Examples are presented of tropical tree commodity plantation crops, tea, coffee, rubber and oil palm, as models for farm system development. They are environmentally benign in comparison with annual food crops, have been organized on a large scale with smallholder participation, and make significant contributions to local and national economies. It is suggested that lessons learned in their development might be used in the large-scale development of other potentially major tree crops, including timber, fruit and nut producing species.

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.

The International Benchmark Sites Network for Agrotechnology Transfer (IBSNAT) project has established an international network of co-operating farming systems researchers. A decision support system that includes a number of crop models and databases has been developed to assist in the evaluation of new agrotechnology packages in the tropics and sub-tropics. Standards have been established for the recording of ‘minumum data sets’ from field experiments to allow the crop models to be validated for specific sites. The decision support system, still under active development, has the potential to reduce substantially the time and cost of field experimentation necessary for adequate evaluation of new cultivars and new crop management systems.

A wide variety of training activites has been carried out related to farming systems research (FSR). The majority have had one or more of the following objectives: to introduce the farming systems perspective, to teach new research methods, and to promote the institutionalization of FSR. Many of these objectives are important, but FSR training is not usefully seen as a separate field of endeavour. The goals of FSR training will be better served by reconsidering the roles of universities, national research institutions, and international institutions.

Yields of maize were increased when they followed successfully established pasture legumes in two rotation experiments. The largest increases were obtained after silverleaf and were equivalent in one experiment to the effects of about 30 kg N ha−1 a−1 over four years and in the other experiment to those of 40 kg N ha−1 a−1 over three years. The largest beneficial effect of some of the legumes was on the first crop of maize but in others did not occur until the third or fourth crop. The possible reasons for the different patterns of residual effect are discussed in relation to the nature of the legume residues, the quality of the seedbed following the legumes, and rainfall

On-farm research was conducted in Zambia between 1984 and 1987 to examine the performance of an imported bean variety and identify management practices that could result in higher and more stable yields and to examine their economic feasibility for risk averse smallholder farmers. Results showed that the Brazilian bean variety Carioca was superior to the local variety tested in terms of yield, net economic returns and reliability of performance, especially when used in combination with fertilizer and insecticide.

Specific soil fertility and water retention constraints limit increased crop production in the subsistence-oriented farming systems of Burkina Faso. Previous attempts to introduce apparently promising technologies based on research that had not directly involved the fanner and that had not benefited from farmer-feedback have been largely unsuccessful. Active farmer involvement can help to identify relevant constraints to production and to identify and modify technologies to make them viable. Formal and informal farmer surveys and farmer participation in field experiments have led to the development of potentially useful cropping practices involving the complementary use of mechanical tied ridge and fertilizer-based technology.

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

Three pearl millet and three cowpea genotypes were examined in intercropping systems on deep sandy soils in Niger between 1984 and 1987. The intercropped pearl millet genotypes usually produced at least 80% of their sole crop yields when the cowpea was planted two or more weeks after the pearl millet. The early maturing and spreading cowpea genotype contributed most to LER. All cowpea genotypes yielded more when planted in association with dwarf rather than the traditional tall pearl millet genotypes because they received more light.

Prevention of the enormous losses of crop production in the Third World, both before and after harvest, would make a substantial contribution to the survival and well-being of countless small fanners. Many attempts to reduce the scale of pest attacks by facilitating the purchase of pesticides and fertilizers have failed in the face of maladministration, mistrust, primitive conditions and ignorance. Yet, despite the difficulties, these fanners have evolved a pattern and practice of production which incorporates many positive attributes which have only recently been appreciated by western scientists. Attention is drawn to some of these methods and also to the benefits and limitations of both classical and manipulated biological control. It is concluded that further improvements depend on the ability of entomologists to adapt some of the concepts widely used in China to utilize scientific techniques within a socio-economic structure where even the plastic bag must be regarded as high technology.

Late planting of a 136-day variety of maize led to reduced yields only when planting was later than about four weeks after the start of the main rains. The reductions were caused by drought at the end of the season and by high rainfall in the first 35 days after planting. Drought beginning 80–100 days after planting (DAP) reduced weight per seed but drought beginning earlier than 80 DAP reduced seed number per cob and increased the number of barren plants. Late showers alleviated the reduction in weight per seed but not the other symptoms of drought. High rainfall after planting was associated with reduced plant size at flowering and reduced seed number per cob at harvest.

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 conducted from 1979 to 1986 to compare the amelioration of a highly sodic soil by the application of gypsum compared with that achieved by growing Karnal or Para grass for between one and three years. After studies of the growth of rice and wheat on the experimental plots, the growth of four forage crops, less tolerant of sodic conditions, was studied between 1984 and 1986. The forage yields suggest that their order of tolerance to soil sodicity is Persian clover > Egyptian clover > teosinte > maize, the rabi (winter season) forage crops being more tolerant than the kharif (rainy season) ones.

The potential for using sorghum and millet crop residues as fodder was studied in southeastern Botswana. This region is characterized by low, unevenly distributed rainfall and shallow sandy soils. There were significant differences among cultivars for grain and stover yield, digestibility, crude protein, and mineral content, but no species advantage. Stover from all entries was adequate for cattle maintenance in in vitro dry matter digestibility (IVDMD) and most of the minerals tested, but crude protein and phosphorus levels did not always meet the minimum requirement. The deficient phosphorus levels were compounded by high calcium levels. This mineral imbalance could lead to bone abnormalities and reduced fertility in livestock.

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 physiological basis for responses to daylength of a photoperiod sensitive groundnut genotype (NC Ac 17090) was investigated by comparing its growth and development in natural daylength with that in an artificially manipulated photoperiod in three field experiments. Photoperiod did not influence the thermal time to flowering, or the subsequent appearance of flowers until 900–950 flowers m−2 had appeared. Thereafter flowers continued to appear in short, but not in long, days. In each experiment, long days increased the thermal time between the initiation of each peg and pod, and the thermal time required for each fruit to mature. These fruit initiation and developmental changes were reflected in the partitioning of assimilates to pods, this being substantially less in long days than in short. Changes in pod initiation rate, partitioning co-efficient, and the thermal time taken for a pod to mature were related to mean daylength.

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 effects of intercropping roselle with blackgram, cowpea, soyabean, groundnut and sesame under single, double and triple row planting patterns and at three different intercrop sowing dates were studied from 1983 to 1985. The fibre yield of roselle was reduced by intercropping. The reduction was least with groundnut and greatest with cowpea but was compensated for by the yield of the intercrops. Double and triple row planting systems favoured the productivity of both roselle and the intercrops, increasing the Land Equivalent Ratio (LER) of the cropping system. The best yields of roselle were obtained when the intercrops were sown 15 days after the roselle.

The relation between soil mechanical impedance as a result of soil drying, and root system growth (mass and length density) of rice was investigated in greenhouse and field studies. In a greenhouse experiment, soil drying for 16 days increased mechanical impedance in the 0–20 cm soil layer from near 0 to 2.5 MPa, and decreased root growth by 47% compared to the continuously flooded control. Root length density decreased with decreasing soil moisture and increasing soil mechanical impedance. In a lowland field experiment using a sprinkler irrigation gradient treatment for 19 days during the vegetative growth stage, soil mechanical impedance as low as 0.01 MPa inhibited root growth while values greater than 0.3–0.5 MPa decreased root growth and extension by 75%. The relative loss of potential root growth was continued after reflooding. Root length density, measured at flowering, was linearly related to yield.

Source-sink relations in cassava were investigated following reciprocal grafting among three cultivars of different yield groups. Both rootstock and scion had significant effects on net assimilation rate and tuber yield, demonstrating that both sink capacity and source activity are important in achieving maximum tuber yield. The scion had no effect on tuber dry matter percentage and starch content of the grafts but the hydrocyanic acid content of the tuber was significantly influenced by both rootstock and scion.