Effects of different cultivation methods on soil residual nitrate under winter wheatsummer maize cropping system

A field experiment was conducted in Guanzhong region of Shaanxi Province to investigate the effects of different cultivation methods of water saving irrigation and water conservation and nitrogen rates on soil residual nitrate N under winter wheatsummer maize cropping rotation system.At the fifth crop harvesting,218-329 kg/ha residual nitrate N was found in 0-200 cm depth of soil under different cultivation methods,most of them existed in 100200 cm depth of soil.Compared with other cultivation methods,the residual nitrate N in 0 -200 cm depth of soil under the furrow planting system was the highest.Soil residual nitrate N significantly increased with the increase of cultivation years and N application rates.When N 240 kg/ha was applied,the residual nitrate N in 0 -200 cm depth of soil was about 477 kg/ha at the fifth crop harvesting.The increase amount of residual nitrate N from third harvesting to fifth harvesting was 51.6% of the total amount of applied nitrogen during this period.After the fifth crop harvesting,the amount of nitrate accumulation in 0-80 cm soil profiles under conventional,water-saving and straw mulching cultivation method was lower and increased below 80 cm depth when N fertilizer was applied.The amount of nitrate accumulation in soils under the furrow planting cultivation method was very high when N fertilizer was applied in 0-200 cm soil profiles,and was higher in 0-120 cm soil profiles than other cultivation methods.