A performance evaluation of a one hectare gravity fed drip irrigation system under varying vertical head

Abstract

Determination of emitter discharge variation and water application uniformity is very important in designing drip irrigation system and could serve as the basis for optimizing water use efficiency and crop productivity. This study was carried out at Eureka Farm in Sanyati District­ Zimbabwe, to evaluate the performance of one hectare gravity­fed drip irrigation system under varying vertical pressure heads. The drip system was tested for emitter discharge variation (Q var), coefficient of uniformity (CU) and distribution uniformity (DU). The drip kit comprised of a 10 m3 tank, on an adjustable stand, with one hundred and twenty sets of 100 m long 16 mm diameter drip lines which had the same types of emitters. The operating heads tested were 2 m, 3 m, and 4 m. Emitter discharge was measured at the drip line lengths 12.5 m, 25 m, 37.5 m, 50 m, 62.5 m, 75 m, 87.5 m and 100 m from the manifold. The performances were compared to The American Society of Agricultural Engineers (ASAE) Standards (1999) and used to select the optimum drip lateral lengths for different vertical pressure head. The results indicated as expected that the emitter discharge decreased as the lateral length increased. The emitter discharge variation was within the desirable recommended standard of d” 10% at 100m, 75m and 65m drip lateral lengths for 4m, 3m and 2m tank heights respectively. The results also showed that the coefficient of uniformity (CU) and the distribution uniformity (DU) generally increase with increasing heads and decrease with increasing drip lateral length. The minimum recommended standards for DU and CU for the kit to be considered as good was 80% and 85% respectively. On the basis of the results, appropriate recommendations on the relationship between vertical head and drip lateral length were formulated to minimize non uniformity of water distribution under field conditions.