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Losses of potatoes during storage due to disease, softening of tubers, sprouting and frost damage frequently exceed 25%, particularly when they are stored in field clamps or unmodified farm buildings. Though the condition and health of the crop when stored is of overriding importance, the use of refrigeration and forced-draught ventilation can reduce such losses spectacularly. But the high cost of purpose-built stores requires a high premium price for late-marketed produce.

THE optimum plant density for a crop often decreases as the climate becomes drier. The usual explanation for this, that wider spacing of plants decreases competition for water1,2, overlooks the possible effect of other climatic factors in the size of individual plants. Thus data we have collected from maize density experiments suggest that smaller densities are used for this crop in relatively dry North-east Rhodesia than in relatively moist central England because plants grow much larger in Rhodesia than in England, rather than because water is in comparatively short supply in Rhodesia.