Sugarcane/soybean intercropping with reduced nitrogen addition enhances residue-derived labile soil organic carbon and microbial network complexity in the soil during straw decomposition

Sugarcane/soybean intercropping with reduced nitrogen addition is an important sustainable agricultural pattern that can alter soil ecological functions,thereby affecting straw decomposition in the soil.However,the mechanisms underlying changes in soil organic carbon(SOC)composition and microbial communities during straw decomposition under long-term intercropping with reduced nitrogen addition remain unclear.In this study,we conducted an in-situ microplot incubation experiment with^(13)C-labeled soybean straw residue addition in a two-factor(cropping pattern:sugarcane monoculture(MS)and sugarcane/soybean intercropping(SB);nitrogen addition levels:reduced nitrogen addition(N1)and conventional nitrogen addition(N2))long-term experimental field plot.The results showed that the SBN1 treatment significantly increased the residual particulate organic carbon(POC)and residual microbial biomass carbon(MBC)contents during straw decomposition,and the straw carbon in soil was mainly conserved as POC.Straw addition changed the structure and reduced the diversity of the soil microbial community,but microbial diversity gradually recovered with decomposition time.During straw decomposition,the intercropping pattern significantly increased the relative abundances of Firmicutes and Ascomycota.In addition,straw addition reduced microbial network complexity in the sugarcane/soybean intercropping pattern but increased it in the sugarcane monoculture pattern.Nevertheless,microbial network complexity remained higher in the SBN1 treatment than in the MSN1 treatment.In general,the SBN1 treatment significantly increased the diversity of microbial communities and the relative abundance of microorganisms associated with organic matter decomposition,and the changes in microbial communities were mainly driven by the residual labile SOC fractions.These findings suggest that more straw carbon can be sequestered in the soil under sugarcane/soybean intercropping with reduced nitrogen addition to maintain microbial diversity and contribute to the development of sustainable agriculture.

Analysis on Waxy Corn/Soybean Intercropping Pattern and Economic Benefit

The research mainly analyzed effects of waxy corn/soybean intercropping on yields of the two crops, as well as agronomic characters, and the economic benefits of the mode. The results showed that although yields of waxy corn and soybean went down by 21.19% and 31.04% per unit area, land equivalent ratio（1.48） kept higher than 1, suggesting the intercropping improves land use rate. Besides, due to the practice of intercropping, many characters of waxy corn grew, but of soybean declined. The economic benefits from high to low were waxy corn/soybean intercropping, monoculture of waxy corn, and monoculture of soybean.

Suitability of the DNDC model to simulate yield production and nitrogen uptake for maize and soybean intercropping in the North China Plain

Intercropping is an important agronomic practice. However, assessment of intercropping systems using field experiments is often limited by time and cost. In this study, the suitability of using the DeNitrification DeComposition(DNDC) model to simulate intercropping of maize(Zea mays L.) and soybean(Glycine max L.) and its aftereffect on the succeeding wheat(Triticum aestivum L.) crop was tested in the North China Plain. First, the model was calibrated and corroborated to simulate crop yield and nitrogen(N) uptake based on a field experiment with a typical double cropping system. With a wheat crop in winter, the experiment included five treatments in summer: maize monoculture, soybean monoculture, intercropping of maize and soybean with no N topdressing to maize(N0), intercropping of maize and soybean with 75 kg N ha–1topdressing to maize(N75), and intercropping of maize and soybean with 180 kg N ha–1topdressing to maize(N180). All treatments had 45 kg N ha–1as basal fertilizer. After calibration and corroboration, DNDC was used to simulate long-term(1955 to 2012) treatment effects on yield. Results showed that DNDC could stringently capture the yield and N uptake of the intercropping system under all N management scenarios, though it tended to underestimate wheat yield and N uptake under N0 and N75. Long-term simulation results showed that N75 led to the highest maize and soybean yields per unit planting area among all treatments, increasing maize yield by 59% and soybean yield by 24%, resulting in a land utilization rate 42% higher than monoculture. The results suggest a high potential to promote soybean production by intercropping soybean with maize in the North China Plain, which will help to meet the large national demand for soybean.

Effects of intercropping systems of trees with soybean on soil physicochemical properties in juvenile plantations

The intercropping system of tree with soybean in juvenile plantations, as a short-term practice, was applied at Lao Shan Experimental Station in Mao＇er Shan Forest of Northeast Forestry University, Harbin, China. The larch （Larix gmelinii）lsoybean （Glycine max.） and ash （Fraxinus mandshurica） intercropping systems were studied in the field to assess the effects of the intercropping on soil physicochemical properties. The results showed that soil physical properties were improved after soybean intercropping with larch and ash in one growing season. The soil bulk density in larch/soybean and ash/soybean systems was 1.112 g·cm^-3 and 1.058 g·cm^ 3, respectively, which was lower than that in the pure larch or ash plantation without intercropping. The total soil porosity also increased after intercropping. The organic matter amount in larch/soybean system was 1.77 times higher than that in the pure larch plantation, and it was 1.09 times higher in ash/soybean system than that in the pure ash plantation. Contents of total nitrogen and hydrolyzable nitrogen in larch/soybean system were 4.2% and 53.0% higher than those in the pure larch stand. Total nitrogen and hydrolyzable nitrogen contents in ash/soybean system were 75.5% and 3.3% higher than those in the pure ash plantation. Total phosphorus content decreased after intercropping, while change of available phosphorus showed an increasing trend. Total potassium and available potassium contents in the larch/soybean system were 0.6% and 17.5% higher than those in the pure larch stand. Total potassium and available potassium contents in the ash/soybean system were 56.4% and 21.8% higher than those in the oure ash plantation.