Effect Of Leguminous Green Manure In Summer On Soil Properties And Winter Wheat Growth In Dryland And Its Mechanism

Resources-saving and envrionment-friendly agriculuture is the aim of modern agriculutural development, with the characteristics of increasing resources use efficiency, keeping soil healthy, saving energy and reducing emission of greenhouse gasses. Loess Plateau is one of the main areas with low soil fertility in China. In this area tranditionally, summer fallow period is more than 3 months long and there is more than 2 million hectare summer fallow land. Field experiment and nylon mesh bag decomposition experiment were carried out to investigate the effect of leguminous green manure in summer fallow period on soil properties, winter wheat growth and nutrients uptake and to reveal the mechnism of improving soil fertility and fertilier use efficiency by green manures'incoporation into soil. The results showed that:1. Huai bean and mungbean had greater biomass than soybean among tested manures. Huai bean contributed the most nitrogen and potassium by incoporation to soil while soybean contributed the least. Mungbean contributed the maximum phosphorous to soil while soybean contributed the minimum. Huai bean had greater root nodules and significant higher nitrogen content than mungbean and soybean. Compared to summer fallow, cropping green manures could increase soil organic matter, total N and available K content. No remarkable differences of soil CEC and soil bulk density was found between green manure treatments and summer fallow after 4 weeks of incoporation. However, the trend was showed that growing green manures resulted in soil pH increase and soil bulk density descrease. There was no differences of soil pH among treatments after winter wheat harvest. Green manure plants consumed much soil water during growth period. After wheat harvest, soil water storage in 0～200 cm depth of green manure treatments was still lower than summer fallow treatment. No significant differences of soil properties were found among three green manure treatments. Planting and incoporation of leguminous green manures in summer fallow period is an effective way to improve soil fertility in dryland.2. Yield and nutrients uptake of winter wheat reduced significantly when leguminous crops were planted and incoporated into soil in summer fallow period, compared with fallow in summer. Due to more soil moisture consumption during green manures growth period and drought in wheat growing season. The winter wheat seedlings and tillerings of green manure treatments reduced significantly, resulting in the significant decrease of spike number of green manure treatments, which was the direct cause of reduction of prodution. Harvest index and 1000-kernel weight were increased due to green manure incoporation. N, P and K content of winter wheat was higher for green manure treatments than summer fallow treatment. For both of summer fallow and green manure treatments, application of N fertilizer increased wheat N concentration, reduced wheat P concentration in seeds and glumes, increased P concentration in stems and leaves, and increased P uptake by wheat significantly. When leguminous crops were planted and incoporated into soil in summer fallow period, N rate 108 kg hm-2 (reduced rate) treatment showed higher wheat yield than that of N rate 135 kg hm-2 (common rate) treatment. N use efficiency by wheat of green manure treatments was higher than that of summer fallow treatment.3. Nylon mesh bags method was used to monitor the nutrients release of Huai beans, soybeans and mungbeans plant to soil during 287 days period. The results showed that all those green manures had an initial rapid decaying and then a slow decaying, and degradation peaked in the first month. During the stable phase of decomposition, Huai bean had higher residual ratio than soybean and mungbean. The release of different nutrients in green manures varied. Nitrogen, phosphorus and potassium released rapidly in the initial 21 d, of which the most complete released element was potassium. After 287 d degradation period, the residual ratio of K was 3.2 %～5.9 %, which was the lowest of all nutrients, while P was 33.5 %～41.8 % and N was 46.3 %～64.7 %. Calcium in green manures had the highest residual ratio, and had no significant change during decomposition. The residual ratio of Ca was 74.8 %～89.8 % after 287 d. The release of magnesium was similar to potassium. After 28-days fast release, residual ratio of Mg dropped down to approximate 30 %. Residual ratio of copper erratic fluctuated. There was significant release of iron within the first 21d followed by a long slow release period. Residual ratio of zinc declined in the first 49d. From 49d to 175d, the residual ratio of zinc in soybean and mungbean remained unchanged while it increased significantly for Huai bean's. After 175 d, the residual ratio of zinc in those three types of green manure decreased dramatically. The residual ratio of manganese showed downward trend during the decaying period and fell to 67.3 %～74.1 % after 287 d, which was just below calcium. Differences of nutrients release status of three green manures depended on nutrients. The residual ratio of nitrogen, calcium, iron, copper and zinc varied among three green manures, while no significant differences of residual ratio of potassium and magnesium was found among them. Mungbean had the lowest residual ratio of all nutrients but C, N, Cu and Zn. Soybean had the highest residual ratio of all nutrients but C, N, Cu and Fe.