Productivity of vegetable crops in a region of high solar input. II. Yields and efficiencies of water use and energy

Abstract

Details are given of final yields and size gradings of three potato crops grown under conditions of high solar input and high temperatures in the Murrumbidgee Irrigation Areas of New South Wales. Total yields were up to 50 t ha-l. Differences resulting from different irrigation treatments were surprisingly small, although mean tuber weight was slightly less in the drier treatments. Water use was about 300 g for each 1 g dry weight produced, and efficiency was slightly greater in the wetter irrigation treatments. Reductions of 21 %and 34 % of the total solar input, using shade covers, markedly reduced yields, and there was no statistical interaction with irrigation treatment. Tuber numbers also decreased with decreasing solar input, though not as much as yields, and mean tuber size was greatest on unshaded plots, least under 34% shade. Tuber moisture percentage at harvest was not affected by the different irrigation treatments, but was reduced in two experiments as shading increased. There were only small differences in plant and stem numbers per unit area between any of the treatments, though stem numbers decreased significantly as shading increased. High crop growth rates were achieved especially during the tuber bulking periods, when up to 22.8 g m-2 day-1 of dry matter were produced in each of two experiments, achieved with conversion efficiencies of photosynthetically active radiation of 3.5 % (spring-planted crop) or 6.1 % (summer-planted crop). The results are in agreement with the hypothesis that assimilation in the potato depends primarily on the 'sink' strength of the developing tubers, which is determined in the 2 or 3 weeks following the onset of initiation. The main effects of differences in solar input appear to be determined in this period. It is suggested that a practical approach to increasing yields in this region may be to increase the numbers of tubers which develop per unit area by increasing plant density and encouraging early haulm growth.