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Summary The effect of irrigation levels, 50, 75 and 100% of the net irrigation requirement IR n (IR 50 , IR 75 and IR 100 ) and bitumen concentration, 0, 50 and 75 g/m 2 (BL, B 1 and B 2 ) at a plant density of 8 plants/m 2 and the effect of plant densities of 5 and 8 plants/m 2 at IR 75 on soil moisture and salinity, plant growth and water use efficiency were studied in two field experiments conducted in sandy soil located at Regwa experimental farm. Treatments were arranged in a split-plot design replicated four times. Soil moisture conserved in the 5–20 cm layer within three days after irrigation increased with increasing bitumen concentration regardless of irrigation treatments. Soil moisture content in the root zone (0–60 cm) three days after irrigation, was affected by bitumen treatments (1% level). Mulching the soil surface with bituminous emulsion up to 75 g/m 2 decreased the mean salt concentration in the root zone (10% level). The least EC values were found under the condition of B 1 and IR 100 . Irrigation treatments affected significantly these values (1% level). Plant height, stem diameter and flower disk diameter increased significantly (1, 5 and 5% level resp.) with increasing irrigation level. The effect of bitumen concentration on those parameters in descending order was B 2 > B 1 > BL. The negative effect of the deficit in water supply on seed yield was obviously greater than the positive one due to bitumen mulch. Decreasing planting density from 8 to 5 plants/m 2 approximately doubled the yield of seeds. The effect of planting space on increasing yield was evidently greater than that of bitumen mulch. Although water use efficiency at IR 50 was the same as that at IR 100 , yet the seed index of the 2nd was approximately twice that of the 1st, i.e. seed quality of plants growing at IR 50 was poor. |
