SUPPLEMENTAL IRRIGATION TO IMPROVE WHEAT PRODUCTION AND WATER USE EFFICIENCY UNDER RAINFED FARMING CONDITIONS

The stochastic behaviors of rainfall pose serious limitations for sustained and profitable crop production in rainfed areas; farmers hesitate to apply fertilizers when they are not sure about rainfall. In view of these limitations a research study was conducted for three years (2003-2006) at field station of Water Resources Research Institute (WRRI), National Agricultural Research Centre(NARC), Islamabad to examine the effects of supplemental irrigation (SI) on wheat production and water use efficiency (WUE). Irrigation treatments employed under the experiment were: i) Rainfed without irrigation and fertilizer application (I0); ii) SI of 25 mm was applied to non-fertilizer field at 75% management allowed deficit (MAD) (I1); iii) Rainfed with fertilizer application at sowing time (I2); and iv) SI of 25mm was applied at 75% MAD and at the time of fertilizer application as top dressing (I3). Supplemental irrigation increased the crop yield during the years 2003-2006 under both fertilizer and non-fertilizer conditions. Increased in grain yield under non-fertilizer conditions (I1) ranges between 770-980 kg/ha, which is 27 to 48% higher than the rainfed yield (I0). Supplemental irrigation and split application of fertilizer (treatment I3) increased the grain yield within the range of 1000-1350 kg/ha, which is 27-49% higher than yield under treatment I2. Whereas, due to synergetic effect of supplemental irrigation and fertilizer application, increased in grain yield ranges between 1550-2030 kg/ha, which is 49% to 100% higher than the rainfed and non-fertilizer field. WUE was calculated for rain (WUEr), for total water (grass: previous soil water storage + rain + irrigation) (WUEg), for SI water only (WUEsi) and for synergetic effect (SI water + fertilizer application) (WUEsis). Water use efficiencies namely the WUEr, WUEg and WUEsi, during the period of three years under non-fertilizer conditions ranges between 6.2-7.1, 7.9-8.5 and 19.6-30.8 kg/ha/mm of water respectively. The water use efficiencies WUEr, WUEg and WUEsi, under fertilizer conditions ranges between 7.0-8.7, 8.5-11.1 and 26.8-40 kg/ha/mm of water respectively. Whereas, the WUEsis was 40.2, 62.0 and 40.6 kg/ha/mm of water during the year 2003-04, 2004-05 and 2005-06 respectively. Supplemental irrigation increased both the wheat production and water use efficiency by supplying irrigation water at critical moisture stress and improving level of input.