CROP WATER STRESS OF TOMATO AS AFFECTED BY IRRIGATION REGIMES

A field experiment was conducted at the Irrigation Research Station, Kadawa Kano State, Nigeria (located 11o 30' N, 08o 30' E and 486 m above mean sea level) during 2012/2013 dry season to evaluate crop water stress index of tomato (lycopersicon enculentum; UC82B) as affected by irrigation regimes. The experiment consisted of four levels of irrigation water application depth of 100%, 75%, 50% and 25% replacement of moisture depleted and three irrigation intervals (7, 14 and 21 days) combined in Randomized Complete Block Design in a Split plot arrangement and laid as treatments in plots (3 m x 3 m basin) and replicated three times. Irrigation water was applied to each basin using a calibrated PVC pipe. The soil moisture was monitored throughout the crop growing season with theta probe. The crop canopy temperature (Tc) in the experimental plots was measured with a portable hand-held infrared thermometer. The dry and wet bulb temperatures were measured with an aspirated psychrometer in the open area adjacent to the experimental plots. The mean air temperature (Ta) was determined from the average of the dry bulb temperature readings during the measurement period. The mean vapor pressure deficit (VPD) was computed as the average of the calculated instantaneous VPDs, using the corresponding instantaneous wet and dry bulb temperatures. The Crop water stress index increases with decrease in percentage of moisture depletion replacement from 100% to 25% and increase in the irrigation interval from 7 days to 21 days. The most stressed tomato was at 25% replacement of moisture depleted in 21 days (I21D-25%) with stress index of 1.000 and the fully watered (none stressed) tomato was when irrigated fully at 7 days (I7D-100%) with stress index of 0.003. Hence, a tomato can give a best yield and optimum water management with no stress under high water table condition, when irrigated at 7 days with 25% replacement of its moisture depleted.