v/F _o, ETR, Chl a, and Chl b have a significant positive impact on crop yield (Li et al., 2023). In this study, photosynthetic potential was main factor causing differences in the early growth stages of cotton. OF_0.8, OF_1.0, and OF_1.2 treatments enhanced photosynthetic performance. In the late growth stage (from LFB to BO stage), ETR was the key driver reflecting photosynthetic capacity. OF combined with an appropriate amount of CF can improve crop yield due to the optimized relationship between photosynthetic capacity (P _n, G _s and Y(II)) and crop yield formation and can promote the transport of photosynthetic products to the grains, resulting in an increased seed yield (Guo et al., 2020). These findings indicate that OF combined with CF is a promising fertilization method for efficient cotton production under a mulch drip irrigation system.

Overall, our study elucidates that an optimum combination of organic and conventional fertilizer at a reduced rate could be an improved strategy to optimize nutrient uptake, enhance soil fertility and productivity and harness the maximum leaf photosynthetic efficiency. An integrated approach not only promotes better growth and higher yield but also minimizes the potential off-farm loss of chemical inputs, thereby reducing collateral environmental pollution. Further investigation with different organic inputs under various management systems can provide farmers with further strategies to utilize integrated nutrient management practices for cotton production.

In this study, OF combined with 80% CF increased seed cotton yield by 5.6−21.2% and economic coefficient by 8.4−27.6%. Furthermore, OF combined with 80% CF resulted in a higher Chl content, P _n, E, G _s, Y(II), ETR, and qP but decreased NPQ. The seed cotton yield and economic coefficient were positively correlated with P _n, F _v/F _m, G _s and Y(II) from FB to BO. Improvements in these attributes further resulted in a higher economic coefficient and seed cotton yield in both years. Hence, OF (dissolved organic matter content > 20.8%, with a total application amount of 1329 kg ha⁻¹) combined with 80% CF (N−P₂O₅−K₂O: 182−104−76 kg ha⁻¹) is a promising option to improve leaf photosynthetic performance and light energy utilization efficiency, resulting in a higher seed cotton yield and economic coefficient. Our study validated the superior performance of integrated nutrient management in cotton using organic liquid fertilizer in combination with chemical fertilization at a reduced rate, thereby providing farmers with alternative strategies for cotton management to support clean production. Our results provide new insights into sustainable cotton production using integrated crop management strategies under mulch drip irrigation.

The original contributions presented in the study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding authors.

XS, JW, and HL conceived the main idea and designed the experiment. XH, AK, JN edited and provided suggeston in this article. NL, JL and helped in data collection. FS and YT helped in labortory analysis. All authors contributed to the article and approved the submitted version.