Responses of Greenhouse Tomato and Pepper Yields andNitrogen Dynamics to Applied Compound Fertilizers

Yield and N uptake of tomato(Lycopersicum esculentum Mill．)and pepper(Capsicum annuum L．)crops in five successive rotations receiving two compound fertilizers (12-12-17 and 21-8-1l N-P2O5-K2O)were studied to determine 1) crop responses，2)dynamics of NO3-N and NH4-N in different soillayers，3)N balance and 4)system-level N efficiencies．Five treatments (2fertilizers，2 fertilizer rates and a control)，each with three replicates，were arranged in the study．The higher N fertilizer rate，300 kg N ha^-1(versus 150 kg N ha^1)，returned higher vegetable fruit yields and total aboveground N uptake with the largest crop responses occurring for the low-N fertilizer(12-12-17)applied at 300 kg N ha^-1 rather than with the high-N fertilizer(21-8-11)．Ammonium-N in the top 90 cm of the soil profile declined during the experiment，while nitrate-N remained at a similar level throughout the experiment with the lower rate of fertilizer N．At the higher rate of N fertilizer there was a continuous NO3-N accumulation of over 800 kg N ha^-1．About 200 kg N ha^-1 Was applied with irrigation to each crop using NO3-contaminated groundwater．In general，about 50％ of the total N input was recovered from all treatments．Pepper、relative to tomato，used N more efficiently with smaller N losses，but the crops utilized less than 29％of the fertilizer N over the two and a half-year period．Local agricultural practices maintained high residual soil nutrient status．Thus，optimization of irrigation is required to minimize nitrate leaching and maximize crop N recovery．