[Effects of tillage and nitrogen application rate on soil nitrogen transformation and yield in a winter wheat/summer maize multiple cropping system].

In the winter-wheat and summer-maize multiple cropping system in lime concretion black soil of Huanghuaihai Plain, the effects of three tilling methods (conventional tillage, rotary tillage, subsoiling tillage) in wheat season coupling with three nitrogen treatments (120 kg·hm, 225 kg·hm, 330 kg·hm) before maize sowing on the activities of microorganisms and enzymes re-lated nitrogen transformation, and inorganic nitrogen content in the rhizosphere soil during the main growth stages of maize, as well as the yield were investigated. The results showed that the rotary tillage had the highest ammonification intensity, and the more nitrogen was put in, the higher were the activities of microorganisms and enzymes related to soil nitrogen transformation. The activities of nitrification, denitrification and urease of subsoiling tillage was significantly higher than those of conventional and rotary tillage. Furthermore, in subsoiling tillage treatment, increasing nitrogen fertili-zer could promote soil nitrogen transformation while excessive nitrogen input inhibited soil nitrogen transformation, though the latter had higher yield and soil inorganic nitrogen content. The treatment of subsoiling tillage coupling with 225 kg·hm nitrogen, was best for soil nitrogen transformation while the treatment of subsoiling tillage coupling with 330 kg·hm nitrogen, had the highest corn yield.