Studies on the irrigation of sugar-cane

Abstract

Eleven replicated irrigation trials on sugar-cane, together with some preliminary observation tests, were conducted in the Bundaberg region of southern Queensland during four seasons, 1961–62 to 1964–65. Irrigation control was through actual measurements of potential evapotranspiration of cane (Etc) or grass (Etg) with lysimeters. In conjunction with the lysimeter work, pan evaporation (Ep), mean air temperature (Ta), and sufficient data to calculate Penman's potential evaporation (E0) were recorded. Etc consistently exceeded Ep, and Etg slightly exceeded Ep in summer. Et was fairly well correlated with Ep and Ta, but less well correlated with E0. The inclusion of Ta in regressions of Et on Ep or E0 improved these regressions; Ta presumably reflects the additional external source of energy which was causing the high Et values. Yield responses to irrigation were very different on two soil types: on a deep red volcanic loam they were 10 times as great as those on a heavy alluvial clay. The reasons for the poor response on the alluvial clay appear to be threefold: (i) a permanently moist (but saline) subsoil maintained some growth in dry weather; (ii) growth in soils kept moist by irrigation virtually stopped when heavy rain fell; (iii) heavy rain falling on previously dry soil resulted in an abnormal increase in growth rate, an effect which was associated with a dramatic increase in soil mineral nitrogen. The most satisfactory indicator of water use by cane was Etg; growth rate data indicated that 100% Etc is required, but yield data suggested that 66% Etc is adequate. The latter value approximates to 100% Etg or 100% Ep in the summer months. Growth, and therefore growth response to irrigation, is very severely curtailed when mean temperatures fall below 70°F; soil temperature appears to be the critical factor. Growth rate was too susceptible to factors such as temperature to be of any value as an indicator of the need for irrigation.

Water use efficiencies in relation to sugarcane yields

“…(Anon, 1968 Bosshart, 1982;Chang, Wang & Yao, 1983). However, the magnitude of the yield response to the relief of moisture tension is strongly influenced by soil type (Yates, 1967;Thompson, 1977;Shih, 1985) to the extent that economic yield responses may be infrequent (Wilson, 1980) or, even, that irrigation may depress yields (Yates, 1967;Chapman, 1980). It must be concluded, therefore, that detailed field experimentation should precede any substantial investment in imgation works.…”

“…The first is that sugarcane virtually ceases growth when mean-day temperatures fall below about 20°C; thus there is no direct response to irrigation under these conditions (Yates, 1967). However, excessively prolonged moisture stress in the winter may damage the plant and so delay recovery in the spring, thus reducing yields (Moberley, 1974).…”