Estimating on-farm wheat yield response to potassium and potassium uptake requirement in China

Understanding grain yield response to potassium fertilizer supply and potassium uptake requirements is essential for devising optimized potassium fertilizer management policies in China. Currently, potassium fertilization is often ignored due to high natural levels of potassium in the soil. We conducted 836 on-farm experiments at 209 sites in China to quantify wheat (Triticum aestivum L.) grain yield response to potassium application rates, and evaluate potassium uptake requirements with increasing grain yield. Across all 209 sites, wheat grain yield increased by 70% from 3.3 Mg ha−1 at a control level to 5.6 Mg ha−1 for recommended potassium treatments (RKR, 102 kg K2O ha−1). With 150% RKR treatments, no yield gains were achieved, while there was a notable decrease in potassium use efficiency. The potassium uptake requirements per Mg of grain (Kreq) increased from 21.1 kg with RKR treatments to 21.9 kg with 150% RKR treatments, which indicated that a luxury potassium uptake occurred under excessive potassium application. Under RKR treatments, Kreq decreased from 23.8 kg with <4.5 Mg ha−1 to 20.2 kg with >7.5 Mg ha−1, which was attributed to the increase of the harvest index (from 45.5% to 48.6%) and decline in grain potassium concentrations (from 4.7 g kg−1 to 4.0 g kg−1). When the grain yield was <7.5 Mg ha−1, potassium accumulation during post-anthesis was lower than that at pre-anthesis, by −78.5 kg ha−1 and −30.8 kg ha−1 with <6 Mg ha−1 and 6-7.5 Mg ha−1 yield ranges, respectively, but higher than that at pre-anthesis when the grain yield was >7.5 Mg ha−1 and by 18.2 kg ha−1. In summary, potassium fertilization can increase wheat grain yield in China and total potassium uptake requirements were shown to decrease with increasing grain yield. This suggests that potassium optimization must be taken into account in management decisions for high-yielding wheat production in China.