Irrigation scheduling with skimmed groundwater to manage root zone salinity

Different skimming well technologies are being used to extract relatively fresh groundwater lenses from aquifers underlain by salty groundwater layers in the Indus basin. However, the discharge rates from these skimming wells are too low to apply efficiently on surface irrigated croplands. The salinity in the root zone also increases with the application of skimmed groundwater. Therefore, the limited water supply coupled with high pumping cost and salinity hazards, makes it more important than ever that irrigation water be used efficiently and judiciously. Different water saving techniques was evaluated in this study. In the first experiment, two furrow irrigation techniques, alternate furrows and regular furrows, for maize production, were evaluated. The application efficiency of alternate furrows was 45% greater than regular furrows. The water use efficiency obtained from alternate furrows was 49% greater as compared to regular furrows. Alternate furrows require less water input per irrigation and reduces the pumping cost without reducing crop yield significantly. With the application of the same quality skimmed water, the soil salinity in alternate furrows was relatively less than regular furrows most probably due to the less application of skimmed water. In the second experiment, wheat was sown by bed & furrow, zero-tillage and conventional (basin) methods. The application efficiencies of bed & furrow and zero tillage fields were 37.15 and 38.54%, respectively and were about 45% greater than the conventional methods of wheat sowing. The total water applied was 34, 39 and 30 cm for bed & furrow, basin and zero tillage fields, respectively whereas the WUE was 1.22, 1.09 and 1.41 Kg m-3 for bed and furrow, basin and zero-tillage fields respectively. The farmer applied 79 cm of water, almost double than water applied under the scheduled fields, with a WUE of 0.63 kg m-3.The evaporation pan attached with a Marriate bottle was used to decide the time ofirrigation. The irrigation was applied at 30 and 40% MAD for maize and wheat respectively. Soil moisture were also determined gravimetrically before each irrigation. The evaporation under predicted the soil moisture deficit in both experiments and therefore may be safe to use for irrigation scheduling where skimmed water is used for irrigation purposes.