Effect of sowing date on growth and development of irrigated peanuts, Arachis hypogaea L. cv. Early Bunch, in a monsoonal tropical environment

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Abstract
An experiment was conducted to study the effect of sowing date on the growth and development and commercial yield of Early Bunch peanuts under irrigation in the monsoonal tropical environment of the Ord River Irrigation Area. Sowing dates, which ranged from 7 December to 1 March, represented a wider range than that currently considered optimal for peanuts in this environment. Differences in above-ground dry matter production among sowing dates were primarily the result of differences in cumulative interception of incident light due to different leaf area duration. Later sowings showed progressively slower canopy development, with those in February and March intercepting only 75 and 60% of the cumulative light intercepted by those in December-January. Vegetative development was very responsive to sowing date, with progressive reductions in vegetative dry matter occurring as sowing was delayed between January and March. The proportion of vegetative dry matter as leaf and stem was also affected by sowing date, in that the leaf to stem ratio measured at approximately 75 days after emergence was greater for later sowings. This effect was associated with temperature and photoperiod during the period from emergence to day 75. Pod development was less affected by sowing date than vegetative yield, with accumulation rates and commercial pod yields being reduced by 28 and 31%, respectively, for the final sowing date (1 March). This was the result of a greater proportion of assimilate being partitioned to the reproductive components in later sowings. Pod numbers were more sensitive to sowing date than pod yield, but later sowings tended to compensate for lower pod numbers by having higher average pod weights. Later sowings also tended to have larger sound mature kernels, and this was associated with temperature and photoperiod during kernel development.