Effects Of Green Manure Return On Winter Wheat Yield And Soil Carbon And Nitrogen In Dryland

The growth of legume green manure can not only fixed nitrogen in the atmosphere,but its roots and nodules can also encourage microbial activity,fertilizer cultivation and soil enhancement.There have been studies on the improvement effects of green manure return on crop yield and soil fertility,but there are few studies on the improvement benefits of green manure return on three main food crops(wheat,rice,and maize)and farmland soil globally,as well as on the overall benefits of nitrogen reduction and green manure return based on longterm positioning experiments.Therefore,a global meta-analysis was conducted to study the effects of green manure return on the yield increase of wheat,rice and maize and the improvement of soil physical and chemical properties.Furthermore,using long-term positioning experiments in dryland wheat field(Changwu)on the Loess Plateau,the effects of nitrogen reduction and green manure return on aboveground biomass,nutrient accumulation,photosynthetic characteristics,soil carbon and nitrogen nutrients and aggregates of winter wheat were examined in order to provide theoretical foundation and practical experience for high yield soil improvement of winter wheat planting in dryland on the Loess Plateau.The following are the key findings of the study:(1)The return of green manure increased crop yield and improved soil physical and chemical properties.The results of global meta-analysis showed that the grain yield of wheat,rice and maize increased by 12%,9% and 20% respectively,compared with fallow control,and that the average increase of the three food crops was 12%.In terms of soil physical and chemical properties,the contents of organic carbon,total nitrogen,available phosphorus and available potassium were increased by 10%,12%,8% and 8%,respectively,while soluble organic carbon,microbial biomass carbon and easily oxidized organic carbon were increased by 6.7%,26.7% and 3.8%,respectively.For soil aggregates,the stability of soil aggregates was improved by returning green manure to field,and the content of water-stable large aggregates,mean weight diameter and geometric mean diameter were increased by 6%,12%and 3%,respectively.More soil water is used while planting green manure,and most of this water is used in the top 0-1 meters of the soil.Green manure returning decreased soil nitrate nitrogen leaching by 44% as compared to fallow control,and the effect on non-legume green manure returning was more pronounced.Returning green manure to farmland increased soil carbon sequestration rate by 80% on average.(2)The growth and nutrient utilization of winter wheat were improved by nitrogen reduction and green manure return.Long-term location experiment results showed that,nitrogen reduction and green manure return measures(GM)increased the grain yield of winter wheat by 6% compared with low nitrogen(LN)mode,while there was no significant difference between HN(farmer mode)and LN(nitrogen reduction mode).GM significantly increased the above-ground biomass of winter wheat by 22%,and increased the accumulation of carbon and potassium in stem by 23% and 19% compared with LN,respectively,but had no significant effect on above-ground nutrient content of winter wheat.Compared with HN,LN and GM increased the nitrogen uptake rate by 39% and 42%,respectively,while GM increased the nitrogen partial factor productivity by 63%.For agronomic traits,with the growth and development of winter wheat,leaf area and leaf area index(LAI)increased from regreening stage to jointing stage,reached the maximum value at jointing stage,and then tended to decrease slowly and gradually stabilized.The leaf area and LAI of GM were significantly higher than those of LN and HN in most periods.(3)Nitrogen reduction and green manure return improved soil carbon and nitrogen levels in dryland wheat fields.The results of long-term positioning experiment showed that the fresh weight,dry weight and biological return amount of legume green manure were in the order of stem and stem and leaf > root system > root nodules.However,for the nutrient content and nutrient return amount of legume green manure,the nutrients of carbon,nitrogen,phosphorus and potassium in root nodules were higher than those in stem and leaf,but the total nutrient return amount of stem and leaf was the highest.GM increased soil total carbon and organic carbon by 6% and 20% compared with HN,but had no significant effect on p H and bulk density.With the increase of soil depth,the content of soil organic carbon and its components decreased.GM significantly increased the contents of total nitrogen,nitrate nitrogen and microbial biomass nitrogen in 0-40 cm soil layer.Soil total nitrogen,nitrate nitrogen and microbial biomass nitrogen contents of GM were increased by 21%,88% and50% in 0-20 cm soil layer,and by 9%,37% and 60% in 20-40 cm soil layer compared with LN,respectively.For active carbon in soil,compared with LN,GM increased particulate organic carbon,mineral-bound organic carbon,dissolved organic carbon and microbial biomass carbon by 53%,12%,34% and 14% in 0-20 cm soil layer,respectively,but there was no significant difference in 20-40 cm soil layer.GM was more sensitive to 0-20 cm soil organic carbon,but less sensitive to 20-40 cm soil layer.The sensitivity index of easily oxidized organic carbon and particulate organic carbon was the highest,which were 282% and 128%,respectively.Further investigation showed that the proportion of soil organic carbon components in organic carbon content from high to low was: mineral-bound organic carbon,particulate organic carbon,easily oxidized organic carbon,microbial biomass carbon,dissolved organic carbon.For soil aggregates,GM increased the content of large aggregates and the mean weight diameter by 23% and 40% compared with LN,respectively,but had no significant effect on the content of carbon and nitrogen and C/N of soil aggregates of different particle sizes.In conclusion,nitrogen reduction and green manure return can increase crop yield,improve soil aggregate structure,and thus increase soil organic carbon,total nitrogen and organic carbon components,providing alternative management measures for wheat production in dryland.