Water requirements of irrigated maize in Nyasaland

Abstract

Changes in soil moisture under an irrigated maize crop were studied in two consecutive seasons in the Lower River area of Nyasaland. Irrigation was based on open-pan evaporation; the recorded evaporation in inches was multiplied by a series of irrigation factors, and irrigation was applied to balance the calculated deficit in each case. Soil moisture changes were recorded by measuring the electrical resistance of gypsum units with a Bouyoucos meter. The minimum irrigation required to hold the resistance constant is then approximately equal to the loss of soil moisture. It is shown that the ratio of crop water requirement to open-pan evaporation was not constant throughout the growing season of the crop but rose sharply about the time of the emergence of the tassels. The same irrigation factors gave similar patterns of soil moisture use in both seasons, although the evaporation, and hence the irrigation water applied, was appreciably different. The importance of linking results of irrigation experiments and recommended irrigations with observed or calculated evaporation figures is discussed.