Growth, flowering and fruiting of cacao under controlled soil moisture conditions

Young clonal cacao trees have been grown under controlled soil moisture conditions for 20 months in a glasshouse. Weighable soil containers were used, and water was added to restore the soil to field capacity each time the total available water, which was about 40 lb. for each plant, had been depleted to 85 percent (wet treatment), 50 percent (medium treatment) or 15 percent (dry treatment). Plants were either given one of these treatments for the whole experiment, or one treatment was given during the natural dry seasons and another during the natural wet seasons. Plants given a dry treatment at any time lost their apical dominance and flushed vigorously about 10 days after each watering, though many flushes subsequently withered. The other plants flushed normally, except that the continuously wet plants ceased to flush towards the ende of the experiment. The mean expanded area of each leaf was greatest during wet and least during dry periods, and plants which had suffered the least soil moisture deficit throughout growth had the greatest net leaf area and dry weight accumulation. There was little difference in the rate of transpiration per unit leaf area between plants during periods of high compared to medium soil moisture, but the rate was less during dry periods. Dry weight increases both per unit of water transpired and per unit of net leaf area were greatest in the wettest plants. There was little difference between the effects of the wet and the medium treatments on flower production or setting or on cherelle wilt, though ultimately slightly more pods ripened on the wet plants. Plants in a dry period developed few flowers, but initiation was apparently stimulated, for in a subsequent wet or medium period flowering was exceptionally heavy; setting was poor and cherelle wilt high, however. It is concluded that irrigation on a greater scale than is practised at present is likely to be beneficial to the growth and yield of cacao