Changes in radiation-use efficiency under different environmental conditions in rainfed pigeonpea (Cajanus cajan)

A study was conducted during 1992-93 on the environmental effects on radiat ion-use efficiency of pigeonpea [Cajanus cajan (L.) Millsp.] through differ ent sowing dates and years. Delaying the sawing time from 30 June to 9 Augu st produced a steady and sustained decrease in mean seasonal radiation-use efficiency during both years. The base line radiation-use efficiency values for early sowing, ie 30 June were 1.82 and 1.61 g/MJ in 1993 and 1994 resp ectively. Higher efficiencies in 1993 were indeed attributed to warmer temp erature. These variations in radiation-use efficiency could reflect the dif ferences in biomass productivity. Across and sowing dates, a negative and s ignificant association between radiation-use efficiency and maximum tempera ture during vegetative period was found in 'GT 100' and 'BDN 2' pigeonpea B esides, during reproductive period, maximum and minimum temperatures appear ed positive and closely related to radiation-use efficiency in 'GT 100' pig eonpea This relation showed that pigeonpea grown in cooler environment gave rise to lower radiation-use efficiency and thereby affecting dry-matter ga in in pigeonpea canopies. Mean vapour pressure deficit, bright sunshine hou rs, photosynthetically active radiation and soil-water content also affecte d the radiation-use efficiency during vegetative period. The bright sunshin e, photosynthetically active radiation and minimum temperature were found t he most important environmental variables determining the variation in radi ation-use efficiencies across varied environments. The radiation-use effici ency declined rapidly near attainment of podding phase. Narrow row spacing (60 cm) also showed an increase in radiation-use efficiency. Base line radi ation-use efficiency for crop growth modeling would be inappropriate withou t considering the observed effect of environmental and management condition s.