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.

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.

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.

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.

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.

Tea shoot development was measured by sequentially sampling shoots from seven clones growing at Nsuwadzi Research Station, Mulanje, Malawi. A Gompertz growth curve best described the increase in shoot length with time, an exponential curve described the relation between dry weight and shoot length, and a quadratic curve related dry weight to fresh weight. The parameters of these curves differed among clones and provide a basis for exploring genetic influences on tea yield. The most rapid elongation of shoots of all clones occurred about 42 days after plucking, considered the optimum age for harvest at Mulanje. Clones selected at Mulanje produced longer shoots with greater dry weight but slightly lower dry matter content per unit stem length than clones selected at Kericho, Kenya. The dry:fresh weight ratio of 0.22 used at Mulanje to calculate dry matter yields was too high for most clones.

The yield of ginger following different dates of planting and harvesting was investigated at Umudike. The largest yields of stem-tubers were obtained seven months after planting while maximum yield of shoots was attained five months after planting. The interaction of yield with time of planting and age at harvest was highly significant. Maximum yields were obtained from mid-April plantings harvested six or seven months later in two years with contrasting weather patterns.

When an intercrop fails to produce a required proportion of the sole crop yield, but produces a yield advantage over the sole crop, the method of sole crop supplementation has been suggested by many authors including Mead and Willey (1980) and Riley (1985). Modifications to the Land Equivalent Ratio (LER), used for assessing yield advantages, have been suggested and referred to as staple LERs (SLERs) and Effective LERs (ELERs). In this paper, a graphical method of estimating the SLER and ELER values (and consequently their yield advantages) is presented. The graphical estimation of the confidence interval for the SLER and ELER values is also shown.

Ten wheat and six barley genotypes were tested for their response to soil salinity regimes varying from 0 to 16 mmhos cm−1. Barley showed remarkable resistance to salt stress, linked to its capability to resist efflux of potassium ions from the plant system. Both crops showed substantial yield reductions at 12 mmhos cm−1, but barley still outyielded wheat by over 50%. There were significant interactions between salinity levels and genotypes in wheat but not in barley.The wheat variety Sonalika showed poor salt tolerance. The implications of these findings in breeding salt-tolerant varieties are discussed.

A field experiment was conducted on sandy loam soil at Hisar, India during the autumn seasons 1984–85 and 1985–86 to study root characters, evapotranspiration, water use efficiency, moisture extraction pattern and plant water relations of rape genotypes under varying irrigation schedules. Root volume and dry weight increased, while tap root and lateral root lengths decreased with irrigation. Increased irrigation frequency increased evapotranspiration but decreased water use efficiency. The relative water content and osmotic potential of the leaves increased with more frequent irrigation, but plant water retention capacity decreased. There were genotypic differences between the characters examined.

The effect of no-tillage and mulch on soil properties and tuber yield of cassava was studied over a five year period on an infertile, acid Ultisol in south-eastern Nigeria. Mulch was applied at a rate of 12 t ha−1 as a split application once at planting and once six months after planting. No chemical fertilizers were used during the trial. Bulk density and proportion of micropores (pore radius, r, <1.4 µm) were greater, and proportion of macropores (r>14.4 µm) lower, with no-tillage. Water infiltration was increased by mulching, being greatest in tilled, mulched plots. Soil chemical properties were not significantly affected by tillage system, although levels of exchangeable calcium, magnesium and potassium were higher and acid saturation lower with mulching. Soil physical and chemical properties were best with tillage and mulching, and poorest when neither tillage nor mulch was used. Cassava tuber yield was unaffected by tillage system but increased by mulching.