EFFECT OF WATER-STRESS ON POTATO GROWTH, YIELD AND WATER-USE IN A HOT AND A COOL TROPICAL CLIMATE

Irrigation experiments are described in which three cultivars were subjected to varying degrees of drought in the cool and hot seasons in Lima, Peru. The most severely droughted plots received, on average, 20 % and 35 % less water than the well-watered control plots, resulting in 20 % and 52 % yield reduction in the cool and hot seasons, respectively. Average fresh tuber yields ranged, according to cultivar, from 1370 to 2450 g/m2 in the summer and from 2800 to 4450 g/m2 in the winter, with tuber dry-matter percentages of c. 17% and 20 %, respectively. The production of total dry matter per unit intercejtled solar radiation (the conversion coefficient, estimated from the slope of the regression, in g/MJ) was markedly less during the hot season but, regressed on a photo thermal quotient ∑((MJ/m2)/(°C > 4-5°C)), a common relationship across seasons was achieved. The conversion coefficient was less in droughted than in well-watered plots, more so in the hot season. Crop transpirational and evapotranspirational water use efficiencies (WUE) were less in the hot season largely because of the greater saturation vapour-pressure deficit. However, because of greater harvest index (HI) and more-efficient intercejtlion of solar radiation per unit of applied water by droughted than by well-watered plots in the summer, and despite a lower conversion coefficient, droughted plots showed greater WUE. Based on total water applied and final fresh tuber yields, WUE was, on average, 3–9 and 12–4 kg/m3 in the hot and cool seasons, respectively, values close to the extremes of the range of published values. Low HI in the summer was, to some extent, responsible for this seasonal difference. © 1990, Cambridge University Press. All rights reserved.