Long-term application of K fertilizer and straw returning improve crop yield, absorptive capacity of K, and soil nutrient natural supplying capacity in North China

With the aim of increasing the grain crop yield and the level of soil nutrition in the fluvo-aquic soil in North China, the effects of long-term application of K fertilizers and straw returning on crop yield and soil nutrient supplying capacity were investigated in the long-term K localization experiment (1992–2009). The results revealed that wheat and maize responded to K fertilizer in an identical manner and the average yield of wheat and maize for 17 years were NPKSr > NPK > NPSr > NP. Application of K fertilizer on the basis of NP fertilizers could increase the yield of wheat and maize while the grain and straw yields in each treatment were significantly higher for maize than for wheat. The yield of wheat and maize was increased by 6.74% and 22.32% respectively when applied with NPK fertilizers compared to NP fertilizers. With the NPSr fertilizing mode, the yield of wheat and maize was increased by 2.84% and 10.62% compared to the NP mode respectively. The NPKSr fertilizing mode gave the best yield for wheat and maize, resulting in 10.34% and 23.81% increase respectively compared to the NP mode. The yield stability of wheat was significantly higher than that of maize. Under the condition of long-term fertilization, the K uptaken by wheat and maize was degressive by the sequence of NPKSr > NPSr > NPK > NP, mainly deposited in the straw but not in the grain. In this work, the soil natural ability for applying K was gradually reduced as the planting years proceeded and the changes were fitted by linear equations. The natural supply ability of K element in land planted wheat was higher than that in land planted maize.