Responses of Greenhouse Tomato and Pepper Yields and Nitrogen 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 (12-12-17and 21-8-11 N-P_2O_5-K_2O) were studied to determine 1) crop responses, 2) dynamics of NO_3-N andNH_4-N in different soil layers, 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 thestudy. The higher N fertilizer rate,300 kg N ha^(-1) (versus 150 kg N ha^(-1)), returned highervegetable fruit yields and total aboveground N uptake with the largest crop responses occurring forthe 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, whilenitrate-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 NO_3-N accumulation of over 800 kg Nha^(-1). About 200 kg N ha^(-1) was applied with irrigation to each crop using NO_3-contaminatedgroundwater. 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 than29% of the fertilizer N over the two and a half-year period. Local agricultural practices maintainedhigh residual soil nutrient status. Thus, optimization of irrigation is required to minimizenitrate leaching and maximize crop N recovery.

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 21-8-11 N-P2O5-K2O) were studied to determine 1)crop responses,2) dynamics of NO3-N and NH4-N in different soil layers,3) N balance and 4) system-level N efficiencies.Five treatments (2 fertilizers,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-i),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.