Yield Traits and Water and Nitrogen Use Efficiencies of Bell Pepper Grown in Plastic-Greenhouse

We report the results of a two-year study assessing the effects of nitrogen fertilization and irrigation regimes on yield traits and on water and nitrogen use efficiency of greenhouse-grown bell pepper (Capsicum annuum L.). The trials involved the combination of four N doses (0, 100, 200, 300 kg ha-1) with two irrigation regimes (100% restitution of ETc; repeated cycles of water stress starting from fruit set). In the second year, the crop was transplanted one month earlier than in the first year and was mulched with plastic sheeting. The highest yield in both years was obtained by associating 100% restitution of ETc and the N dose of 200 kg ha-1. The marketable yields were 37 and 72 t ha-1 in 1998 and 1999, respectively. Doubling of the yield in the second year was probably due to the earlier transplantation and mulching, confirming the numerous benefits of the latter technique. The water deficit imposed during the late flowering-early fruit set phase had negative effects on the crop, with declines of the marketable yield of up to 44% due to the reduced number and weight of the fruit and the increased waste, mainly peppers with blossom-end rot, cracking, sun-burn and malformations. The peppers grown under water stress were richer in dry matter and soluble solids. The yield declines due to water deficit varied in relation to the N dose, as confirmed by the numerous interactions recorded between irrigation regime and nitrogen level.Without nitrogen fertilization, the quantity and quality of the fruits remained unchanged, while the maximum dose (300 kg ha-1) enhanced the negative effects of the water deficit on the number (-52%) and weight (-161%) of marketable peppers. Moreover, the waste peppers reached 31% of the total production (by weight), with over 21% affected by blossom-end rot. Water stress led to a drastic reduction of the total above-ground dry biomass (40%) and a significant decrease of nitrogen absorption by the plant (54%) with preferential translocation towards stems and leaves, as shown by lower Harvest Index (HI) values. Regarding the water use efficiency (WUE), the above-ground dry matter WUE (AGWUE) remained unchanged while the total yield WUE (TYWUE) and marketable yield WUE (MYWUE) decreased. The N dose of 200 kg ha-1 maximized the yield and quality of the peppers, with and without water stress, and the values of water and nitrogen use efficiency were maximal in these conditions.