Underestimated potassium supply from crop residue return in China’s major cereal systems

Abstract

Context: Potassium (K) is essential for crop productivity, yet China’s heavy reliance on imported potash threatens national food security. While crop residue return is a key strategy for recycling K, residue-derived K inputs remain poorly quantified. Existing estimates are highly uncertain because they rely on static average parameters (harvest index and K concentrations), neglect regional and yield-related variability, and lack quantitative data on crop residue return rates. Objective: This study developed a regionalized, yield-dependent statistical modelling framework to accurately quantify crop residue production and K accumulation, and evaluated K recycling and soil K balance across China’s major maize, wheat, and rice systems. Methods: Here, 20,756 observations from the literature and field trials were synthesized to derive regionalized parameters for grain and residue K concentrations and to develop harvest index–based regionalized linear mixedeffects models for predicting residue yields of the three major cereal crops. Additionally, a nationwide survey of 5805 farmers was conducted to quantify crop- and region-specific residue return rates. Results: The harvest index of maize and rice has increased markedly over recent decades. A critical physiological finding was the occurrence of luxury K uptake, whereby crops absorb K in excess of target yield-related requirements, often leading to greater K accumulation in crop residues rather than in the grains. By 2020, total residue production reached 620 Mt, while residue K accumulation amounted to 10.7 Mt, which is 35.4% above previous estimates. Driven by the confluence of yield-induced luxury uptake and expanded residue retention, residue K return nearly doubled from 5.49 Mt in 2010–9.25 Mt in 2020. This influx clearly outpaced the growth in mineral K fertilizer input (2.89–4.53 Mt), effectively pivoting China’s cereal crop soil K balance from a − 2.23 Mt deficit to a 1.2 Mt surplus. Additionally, residue return provided a significant carbon sequestration benefit of 46.7 Mt C annually. Conclusions: K supply from residue return in China’s major cereal systems has been substantially underestimated. Large amounts of K stored in cereal crop residues are increasingly recycled to croplands through residue return. The switch from a soil K deficit to a modest national K surplus indicates requires re-evaluating and optimizing current K fertilizer recommendation schemes, including reducing K input from fertilizer and manure in cropping regions with a large K surplus.