General mathematical relations between yield parameters, plant populations and rainfall were developed for an indigenous sorghum from the results of 28 population/row spacing trials conducted at four sites over five seasons. Populations maximizing yield increased from 25 000 to 69 000 plants ha−1 over the rainfall range 200–700 mm (pre-planting to harvest total). Tillering partly compensated for low populations but yields from 10000 plants ha−1 at 300 and 600 mm rainfall were only 80 and 61% of potential maximum, respectively. Row spacing at constant population affected tiller numbers and eventual panicle weights but not panicle numbers, and any yield differences were unrelated to rainfall.

Field experiments were carried out to study the effects of elemental sulphur on irrigated groundnut. The sulphur was applied at rates of 50, 100 or 150 kg ha−1, either at sowing, at flowering or in two equal splits at sowing and flowering. Shoot dry weight, total sulphur content of leaves, nodule number per plant and pod yield were all significantly increased by sulphur treatment, but nodule dry weight was unaffected. The greatest response lay at or below 50 kg ha−1 applied at sowing. There were no further increases in response above this level.

Results of a two-year field study show that even under hot northern Indian conditions, sugar-beet planting dates can be advanced to 20 September to permit an early harvest from mid-March onwards. Seeding the crop on the northern side of east-west ridges gave root yields of 45–50 t ha−1 with a sucrose content of 12–14%. Transplanting gave the highest tonnage but led to a high incidence of branched tap roots. For timely planting during October, direct seeding in north–south rows was also satisfactory. Such staggered seeding and harvest schedules could help extend the milling period to 90–100 days as against the present 45–50 days.

Regional population recommendations for sorghum production in Botswana were calculated by applying long-term meteorological records to an experimentally developed model linking sorghum yield to plant population and rainfall. The basic recommendation at any place was taken to be that population maximizing local long-term yield means while keeping the risk of crop failure to one year in ten or less. Values ranged from 25 000 to nearly 70 000 plants ha−1, according to rainfall amount and reliability. The modifications of these basic recommendations necessary to allow for differences in standards of husbandry and for sorghum variety are discussed.