Effect of long-term application of potassium fertilizer and wheat straw to soil on yield of crops and soil potassium in fluvo-aquic soil and brown soil of northcentral China

Experiments of long-term application of K fertilizer and wheat straw to soil in Hebei fluvo-aquic soil and Shanxi brown soil in northcentral China were started in 1992. Effect of application of K fertilizer and wheat straw to soil on crop yield and status of soil K in the plough layer under different planting systems was studied. The results showed that K fertilizer and wheat straw could improve yield of wheat and maize, and yield in treatments of NPK and NPK+St was significantly different from yield of the NP treatment. The effect of K fertilizer and wheat straw application differed with fixed experimental sites. In two fixed sites, variation of wheat yield in each treatment（CV≤13%) was lower than maize yield（CV＞14%）, and efficiency of yield increase in maize was higher than in wheat in Hebei. In contrast with Shanxi, the waste of soil potassium was more serious in the rotation system in Hebei. Application of K fertilizer and straw could improve the content of water-soluble K（average increase was 5.8 mg/kg in 0-20 cm layer of Hebei, 16.9 mg/kg in Shanxi, same as follows）, non-specifically adsorbed K（21.2 mg/kg，35.9 mg/kg）, non-exchangeable K（75.1 mg/kg，57.5 mg/kg）, mineral K（0.03％，0.01％）, and total K compared with NP treatment in 0-20 cm and 20-40 cm soil layers, but reduce the proportion of mineral K and improve proportion of other forms of K in the two fixed sites. The content and proportion of all forms of K decreased with depth, except mineral K. The content and proportion of specifically adsorbed K were not significantly affected by K fertilizer and straw application or soil depth. In summary, the effect of K fertilizer directly applied to soil was better than wheat straw returned to soil, and the effects of both methods on each form of K in topsoil was stronger than in subsoil.