Effects of green manures during fallow on moisture and nutrients of soil and winter wheat yield on the Loss Plateau of China
The application of catch crops as a green manure can enhance soil fertility owing to improving soil nutrients. We conducted one year field experiment to evaluate the effect of catch crops [Rapeseed (Brassica napus L.) under different sowing rates and Soy bean (Glycine max L.)] with biological organic fertilizer 1,500 kg/ha on wheat yield and soil nutrients. The green manures were sown on 3th July 2015 during summer fallow. At the beginning, there were five treatments as follows: R1 (Rapeseed and sowing rate was 7.5 kg/ha); R2 (Rapeseed and sowing rate was 15 kg/ha); R3 (Rapeseed and sowing rate was 22.5 kg/ha); S (Soy bean and sowing rate was 105 kg/ha); C (Control was bare field). Every green manure treatment was split into two treatments on 27th September 2015. One treatment we turned the above ground biomass of green manure into the soil. And another treatment we harvested the above ground biomass of green manure. The above ground biomass turned into soil treatments were G1, G3, G5 and G7. The above ground biomass harvested treatments were G2, G4, G6 and G8. The treatment C was still the bare field. Soil samples were taken twice to measure soil moisture and nutrients at two stages. One stage was in autumn before winter wheat sowing and another stage was in next year summer after wheat harvest. The significantly highest 1,000-grain weight and grain yield belonged to the treatment C, which were 10.69%-36.87% and 16.86%-72.5% higher than that of the green manures treatments. After wheat harvest, the 0-20 cm soil available N and total N of G7 were 51.40%-20.45% and 95.12%-125.35% significantly better than that of other treatments. The significantly highest soil total P of 0-20 cm belonged to G3 after wheat harvest, which was 25%-45.83% better than other treatments. Before wheat sowing, the treatment C kept the significantly lowest soil available K of five layers. The 0-20 cm and 20-40 cm soil organic matter of the treatment S was 40.28%-71.12% and 53.92%-122.67% significantly higher than other treatments before wheat sowing. Therefore, growing rapeseed and soy bean during summer fallow in this region significantly reduced 1,000-grain weight and grain yield of subsequent winter wheat. But the incorporation of green manures improved the soil nutrients to some extent.