A long-term trial with Leucaena leucocephala was initiated in 1982 to test the sustainability of Leucaena-based alley farming compared to a conventional cropping system without trees and with continuous cultivation of maize. It assessed the integration of short grazed fallows in rotation within Leucaena alleys and their effect on soil fertility and crop yields.

The various treatments had no effect on soil pH during the four-year period of the trial. The organic carbon and total nitrogen contents of the soils under conventional cropping were lower by the end of the fourth year than those under alley cropping and alley grazing treatments, whereas soil phosphorus levels were lower in the alley cropping and grazing plots. Foliage dry matter production of Leucaena under alley cropping management ranged from 6.0 to 6.7 t ha−1 a−1 under continuous cropping and reached 8 t ha−1 when alley cropping was preceded by a grazed fallow. Crop yields were consistently higher with alley cropping than with conventional cropping. Alley cropping plots in rotation with two year grazed fallows gave significantly higher crop yields during cropping years than those under continuous cultivation.

Effects of plant density were studied in field experiments carried out over four successive years as part of an evaluation of the potential of jackbean and in order to determine appropriate cultural practices for the crop. Flowering, biomass accumulation, and seed yield and its components were examined. Increased plant density led to earlier canopy development and biomass accumulation, and to increased seed yield in long growing seasons. Maximum seed yield ranged from about 1.0 to 3.8 t ha−1 between years of short and of prolonged rainy seasons, respectively. Plant size and branching were reduced at high density. Variation in seed yield was associated with differences in pod number; single seed weight and number of seeds per pod remained more constant

Effects of defoliating jackbean for forage production and time of sowing were studied in field experiments as part of an evaluation of the potential of jackbean and in order to determine appropriate cultural practices for the crop. In a long growing season, seed yield after cutting for forage was similar to that of an uncut crop but was reduced by two thirds in a short growing season. Flowering appeared to be stimulated in short days. Delayed sowing after the beginning of the rainy season progressively reduced seed yields

A field experiment was carried out to compare the performance of 18 accessions of jackbean from different origins. Plant development and phenology, final plant biomass, and seed yield and its components were evaluated. Flowering time ranged from 56 to 109 days after sowing. Bush and climbing types were identified and differences in seed yield were recorded, the largest yield occurring in a mid-season flowering accession. It was concluded that more material should be screened since germplasm introduction appears to be a promising route to larger jackbean yields in Yucatan

The effects on yield of varying the planting date and planting pattern of morphologically different cowpea cultivars intercropped with pearl millet were studied in two field trials. The interaction between cowpea cultivars and planting date was highly significant. There was a sharp reduction in cowpea yields with late planting. Millet yields were reduced less when sown simultaneously with early cowpea cultivars than when sown with a late maturing local cultivar. Early maturing cowpea cultivars planted in closely spaced hills had less effect on millet yields than a late maturing cultivar sown in widely spaced hills. An appropriate cowpea cultivar for intercropping with peal millet would be one that was weakly competitive and that yielded both grain and fodder.

The nutritive value and yield of forage legumes and barley harvested as immature herbage, hay and straw were measured in two experiments. The voluntary feed intake of peas at all stages of maturity and immature herbage from woollypod vetch was substantially lower than that of common vetch and chickling. At each stage of maturity barley was less digestible than all the forages except immature peas. Despite exceptionally cold weather in February/March 1985, yields of common vetch were higher in 1984/85 than in 1985/86 when there was less rain. Peas yielded the most hay, and chickling yielded less seed and straw than common vetch, peas and barley. Yields of digestible dry matter from straw and seed exceeded those from hay but protein yield at the two stages was similar. Mechanical baling substantially reduced the yields of baled hay but these losses would be reduced to less than 10% if the residues were grazed.

The design of a low cost and relocatable rain out shelter used for drought studies in the field is described. This design, covering 162.5 m2, enables reasonable plot sizes to be used and minimizes aerial and sub-aerial edge effects. A fully retractable vinyl cover results in minimal modification of the surrounding crop environment.

Three short duration and one long duration groundnut genotypes, grown either ‘sole’ or as intercrops (in 1:1 ratios of the short duration with the long duration genotypes), were compared in four trials. The intercrop treatments resulted in Land Equivalent Ratios (LERs) of up to 1.25 for pod yield and total biomass despite moderate or severe water deficits at the end of the season. Specific combinations of genotypes were necessary to maximize the LER. The results indicate there is scope for achieving greater productivity in environments with a variable season length by growing late and early genotypes together in an intercrop system.

Much recent research has been directed at intercropping. Although the planning and analysis of these experiments often raises complicated statistical questions, many statisticians have concentrated on sophisticated graphical and numerical procedures for summarizing results, without considering what system of intercropping, if any, is on balance advantageous to the farmer and how its advantage is to be measured. This paper surveys aspects of intercropping that need examination before farmers can be advised, such as the value of produce, and the effects of intercropping on yields and costs. Any synergism of productivity occurring directly or in the longer term is a central but not necessarily decisive aspect of the problem. A recently described experiment is used as an example. The main conclusion is that experiments on these topics need to be large and well-designed, with repetition in several years, and that interpretation must allow for alternative sets of numerical values expressing values and costs.

Shoot extension rates and numbers recorded over an 18 month period in Tanzania from three contrasting clones were analysed to determine variation between and within seasons. Clonal differences in base temperatures for shoot extension ranged from 10.3 to 14.5°C, whilst variability in the response of shoot growth rates to temperature could be ascribed to the shoot selection technique employed. Considerable clonal variation in shoot population densities occurred, with maxima ranging from 200 to 1200 shoots m−2. Total active shoot extension, the product of shoot growth rates and population densities, varied between 4 and 35 m m−2 week−1, shoot numbers being the dominant component. The implications of these results are discussed in terms of shoot measurement techniques, clonal selection criteria, yield modelling and harvesting policies.

Stages in oil palm inflorescence development which determine the number and weight of the fruit bunch components were identified by thinning to intervene in development and dissection of a sample of the felled palms. This showed that the ratio of female to total inflorescences and the number of flowers per spikelet were determined eight leaves prior to spikelet initiation. The number of spikelets per inflorescence was linked with the meristematic development of the primary axis. Inflorescences were prone to abortion at the onset of rapid expansion of the primary axis. The weight of the frame responded to thinning at these three developmental stages. The weight of single fruits responded shortly after the fruit set was fixed at anthesis; the response levelled off in axils of the six older leaves. At the start of an abortion phase nearly all aborted inflorescences were female, but subsequently female and male inflorescences aborted in equal proportions. Our study suggests that the number and weight of fruit bunch components are determined at a specific developmental stage but that the time to anthesis may vary considerably as a result of fluctuations in the speed of inflorescence development.

Yield components in oil palm were recorded in a spacing experiment comparing 56, 110, 148 and 186 palms ha−1. The higher densities reduced the number of female inflorescences (due to a decrease in the proportion of female to total inflorescences and an increase in the proportion of leaves with aborted inflorescences), the weight of the frame and the number of flowers per inflorescence. The results suggest that the production of seed per bunch can be increased by at least 15% by thinning around selected palms in seed gardens. The sex ratio and the components of flower number per inflorescence were more sensitive to competition for light than the weight of the frame and floral abortion. Components determining the oil and kernel extraction showed no response to density when assisted pollination was used, but with the successful introduction of insect pollinators, oil and kernel extraction increased with planting density as a result of an increase in fruit per bunch.

Twenty one strains of Brassica carinata were tested under irrigated, rainfed and saline soil conditions and five strains under late sowing conditions along with five varieties each of B. juncea, B. napus and B. campestris var. yellow sarson, brown sarson and toria. Brassica juncea had the largest seed and oil yield under irrigated conditions but B. carinata performed much better than other species under late sowing, rainfed and saline soil conditions.