Strategies for the implementation of integrated pest management (IPM) of cotton differ significantly depending on the agroecosystem and incidence of pests. Examples of successful IPM programmes from different countries, including those which involve insecticide treatments, are given in contrast to cases of inappropriate use of insecticides leading to pest resistance and crop failure. Inter-disciplinary research and farmer participation on a regional basis is necessary if IPM is to be implemented successfully.

Genetic engineering of crop plants has been in progress since the dawn of agriculture, about 10 000 years ago. For millennia the genetic make-up of our crop plants has been changed by mankind's selection of naturally occurring variants. As the trade routes were developed, novel plant types were introduced into new environments and provided more variation from which to choose. At the end of the nineteenth century an understanding of the laws of heredity was gained and plant breeding protocols were devised whereby selection became accompanied by deliberate crossing. As the knowledge of the genetic structure of crop plants improved, new ways of manipulation were invented and exploited. Indeed plant breeding became a testing bed for new ideas in genetics. For the plant breeder the techniques which were most widely employed in the past were those which aided breeding, for example techniques which speeded up the production of new varieties, but still used traditional routes of crossing and selection. This was a transitional phase between plant breeding as an art and plant breeding as a science.

The experiment examined how nitrogen applied to a maize crop was partitioned when the maize was intercropped with beans. Treatments consisted of 2, 4 and 6 rows of beans at within-row spacings of 20 or 10 cm sown between ‘maize' rows in which maize was either present or absent. Nitrogen was applied at 0, 30, 60, 90 or 120 kg ha−1. Maize showed a large response to nitrogen and this was little affected by beans. All bean rows in all positions showed some response to nitrogen. The largest response was from the rows closest to the maize, but this response was similar whether these rows were 20, 40 or 60 cm from the maize. Beans gave a much greater response in the absence of maize, indicating that the main factor determining the partitioning of the nitrogen between the two crops was the superior competitive ability of the maize. It is suggested that the approach could be suitable for examining nitrogen partitioning in other non-legume/legume situations.

On-station participatory evaluation of varieties was used to identify the characteristics of pearl millet (Pennisetum glaucum L. Br.) preferred by farmers in western Niger. Large numbers of productive tillers, large grain size, plant height of about 250 cm and a crop cycle of 100 d or less were the main traits that motivated farmers' preference for ICMV IS 92222. High grain yield was of less concern to farmers than these factors. Small grain size, short or thin panicles, short or thin stalks and a crop cycle of 110 d or more are traits likely to be rejected by farmers. Evidence of gender-based trait preferences was significant only for short or thin panicles and thin stalks. There was no evidence of location-driven trait preferences. Farmer participation in the on-station varietal evaluation provided a means of identifying a wide range of traits that were valued by farmers and could provide guidance on farmer demand for use in varietal evaluations.

Two methods, namely combined plot analysis and integration of variograms, have been applied to investigate and compare plot-to-plot yields of intercropped millet (mean yield of about 1.9 t ha−1) and maize (mean yield 4.25 t ha−1) on terraces in Nepal. Combining plots diminishing the residual variance of millet from 0.52 (t/ha)2 of the original 1 m×1 m units to 0.08 (t/ha)2 for 4 m×4 m plots, the largest for which reliable estimates could be derived. The residual variance of maize declined from 4.91 (t/ha)2 of the original units to 0.61 (t/ha)2 for 4 m×4 m plots. Orientation was immaterial. The variogram for millet was isotropic and bounded with a range of approximately 4 m. Within-plot variance calculated from the variogram increased, and experimental error decreased, as the size of plots increased to this value, beyond which there was little gain. The variogram for maize was unbounded, and so gave no ‘natural' upper limit for plot size, that is, over the range studied, up to 6 m×6 m. It was also anisotropic with larger gradient in the direction from front to back of the terrace than along the contour. The reduction in residual variance was greatest for narrow plots elongated in this direction. Formulae are provided from which to calculate from the variogram approximate residual variances for experiments of given area and size, shape, and orientation of plots. Its application gave similar results to those from the combined plot analysis. Overall, the results from the two methods were consistent.

A technique for leaf area measurement utilizing water spray as an inexpensive substitute for electronic equipment was developed and tested with leaves of potato (Solanum tuberosum L.). The leaf areas measured by the spray method were highly correlated with those measured by an electronic area meter. Measurements of leaf area obtained by the spray method were significantly more highly correlated with those obtained by the area meter than were the measurements of dry weights. The main advantages of the new method are precision, accuracy and immediate results at a low cost.

A review is presented of available documents containing statistical methodology for participatory on-farm research. Further needs in this area of work are commented upon.

The importance of vegetable crops has been increasing in West Africa for the past forty years. This paper describes the evolution of intensive mixed vegetable production in the Niayes area near Dakar between 1970 and 1990. The importance of cultivation in low-lying areas with very few inputs have decreased but irrigated cropping systems have become more important due to the better adaptation of vegetative material, application of more fertilizers and better control of pests and diseases. This intensification appears to be irreversible, in spite of the negative effects of the more intensive use of land.

The response of potatoes (Solanum tuberosum L.) to application of inorganic and organic fertilizer was studied in long-term field experiments between 1987 and 1994. Responses to phosphorus and nitrogen were tested at 27 sites and to potassium at 17 sites. The sites represented various agro-ecological zones in Kenya. Phosphate (triple superphosphate, TSP) and nitrogen (calcium ammonium nitrate, CAN) fertilizer were applied at 0, 25, 50 or 75 kg P2O5 ha−1 and 0, 25, 50 or 75 kg N ha−1. Potassium (muriate of potash) was tested mainly on sites with low levels of K in the soil at rates of 0 or 50 kg K2O ha−1. Farmyard manure was applied at 0 or 5 t ha−1 with or without N and/or P2O5 fertilizer.

Over the study period average yields varied considerably between sites and agro-ecological zones. At 16 of the 27 sites, potatoes responded strongly to the application of P2O5 and at 9 sites to N application. A significant response to K2O application was found at three out of the 17 sites. Nutrient use efficiency ranged from 13 to 214 kg tubers per kg P2O5 and from 20 to 113 kg tubers per kg N applied. In the majority of the sites, both N and P response followed a linear function which suggests that application rates higher than 75 kg N ha−1 and/or 75 kg P2O5 ha−1 could be beneficial. Economic analysis revealed that in most cases fertilizer application was highly profitable for potatoes.

The critical soil P value was about 15 ppm (mod. Olsen) for optimal potato nutrition; on soils with higher P levels generally no P response was found. The respectively critical soil K value was found to be about 0.55 meq 100 g−1 (modified Olsen). Farmyard manure at 5 t ha−1 significantly increased yields of potatoes at 9 of the 27 sites. On soils with P levels below 12 ppm, there was a positive effect on potato yields with a combination of 50 kg P2O5 ha−1 and farmyard manure, although significant differences were achieved in only one out of the 19 sites.

Studies were carried out at three locations in Ghana to investigate the effects of Glyricidia maculata shade intensity and of the spacing of coffee on the growth and yield of improved robusta coffee. The three locations selected fall within ecological zones which could be described as suitable, moderately and marginally suitable in terms of rainfall availability and soil conditions.

The experimental design was a split plot with shade as the main plot and coffee spacing as the sub-plot. The four levels of shade were: no shade, and Glyricidia maculata at densities of 70, 90 and 185 per ha corresponding to sparse, moderate and heavy shade conditions. The coffee spacings were 3 m×2 m, 3 m×2.2 m, 3.5 m×2 m and 3.5 m×2.5 m giving plant populations of 1670, 1520, 1430 and 1140 per hectare, respectively.

There were no effects of shade or spacing on coffee seedling growth at all locations during establishment. Sparse shade gave higher yields in the suitable areas. Moderate shade was required for the moderately and marginally suitable areas. In general, closely spaced coffee gave higher yields than the widely spaced coffee at the suitable and moderately suitable areas whilst there was virtually no response to coffee spacing in the marginally suitable area. There were no interaction effects of shade and spacing on coffee growth or yield. Biennial alternation of coffee-bearing associated with seedling materials was observed in this study.