不同盐渍化土壤中微生物对氮肥的响应

【目的】 研究河套灌区土壤不同盐渍化程度下土壤微生物对氮肥的响应机理，为河套灌区盐渍化土壤中确立适宜的氮肥施用量提供理论依据。 【方法】 2015—2016年在内蒙古磴口县坝楞示范基地进行了两年田间试验，供试土壤为粉沙壤土，供试作物为玉米。设置轻度 (0.77～1.24 mS/cm) 和中度 (1.24～1.77 mS/cm) 盐渍化土壤为主区，副区为施氮水平，共设4个施氮水平为N 0、135、270、405 kg/hm2，研究轻、中度盐渍化土壤下不同施氮水平对土壤微生物的影响，探寻土壤盐渍化和氮肥对微生物的交互作用。 【结果】 土壤盐分随着施氮量的增加而增加；细菌、真菌、放线菌数量和微生物量碳、氮含量均随着施氮量的增加呈现出先增加后降低的趋势，在N 270 kg/hm2处理微生物数量和生物量均达到最高值。回归分析表明，土壤微生物与氮、土壤盐分之间呈现出极显著的二元二次非线性回归关系，由回归方程各系数可知，在盐渍化土壤中，单独施用氮肥均可以增加土壤微生物，而土壤盐分增加，土壤微生物减少；在轻度盐渍化土壤中，土壤盐分和施用氮肥对微生物具有正效应，即共同促进了土壤微生物的增加，而在中度盐渍化土壤中，土壤盐分和施用氮肥对微生物具有负效应，即抑制土壤微生物的增加。 【结论】 土壤盐渍化程度越高，土壤中微生物数量和生物量越少，施氮量为N 270 kg/hm2时微生物数量和生物量均达到最大值；土壤微生物与氮、土壤盐分之间呈现出极显著的二元二次非线性回归关系，在轻度盐渍化土壤中，土壤盐分和施用氮肥共同促进土壤微生物的增加，而在中度盐渍化土壤中，土壤盐分和施用氮肥抑制了土壤微生物的生长和繁殖。

Responses of soil microbes to N fertilizers in two saline soils

【Objectives】 To study microbial response to nitrogen fertilizer in saline soils with the goal of optimizing fertilizer application, improving environmental quality, and sustaining agricultural production. 【Methods】 Field experiments were conducted in Baleng Demonstration Base located in Dengkou County, Inner Mongolia. The tested soil was silt loam and the tested crop was maize. The experiment had a split design with the soil salinity level as the main effect while the nitrogen fertilizer rate was the split effect. Two fields had mild (0.77–1.24 mS/cm) and moderate (1.24–1.77 mS/cm) degree of salinities, and four nitrogen levels of 0, 135, 270 and 405 kg/hm2 coded as N0, N1, N2 and N3 were used. The soil salinity under different N levels was measured, and the population of soil microorganisms were investigated. 【Results】 Soil salt concentration increased with the increase of N application rate under the same degree of salinization. Populations of bacteria, fungi and actinomycetes and overall microbial biomass carbon and nitrogen contents first increased with the increase of N application followed by decreasing. In N2 treatment (i.e., N 270 kg/hm2), microbial populations and biomass reached peaks. Microbial populations showed a significant non-linear relationship with nitrogen fertilizer rate and soil salt concentration. In the soil of mild salinity, both N fertilizer and increase of salinity led to increase of microbial population, where the opposite was observed for the soil with moderate salinity. 【Conclusions】 The higher the degree of soil salinization, the lower the microbial populations. The microbial populations and biomass all reached the maximum with the N application rate of N 270 kg/hm2. Soil microbial population had a significant binary quadratic nonlinear relationship with N fertilizer rate and soil salinity level. The increase of soil salinity and nitrogen fertilizer promoted the growth of soil microbes in mild saline soil, but the effect became negative in moderate saline soil.