Yield and Potassium Balance in a Wheat-Maize Cropping System of the North China Plain

This study examined the effects of long-term K fertilization on crop yields and K use efficiency and balance under a wheat (Triticum aestivum L.)-maize (Zea mays L.) cropping system in the Fluvo-Aquic soil of Yucheng Comprehensive Experiment Station in the North China Plain (NCP). Results showed that the native K supply could maintain annual grain yields at stable levels at 10.7 Mg ha(-1) for >19 yr with applications of N and P alone. The application of K alone significantly improved maize yield by 46% but wheat showed no response. The agronomic efficiency, physiological efficiency, and partial factor productivity but not apparent use efficiency of wheat were significantly lower than the average values previously reported. In addition, only 43% of K found in the aboveground biomass of wheat and maize came from an annual application of fertilizer. The application of K caused a large K surplus, even with balanced fertilization, in which 33% of applied K was left in the soil, mostly in the 0- to 20-cm depth due to its surface application. The data indicated that the native K supply in the NCP might sustain normal wheat yields for about 10 to 30 yr. Generally, in a Fluvo-Aquic soil with a high content of soil available K, soil K can be used. In this study, 471 kg ha(-1) yr(-1) K input was excessive for the growth of maize and wheat, and at least 120 to 150 kg ha(-1) yr(-1) K could be saved with the use of balanced fertilization.