Responses to Potassium Application and Economic Optimum K Rate of Maize under Different Soil Indigenous K Supply

Potassium (K) is an essential macronutrient for maintaining crop productivity, but the economic benefit of K fertilizer often has been neglected. We collected a database from 60 maize field experimental sites in Northeast China between 2005 and 2012 to study the impacts of potassium (K) application rates on yield, K concentrations in grain and straw, plant K uptake, and to evaluate the economic optimum K rate (EOKR) for maize under different levels of soil indigenous K supply (IKS). The results showed that the average maize yield in K rec treatment (the recommended K rate) was highest and was 32.1% higher than that in K 0 treatment (no K fertilization). Compared to K 0 , the application of K did not significantly increase grain K concentration, whereas it significantly increased K concentration in the straw. Plant K uptake in K 150 treatment (150% of the recommended K rate) was higher than that in K rec treatment, but grain yield was lower than that in K rec treatment. Thus, the result indicates that luxury K absorption occurred in K 150% treatment due to excessive K application. Thus, the application rate of K should be further optimized. Based on the modified Mitscherlich model, the average economic optimum K rate (EONR) was 135.24, 124.27, and 96.54 kg K 2 O/ha for the low, medium, and high levels of soil indigenous K supply (IKS), respectively. The average economic optimum yield (EOY) at a high IKS level was similar to the average yield in K rec treatment, whereas the EOKR could reduce by a K rate of 37.9–63.7 kg K 2 O/ha compared to K rec treatment. This study highlights the importance of K application to improve grain yield and provides a promising fertilizer recommendation method for minimizing fertilizer inputs and optimizing maize production.