Influence of the Application Rate of Organic Manure on Nitrate Migration and Accumulation in Greenhouse Soil

An experiment was conducted on a vegetable planting base in Damintun Town, Xinmin City, Liaoning Province to study the influence of the application rate of organic manure on nitrate migration and accumulation in a greenhouse soil planted with lettuces. The soil was treated with organic manure at five rates (0, 20, 40, 60, and 80 t·hm^-2). The results showed that the migration and accumulation characteristics of nitrate in the soil were affected by both the vegetable growth stage and the application rate of organic manure. For each treatment, the contents of soil nitrate were lower in the medium term (November) of lettuces growth than in the early (October) and late (December) periods. The accumulation of soil nitrate in each period was increased with the application rate of organic manure. The vertical profile of nitrate migration in soil indicated that the low application rates of organic manure (20 and 40 t·hm^-2) could not lead to significant accumulation of nitrate. When organic manure was applied at 60 t·hm^-2 and 80 t·hm^-2, the accumulation of nitrate in each soil layer was much higher, especially in the 80~120 cm layer where nitrate leaching occurred.