Growth response of mustard [Brassica juncea(L.) Czern & Coss] to irrigation levels in relation to temperature and radiation regimes

Field experiments on mustard were conducted for four consecutive years to quantify crop growth and development in relation to thermal time under arid conditions. The crop was maintained under (a) three irrigations (control), each of 60 mm depth, (b) at 50% potential evapotranspiration (PET) irrigation level, and (c) at 100% PET irrigation level. Growth of mustard in relation to accumulated growing degree days under all treatments was closely represented by Hoerl function (product of power and exponential type of curve). The correlation coefficients ranged between 0•95 and 0•99 and were significant atp = 0•01. The crop irrigated at 100% PET level required less thermal time (40°C d) compared to control crop (45°C d) for appearance of each leaf tip on the main shoot. Heat and energy use efficiencies were higher for the crop irrigated at 100% PET. However, water use efficiency was higher for the crop maintained at 50% PET rates. Measurements of light distribution within canopy revealed that red to infrared ratio at the bottom of the crop canopy was the lowest at peak flowering stage as compared to other stages