Effect of intensively cropping greenhouses in semiarid regions on soil salinity and nitrogen fertilizer requirements of cucumber

The soil of a greenhouse located in the semiarid Lebanese coast of the Mediterranean sea, and which has been in intensive crop production for the past ten years, was chemically analyzed. Results were: NO₃‐N = 225 ppm, NH₄‐N = 56 ppm, pH = 7.0 and salinity (ECe) = 2.5 dS/m. Irrigation water salinity (ECw) = 0.4 dS/m. Cucumber (Cucumis sativus L. cv. Lolita), a parthenocarpic beit‐alpha type plant, was grown in this greenhouse, and was treated with nitrogen (N) fertilizer at the rates of 0, 81 and 162 kg N/ha. The N was split into six equal weekly applications, with the first application made on the first week of fruit production. Total fruit yield for the first 8 weeks of harvest was 71.4, 63.4 and 60.2 ton/ha for the plots receiving 0, 81 and 162 kg N/ha, respectively. Leaf petiole NO₃‐N concentration was higher than the recommended level in all treatments throughout the experiment. At last harvest, NO₃‐N concentration in leaf petiole was 12500, 15500 and 19500 ppm in plants receiving 0, 81 and 162 kg N/ha, respectively. Soil salinity has sufficient to cause yield reduction for many greenhouse crops. In contrast, soil mineral N has sufficient to meet the N requirement for an entire season for many annual crops.