Effects of fallow and plant growth in summer on the movement of residual nitrate in aquic soil on North China Plain

This study was to investigate nitrate distribution and movement in 0-200 cm soil layers among three land management systems in summer, such as Sorghum hybrid Sudangrass（Pacesette）, spring maize and fallow in North China Plain. The results showed that soil nitrate in all treatments gradually leached downword during the whole plant growth season, and in the systems of Sorghum hybrid Sudangrass and spring maize it gradually declined, but in summer fallow system it increased with a wave-manner. After harvest, compared with pre-plant, nitrate in 0-200 cm soil layers with the treatment of summer fallow enhanced, but of Sorghum hybrid Sudangrass and spring maize it decreased, then accumuled into 60-80 cm soil depth. By contrast with fallow, plant absorption of soil nitrate could significantly reduced the leaching downword, while summer fallow was on the contrary. Root length density and dry weight decreased with the soil depth and the root length density of Sorghum hybrid Sudangrass at soil depth of 0-30 cm was significant higher than that of maize. There was a significant positive relation between plant root length density and soil nitrate decrease in 0-60 cm soil layer. Nitrogen absorption in the topsoil of Sorghum hybrid Sudangrass was more than that of maize. This showed that the former had larger capacity to intercept residual nitrate and hold its leaching. It also presented that plant had the function of ‘safety net'.