Modality of fertigation of protected cucumber and nitrogen use efficiency under field conditions

Cucumber and tomato are the most important protected vegetables in coastal Lebanon. Recent research established that in these intensive systems, irrigation and fertilization are still empirically applied. Techniques such as fertigation are used but associated to traditional practices of soil application of fertilizers and animal manure addition. In 1997, a pot experiment was conducted in order to find the optimal irrigation frequency and modality of fertigation. For this, four frequencies of irrigation were combined with two modalities: discontinuous irrigation as practiced by the growers and continuous irrigation, as recommended by the scientists. In these closed-system conditions, the frequency of irrigation influenced the dry matter production. In addition, the percentages of nitrogen derived from fertilizers were very high, from 89 to 95%. The discontinuous modality allowed for greater nitrate leaching. The evaluation of the main findings for plants grown in the soil, was conducted in 1998, in a greenhouse, 35 km north of Beirut. The treatments were reduced to two frequencies of irrigation combined with the two modalities of fertigation. The objectives were to assess, with the use of 15N labelled fertilizers, the most efficient treatment as far as plant performance and losses from the plant-soil system are concerned. (author)