The effect of environmental factors on growth, pod-set and yield of short duration pigeonpea ( cajanus cajan (L.) miltsp.)
Four experiments were conducted to investigate effects of temperature, humidity, soil water deficits, photoperiod and sowing date on growth, pod-set and yield of different varieties of pigeonpeas. The varieties were chosen to include determinate (ICPL4, ICPL87, ICPL151) and indeterminate (ICPL81, UPAS120) types. Temperature and photoperiod treatments imposed from flower initiation to harvest in a naturally lit glasshouse had no effect on shoot and root dry weights, but the pod number and grain yield were reduced except in one genotype when the day temperature was increased from 300 to 400C. Variation in day/night temperatures showed that low night temperature delayed flowering and inhibited podset. Pod-set occurred at 30/150C and 30/250C day/night temperature in ICPL4 and ICPL81 but no pod-set was observed at 30/50 in a~l the genotypes day temperature under growth and at 30/150 in ICPL87. High chamber conditions caused complete flower abscission regardless of the night temperature and high leaf shedding occurred which influenced the biomass production. High humidity and increased soil moisture increased leaf area for ICPL87 but reduced that for ICPL81. At high humidity the shoot dry weight decreased for ICPL81 at high soil moisture but an increase was observed for ICPL87. The flower number declined at high humidity and increased soil moisture for ICPL87 but was not affected for ICPL81. High humidity reduced the number of pods, percentage pod-set and grain yield regardless of the moisture regime. Delayed sowing at this site is characterised by declining day-length, temperature, as well as rainfall. The results of the sowing date experiment showed that delayed sowing led to a decline in leaf area and shoot dry weight at flowering as well as at maturity. Late sowing reduced the number of flowers, pods, branches, and percentage pOd-set which led to a decline in grain yield. The following conclusions may be made from the results of this work: 1. Increased day temperature reduced the grain yield as a result of greater flower abscission and pod abortion. Both day and night temperature are important for growth after flowering and pod-set in the genotypes studied. 2. 'Severe' water stress can limit the yield of these genotypes and the indeterminate genotype tolerated the water-limited situation better than the determinate. 3. A major effect of the date of sowing at this location and the genotypes used is the reduction in plant size due to reduced branching and stem size.