Productivity of Vegetable Crops in a Region of High Solar Input. III. Carbon Balance of Potato Crops

Abstract

The carbon balance of potato crops has been studied by measuring canopy net photosynthesis and dark respiration losses with a field assimilation chamber and semi-closed gas analysis system. Results are given for the latter part of growth in both a spring-planted and a summer-planted crop.

Net CO₂ uptake increased with solar input to reach 35–40mg dm^-2 (ground area) h^-1 at 400–450 W m^-2, but light saturation then occurred and little or no further uptake resulted from increases in solar input up to 1000 W m^-2. This supports the previous conclusion that net photosynthesis in the potato is determined by the size of the 'sink' provided by the developing tubers. The imposed experimental variables of reduced solar input (21 and 34% shade) and soil moisture were found not to affect the relation between solar input and CO₂ uptake, and the effect of chamber temperature was also very small.

Dark respiration rates of the canopy were markedly sensitive to temperature, and also to the solar input prior to measurement. Respiration from the below-ground plant parts accounted for a considerable part of the total plant respiration. In all, 15–20 % of the net assimilation during daylight hours was lost by night respiration. There was little variation in CO₂ efflux from uncropped soil during the experiments.

Dry weight changes calculated from the gasometric measurements were in accordance with those found from previous growth analysis.

* Part II, Aust. J. Agric. Res., 1973, 24, 751–62.