Research on biological nitrogen fixation of grass-legume mixtures in a semiarid area of China Effects of straw mulch no-tillage on community composition of soil nitrogen transferous bacteria Effect of fertilizer application mode on edaphon in black soil in Songnen Plain Relationships between grasses and legumes in mixed grassland: a review Researches on Bi-directional N transfer between the intercropping system of groundnut with rice cultivated in aerobic soil using 15N foliar labelling method Study on Nitrogen Transfer between Acacia melanoxylon and Eucalytups urophylla Seedlings