Effects of AMF inoculation and nitrogen fertilizer reduction on nitrogen uptake in pepper-soybean intercropping systems

Objectives In Yunnan Province, leafy and high-profit fruit vegetables account for 62.19% of the total facilities cultivation, the continuous application of nitrogen fertilizer (N) in large quantity has restricted the further improvement of vegetable yield and quality, and deteriorated soil fertility. Targeting on the situation, we studied the effects of microbial agent, N reduction and planting patterns.

Methods A three-factor pot experiment was conducted, using a continuous leafy vegetable production soil, and pepper (Tianjiao No.6 F1) and soybean (Diandou No.7) as test materials. Plant patterns included pepper, soybean monoculture, and intercropping. Under each pattern, three N rates: 0, 100, 200 mg/(kg, soil) were set up and denoted as N0, N1, and N2; and each N rate contained AMF inoculation and no inoculation (denoted as AMF, and NM). After harvest, the plant biomass, N concentration, the root length and AMF infection rate were investigated. Soil samples were collected at the same time for the determination of protease, urease and nitrate reductase activity, and nitrate and ammonium N content, and mycelium density.

Results AMF inoculation, N rate and plant pattern, and the interaction of the three factors showed extremely significant effect on the plant biomass, root length, and AMF infection rate (P<0.01). N1 significantly increased root infection of pepper and soybean, with the highest infection rate under intercropping pattern. Under N1 condition, AMF inoculation significantly increased plant biomass and N uptake, but inhibited root elongation of pepper and soybean, likely, intercropping significantly increased plant biomass but inhibited root elongation. N2 rate increased soil ammonium N and nitrate N content significantly, but AMF inoculation decreased rhizosphere ammonium N and nitrate N content, and intercropping decreased pepper rhizosphere soil nitrate N and soybean rhizosphere soil ammonium N content. AMF inoculation and intercropping increased the activities of soil protease, urease and nitrate reductase. N1 increased soil hyphae density significantly, AMF inoculation increased that in intercropped pepper rhizospheric soil.

Conclusions Combined with intercropping and AMF inoculation, reducing N application rate could increase the root AMF infection, increase hyphae density in soil, enhance nitrogen cycling related enzyme activities, thereby improve plant growth and root elongation, increase nitrogen uptake and the utilization rate of soil N, and reduce soil N residues. Intercropping, AMF inoculation, and N reduction is an prospective combination measurement for the efficient and sustainable facilities vegetable production in Yunnan Province.