Effects of two years′ incorporation of leguminous green manure on soil properties of a wheat field in dryland conditions

In order to improve soil quality under dryland conditions,a field experiment was undertaken in the Weibei area to investigate the effects of leguminous green manure(soybean,Huai bean and mung bean) and a range of nitrogen fertilizer rates(N0,0 kg N/hm2;N108,108 kg N/hm2;N135,135 kg N/hm2 and N162,162 kg N/hm2) during winter wheat growth on soil fertility over two years.A split block design with three replications was used.Soil samples were collected from a depth of 0—200 cm in July 2011 and were analyzed for soil moisture,NH+4-N and NO-3-N.Soil samples from 0—20 cm were air-dried and analyzed for soil organic matter,active organic matter,total N and available K contents. Incorporation of leguminous green manure significantly improved soil organic matter(SOM),active organic matter(SAOM),total N concentrations and the carbon pool management index(CPMI) but did not increase soil available K.SOM,SAOM,CPMI and total N concentrations in the green manure treatments were 3.9%—11.7%,3.2%—7.6%,2.7%—7.6% and 4.5%—10.8% higher than those in the summer fallow treatment(CK),respectively.The effects of planting leguminous green manure on soil quality varied among green manure types.The mung bean treatment had higher biomass returned into the soil,but contributed less to soil fertility compared with the soybean and Huai bean treatments;Huai bean had the greatest influence in improving soil properties.Based on the data from 2008 to 2010,the fresh biomass of mung bean was 24.5% and 25.3% higher than for soybean and Huai bean separately.However,K incorporation was 13.6%—24.4% lower than that in the other two types.N incorporation was also lower,as was P incorporation of soybean which was 28.3% lower than for mung bean and Huai bean.Green manure plants used much soil water at the growth period,which resulted in less water storage in the 0—200 cm soil depth before incorporation of green manure,before winter wheat sowing and after wheat harvest.Water storage in the 0—200 cm depth in the green manure treatments at the full flowering stage was 39.2—51.4 mm lower than that in the summer fallow treatment.However,water consumption during the wheat growth period was almost the same in the green manure and summer fallow treatments.Green manure treatments had a 6.5%—8.8% higher water use efficiency compared to summer fallow resulting from the greater wheat yield for the green manure treatments.Compared with the N0 treatment,application of N fertilizer during winter wheat growth had a significant increase in water use efficiency(WUE).Applying N fertilizer increased WUE by 11.6%—16.7% compared to the N0 treatment.However,no significant influence on other soil properties was observed under the N application treatments. In conclusion,incorporation of leguminous green manures during the summer fallow period was an effective way to improve soil fertility and increase soil water use efficiency in this dryland system.