Evapotranspiration rates and water utilization of moth bean under two soilmoisture conditions

Moth bean (Vigna aconitifolia (Jacq.) Marechal) was grown under rainfed and 100% potential evapotranspiration (PET) irrigation (unstressed) conditions to quantify the influence of moisture availability on evapotranspiration ( ET) rate, and water and heat use efficiencies. The experiment was carried o ut in gravimetric lysimeters, installed at Central Arid Zone Research Insti tute, Jodhpur, during 1991 and 1992. The evapotranspiration (ET) rate from 100% PET (unstressed) crop was maximum (6.6 mm day(-1)) during 7th week aft er sowing, and lowest (2.2 mm day(-1)) during crop emergence stage. The max imum evapotranspiration rate coincided with peak pod formation stage in the crop. Water use efficiency of the crop was 2.3 to 3.5 and 2.2 to 2.4 kg ha (-1) mm(-1) for unstressed and rainfed crop, respectively. At cardinal temp eratures of 8 degreesC (base temperature below which moth bean development ceases), 33 degreesC (optimal temperature for development) and 45 degreesC (maximum temperature at and above which no development takes place), the cr op required 1351 to 1569 degrees Cd growing degree days (thermal time) to r each physiological maturity. Linear relationship was developed between ther mal time and leaf tip appearance. The leaf tip appearance on the main shoot of moth bean in relation to the thermal time was linear under both moistur e conditions, requiring about 52 to 58 degrees Cd leaf(-1). However, leaf t ip appearance on primary branch was slightly faster and required 49 to 53 d egrees Cd for each new leaf. Appearance of first primary branch was earlier (at about 300 degrees Cd after emergence) under the unstressed condition a s compared to the rainfed crop under the potential ET (at 360 degrees Cd). Hence, it may be concluded that despite low water requirements, the crop gr owth is considerably influenced by the moisture availability during crop gr owing period in the region.