Water management of irrigated grain sorghum in central Gezira

Grain sorghum [Sorghum bicolor (L.) Moench] is the staple food crop of Sudan. The frequently occurring drought cycles in rain-fed sectors that cause insufficient production has led to dependence on irrigated sorghum to fill food gaps that may arise. Field experiments were conducted in 2004 and 2005 in the Gezira Research Station, to determine the optimum CWR and the effects of water stress on sorghum yield variety Wad Ahmed. Three irrigation intervals were used;weekly (W 1- assumed to be optimum), fortnightly (W2- as traditionally used) & three weeks (W3- under water stress). Soil moisture monitoring was carried out under intensive gravimetric soil sampling to the depth of one meter. An average grain yield was 3.63,3.13, and 3.00 t ha-1 in 2005 from WI, W2 and W3 respectively. The low yield in 2004 was attributed to heavy birds attack. The amount of water used was (663, 594, and 542 mm in 2004 and 625, 553, and 512 mm in 2005 by WI, W2 , and W3 respectively. Sorghum responded to irrigation with a linear increase in grain and forage yield as water use increased. Weekly irrigation interval resulted in significant increase in grain and forage yields compared with the other treatments. The WUE as grain was 5.8,5.7 & 5.9 kg ha-1 mm-1 in 2005 for WI, W2 & W3 respectively. For forage yields the WUE obtained were 27, 22 & 21 kg ha-I mm-1 in 2004 and 28, 28 & 24 kg ha-1 mm-1 in 2005 for WI, W2 & W3 respectively. According to the results obtained in 2005 the variety Wad Ahmed was found to be a semi-drought-resistance as the crop response factor Ky equals to 0.9, meaning that Wad Ahmed can withstands water stress up to 3 weeks. The measured values of the differential crop coefficients for WI, W2 and W3 using the Penman-Monteith formula at the four crop growth stages (initial, crop development, mid-season, and end) were (0.50, 1.06, 1.28, and 0.52), (0.50, 0.82, 1.16, and 0.54), and (0.50, 0.86, 1.15, and 0.23) for ea c h treatment respectively. These coefficients are greater than those suggested by FAG 56. It is concluded that continuous terminal water stress at the end of each irrigation cycle, with traditional 2 weeks intervals or more, will significantly reduce grain & forage yields of a semi-drought tolerant variety such as Wad Ahmed. Total seasonal net irrigation savings were found to be around or less than one traditional ilTigation. Thus reducing the number of inigations by 50% or more would not result in similar water savings, in contrary it will lead to increased terminal water stresses and significant yield reduction