The line-source sprinkler irrigation system provides a continuously variable water application rate, which depends on distance from the line-source. The system is simple to set up and minimizes the amount of land required for experimental work. As the irrigation treatments are allocated systematically, the assumptions of analysis of variance are not satisfied. It is proposed that the effects of irrigation treatments be assessed using analysis of covariance, with distance from the sprinkler line as covariate, thus adjusting for a linear fertility trend. This method of analysis provides an approximate residual mean square for the fitting of response curves, but could be vulnerable to a quadratic fertility trend.

A simple Stress Time Index (STI) for predicting yield loss in the tea crop due to drought is proposed, based on the daily summation of the difference between the potential soil water deficit and a specified limiting value. Validation of the technique with results from a line-source irrigation experiment with a single clone in the Southern Highlands of Tanzania suggests that there is a linear relationship between STI and relative yield loss during the warm dry season. As a result of changes in the composition of the shoot population at each harvest the apparent critical deficit at which shoot growth is restricted increases from below 20 to 300 mm as the dry season progresses. The rate of yield loss with increasing STI also varies through the dry season for the same reason.

The results of international research on the water relations and irrigation needs of onions have been synthesised in an attempt to link fundamental studies on crop physiology to irrigation practices, and consequent impacts on crop yield, quality and storage. Following a brief introduction on its origins and centres of production, a synthesis of research on crop development including plant water relations, crop water requirements, yield response to water, irrigation systems and scheduling are presented. Most of the evidence stems from research conducted in arid and semi-arid regions, notably the USA, India, Spain and Turkey. The findings confirm that onion seasonal water requirements are highly variable depending on agroclimate, location and season, as are the crop coefficients (Kc) which range from 0.4 to 0.7 (initial stage), 0.85 to 1.05 (middle development) and 0.6 to 0.75 (final stage). Seasonal irrigation needs are reported to vary from 225 to 1040 mm to produce between 10 and 77 t ha−1. The most sensitive stages for water stress are at emergence, transplanting and bulb formation. Final crop quality can also be affected by water excess. Water stress at specific stages can negatively impact on quality leading to reduced size and multi-centred bulbs. In recent years, pressure on water resources, retailer demands for quality assurance and rising production costs have meant that onion irrigation has switched from traditional low efficiency (furrow) methods to more efficient advanced (sprinkler and drip) technologies. For scheduling, optimal soil water potential thresholds for triggering irrigation were found to be between −17 and −27 kPa for drip and furrow irrigation. Research is underway to maximise water use efficiency in onions, but the deficit irrigation regimes being tested under experimental conditions have yet to be adopted commercially.

The effect of the root hemiparasitic angiosperm Striga hermonthica on the gowth, photosynthesis and partitioning of biomass in maize was studied in glasshouse experiments in two seasons. In both seasons, nitrogen was applied to the plants at rates equivalent to 20, 60 and 120 kg ha−1. There was no significant Striga×nitrogen interaction on the responses measured. Averaged across all nitrogen treatments, maize plants infected with S. hermonthica had smaller leaf areas and accumulated less biomass, than did uninfected plants. The leaf area of infected and uninfected plants increased asymptotically from emergence to the final harvest (about the 18-leaf stage) at which time the leaf area of infected plants was 63% that of uninfected plants. The rates of photosynthesis of the youngest, fully expanded leaves of infected plants, averaged across N treatments, were significantly lower than for uninfected plants. However, stomatal conductance and the sub-stomatal CO2 concentration were unaffected by Striga infection. Although infection with Striga significantly reduced shoot biomass (dry weight at final harvest was 37% that of uninfected plants in 1995 and 63% in 1996), there were no significant effects of Striga infection on root biomass so that the infected plants partitioned a significantly greater proportion of their total biomass to roots compared with the uninfected plants. The allometric coefficients, though, were similar for both infected and uninfected plants. Averaged across infected and uninfected plants, application of nitrogen increased total leaf area per plant and root and shoot biomass but did not change the proportion of total biomass partitioned to roots. These results did not show a major effect of nitrogen on the relative growth response of maize to infection with Striga.

Twelve seedling cocoa families were evaluated as rootstocks in Sabah, Malaysia using three commercial cocoa clones as scions. The average yield was about 3 t dry cocoa beans ha−1. Yields on pure Scavina rootstock were about 10% above average and those on pure West African Amelonado about 10% below average. However, the effects of rootstock on yield were correlated with those on vigour and there was no effect on the ratio of yield to continuing vegetative growth. Rootstock did not influence bean weight or number of beans per pod or the uniformity of the trees. There was no indication of an interaction between rootstock and scion for any of the traits that were studied. The rootstock effect is considered large enough to warrant its control in critical work, especially field experiments with budded cocoa, but development of high performance scions is a higher priority in cocoa than intensive work with rootstocks.

Combined socio-economic and agronomic surveys were conducted during two growing seasons with 20 rice (Orgyza sativa) farmers in the irrigation scheme of Guédé, northern Senegal. Farmers' knowledge of recommended cropping practices was relatively poor. The surveys identified sub-optimal timing of N fertilizer application and late harvesting as major constraints. Before the start of the second season, farmers were given field-specific recommendations on timing of key crop-management interventions. Average yield compared with the first season increased by more than 1 t ha−1, which was attributed to a slightly higher recovery efficiency of fertilizer N (REN) (average: 0.47 kg crop N kg−1 fertilizer N), a change in cultivars used (resulting in a better uptake of indigenous soil N) and more favourable weather conditions in general. It is concluded that if farmers are given better access to information, improved rice technologies, inputs and decision making, rice production on irrigated land in West Africa may leap forward rapidly, as potential production gains are still large.

Water use efficiency of maize (Zea mays) and cowpea (Vigna unguiculata) was investigated, with and without tillage, under four irrigation frequencies in which 12 mm of water was applied at 2, 4, 8 and 12 day intervals, using a sprinkler system. Both maize and cowpea under no-tillage yielded more than with conventional ploughing. Water use efficiency of maize without tillage was 18·3, 17·5, 57·8 and 100% greater than with tillage at irrigation frequencies of 2, 4, 8 and 12 days respectively. Whereas the leaf water potential of cowpea was not affected by tillage, that of maize was generally higher for no-tillage compared with conventional ploughing.

The Agricultural Technology Improvement Project (ATIP) has been conducting on-farm research in Botswana with the goal of identifying improved arable production technologies. In an effort to increase the role of farmers in technology design and assessment, ATIP set up farmer groups that meet on a regular basis to discuss farming problems and on-farm trials. This article reviews and evaluates ATIP's experiences with farmer groups. A typology of technology development groups is proposed and group management issues are discussed.

Under controlled environment conditions a semi-dwarf wheat, Mexico 120, was subjected to temperature regimes representative of the extremes that occur during the dry (winter) season of the Ord River valley in northern Australia. High temperatures (35°C by day: 18°C by night) such as occur at the beginning and end of the dry season were compared with low temperatures (30°C by day: 13°C by night) such as occur in mid-season. Day length was constant at 12 hours. High temperatures from floral initiation onwards adversely affected floret development, and after ear emergence reduced grain filling to nil. Net assimilation rates were reduced by high temperatures. Major effects on yields were caused by high temperatures well before anthesis. The critical temperature after anthesis is apparently between 32° and 35°C.

Barley (Hordeum sativum) and field beans (Vicia faba) were grown in pure stands, alternate-row mixtures and within-row mixtures in two field experiments. In both experiments the Land Equivalent Ratio (LER), based on seed yield, was consistently greater than 1.0 only when the crops were grown in alternate rows. The LER was greatest (1.8) when the mixture included more barley than beans. Reasons for the yield advantage of alternate row planting are discussed. Barley was more competitive than beans in mixtures, but this was not significantly affected by planting pattern.

Several parameters of seed vigour were monitored during seed development and maturation in three contrasting genotypes of soyabean (Glycine max)— the USA cv. Bossier, the Indonesian line TGM 737p, and the cross between these two parents TGx 536–02D—grown in three different temperature regimes. Evidence of a decline in seed quality in the pre-harvest environment was seldom detected until harvest maturity, when seed moisture content had declined naturally to 14–15%. Atypically, an increase in the susceptibility of freshly-harvested shelled seeds to imbibition damage was detected before harvest maturity for cv. Bossier in the two warmer regimes. Seeds of cv. Bossier were also far more vulnerable after harvest maturity to pre-harvest deterioration in the warmer environment than the other two genotypes. From these results and those from two earlier studies, it would appear that the main seed quality characteristic of TGm 737p that has been incorporated successfully into the cross is resistance to soaking damage, rather than enhanced air-dry seed storage longevity per se.

Desarrollo y vigor de la semilla en la soja

Canopy characteristics (leaf area index, fractional light interception, extinction coefficient) of mature trees of ten clonally propagated cacao cultivars were measured over a period of 14 months at an experiment site in Bahia, Brazil. Differences in leaf area index between clones became more pronounced over time. When an approximately constant leaf area index was reached (after about nine months), the leaf area index varied between clones from 2.8 to 4.5. Clonal differences in the relationship between leaf area index and fractional light interception implied differences in canopy architecture, as reflected by the range of extinction coefficients (mean values ranged from 0.63 for the clone TSH-565 to 0.82 for CC-10). The results demonstrate the potential for breeding more photosynthetically efficient cacao canopies.

The effects of pre-flowering drought on millet were studied in two experiments, an on-station, dry-season trial under irrigation and an on-farm trial where drought was induced by natural rainfall regimes (one wet, two dry years). The on-station experimental conditions were adjusted to those of Sahel farms, particularly through low plant density, low soil fertility and an irrigation regime that simulated the natural rainfall pattern. The replanting (5–10%) of missing hills in the on-farm trial increased stand variance significantly, whereas small quantities of applied N reduced it. Grain yield and grain number were equally seriously affected by drought in both experiments; yields were 700–800 kg ha−1 in the control years compared with 200–300 kg ha−1 in drought years. Both experiments showed sub-populations of early-, intermediate- and late-flowering millet plants. Fertile tillers were concentrated in the group of early-flowering plants. Only this group when subjected to moisture stress could secure part of the grain production by delaying, to a maximum of 18 d, the development of fertile tillers beyond the period of stress. Later-flowering plants, mostly uniculm, would be either sterile or unaffected by drought, depending on the exact coincidence of panicle development and drought. Drought did not alter the number of fertile hills per stand, because earlier- or later-flowering plants in the same hill compensated for sterile plants. The period of flowering in a stand was stretched over 40–45 d independently of drought, and this occurred both in the on-station experiment comprising 19 plants per treatment and in the on-farm experiment comprising about 700 hills. Although stand variance was reduced by better crop management and resulted in more fertile hills, more panicles per hill, and taller hills of more uniform height, the spread in flowering period of the millet population tended to be unaffected. Stand variability therefore appeared to be of paramount importance in accounting for drought avoidance.

Small ruminants are an integral part of mixed-farming systems throughout southern Ethiopia. Yet, they have received little research attention or institutional support. Characterizing the existing small ruminant production systems and analysing their production constraints are important tools to diagnose the status and trends of the systems, and thus to identify areas for future interventions. A survey was conducted between April and July 2004 in the Adilo and Kofele areas of the southern mixed-farming systems of Ethiopia to explore reasons for keeping small ruminants and to evaluate the existing status of and the prospects for the small ruminant sector. Additional information was obtained during discussions with key informants who had experience of small ruminant keeping. Small ruminants fill several roles in the study area. However, the principal purpose of keeping sheep and goats was to generate cash income. Sheep milk consumption was widespread around Kofele unlike most agricultural systems in the country. Nearly all respondents in Adilo reported fattening their sheep before sale, while such a practice was uncommon in Kofele. Informal insurance schemes were evolving among the sheep keepers in Adilo, and these can be considered as entry points for future interventions. The common problem identified from both individual interviews and group discussions was feed shortage. The identification of alternative feed resources and strategic feeding management might be options for development. Small ruminant disease was the major constraint in Kofele, where marshy areas are increasingly assigned for grazing in the rainy season as suitable land is more and more used for cropping. The growing demand for meat from small ruminants, the improving transportation infrastructure and the experience of farmers in small ruminant keeping are providing opportunities to enhance the contribution of the sector. A thorough monitoring of the productive and economic performance of small ruminants is required to capture the full picture of their contribution thereby directing possible intervention areas to maximize benefits to the farmers.

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.

Fusarium and Lasiodiplodia species invade feeding lesions caused by mirid bugs (Distantiella theobroma [Dist.] and Sahlbergella singularis Hagl.) and inflict serious damage and yield loss to susceptible cacao (Theobroma cacao L.) varieties in West Africa. As it is the fungal invasion rather than the physical feeding injury by mirids that cause dieback and tree death in cacao, a dieback resistance strategy in cacao crop must take into account resistance to these causal agents. Twenty-nine and 15 cacao genotypes were screened in the laboratory and the greenhouse, respectively, for resistance to isolates of Fusarium decemcellulare and Lasiodiplodia theobromae at Imperial College London's Biological Sciences Campus, UK. Resistance was assessed as the size of necrotic lesions, distance of fungal colonisation in the stem and the proportion of seedlings with dieback symptoms. Genotypic differences were found in both laboratory and greenhouse tests among various cacao genotypes, and the clones showed a wide range of disease reactions from highly resistant to very susceptible. The pathogenicity of F. decemcellulare and L. theobromae were similar in this study, which suggests that a breeding programme for controlling one of the pathogens can have benefit against the other. Direct significant correlations (r = 0.7) were obtained between visual dieback assessment scores and the percentage cross-sectional area of stem necrosis. Moreover, the response of inoculated stem segments corresponded to the reaction of intact plants despite the variation in the used methodology. Three cacao genotypes (CATIE 1000, T85/799 and MXC 67) were resistant or moderately resistant to F. decemcellulare and L. theobromae. These genotypes could be useful sources of resistance to both pathogens and other wilt causing pathogens in cacao.

Striga hermonthica is a parasitic weed that attacks maize, sorghum and other staple cereal crops and has long been considered one of the greatest biotic constraints to cereal production in Africa. Use of resistant or tolerant maize varieties, a maize–legume rotation using trap crops that stimulate suicidal germination of Striga and the application of nitrogen fertilizer are all effective in reducing infestation and damage. This paper reports on the use of a participatory research and extension approach in assessing the performance and scaling-up of integrated Striga control packages in three agro-ecological zones in Borno State, Nigeria. The participatory process which encourages close interaction between research, extension and farmers, involved 30 local communities and 228 farmers representing 193 farmer groups in identifying their own problems and seeking solutions to them. Results showed not only effective Striga control but productivity increases of over 200%. The involvement of local farmers and groups in the evaluation process, firstly, helped to confirm that Striga control can best be achieved using soyabean followed by Striga-resistant maize together with productivity-increasing management practices and, secondly, promoted farmer-to-farmer extension. A participatory adoption assessment exercise indicated widespread adoption of new varieties and management practices, despite the need for increased labour. Great potential exists to scale out the results to similar areas of Guinea and Sudan savannas in the West Africa region.

Farmer-managed trials with browse trees were undertaken at two locations in southeast Nigeria. The fast-growing tree species Leucaena leucocephala and Gliricidia sepium were either inter-planted with crops as alley farms or planted in pure stands as intensive feed gardens. At both locations, most of the trees established successfully under farmer management. However, the quality of establishment was uneven, and the rate of utilization generally poor, especially at one site. The limited success of the trials is traced to a number of related sociological, institutional and edaphic factors. These include poor soil fertility; the incompatibility of established cropping patterns and rotation practices with the planting of trees on farms; the division of labour and organization of decision-making within the household; and land and tree tenure rules. It is argued that farmer-managed trials are necessary to reveal the importance of sociological and institutional factors in farmers' decision making, and that such trials require a high level of farmer autonomy in their management.

Boron deficiency in cotton occurs widely in northern Nigeria, where its extent and severity appear to be increasing, particularly under intensive agriculture. The deficiency may be aggravated by fertilizer application, specially nitrogen. Soil boron status varies greatly but is generally very low and often less than is considered necessary elsewhere. Superphosphate containing added boron corrects deficiency safely and satisfactorily.