During two consecutive winter seasons (2016–2017 and 2017–2018), trials were executed at research farm of the Indian Agricultural Research Institute (IARI), New Delhi (located at latitude 28°38′0839″ north and longitude 77°09′1442″ east; Figure 1). The experimental farm is situated in a subtropical semi-arid climate and is classified as the Mehrauli series of the Inceptisol order. The soil of the experimental plot is sandy clay loam and mildly alkaline, with pH 8.10 (non-saline) and electrical conductivity 0.24 dS m⁻¹ (Jackson, 1973). The topsoil (0–15 cm soil depth) contained 0.43% organic carbon (Walkley and Black, 1934), 191 kg ha⁻¹ of available nitrogen (N) (Subbiah and Asija, 1956), 11.9 kg ha⁻¹ of available phosphorus (Olsen et al., 1954), and 208 kg ha⁻¹ of available potassium (K) (Jackson, 1973). Monthly weather data for the experimental period (2016–2017 and 2017–2018) were obtained from a nearby meteorological observatory situated at ICAR-IARI in New Delhi (Figure 2).

In the experimental field, individual plots (5.6 m × 4.2 m) were prepared by manual laborers with the help of spade to avoid the mixing of the soil in different plots with different nutrient treatments. Experiment was conducted in split plot design, where the main plots consisted of three tillage methods: conventional tillage with no residue (CT – R), no-tillage with no-corn residue (NT – R), and no-tillage with maize residue @ 2.5 Mg ha⁻¹ (NT + R). The subplots were assigned five P management strategies: P1 (Recommended N and K, and No-P), P2 (Recommended N and K, and 17.2 kg P ha⁻¹), P3 (Recommended N and K, and 17.2 kg P ha⁻¹ + PSB culture), P4 (Recommended N and K, and 17.2 kg P ha⁻¹ + compost inoculant culture), and P5 (Recommended N and K, and 34.4 kg P ha⁻¹). Each treatment combination was replicated three times. Under the NT + R treatment, maize residues (from the preceding crop) were incorporated at a rate of 2.50 Mg ha⁻¹. A compost inoculant containing a mixture of Trichoderma viride, Aspergillus awamori, Aspergillus nidulans, and Phanerochaete chrysosporium was used, along with a PSB culture acquired from Microbiology Division of IARI, New Delhi.

Fertilizers were applied according to the treatment plan, utilizing urea, diammonium phosphate, and potassium chloride as inorganic nutrient sources for nitrogen, phosphorus, and potassium, respectively. The recommended dose of fertilizer (RDF) was 150 kg N ha⁻¹, 34.4 kg P ha⁻¹, and 49.8 kg K ha⁻¹. At sowing, the full dose of K and half dose of N were applied (basal dose), while the remaining nitrogen was top-dressed during the first, second, and third irrigations as per the treatment plan. P doses were administered based on the recommended guidelines of the treatment plan. Prior to sowing the crop, a suitable culture of microbial consortia was used for seed treatment. In a plastic bucket, a mixture of 20–25 L of warm water (60°C) and 2.5 kg of jaggery was prepared, and wheat seeds were soaked in this solution for 30 min. Following the recommended guidelines, the seeds were treated with the appropriate carrier (PSB culture) at a rate of 20 g kg⁻¹ and shade dried for 6–7 h before sowing in their respective treatment plots. In certain plots, immediately after sowing the crop, the compost inoculant culture was mixed with water and applied over the crop residue at a rate of 1,250 ml per hectare. Wheat variety “HD 2967” was sown in I^st week of November by manually at rate of 100–125 kg seed ha⁻¹ with a row spacing of 20 cm and harvested at II^nd week of April during both the year. Standardized package and practices of crop cultivation were followed for both test years.

The aboveground biomass yield from each net plot area was manually harvested using a sickle and threshed using a pullman thresher after sun-drying for 1 week. The harvested biomass was then oven-dried at 65°C for 72 h. The weight of the grains was recorded after they had been cleaned and sun-dried for 1 week following the final harvest. The wheat grain yield was assessed when the seed's moisture content fell within the range of 12%−14%. The per plot grain yield was measured and converted as Mg ha⁻¹.

Agronomic efficiency (AE) was determined using the below formula as given by Karlovsky (1982)

Crop recovery efficiency (CRE) was calculated through below formula as given by Shabnam and Iqbal (2016)

The total amount of energy used in all inputs was calculated by combining their energy equivalents for direct and indirect energy of renewable and non-renewable production inputs as follows

In the current investigation, we analyzed the data from three independent replicates of each treatment using common linear modeling techniques implemented in the Statistical Analysis System 9.3 software package (SAS Institute, Cary, NC). Analysis of variance (ANOVA) was conducted for split plot design to know the significance of the “F” value. For multiple comparisons of treatment means, the critical difference (least significant difference-LSD) at 5% level of significance was employed.

To assess grain quality features, principal component analysis (PCA) was conducted to identify statistically significant Eigenvalues that would help in selecting a minimum dataset of prominent grain quality parameters.

Significant variations in wheat yield attributes were observed (p < 0.05) under different tillage and residue management options, except for spike length and thousand grain weight, throughout the study period (Table 1). Retention of crop residues increased crop yield by 4.17%−21.6% regardless of tillage treatments without residue retention. The highest significant values for tiller counts (416–423), number of grains per spike (33.8–34.7), and number of spikelets per spike (18.7–19.6) were observed under the NT + R treatment compared to CT – R and NT – R. Similarly, the NT + R treatment showed a significant improvement in grain yield (~23.5%) and straw yield (~18%), followed by NT – R during the study period. The application strategies for P had a significant (p < 0.05) influence on yield-attributing traits and crop production, except for 1,000 grain weight. The P5 treatment exhibited the greatest increase in all harvestable yield attributes. As the rate of P application increased, there was a notable increase in the number of tillers per square meter (2.8%−10.4%), spike length (1.6%−12.5%), number of spikelets per spike (5.62%−57.6%), and number of grains per spike (4.01%−15.6%). The increase in grain yield (34.7%−70.4%) was almost equivalent to the increase in straw yield (33.2%−60.7%) with the rising P application rate. The interaction effect of tillage, residues, and P management practices on wheat yield was significant (p < 0.05) during both years of the study (Figure 3). Among the different treatment combinations, the combined application of NT + R with the P5 treatment resulted in a significant enhancement of grain yield by ~43.2% compared to the CT – R with the P1 treatment combination.

Tillage and residue management did not have a significant impact (p < 0.05) on amino acid composition and wheat grain protein content (Supplementary Table 2). However, they did have a significant impact on cumulative amino acids and net protein yield throughout the study years, following the order: NT + R > NT – R > CT – R (Table 2). The NT + R treatment showed a notable increase in amino acid yield, including lysine (~25.2%), methionine (~23.1%), proline (~22.0%), glycine (~20.4%), alanine (~31.4%), cystine (~18.7%), phenylalanine (~18.5%), and net protein yield (~21.2%) compared to CT – R. The P management practices had a significant (p < 0.05) impact on amino acid composition and wheat grain protein content (Supplementary Table 2). The P5 treatment exhibited the highest amplification of amino acid content (3.28 and 3.30% lysine, 1.91 and 1.92% methionine, 8.23 and 8.25% proline, 6.26 and 6.27% glycine, 7.76 and 7.78% alanine, 3.58 and 3.60% cystine, 4.91 and 4.95% phenylalanine) and protein content (10.8 and 10.9%), which was statistically similar to P3 and P4. Notably, a significant increase in amino acid yield (~65.7% lysine, ~59.1% methionine, ~60.7% proline, ~59.9% glycine, ~69.1% alanine, ~22.2% cystine, ~7.10% phenylalanine) and net protein yield (~12.6%) was recorded under the P5 treatment, followed by P3 throughout the 2-year experimental period (Table 2).

Principal component analysis (PCA) was conducted to study the amino acids and net protein yield in wheat grain. Two principal components (PCs) with eigenvalues ≥1 were generated, explaining a total variation of 97.7% of the total variance since they possessed eigenvalues >1.0 (Supplementary Table 2). The loading plot showed that PC1 (80.9%) exhibited significant positive loadings for proline yield, protein yield, glycine yield, and alanine yield. Similarly, PC2 had higher loadings for lysine yield, cystine yield, phenylalanine yield, and methionine yield. The quadrant first score plot identified treatments such as NT + R, P5; NT + R, P3; NT + R, P4; NT – R, P4; and NT + R, P2, showing positive heavy loadings on PC1. Notably, the fourth quadrant included diverse treatments such as NT – R, P5; NT – R, P3; and CT – R, P5 (Figure 4).

A significant interaction was observed between different tillage practices and P management strategies (p < 0.05; Table 3). The P agronomic efficiency was significantly higher for the treatment combination of P3 with NT + R (~128 kg grain kg⁻¹ of applied P) compared to other treatment combinations. In the first year, the highest P recovery efficiency was observed for the combination of NT + R and P3 (77.3 kg P uptake kg⁻¹ of P applied). Similarly, in the second year, a higher P recovery efficiency of 71.4 kg P uptake kg⁻¹ of P applied was observed with the NT + R and P3 treatment combination. This result was not significantly different from the NT – R and P3 treatment combination but was considerably superior to the CT – R and P3 treatment combination.

The energy dynamics were significantly influenced by different combinations of tillage practices, residue management, and P management strategies (Figures 5–7). A notable increase of 27% in energy gross return was observed in the NT + R treatment compared to the other tillage practices. The NT + R treatment resulted in the highest energy input, with a maximum of 50.1 and 50.2 × 103 MJ ha⁻¹, while the lowest energy input was observed under NT – R, with 18.8 and 18.8 × 103 MJ ha⁻¹. Implementing NT – R tillage practices led to a significant increase in net energy returns by ~32% and energy use efficiency by ~58% compared to ZT + R and CT – R. Throughout the study period, the P5 treatment exhibited the highest gross energy returns (184 and 192 × 103 MJ ha⁻¹), energy input (30.04 and 30.09 × 103 MJ ha⁻¹), and net energy returns (154 and 162 × 103 MJ ha⁻¹) compared to other treatments in terms of P management options. The interaction effect showed a significant increase (~58%) in energy use efficiency in the NT – R with P3 treatment combination. The next highest energy use efficiency was observed in the NT – R with P4 and NT – R with P5 treatment combinations.

In our study, CA improved crop productivity and sustainability of wheat in maize-wheat cropping systems. The NT + R treatment ensured higher nutrient availability (N, P, K), leading to better crop establishment, reduced weed infestation, and efficient nutrient utilization, resulting in higher grain yield and straw yield compared to the NT – R treatment during both years of experimentation (Busari et al., 2015; Page et al., 2019). The addition of crop residues played a role in preserving soil moisture and enhancing nutrient availability, promoting cellular reproduction, expansion, and overall crop growth, resulting in higher economic yield (Jinger et al., 2020; Jat et al., 2021). Additionally, the P management strategies significantly influenced yield-attributing traits and crop production throughout the trial period. The P5 treatment performed better in terms of yield attributes compared to P1, as higher available P in less weathered Inceptisols facilitates plant metabolism, energy conversion, and photosynthetic assimilation, leading to improved aboveground biomass assimilation, root growth, and supportive yield attributes (Ahmed et al., 2017). In our study, the combination of NT + R with P5 resulted in significantly superior grain production (6.56 and 6.80 Mg ha⁻¹, respectively) compared to CT – R along with P1 treatment combination (Figure 3) due to the balanced acquisition of available N, P, and K under conservation agriculture (Anwar et al., 2016; Rehim et al., 2016).

Amino acids and protein content in crops are the end products of successful growth and development, often regulated by the rate of carbon uptake and conversion into harvestable products. In our study, wheat grain quality in terms of lysine, methionine, proline, glycine, alanine, cystine, phenylalanine, and protein content was assessed. Wheat grown under NT + R treatment yielded significantly higher amino acids and net grain protein content. This can be attributed to increased root activity and improved soil aeration, facilitating nutrient uptake, particularly nitrogen, and its translocation from vegetative parts to the grain in standing wheat crop (Fernandez et al., 2018). Enhanced growth, productivity, and elevated levels of amino acids and protein ultimately led to increased overall yields of amino acids and protein (Babu et al., 2020; Kumar et al., 2023a). The observed improvements in amino acids and net protein yield may be due to the rising P levels, which could result in increased amino acids and improved nitrogen nutrition for the crops. This could be attributed to greater root development, more effective nutrient and water uptake by plants, and higher grain yield (Jamal and Fawad, 2019; Garutti et al., 2022). Under higher P nutrition levels (P5), maximal values of amino acids (lysine, methionine, proline, glycine, alanine, cystine, and phenylalanine) and protein content were observed, which were comparable to P3 and P4 treatments. The increase in the limiting amino acids of wheat grain, lysine (8.20%−11.6%), and methionine (4.02%−11.7%), was more prominent with the increase in P application levels. However, tillage practices had minimal impact on modifying grain amino acid content in wheat. The increase in external P application promoted wheat growth and enhanced crop nutrient uptake, leading to the observed increase in wheat grain amino acid content (Yi et al., 2023). The increasing P integration rates stimulated root activity, nutrient absorption from the soil solution, and translocation from source to sink, indirectly influencing protein and amino acid levels (Kumar and Saini, 2022). Moreover, the abundant P supply may require the breakdown of carbohydrates into acetyl co-enzyme A, an essential component for the production of amino acids and proteins (Haokip et al., 2019; Ali et al., 2020). Thus, external application of P amplified the grain amino acids and net protein yield in our study. Similar to Babicki et al. (2016), the PCA score plot displayed that treatments such as NT + R, P5; NT + R, P3; NT + R, P4; NT – R, P4; and NT + R, P2 showed positive heavy loading on PC1. Notably, the fourth quadrant included diverse treatments such as NT – R, P5; NT – R, P3; and CT – R, P5.

The P agronomic efficiency was significantly higher under the NT + R with P3 treatment combination compared to other combinations, as it resulted in enhanced grain yield per unit application of external P fertilizers (Johnston and Poulton, 2019). Furthermore, the inclusion of PSB in the P3 treatment led to higher P agronomic efficiency, saving 50% of P fertilizers while increasing grain yield. This increased wheat yield per unit P nutrient utilization contributed to improved P agronomic efficiency (Guelfi et al., 2022). In the first year, the NT + R and P3 treatment combination exhibited notably higher P recovery efficiency compared to other combinations. Similarly, in the second year, the same combination of NT + R and P3 treatment showed a higher P recovery efficiency, which was not significantly different from the NT – R and P3 treatment, but was significantly superior to the CT – R and P3 treatment combination. The solubilization of fixed P by PSB and the band placement of P fertilizers may explain this, as the amount of P sorbed is influenced by the soil-to-applied P ratio (Bijarniya et al., 2020). The higher grain yield and increased P uptake led to improved root growth dynamics, resulting in greater efficiency in P recovery and higher P utilization efficacy under the P3 treatment (Salim et al., 2023). This enhanced nutrient cycling enhances phosphorus utilization by plants, particularly when combined with a reduced amount of chemical fertilizer (Luo et al., 2017; Ven et al., 2019). The combination of chemical fertilizer and biofertilizer (PSB) can have synergistic effects on phosphorus availability and plant uptake. PSB facilitate the release of phosphorus and promote nutrient cycling through the decomposition of organic matter, releasing nutrients into the soil solution, thereby making them more available to plants (Nunes et al., 2022). The use of biofertilizers can potentially reduce phosphorus fixation by producing organic acids and enzymes that can dissolve or chelate soil-bound phosphorus, making it more accessible to plants (Yuan et al., 2016). Therefore, when biofertilizers are combined with a reduced amount of chemical fertilizer, overall P availability and recovery efficiency can be improved. By reducing the amount of chemical fertilizer applied and supplementing it with biofertilizers, nutrient losses can be minimized. This reduction in nutrient losses ensures that more phosphorus remains available in the soil for plant uptake, resulting in a higher phosphorus recovery efficiency for the P3 treatment compared to the P4 and P5 treatments. Additionally, at higher levels of applied P, plants utilize a smaller proportion of the added P, leading to a decreased P recovery efficiency (Kumar et al., 2023a,b).

In our study, the energy dynamics were significantly influenced by diverse tillage practices, residue management, and P management strategies. The implementation of NT + R tillage practices resulted in a notable increase in net energy returns by 87.9% compared to CT – R, while the gross energy returns were statistically similar to NT – R. The higher energy input in the NT + R system was attributed to the addition of residues (2.5 Mg ha⁻¹), whereas the NT – R and CT – R systems had lower energy inputs due to reduced tillage practices. Consistent with Kumar et al. (2021), the higher energy demand was primarily driven by the high energy value of the residues (12.5 MJ kg⁻¹). During both years, the NT – R method achieved the highest net energy returns and energy use efficiency, which were significantly greater than those achieved through NT + R and CT – R. This was mainly due to reduced energy usage and increased energy production resulting from higher grain and stover harvest. However, the excessive addition of crop residues can reduce the effectiveness in achieving energy balance and energy use efficiency, as the residues have a high potential energy value (Jat et al., 2018). Therefore, our results indicate that reduced tillage methods significantly increase yield and net energy income compared to conventional tillage (Kumar et al., 2023b). In terms of P management approaches, the P5 treatment consistently exhibited the highest gross returns of energy, energy input, and net returns of energy over the 2-year period. The interaction effect confirmed a percent increment of 56.3 in energy use efficiency for the NT – R with P3 treatment combination, followed by NT – R with P4 and NT – R with P5 (Kumawat et al., 2018; Haokip et al., 2020).