旱地不同绿肥品种和种植方式提高土壤肥力的效果

【目的】黄土高原旱地土壤贫瘠，夏闲期雨热资源难以被充分利用。本研究通过田间试验研究不同夏季绿肥品种及其种植方式对绿肥鲜重、绿肥养分还田量、土壤养分含量、土壤酶活性、土壤水溶性有机碳和微生物量碳含量的影响，旨在筛选出适宜当地夏闲期种植的绿肥品种及种植方式，为促进黄土高原地区农业可持续发展提供理论依据和技术支持。 【方法】本研究采用随机区组设计，以夏季裸地休闲为对照，设绿肥 (绿豆、长武怀豆、毛叶苕子、油菜) 和绿肥种植方式 (麦后播种、麦田套种) 为研究因素，共 9 个处理。绿肥盛花期全区齐地收割地上部并称重计鲜草产量，分析绿肥地上部氮磷钾含量；每个小区采集 50 株绿肥下长、宽、深均为 20 cm 的土体中的根系，称重并进行分析；绿肥收获翻压 20 天后，于各小区采集 0—20 cm 土壤样品，测定土壤养分含量，土壤微生物量碳，土壤水溶性有机碳含量以及主要酶含量。【结果】绿肥麦后播种生物量要高于麦田套种；麦后播种以怀豆和油菜生物量较高，套种以油菜生物量显著高于其他处理。不同种植方式下绿肥总养分还田量与生物量规律类似；麦后播种长武怀豆显著提高了氮素和磷素还田量，麦后播种油菜显著提高了磷素和钾素还田量；套种时氮、磷和钾还田量由高到低顺序为油菜 > 毛叶苕子 > 绿豆 > 长武怀豆，不同绿肥间差异达到显著水平。翻压油菜土壤有机质、速效磷及速效钾含量都要显著高于休闲处理；麦后播种长武怀豆并翻压 2 年后，0—20 cm 土壤有机质、总氮、矿质氮、速效磷及速效钾含量较休闲分别提高了 12.4%、22.2%、95.9%、28.6% 和 11.2%。种植绿肥与休闲相比，土壤水溶性有机碳和微生物量碳含量均有所提高，其中套种油菜增加达显著水平，麦后播种各绿肥间土壤微生物量碳含量差异不显著，但都显著高于休闲。与休闲相比，麦后播种绿肥均提高了土壤酶活性；套种绿肥除绿豆处理的脲酶和过氧化氢酶低于休闲外，其他处理均提高了土壤酶活性。土壤各测定指标与绿肥生物量之间均有显著或极显著的正相关关系，表明土壤肥力的提高主要取决于还田绿肥的生物量。【结论】长武怀豆和油菜翻压入土后，能够增加土壤的养分含量和酶活性，培肥效果优于绿豆和毛叶苕子。麦后播种绿肥的生物量、养分还田量显著高于套种，土壤养分含量及土壤酶活性也较高。所以在黄土旱塬地区可选择麦后播种长武怀豆和油菜可有效改善土壤肥力。

Effect of improving soil fertility by planting different green manures in different patterns in dryland

Objectives]The soil of dryland areas of the Loess Plateau is often barren, the heat and precipitation resources can not be fully utilized during summer fallow period. Therefore, a field experiment was conducted to investigate effects of green manure crop varieties and planting patterns on their biomass, nutrient contents, soil nutrient contents, soil enzyme activities, soil microbial biomass carbon (SMBC) and dissolve organic carbon (DOC) to determine the best green manure crop variety and planting pattern, which can be regarded as the theoretic base and technical support for the development of sustainable agriculture in the Loess Plateau.Methods]An experiment with randomized complete block design was conducted. The bare fallow in summer was used as control, two factors were green manure varieties (Mung bean, Huai bean, Hairy vetch and Rape)and planting patterns (after wheat harvest and intercropped with wheat), counting to 9 treatments. The green manure was harvested in full blooming stage and the yield of fresh grass was weighted, the N, P and K contents were analyzed. The root samples were collected inside volume 20 cm × 20 cm × 20 cm at the bottom of 50 plants in each plot and weighted, soil samples (0–20 cm deep) were collected 20 days after the green manure was returned into field, and the contents of nutrients, soil microbial biomass carbon (SMBC) and dissolve organic carbon (DOC), as well as the activities of main soil enzymes, were determined.Results]The results indicated that the after wheat harvest had greater biomass than intercropping, the Huai bean and rape treatments had greater biomass than other green manures in the after wheat harvest, and the biomass of rape treatments was significantly increased in contrast with other green manures in the intercropped with wheat. The changes of green manure nutrient contents were similar to those biomass in different planting patterns. Huai bean provided the highest amounts of nitrogen and phosphorous, while rape offered the highest amounts of phosphorous and potassium through incorporation in the after wheat harvest, and the amounts of nitrogen, phosphorous and potassium through incorporation in the intercropped with wheat were rape > hairy vetch >Mung bean > Huai bean. The rape treatment significantly increased soil organic matter (SOM), available phosphorous and available potassium compared with the fallow. After 2 years of the after wheat harvest, the Huai bean treatment enhanced soil organic matter(SOM), total nitrogen, mineral nitrogen, available phosphorous and available potassium contents in the depth of 0–20 cm by 12.4%, 22.2%, 95.9%, 28.6% and 11.2%, respectively, compared with the fallow. Incorporation of green manure during summer fallow period increased soil microbial biomass carbon (SMBC) content and dissolve organic carbon (DOC) content compared with the fallow, and the rape treatments significantly increased soil microbial biomass carbon (SMBC) and dissolve organic carbon (DOC) in the intercropped with wheat. There were no significant differences of soil microbial biomass carbon (SMBC) between the green manure treatments in the after wheat harvest, however, the contents were greater than those of the fallow (P< 0.05). Green manure in the after wheat harvest enhanced soil enzyme activities compared with the fallow, and other intercropped with wheat green manures increased soil enzyme activities except the Mung bean treatment which decreased the enzyme activities of urease and catalase. The significant correlations between soil properties and green manure biomass indicated that the soil fertility was determined by the amount of green manure biomass to soil.Conclusions]The Huai bean and rape treatments could significantly increase soil nutrient contents and soil enzyme activities and they were better than Mung bean and hairy vetch. As for the planting patterns, the after wheat harvest was better than the intercropped with wheat. Huai bean and rape as green manure applied after wheat harvest can effectively improve soil quality in dryland of the Loess Plateau.