Nitrate leaching from sunlight greenhouse soils with different cultivation years during summer fallow periods

Nitrate contents in 13 soil profiles of sunlight greenhouses and their changes during summer fallow periods were determined in two continuous years (2006 and 2007) in Yangling, Shaanxi Province to evaluate the accumulation and leaching loss of nitrate during the summer fallow. After harvesting the vegetable, excessive amount of nitrate was accumulated in the soil profiles. The average residual nitrate in 0-200 cm soil profiles after harvesting in 2006 and 2007 were 667.6 kg/hm2 (in the range of 492.2-800.4 kg/hm2) and 781.8 kg/hm2 (in the range of 491.2-1 070.7 kg/hm2), respectively. The contents of nitrate and electronic conductivity (EC) significantly increased after summer fallow in 2006 with less precipitation (65 mm); while the nitrate content and EC significantly decreased after fallow in 2007 with heavy precipitation (214 mm), indicating the leaching of nitrate in this year. The nitrate loss from 0-200 cm soil profiles was 298.5 kg/hm2, with the range of 223.8-658.0 kg/hm2 during summer fallow period in 2007. The extents of nitrate leaching were variable among different cultivated-years greenhouses. On average, the leaching loss of nitrate followed the order of greenhouses of 1998 >greenhouses of 2004 > greenhouses of 2002. It is concluded that the amount of precipitation during summer fallow is the key factor controlling the leaching loss of nitrate accumulated in soil profile of greenhouse.