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

Abstract

A study was conducted during 1992-93 on the environmental effects on radiation-use efficiency of pigeonpea
[Cajanus cajan (L.) Millsp.] through different sowing dates and years. Delaying the sowing time from 30 June to 9
August 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 respectively.
Higher efficiencies in 1993 were indeed attributed to warmer temperature. These variations in radiation-use
efticiency could retlect the differences in biomass productivity. Across and sowing dates, a negative and significant
association between radiation-use efficiency and maximum temperature during vegetative period was found in "GT
100' and 'BDN 2' pigeonpea. Besides, during reproductive period, maximum and minimum temperatures appeared
positive and closely related to radiation-use efficiency in "GT 100' pigeonpea This relation showed that pigeonpea
grown in cooler environment gave rise to lower radiation-use efficiency and thereby affecting dry-matter gain in
pigeon pea canopies. Mean vapour pressure deficit, bright sunshine hours, photosynthetically active radiation and soilwater
content also affected the radiation-use efficiency during vegetative period. The bright sunshine, photosynthetically
active radiation and minimum temperature were found the most important environmental variables determining the
variation in radiation-use efficiencies across varied environments. The radiation-use efficiency declined rapidly near
attainment of podding phase. Narrow row spacing (60 cm) also showed an increase in radiation-use efficiency. Base
line radiation-use efficiency for crop growth modeling would be inappropriate without considering the observed effect
of environmental and management conditions.