Effect Of Different Factors On Accumulation And Leaching Of Nitrate In Greenhouse Soil

Compared with the crops cultivated in open land, the crops cultivated in greenhouse have high yield, and excessive application of fertilizers is very common in their production. It results in the significant accumulation of different nutrients in the greenhouse soils. Under the greenhouse production, the closed environment is formed; and lack leach of precipitation, high temperature and evaporation result in high salinity of the soils. Excessive application of nitrogen fertilizer leads to low efficiency of N fertilizer and accumulation and leaching of nitrate. It may pollute the groundwater. Sunlight greenhouses play an important role in the vegetable production in Shaanxi Province. And the problem of excessive accumulation of soil nutrients is also serious. After harvesting the vegetable crops, there is a fallow period in this region. This period is also the rain season. It is unclear how the nitrate changes in the fallow time of this area; this is an issue deserved to study.In this study, we used the sunlight greenhouses with different cultivating histories in Yangling, Shaanxi Province to study the nitrate accumulation in each year after harvest the crop, and the leaching of nitrate in soil profile during the fallow seasons of two years. And a soil column experiment was also used to study the leaching of nitrate and some other nutrients in greenhouse soils. The main results were as follows:(1) The concentrations of organic matter, total nitrogen, available phosphorus and available potassium in soils were increased with the age of sunlight greenhouses. Soil available phosphorus and potassium accumulated dramatically each year in top layer, at the annually rate of about 254.1% and 36.5%, respectively. As the age of greenhouse become older, the eclectic conductivity increased significantly in the 0～20 cm soil layer, but not in the deeper layers. Nitrate content was the highest in the top soil layer of greenhouse with different ages, and which accumulated obviously in the top soil layer, but small change in the under 20 cm layers.(2) The total amount of residual nitrate in the soil after harvest in 2006 and 2007 were 667.60 (range 492.2～800.4 kg/hm2) and 781.82 (range 491.2～1070.7 kg/hm2), respectively. It is obvious that a large amount of nitrate remain in the soil of sunlight greenhouse.(3) The nitrate content in August was 9.37 mg/kg higher than July in 2006 fallow period. Contradictory results showed in 2007 fallow period. The amount of residual nitrate in the end of fallow period was 569.4 kg/hm2(range 412.8～715.6 kg/hm2). The loss of nitrate amount during this period was in the range of 223.8～658.0 kg/hm2 in the 0～200 cm soil profile.(4) Nitrate concentration and amount in soil column solution showed a decreasing trend as the continuous of leaching and incubation. The concentration and amount of nitrate leached were much higher than that of ammonium. Nitrate concentration of were higher in low simulated rainfall treatment than the high treatment, and the amounts of nitrate leached were the opposite. The electric conductivity decreased steadily; and high EC of leaching solution was observed in low rainfall treatment.(5) Potassium concentration in the solution leached from soil column showed a declined trend; and the potassium concentration in Xi'an soil treatment was higher than that of Yangling soil. And lower simulated rainfall had a higher potassium concentration in the solution. Calcium and magnesium concentrations in Xi'an treatment were higher than that of Yangling, and they presented a decrease trend with time going on.