Effects of irrigation water temperature on growth of some legume species in glasshouses

Abstract

Five species of legumes growing in pots in a heated glass-house in mid-winter were irrigated daily with water adjusted to temperatures between 5� and 30�C. There was an immediate effect on substrate temperature (at 2.5 cm depth) amounting to a 5�C rise or fall above or below ambient in the warmest and coldest water temperature treatments respectively, but substrate temperatures returned to normal within two hours. Treatment had no effect on the growth of lupin (Lupinus angustifolius)or bean (Phaseolus vulgaris) but the form and growth of soybean (Glycine max), lablab (Lablab purpureus), and cowpea (Vigna unguiculata) responded significantly. The magnitude of the effect was greater in irrigation water temperature treatments below 20�C than above. The amount of the response was quite disproportionate to mean substrate temperatures which, on a mean hourly basis over 24 hours, showed less than 1�C difference between any two treatments. No nodulation differences occurred with any species in any treatment and analysis of nitrogen reaching the shoot indicated that the responses were not due to effects on nitrogen fixation as distinct from plant growth. Substrate temperatures were consistently about 5�C below the ambient temperature of the glasshouse. Measures to alleviate both this loss of heat and the effect of midwinter tapwater temperature on plant growth in glasshouses are discussed.