Yield and Nitrogen Balance of Greenhouse Tomato (Lycopersicum esculentum Mill.) with Conventional and Site-specific Nitrogen Management in Northern China

In a greenhouse experiment with tomato, the N fertilizer reduction potential, tomato yield, N use and environmental implications were examined, in a comparison of site-specific N management with conventional N fertilization during three successive growing seasons from Feb. 2004 to Jun. 2005 in Shouguang, a typical greenhouse vegetable production region in Shandong province, Northern China. Fertilizer N recommendation with site-specific management was based on the difference between N target value and soil initial nitrate-N content (0-0.3 m) with pre-sidedress soil nitrate testing (PSNT) and nitrate-N applied from irrigated water. The same basal dressing of 8, 11 and 8 t ha-¹ of chicken manure (supplying 260, 360 and 316 kg N ha-¹ in the first, second, and the third growing season, respectively) was broadcasted with conventional N, site-specific N and N from manure three treatments. The N target value with site-specific management was 300 kg N ha-¹ in the first season, and then modified to 200 kg N ha-¹ in the second and third seasons. In comparison with the fertilizer N applied rate with conventional N management (870, 720 and 630 kg N ha-¹ in the three seasons, respectively), site-specific management reduced N fertilizer by 62, 78 and 80% without significant influences on tomato yield. The fruit yield of tomato with only basal dressing manure treatment was significantly decreased in the second season, compared with conventional N management. The nitrate content in 0-0.9 m soil depth with site-specific management was much lower than that with conventional N management in all three seasons. The 53-83% of emitted nitrous oxide (N₂O) was measured from transplanting to the first sidedressing in the three seasons, strongly related to drying-wetting soil process. As a result, the cumulative emission with site-specific management was only reduced by 38% than that with conventional N management throughout three seasons. Considering N release from mineralization and irrigation water, site-specific N management could efficiently control N application in intensive irrigated-vegetable production region. Thus, it is valuable to obtaining vegetable crops with high yield and economic return while alleviating the risk of environmental pollution. But it is necessary to optimize irrigation regime to minimize N loss through nitrate leaching and N₂O emission.