An on-farm study was carried out at 17 different sites within the Western Hills of Nepal during the spring and summer seasons of 1993 and 1994 in order to monitor the plant population density dynamics of the maize (Zea mays L.) crop under farmers' management. Five farmers were selected randomly at each site and a 20-m2 plot was demarcated just after maize sowing. The maize stands within the 20-m2 plots were first recorded 20 d after sowing, and then at 10-d intervals until harvest. Farmers were allowed to perform all cultural practices on their own. On average, the initial plant stand across all locations and over two seasons was 69 100 ± 1800 plants ha−1, which resulted in 37 300 ± 1700 plants ha−1 at harvest, a 46% reduction from the initial stand. At most locations, the population declined by 30–40 × 103 plants ha−1 between emergence and harvesting and in no cases were the recommended plant populations achieved at harvest. Populations varied across sites and seasons. The rate of population decline was higher in the low and mid hills compared to high-altitude areas. Thinning which is carried out between 30 and 60 d after sowing at most sites was the major cause of population reduction, and delay in thinning was intended to increase fodder production from the thinned maize. In addition, the removal of barren plants at the silking stage and of smutted, lodged and damaged plants attributed to about 12% of total reduction in plant population. The larger the initial stand, the larger was the proportion of barren plants to be removed. No clear relationships were observed between soil fertility and final plant stand at harvest.

The results of a survey showed that one of the most critical constraints in sesame production in southern Tanzania is sesame flea beetle (Alocypha bimaculata, Jacoby). Local methods used by farmers to control, avoid or compensate for the damage caused by flea beetles were identified. Farmers regarded resistance against the flea beetle as a very desirable objective in a sesame breeding programme, but a number of other important characteristics, such as disease and drought resistance, was also mentioned. At three locations in southern Tanzania twenty sesame varieties were screened for resistance to flea beetles by counting the number of surviving plants at the 1–2 true pairs of leaves growth stage. The results suggest that there were significant differences between varieties in terms of their susceptibility to this pest, which suggests that a resistance breeding programme may be successful.

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.

Common bean (Phaseolus vulgaris L.) germplasm was screened for resistance to charcoal rot (Macrophomina phaseolina) under field conditions at Kiboko and Katumani, eastern Kenya. Of the 313 bean accessions evaluated, 50 lines were resistant and six were tolerant to M. phaseolina, the charcoal rot incidence was less than 25% and between 25% and 50% for the resistant and tolerant lines respectively. Yields ranged from 135 to 1051 kg ha−1 compared with 55 kg for the susceptible control A464. Time to maturity did not seem to influence or affect the susceptibility or resistance to M. phaseolina of the various bean accessions.

The biophysical performance of hedgerow intercropping for soil fertility inprovement was assessed in a farmer-participatory trial in western Kenya over three years. Farmers successfully established dense hedgerows (median 6680 trees ha−1 on plots of 790 m2, but annual yields of hedgerow prunings of Leucaena leucocephala and Calliandra calothyrsus (1–4 t ha−1), were low compared to potentials in the region (4–8 t ha−1). The hedgerows reduced slopes from 7.2 to 4.5% within alleys (p < 0.01) but had no effect on grain yield over five seasons. Little of the variation in grain yield between hedgerow plots and control plots without hedgerows (adjusted r2 = 11%) and among control plots (adjusted r2 = 29%) could be accounted for by linear regression with measured agronomic and socio-economic variables. Fully researcher-managed trials are recommended for agronomic evaluation of complex agroforestry technologies.

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 introduction of appropriate crop rotations is known to be beneficial in many farming systems. One feature of rotations is that it takes a valuable length of time for the advantage of the rotation to take effect. In long-term rotation trials, the observations from the same plot over years are correlated; ignoring such correlations may affect the precision of the estimates of rotation effects. We examined five covariance structures between the plot errors over time to assess the effect of correlations on the standard errors of rotation means and rotation x cycle combination (interaction) means on wheat yields using eight years of data from six two-phase rotations with wheat. Based on wheat yield data from the four cycles of the rotations considered, the compound symmetry covariance structure (constant correlation) between plot errors arising over alternate years gave more efficient estimates of rotation means compared with the other four covariance structures.

Topsoil nitrate was measured every few days under grass, sorghum and bare fallow at two sites in lower Embu District, Kenya. Concentrations were highest soon after the start of rain and within a week most nitrate had been lost. Under bare fallow and sorghum, nitrate concentration increased during dry weather and losses occurred when soil water content exceeded 10%. Modelling of soil water movement indicated that there was no leaching below the rooting zone, so denitrification may be the main route for loss of soil nitrogen. Application of nitrogen fertilizer early in the season is not recommended as it would be lost with the native soil nitrate. The use of phosphorus fertilizer at the phosphorus-deficient site reduced soil nitrate concentration throughout the season and increased nitrogen uptake by sorghum. At the phosphorus-rich site, vigorous sorghum growth kept the soil nitrate concentration low, even though much nitrate was produced and lost in bare fallow. Adequate soil phosphorus is considered essential if the natural nitrogen resources of the soil are to be managed efficiently.

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.

To enhance the diversification of rice varieties for the specific needs of farmers through a participatory varietal selection (PVS) approach, four pre-release and one released chaite rice varieties were distributed in 20 villages of the Western Hills of Nepal in 1991. A survey conducted during June 1993 found that varietal diversity increased in all locations and in 80% of the study area at least two new rice varieties were reported where only CH 45 was grown before the distribution. On-farm varietal diversity was further enhanced by farmer-to-farmer dissemination of new rice varieties. All the rice varieties tested were adopted, but the adoption level varied between locations. Of the households surveyed 37% were growing the new rice varieties and a further 57% were aware of those varieties within two years of introduction. The PVS approach provided farmers with the benefits of new genetic materials five to six years in advance of the formal system and with minimum effort. Institutionalization of the PVS approach and the use of the farmers' network of information and seed exchange, involving relevant grassroots level institutions, can improve the effectiveness of the variety evaluation system.

Comparisons of single cropping, double cropping and relay cropping of soyabeans (Glycine max) with wheat (Triticum aestivum) were made at two sites in Arkansas over a two-year period. The comparisons were made using both soyabean blends and their component cultivars. In relay cropping the yields of pure lines of soyabeans were reduced by 17% compared with single-cropped soyabeans, but the yield of wheat in relay cropping was 15% less than in double cropping. Double cropping reduced the branch number, plant height, node number and leaf area of soyabeans compared with single cropping, but relay cropping reduced only node number and leaf area. Both double cropping and relay cropping gave greater land equivalent ratio (LER) values than single cropping, and double cropping gave greater LER values than relay cropping. Net returns were lowest with single cropping and greatest with double cropping. Soyabean blends gave yields similar to the mean of the component genotypes in all three cropping systems, and the net returns of blends were similar to those of the means of component genotypes.

Hedgerow intercropping is evaluated both economically and from the farmers' viewpoint, based on four years of experience of 45 farmers in western Kenya. Farmers were able to establish and prune the hedges; however, both activities considerably increased labour use during the busiest period of the year. Women did not generally prune the hedges. The average extra maize yield required each year, beginning in the second year, to cover the added cost of hedgerow intercropping was 10.5% (s.d. 5.5) when based on returns to land and 17.5% (s.d. 6.5) based on returns to labour. Although about half the farmers claimed that hedges improved crop yields, after three years of experimentation only about one-fifth planted additional hedges and only 14% did so to improve soil fertility. It thus appears that the potential for its adoption as a soil fertility practice in this area is low. Control plots were of little use as farmers were more interested in contrasting test-plot yields with past yields than comparing the test and control plots. Different types of trials may be required to obtain reliable biophysical data on yield response and socio-economic data on farmer assessment of complex agroforestry technologies.

Erosion trials under natural rainfall were conducted at two locations in the Andean hillsides of south-west Colombia on moderate slopes. Sediment-bound losses of seven cassava (Manihot esculenta) cropping systems per cropping period ranged from 26 to 1726 kg ha−1 for organic matter, 0.9 to 65.5 kg ha−1 for total nitrogen, 0.03 to 2.1 kg ha−1 for exchangeable magnesium, 0.04 to 2.8 kg ha−1 forexchangeable potassium and 0.004 to 0.8 kg ha−1 for Bray-II phosphorus. Runoff water contributed substantially to total available potassium, magnesium and phosphorus losses. Concentrations of soluble phosphorus in runoff water from heavily eroded continuously clean-tilled fallow plots were slightly higher than from cropped and fertilized plots. Enrichment ratios for sediments from these highly aggregated Inceptisols were low. Sand-sized particles were selectively removed by water erosion. The higher proportion of nutrient losses with run-off water in our study stressed the importance of runoff control along with attempts to control soil losses and thus diminish both nutrient losses and surface water eutrophication.

In researcher-designed, farmer-managed experiments with cabbage and hot pepper, ground seashells (GSS) were compared with low-grade phosphate lime (LGP) at rates of 0, 2.5, 5, 7.5 or 10 t ha−1. A randomized complete block design, with replicates spread over different farms, was used. Liming with GSS or LGP at 10 t ha−1 increased cabbage yield from 0.5 t ha−1 without liming to 15.0 and 5.3 t ha−1 respectively. Hot pepper yield was increased from 2.1 t ha−1 without liming to 3.2 t ha−1 at the three highest rates of GSS and LGP. Application of GSS increased the pH, reduced exchangeable acidity and increased the extractable Ca content of the soil. Partial budget analyses revealed that cabbage and pepper growers obtained highest returns with GSS at 10 and 5 t ha−1 respectively.

Two glasshouse experiments were conducted at the Department of Plant Production, University of Helsinki, Finland, to study the effect of foliar application of aqueous 0.1 and 0.3M glycinebetaine on leaf growth of drought-stressed tobacco (Nicotiana tabacum L.) cv. Samsun. Leaf nitrogen and glycinebetaine concentrations were estimated periodically. After 16 days of treatment, leaves were harvested, and fresh and dry weights, and area determined. The number of total and green leaves was also recorded. Significant increases in leaf fresh and dry weights, and area were associated with glycinebetaine application, especially when drought was induced early. The application of 0.3M glycinebetaine reduced leaf area duration. Residual leaf glycinebetaine content remained high 16 days after application. The results indicate that exogenous glycinebetaine has the potential to improve the drought tolerance of leaf tobacco.

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.

A field experiment was conducted from 1992 to 1994 to study the effect of supplying micronutrients to wheat (Triticum aestivum L., cv. Yecora rojo) grown on calcareous soil. Chelated and/or non-chelated forms of Fe, Mn, Zn and Cu were administered through a wide range of foliar applications, sprayed either individually or in combination. All the chelated micronutrients were applied in the form of EDTA with the exception of Fe (EDDHA). However, all the non-chelated elements were in the form of sulphate. The grain yield was significantly increased by the application of individual micronutrients either in the form of sulphate or chelate, but much higher amounts of sulphates were required. Application of micronutrient combinations either in chelated or non-chelated forms gave greater biological and grain yields than individual applications of the micronutrients. Wheat response to micronutrient applications followed in rank order: combined elements > Fe > Cu = Zn > Mn. Application of the micronutrients in sulphate form generally resulted in higher concentrations of these elements in grain than when the chelated forms were applied. Foliar application of the micronutrients in the form of sulphates at higher application rates may be more effective than the chelates due to lower cost despite the higher application rates.

Four contrasting varieties of cassava (Manihot esculenta Crantz) were grown for ten months over two consecutive seasons in hillside Colombia with or without nitrogen, phosphorus and potassium fertilization. Sequential harvests were every two months. The two varieties well adapted to acid soils (CM 489-1 and CM 523-7) had higher yields and exhibited the strongest response to fertilization, highest solar radiation use efficiency, earlier canopy ground cover and higher leaf litter accumulation. The export of potassium, however, was no higher than in the other genotypes, mainly as a consequence of higher potassium use efficiency in the adapted varieties. Significant amounts of total calcium, magnesium and nitrogen accumulated in the whole plant were recycled in the leaf litter during growth. High-yielding varieties adapted to acid soils did not exacerbate soil fertility problems of cassava crops; rather, they were beneficial. Certain growth parameters could be used to select for varieties with low impact on soil fertility.