An investigation of irrigation and groundwater quality in the UAE
Effects of fertigation at diverse water and fertiliser application rates on tomato (lycopersicon esculentum) yield and nutrient uptake efficiencies were studied. The treatment giving optimal water use efficiency reduced fruit yield by ca. 46% but, compared with that giving the greatest fruit yield, substantially reduced the fluxes of N and K leached to groundwater. The background salt concentrations in irrigation water and the fertiliser K facilitated ammonium mobilisation down in the soil profile. Fertilisation for maximum yield increased the fluxes of nutrients leached, and application of water to achieve optimal water use efficiency would be more sustainable. Tomato growth was evaluated also under different irrigation rates, but at constant rate of fertiliser application. A relatively low irrigation rate optimised water use efficiency and gave a yield that not significantly below that a higher irrigation rates. Fertiliser N use efficiency was improved at the N fertiliser application rate of only 70 kg ha-1 used, more than eight times lower than that suggested from the previous experiment. This is a dramatic improvement in terms of the potential flux of N leached to groundwater. A simple drainage flow model was developed to show why lateral water movement helps explain the poor nutrient use efficiency observed in both experiments. Spatial variation in groundwater quality in a major crop-producing region of the U.A.E., was investigated. the distributions of major and trace chemical constituents of groundwater were assessed with reference to effects on drinking water quality compared with WHO standards. In particular, nitrate concentrations in groundwater were examined, to see if nitrate accumulation was a potential cause for concern in the U.A.E. In spite of the beneficial recharge from the Oman Mountain, there is a zone of saline ground water between 24° 20' and 24° 25' that may be attributed to more than 20 years of intensive use of the land for irrigated crop production. Drip irrigation leads to build up of salinity and nature just beyond the rooting volume. These zones are flushed by rare rainfall events that contribute to groundwater recharge.