STUDIES ON THE WATER RELATIONS OF THE SUGAR CANE PLANT

Studies to determine the effect of various soil moisture regimes on the internal water balance and on the growth and yield of sugar cane were conducted in the Department of Agricultural Botany, D.P. College of Agriculture, Philippines from 1965 to 1967. Experiments were also conducted to determine a relationship between some physiological processes and plant growth as a result of moisture stress.\ud \ud The results showed that with an increase in soil moisture stress, growth based on stem height, leaf area, total number of leaves, length of internode and diameter of canes, dry weight of tops and yield based on total millable cana, per cent juice in cane and per cent sucrose content in the juice all decreased significantly optimum growth and yields were obtained at field capacity.\ud \ud The internal water balances in sugar cane, measured by relative turgidity was found to have more profound effect on plant growth rather than the degree of moisture stress in the soils This was concluded since the plants subjected to low atmospheric stress (low air tem perature) made a growth (based on stem and leaf area increment) which was almost independent of soil moisture between the range of field capacity and permanent wilting percentage. This was further attributed to a favor able internal water balance maintained by plants under such conditions.\ud \ud When the relative turgidity in plants was changed from 90 to 80 per cent, the reduction in growth was largely attributed to a reduction in the relative activity of gibberellin-like substances. However, when the relative turgidity fell below 80 per cent, the reduction in growth was attributed to a loss of turgence subsequently inhibiting the net assimilation rate