[Effects of planting density and nitrogen application rate on soil microbial activity under wheat/forage rape multiple cropping].

A field experiment was conducted to study the effects of planting density and nitrogen application rate on the topsoil (0-15 cm) microbial activity under wheat/forage rape multiple cropping. The results showed that multiple-cropping forage rape with wheat could significantly increase soil microbial biomass C (Cmic), soil microbial biomass N (Nmic), soil bacteria number (SBN), soil fungi number (SFN) and soil actinomyces number (SAN), but decrease soil microbial biomass C/N (Cmic/Nmic). The Cmic/Nmic and SBN increased with increasing planting density of forage rape, while Nmic and SAN were in adverse. SFN increased significantly with increasing nitrogen application rate, but Cmic and Nmic decreased first, increased then, and decreased again, with the highest in treatment 1000 kg x hm(-2) N. Also with increasing nitrogen application rate, the SFN and SAN during harvest stage of forage rape decreased first and increased then, while the SAN during seedling stage increased first and decreased then. Soil microbial activities at rape harvest stage were all higher than those at seedling stage, except for SAN in treatment 600 kg x hm(-2) N. SBN and SAN were positively correlated with Cmic and Nmic, but negatively correlated with/Nmic. No significant correlation was observed between SFN and Cmic, and SMBN and Cmic/Nmic.