Modality of fertigation of protected cucumber and Nitrogen Use Efficiency in closed systems

author.Cucumber and tomato are considered to be the most important protected vegetables in coastal Lebanon. Recent works established that in these intensive systems, irrigation and fertilization are still empirically based. Whereas techniques such as fertigation are used associated to traditional practices of soil application of fertilizers and animal manures. Due to the absence of recommendations based on local conditions, over irrigation and over fertilization are common. Furthermore, nutrients were added according to a discontinuous modality, that is with every other irrigation. In this study, the effect of four frequencies of irrigation on protected cucumber were investigated in combination with two modalities of fertigation. The first is a discontinuous way as being practiced by the growers and the second is a continuous way as being recommended by scientists. Nitrogen fertilizers enriched with the heavy isotope 15N allowed to study their use efficiency. The results indicated that the frequency of irrigation influenced dry matter production. In the closed systems adopted in this pot experiment, the percentages of nitrogen derived from fertilizers (%Ndff) were very high ranging from 89% to 94.6%. The nitrogen fertilizers utilizations were found to be slightly different according to the modality of fertigation. The recovery of leached nitrogen and that utilized by the above-ground parts of the plant, would add up to 50% of the N fertilizers