Effects of nitrogen application rate on soil microbial quantity and soil enzymes activities in maize/soybean intercropping systems

To study the effects of nitrogen rate on soil microbial quantity and enzyme activity in maize/soybean intercropping system, a 2-factor design was developed. The main factor in the design was planting pattern, which included monoculture maize (MM), sole soybean (SS) and maize/soybean relay strip intercropping system (IMS). Then the sub-factor of nitrogen application rate N for maize and soybean were no nitrogen application0 kg(N)·hm^-2, NN, reduced nitrogen application180 kg(N)·hm^-2, RN, and conventional nitrogen application240 kg(N)·hm^-2, CN. The results showed that the quantities of fungi and actinomycetes in rhizosphere soil of intercropped maize were 25.37% and 8.79% higher than those of monoculture maize, respectively. Also the quantities of soil fungi, actinomycetes and nitrogen-fixing bacteria in the rhizosphere soil of intercropped soybean were higher than those of sole soybean. Soil protease and urease activities in the rhizosphere soil of intercropped maize and protease activity in rhizosphere soil of intercropped soybean significantly increased compared with the corresponding monoculture. Under different nitrogen application rates, the quantities of soil fungi, actinomycetes and nitrogen-fixing bacteria in the rhizosphere of maize and soybean were higher under RN than under NN and CN, respectively. In addition, nitrogen application increased the quantity of actinomycetes in the rhizosphere soil of maize and soybean. The quantities of nitrogen-fixing bacteria in the rhizosphere soil of maize were 17.78% and 5.67% higher under RN compared with those under NN and CN, respectively. Moreover, the activities of soil protease and urease in the rhizosphere of maize and activity of soil urease in the rhizosphere of soybean were highest under RN compared with those under NN and CN. Reduced nitrogen fertilization increased the degree of soil microbial and enzyme activities in the rhizosphere of maize/soybean relay strip intercropping system, promoted nitrogen uptake of maize and soybean, and thereby saved fertilizer use.