Artificial defoliation of okra 4, 6 and 8 weeks after sowing generally delayed flowering, decreased plant height and stem girth at flowering and reduced the harvest duration. Pod length, pod diameter, mean pod weight and number of pods plant−1 were also decreased by defoliation but pod yield ha−1 was not.

The removal of leaves from the upper half of the stem only had a similar effect to complete defoliation whereas the removal of leaves from the lower half only had no significant effect, indicating that the leaves on the upper stem contributed more to growth and yield than those lower down. Significant time × degree of defoliation interactions occurred for most growth and yield parameters.

In 1981 and 1982, three crop protection regimes were compared with an unsprayed control for cowpea grown alone and in mixtures with maize, sorghum and cotton. Unsprayed cowpea in mixtures with maize had yields which suggested some pest escape in 1981 but not in 1982. When sprayed, only the maize–cowpea mixture showed much yield advantage over sole crops. For maize–cowpea in 1983, a very dry year, only the alternate row mixtures showed a yield advantage and three spray applications gave cowpea yields as good as those resulting from six applications. The late, photosensitive cowpea variety Acq 1696 had better yields than the medium maturity TVx1948·01 F in the mixed crop but was greatly inferior as a sole crop.

The base temperature and thermal time for different development stages of spring wheat cultivars were calculated using a linear relation between the rate of development and the mean temperature. The results show that germination, emergence, tillering and leaf elongation (the vegetative phase) have a base temperature around 2°C but the elongation of the culm and the reproductive phase (tillering-maturity) have a base temperature over 6°C. A general model to describe the time to maturity of spring wheats, which takes account of these different phases, is proposed.

The effects of three shade densities, NPK fertilizers and fertilizer-pest/disease relationship on Amazon cocoa (Theobroma cacao L.) over a 20-year period are reported. Yields equivalent to the mean yield from the unfertilized plots were achieved in about 3, 4 and 6 years in fertilized plots under the no shade (S0), medium shade (S1) and heavy shade (S2) treatments, respectively. There were three growth phases, each characterized by a different yield trend. No appreciable changes in the exchangeable Ca and Mg were observed during the experiments, but K dropped to 68% of its initial value while the available P of the unfertilized and the S0 plots fell by 38%. Fertilizer recommendations for P and K should take account of overhead shade. The effect of N application was often negative. No direct relationship was observed between fertilizer treatment and the incidence of pest/blackpod/swollen shoot virus (SSV) disease of cocoa. SSV infection was greatest under S0. Cocoa farms in Ghana cannot maintain high yields (above 1000 kg dry cocoa ha−1) beyond 15 years of intensive cropping.

The effect of variations in the relative sowing time and density of component crops in a maize/cowpea intercrop were examined in two experiments. In the first experiment, maize and cowpea were sown together, and either 10 or 21 days before or after each other. Maize yield was reduced when sown at the same time or after cowpea; intercrop cowpea yields were less than sole cowpea yields at all sowings. In the second experiment, maize densities of 35, 50 and 70 × 103 plants ha−1 were combined with cowpea densities of 70, 100 and 140 × 103 plants ha−1. Increasing the density of either crop in the mixture resulted in increases in total yield. Maize reduced cowpea yields more than the effect of cowpea on maize yields. In terms of LER and total seed protein yield, there was no advantage of either staggered sowings over simultaneous sowing or of the various intercrop density combinations, except between the lowest and the highest densities of either maize or cowpea. The LERs appeared to follow the trends in cowpea yields and total seed protein yields the trends in maize yields.

The combined effect of soil moisture stress in the root zone and atmospheric evaporative demand on the growth and yield of two chickpea cultivars was investigated using four sowing dates and three irrigation regimes within each sowing date during the 1980–81 and 1981–82 seasons at the ICRISAT research centre. Total water use was different for different irrigation regimes and sowing dates and there were differences in the total dry weight and seed yield of chickpea between the sowing dates and the irrigation regimes. The cultivars did not differ in dry matter production. However, cv. Annigeri yielded more than cv. L-550 under all irrigation regimes. Differences in seed weight were observed between irrigation regimes and sowing dates and there were interactions between sowing dates and cultivars and between irrigation regimes, sowing dates and cultivars. High air temperatures during the period from flowering to maturity reduced the time to maturity of late-sown chickpea and led to reduced seed size and lower yields. The efficiency of use of applied water was also low for the late-sown crop.

A re-analysis of a two-year study designed to investigate the effect of spacing on the yield of two cowpea cultivars in the savanna and rainforest zones of Nigeria confirms plant density and spacing recommendations for the savanna zone while contradicting all but intra-row spacing recommendations for the forest zone. An inter-row spacing of 60 cm and intra-row spacing of 9 cm or closer could be used for improved seed yield in the savanna zone, while a plant density between 120 000 and 166 666 plants ha−1 with an inter-row spacing of 30 cm would be optimum for cowpea production in the forest zone.

Perennial crops, guinea grass and alfalfa, and annual crops, wheat and cotton, were grown in the reclaimed Hula Valley swamp. The aim was to find ways to preserve the peat soil from aerobic oxidation, wind and water erosion; to minimize nitrate accumulation, which causes pollution of the waters draining into the Kinneret Lake (Sea of Galilee); and to select high yielding crops that both fulfilled these needs and ensured a good income for the farmers. Our results showed that high dry matter yields of guinea grass and alfalfa could be obtained. A significant decrease in peat soil erosion and nitrate accumulation was also recorded under these perennial crops, so growing them has both economic and ecological advantages.

The results of two tea irrigation experiments conducted independently in southern Tanzania and Malawi, where severe annual droughts of similar duration occur, were compared. There were marked differences in the dry season yield distributions between the two sites. These could be attributed to the adverse effects of large saturation deficits on plant water status and rates of shoot extension in Malawi. The implications for tea irrigation in particular and for irrigation agronomy experiments in general are discussed. The need to include detailed descriptions of the environment in which experiments are conducted is stressed.

A field experiment was conducted during the monsoon seasons of 1982 to 1984 to investigate the effect of chlormequat chloride (CCC) and its mode and time of application on groundnut. Foliar application of CCC 60 days after sowing at the rate of 200 ppm reduced moisture loss and increased relative leaf water content and yield. Soaking seed in a 0.5% CCC solution also increased relative leaf water content, root nodulation and seed yield.

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.