A simulation model describing the growth and yield of tea (Camellia sinensis L.) is described. The model simulates the behaviour of a population of shoots which develop and extend independently at different rates to simulate the variation observed in natural conditions. The development of each shoot is divided into three phases corresponding to the resting, quiescent and bud-burst phases in temperate trees, with the rate of development in each phase being influenced by temperature, photoperiod and saturation deficit. Photoperiod also influences the onset and release of bud dormancy, and therefore the numbers of actively growing shoots at any one time. As shoots are generally harvested at a specific developmental state or size, the number of shoots plucked at each harvest is the main determinant of yield variation. Sensitivity analysis using annual yields as the output indicated that the model was most sensitive to the values of the two critical photoperiod parameters controlling bud dormancy and shoot development. Good agreement was found between model predictions and observed yields for an experiment in well-irrigated tea in the Southern Highlands of Tanzania, but further testing is necessary before it can be used with confidence in a wider range of environments.

A model predicting biomass production and water use in tea plantations is described. Biomass production is calculated from the amount of light intercepted and a radiation conversion efficiency. Available assimilate (current production plus reserves) is distributed according to the ‘potential’ demand of each of the shoots, stems and roots. Any excess is stored in the stem and root reserve pool. In the case of the demand for assimilate exceeding the supply, allocation is according to the relative demands of each component. Simulations with the model suggest that assimilate supply is unlikely to limit shoot growth under most conditions. Soil water movement and crop water uptake are simulated using the water balance sub-model used by the CERES crop growth models. The model calculates a water stress factor (Φ) as the ratio of actual to potential crop transpiration, and uses this factor to adjust various crop processes such as dry matter production and shoot development and extension rates. Predicted yields match observed yields well across a range of watering treatments and for different years at sites in Tanzania and Zimbabwe, providing some degree of confidence in the model's ability to predict tea yields for environments in East Africa.

Four experiments were conducted to facilitate the improvement of degraded grasslands in north Syria. The first examined the survival of legume seeds fed to penned Awassi wethers. The second and third observed the germination and establishment of legumes from faecal pellets in the field and in a glasshouse respectively. The fourth explored the possibility of transporting seeds from legume-rich (source) to legume-poor (target) grasslands using commercial flocks on communally-owned land. Seeds of small-seeded clovers passed through sheep in greater numbers (58–72%) than did seeds of larger-seeded species (10–40%). Of the clover seeds Trifolium campestre (seed size 0.45 mg) disintegrated least (72% passage) and T. haussknechtii (seed size 2.68 mg) disintegrated most (10% passage). Recoveries of Medicago noeana and Scorpiurus muricatus seeds were larger than expected on the basis of their seed sizes. Maximum rate of recovery was at 36 h after the seed meal for all species, all seeds were recovered by 120 h and 90% of the recovered seeds were passed in 72 h. Ingestion had little effect on the hardness and viability of most seeds. Experiments 2 and 3 suggested that seeds in pellets germinated and established as successfully as naked seeds. Burial increased establishment, whether in the field or under conditions of low moisture stress in the glasshouse. The small-seeded clovers, T. tomentosum and T. campestre, established most successfully whether from pellets or from naked seeds. About 500 seeds m−2 were successfully transported from the source to the target grassland. About half were Trigonella monspeliaca, a naturally-occurring legume found on both the source and target grasslands. Of the species sown on the source grassland, 115 seeds m−2 of Trifolium campestre (33% of the source seed bank), 62 seeds m−2 of T. tomentosum (27%) and 78 seeds m−2 of T. purpureum (21%) were detected in the target. Few medics were transported (for example, <2% of M. noeana). Apart from Trigonella monspeliaca, Trifolium tomentosum (16 plants m−2) was the most frequent species found in the target grassland in the following April. The results suggest that using sheep is a cheap and practical way of dispersing the seeds of pasture legumes and thereby improving the degraded grasslands of north Syria. They clearly demonstrate the role of small-seeded legumes (<1 mg) in grassland improvement, especially the small-seeded clovers.

Farmer-managed tests of Striga hermonthica-resistant maize varieties were conducted in 1994 in a moderately intensified zone in the northern Guinea savanna of Nigeria. Field history, soil properties, current season fertility management, and crop management observations were recorded for 37 farmer-managed trials. Site averages for maize grain yield varied from 300 to 4000 kg grain ha−1. In spite of the tremendous variability observed, the grain yield was significantly higher for the striga-resistant hybrid 8321-18 compared with an improved open-pollinated variety, STR Syn-W, and the farmers' current variety. Correlation analysis and stepwise regression analysis of grain yield on measured variables suggested that maize yield was a function of plant density for all three varieties. The rate of nitrogen fertilizer application was an important variable only for the hybrid, while the day of first weeding was most important for the improved varieties. The yield of the local varieties and STR Syn-W was related to the number of emerged striga at harvest in the stepwise regression, and the yield of the local varieties was highly correlated with the striga-damage score on maize. The striga-damage score was significantly lower on 8321-18 than on the other varieties, suggesting some degree of resistance in the hybrid. The number of emerged striga was lower for the hybrid but not significantly different. Farmers were almost unanimous in ranking the hybrid as least damaged by striga and highest yielding. Besides being related to maize variety, striga-damage score was lower if crop residue was observed on the field at the time of site confirmation. Highest yields (approximately 4 t ha−1) were recorded on fields near the homestead (compound fields) where soil organic carbon values were 2.0–2.5%. Realization of maize yield potential in the absence of manure or fertilizer will only be possible on long-term compound fields. Striga-resistant maize can maintain high yields under S. hermonthica infestation.

Peri-urban dairy producers in West Africa face major production constraints including inadequate and poor quality feeds. In view of the high cost of traditional supplementary feeds such as oilseed cakes, the production of forage, especially legumes, is increasingly being advocated. However, it has not been established whether returns in terms of increased livestock productivity from sown forages will be adequate to encourage smallholder livestock owners to undertake forage production for indigenous livestock.

In three trials involving indigenous Bunaji cows biological and economic responses in terms of milk yields to farmer-planted forage legumes and tree legumes from home gardens were evaluated. Synthesis of the resulting data on labour inputs, forage yields, feed intakes, milk yields, value of outputs and cost of inputs such as seeds and fertilizers showed that for the semi-intensive smallholder and zero-grazed models considered in this study, the margin or profit from using home-grown fodder was 5–8 times the cost of acquiring the feed. The opportunity cost of using the land for forage production rather than for cultivating sorghum, a highly favoured cereal crop, was only 67% of the accrued benefits from milk yields produced by cows supplemented with the forage hays. Thus, there is a real potential for profitable dairy production in peri-urban areas using home-grown fodder.

A three-year study was conducted on an Ultisol to determine the water requirement, yield and fruit-quality traits of three ratoon crops (R1, R2, R3) of ‘Grande Naine’ banana (Musa acuminata Colla, AAA group) subjected to four levels of irrigation. The irrigation treatments were based on Class A pan factors ranging from 0.0 (rainfed) to 1.0 in increments of 0.25. When needed, drip irrigation was supplied three times a week on alternate days. Results showed significant (p < 0.01) irrigation treatment and crop effects on bunch weight, yield, bunch mean hand weight, weight and fruit diameter of the third and last hands, and length of fruits of the third hand. Highest marketable yield (47.9 t ha−1) was obtained from the R2 crop with water application according to a pan factor of 1.0. It was concluded that irrigating the crop according to a pan factor of 1.0 was sufficient to justify the investment of a drip-irrigation system for a farm in the mountain region.

In an on-station agroforestry experiment conducted in south-west Niger, the effects of seven windbreak species and of a soil mulch made from crop residue on wind erosion and pearl millet (Pennisetum glaucum) production were monitored. Within a distance of 20 m, strips of the perennial grass, Andropogon gayanus, reduced total annual soil flux by 6–55% and hedges of Bauhinia rufescens 2 m in height reduced soil flux by 47–77% compared with unsheltered control plots. No significant overall windbreak effect on millet stover and grain yields was found. In contrast, erosion reduction and yield increases due to mulch application were highly significant. Soil mulch is a promising alternative to complex windbreak–millet cropping systems in regions where direct economic benefits for farmers are not ensured by windbreaks.

Experiments were conducted during the winter seasons of 1992–93 and 1993–94 at the Lumle Agricultural Research Centre and its off-station research site at Lopre in Nepal to study the agronomic performance and profitability of barley (Hordeum vulgare) and peas (Pisum sativum) mixed intercropping (that is, without any row arrangement) in the subsistence farming systems of the Nepalese hills. Sole crops of barley (cv. Bonus and Local) at 100kg seed ha−1 were compared with a pure stand of peas (cv. Tikot Local) sown at 60kg seed ha−1 and with peas intercropped with both varieties of barley at 100:40 or 100:20 kg seed ha−1. Results across two locations for two seasons showed that the barley+peas intercropping was advantageous in terms of overall grain yield, land equivalent ratio (LER), monetary advantage, economic return and dietary provision in the subsistence farming system. It also provided yield stability under adverse climatic conditions. Barley genotypes differed in their suitability for intercropping with peas. The yield of Local barley was reduced when peas were intercropped with it at both seed rates but this was not so with Bonus. The most appropriate combinations to realize the maximum advantage from intercropping were Bonus barley+peas at 100:20 kg seed ha−1 and Local barley+peas at 100:40 kg seeds ha−1. A combination of Bonus barley and peas at 100:20 kg seed ha−1 enabled farmers to harvest an additional 400 kg grains ha−1 from peas without significantly reducing the grain yield of barley. The study also verified through formal experimentation that the traditional practice of mixing barley and peas is advantageous.

Cowpea (Vigna unguiculata) farmers from diverse geographical areas in northern Cameroon selected breeding lines from on-station trials for their own fields and explained their reasons (criteria) for making the selections. The average selection intensity employed by farmers varied from 6 to 17% and was similar to that employed by plant breeders. Their selection criteria fell into three broad categories relating to yield, preference and quality, and labour, which were very consistent over years, locations and gender. Selection criteria were strongly influenced by market preferences, reflecting the increasing role of cowpea as a cash crop. Implications of these findings for breeding strategies and genetic resource conservation are discussed.

The on-farm performance of more than 150 000 pre-basic potato (Solanum tuberosum) minitubers of 1–10 g was monitored over two years in contrasting environments in Nepal. Average minituber productivity (grams of basic seed produced per minituber planted) was 171 g in the southern plains and 116 g in the hills. Although the performance of minitubers varied between environments, minituber sizes and potato varieties, the overall results clearly indicated that minitubers can be successfully multiplied by small-scale farmers. This technology therefore allows for the highly decentralized production of basic seed which, in turn, will reduce farmers' dependence on an unreliable and costly supply of bulky conventional seed.