Nutrient requirements determined by grain yield and protein content to optimize N, P, and K fertilizer management in China

Nutrient requirement for crop growth, defined as the amount of nutrient that crops take up from soil to produce a specific grain yield, is a key parameter in determining fertilizer application rate. However, existing studies primarily focus on identifying nitrogen (N), phosphorus (P), and potassium (K) requirements solely in relation to grain yield, neglecting grain protein content, a crucial index for wheat grain quality. Addressing this gap, we conducted multi-site, multi-cultivar, and multi-year field trials across three ecological regions of China from 2016 to 2020 to elucidate variations in nutrient requirements for grain yield and grain protein. The research findings revealed that wheat grain yield ranged from 4.1 to 9.3 Mg ha⁻¹ (average 6.9 Mg ha⁻¹) and grain protein content ranged from 98 to 157 g kg⁻¹ (average 127 g kg⁻¹) across the three regions. Notably, the N requirement exhibited a nonlinear correlation with the wheat grain yield but a linear increase with increasing grain protein, while the P and K requirements positively correlated with grain yield and protein content. Regression models were formulated to determine the nutrient requirements (M_ENR), enabling the prediction of N, P, and K requirements for leading cultivars with varying grain yields and protein contents. Implementing nutrient requirements based on M_ENR projections resulted in substantial reductions in fertilizer rates: 22.0 kg ha⁻¹ N (10.7 %), 9.9 kg ha⁻¹ P (20.2 %), and 8.1 kg ha⁻¹ K (16.3 %). This translated to potential savings of 0.4 Mt. N, 0.23 Mt. P, and 0.17 Mt. K, consequently mitigating 5.5 Mt. CO₂ greenhouse-gas emission and yielding an economic benefit of 0.8 billion US$ annually in China. These findings underscore the significance of considering grain yield and protein content in estimating nutrient requirements for fertilizer recommendations to realize high-yielding, high-protein wheat production, and minimize overfertilization and associated environmental risks.