GROWTH-RESPONSE OF MUSTARD [BRASSICA-JUNCEA (L) CZERN AND COSS] TO IRRIGATION LEVELS IN RELATION TO TEMPERATURE AND RADIATION REGIMES

Field experiments on mustard were conducted for 4 consecutive years to quantify crop growth and development in relation to thermal time unde r arid conditions. The crop was maintained under (a) three irrigations (control), each of 60 mm depth, (b) at 50% potential evapo-transpirat ion (PET) irrigation level, and (c) at 100% PET irrigation level. Grow th of mustard in relation to accumulated growing degree days under all treatments was closely represented by the Hoerl function. The correla tion coefficients ranged between 0.95 and 0.99 and were significant at p = 0.01. The crop irrigated at 100% PET level required less thermal time (40 degrees C d) compared to control crop (45 degrees C d) for ap pearance of each leaf tip on the main shoot. Heat and energy use effic iencies were higher for the crop irrigated at 100% PET. However, water -use efficiency was higher for the crop maintained at 50% PET rates. M easurements of light distribution within canopy revealed that red to i nfrared ratio at the bottom of the crop canopy was the lowest at peak flowering stage as compared to other stages. (C) 1996 Academic Press L imited