Attention is drawn to the large annual fluctuations of clove yields in Zanzibar and Pemba which appear to result from a synchronization of clove production by trees. Linear regression analyses are presented which show that in years of peak production tree yield is often correlated with tree canopy area and that when trees yield in two consecutive years, yield in the second year is usually negatively correlated with yield in the first year; equations including both variables often leave considerable variation in yield unaccounted for. It is suggested that some of the year to year variation in tree yield may result from an environmental stimulus affecting clove bud differentiation.

The intercropping objective of the subsistence fanner in Botswana was identified as a need to secure some cowpea production without reducing the yield of the staple crop, sorghum. Field experiments in which sorghum and cowpea were intercropped in several different environments over three years met this objective on most occasions, but cowpea yields were low compared with their sole crop performance. Although intercropping out-performed monocropping by producing some cowpea yield, land equivalent ratios greater than one and higher gross income and cash returns to draught-power (but not returns to labour) the differences were never large and seldom statistically significant.

Water depth at or shortly after planting is critical for the establishment and subsequent tolerance of excess water in rice. A crop transplanted early in the season produced twice as much grain as a later planted crop. A semi-dwarf variety (CR 1018) and a taller variety (CR 1030) performed similarly after early transplanting, but the tall variety performed better when planted late under excess water. Seedling age did not greatly alter the yields when crops were transplanted early, but after late planting 45-day-old seedlings were best.

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.

The comparative stability of sorghum–cowpea intercropping and monocropping was assessed by determination of variances, regression against an environmental index, and probability of failure to achieve minimum levels of gross income. Significant differences between the cropping systems were not detected in any of the assessments though intercropping did have a lower probability of failure at the income levels for which risk was more than minimal. The failure of intercropping to show clearly greater stability in this study in which the environmental conditions were harsh provides a conflict with the conventional view.

Field experiments were conducted on two soils (clay loam and sandy loam) with varying texture and water table depth to study the effects of two planting methods (dry seeding and transplanting) on the root growth and grain yield of rainfed lowland rice. About 75% of the roots were found in the top 10 cm soil. Root length density at the flowering stage and grain yield in the sandy loam soil, with a water table deeper than 1.5 m, were less in dry-seeded than in transplanted rice, probably because of the greater moisture stress in dry-seeded rice between late tillering and harvest. In the clay loam soil, with the water table mostly at the soil surface, there was no difference in grain yield between dry-seeded and transplanted rice.

Cotton leaf reddening was studied in irrigated vertisols at the Gezira Research Farm over three seasons. The percentage leaf reddening was negatively correlated with seed cotton yield. Plants showing symptoms of reddening produced smaller and fewer leaves which did not persist long enough to sustain the reproductive parts. Deficiencies of nitrogen and phosphorus were found to be responsible for the reddening symptoms. Nitrogen application, late August sowing and frequent control of insect pests all significantly reduced the incidence of reddening. Other possible remedies are discussed.

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 presence of free water on both surfaces of the leaves of shaded and unshaded coffee trees was evaluated at Cenicafé, Colombia. Rainfall was the main source of humidity and dew was not registered during the experiment. Five mm of rain caused canopy saturation and water began to reach the underside of the leaves. The period of wetness lasted 9.7 hours on average and no significant moisture differences were found between leaves on east or west facing branches, at different levels within the tree, or externally or internally positioned on the branches, either for exposed or shaded trees. Between 1700 and 0500 h (local time), a close relation was found between the time of rain initiation and the duration of the period of wetness. Leaves dried out at approximately 1000 h.

Studies were carried out at Kalyani during 1982–83 and 1983–84 to evolve a multiple cropping system with cotton as the main crop. Cotton was intercropped with paddy, greengram, blackgram, peanut and soyabean in the rainy season, and these were also grown as solccrops followed by crops of peanut, lentil, chickpea, wheat and mustard, respectively, in the winter season. All plots were subsequently cropped with sesame in the summer season. There was an increase in total grain yield, land equivalent ratio (LER), area time equivalent ratio (ATER) and relative net return (RNR) values when legumes and cereals were intercropped with cotton. The yield of the winter crops grown with the help of residual soil moisture was in the order: chickpea > mustard > lentil > wheat > peanut. Sesame yielded best after the chickpea and blackgram sequence and yielded almost as well after the lentil and greengram. The greatest net return was obtained from the cotton and paddy (1:1) intercrop followed by sesame.

Extracted leaf protein is now used regularly as human food in several places. For preliminary, or domestic, trials the equipment used is inconveniently large. A miniature extraction unit, which does not depend on electricity, is described.

The introduction of forage or hay crops into fallow land represents a means of increasing feed supplies for small ruminants in north Africa and west Asia. Such fallows lie between zones planted with food crops and traditional grazing areas. Mixtures of vetch with barley, oats or triticale, and peas with barley, were cut at the 10% flowering, 100% flowering (100F) and full pod (FP) stages of the legume component. Effects of crop maturity, weather conditions and cutting height on yield, the chemical composition of the standing crop and re-growth were measured. Barley–vetch mixtures yielded 8147 kg dry matter ha−1 of standing crop at the FP stage in 1983 but only 2283 kg dry matter ha−1 in 1984 under drought conditions. Hay yields were 4377 and 1640 kg dry matter ha−1, respectively. The highest yielding mixture, grown in 1983, was oat–vetch which yielded 8670 kg dry matter ha−1 of standing crop and 4285 kg dry matter ha−1 of hay at the FP stage. Cutting at the 100F or FP stage maximized dry matter yield and minimized the risk of rainfall prolonging hay making. Rain caused slight damage to some hays cut at early stages of maturity. Voluntary intakes and digestibilities of field-cured hays were determined. The voluntary intakes of triticale–vetch hay at the FP stage and all barley–pea hays were low compared with other hays. Hays contained sufficient estimated metabolizable energy (ME) for use in sheep diets during pregnancy and middle or late lactation. ME values averaged 9.2 megajoules per kg dry matter in both 1983 and 1984.

The effect of the field application of chlormequat on the growth, yield and seed oil content of Brassica juncea grown under irrigated and rainfed conditions was evaluated for three consecutive crop seasons. Foliar application at the flower initiation stage increased the number of primary branches, number and length of siliquae, weight of seeds and seed oil content. Chlormequat (50 AS) applied at 80 ml ha−1 increased seed yield by more than 50%. The increase was greater in unirrigated crops.

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.

The performance of a cassava clone susceptible to cassava mosaic disease (CMD) was tested over two successive years for CMD development, plant vigour and yield of fresh tuberous roots. Cuttings from plants with different CMD infection levels were used. There was a significant increase in mosaic incidence, severity and proportion of leaves showing symptoms of the disease in the subsequent crop as the levels of CMD primary infection in planting material increased. Plant height and stem diameter were also adversely affected and the yield of plants from severely affected cuttings was reduced by 60–70%.

Potatoes (Solanum tuberosum L.) in central Africa are often grown between two rainy seasons to avoid late blight infection. The influence of planting date and setaria mulch treatment on soil temperature, soil humidity, late blight development, ground cover with green leaves, intercepted radiation and tuber yield of potato was studied in crops grown at 1850 m above sea level in Rwanda.

The planting dates towards the end of the rainy season resulted in the best yields and these were considerably increased by mulching which retained soil moisture and reduced soil temperature so resulting in a better ground cover. Increased yields in the mulched plots seemed to be due to increased radiation interception rather than to better radiation use efficiency.

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.

The phenology of mung beans is extremely plastic; responsiveness to both photoperiod and temperature is known to modulate flowering. A previous conclusion, perpetuated uncritically now for almost forty years, has been that both (quantitative) short- and long-day flowering responses exist in the mung bean germplasm. However, our re-analysis of the original data leads us to an alternative conclusion: that genotypes of mung bean are quantitative short-day plants with different optimum mean diurnal temperatures for flowering. This alternative interpretation (which is plausible biologically and in evolutionary terms) is discussed.