Sweet pepper and nitrogen supply in greenhouse production: Critical nitrogen curve, agronomic responses and risk of nitrogen loss

Intensive vegetable production in soil is often associated with large N losses to the environment. To contribute to improved N management of sweet pepper, this work developed a critical nitrogen curve (CNC). It also developed N recommendations and examined N use efficiency (NUE) and potential NO3− leaching loss in relation to increasing total available nitrogen (TAN). TAN is the sum of the soil mineral N at planting, N mineralized from soil organic material, and mineral N fertilizer. Three sweet pepper crops were grown in soil with autumn-winter cropping cycles in greenhouse conditions. Five different N concentrations in the nutrient solution were applied throughout the crop cycle: very N deficient (N1), N deficient (N2), conventional N management (N3), excessive N (N4) and very excessive N (N5). A critical N curve of % N c = 4.71 × D M P - 0.22 was determined for sweet pepper. Relative yield of the three crops had a strong linear-plateau relationship (R2 = 0.66) with integrated nitrogen nutrition index (NNIi). Maximum yield was associated with an NNIi of 0.86. In the three crops, total yield, dry matter production (DMP) and crop N uptake were generally strongly related to increasing TAN. An optimal TAN value (minimum TAN for maximum yield) of 425 kg N ha−1 was determined using a linear-plateau regression model. N uptake efficiency (NuptE) decreased exponentially with increasing TAN, from almost 0.90 kg kg−1 in the N1 treatment to 0.30 kg kg−1 in the N5 treatment. The sum of residual mineral N and leached NO3−–N was considered to be potential NO3− leaching loss. Potential NO3− leaching loss increased exponentially, with increasing TAN, to 686–1034 kg N ha−1 in the highest N treatments. For the optimal TAN value, NuptE was 0.63 kg kg−1 and the potential NO3− leaching was 125 kg N ha−1. The CNC and derived NNI values provide valuable information for N management of pepper. Consideration of TAN as the crop N supply enables maximum yield with less fertilizer N and less risk of N loss.