A field study of cowpea, soybean and maize was made at Ibadan, Nigeria, to determine the uptake of mineral nutrients and quantities removed in crop residues and seed. Concentrations of N, the major cations (K, Ca, Mg and Na) and major anions (P, S and Cl), and the micronutrients (Fe, Mn, Zn and Cu) were determined in shoots harvested at flowering and maturity. Concentrations of excess cations in shoots at flowering were 135 cmolc kg−1 for soybean, 158 cmolc kg−1 for cowpea and 58 cmolc kg−1 for maize. In crop residues and seed at maturity, the values decreased to 75 and 56 cmolc kg−1 respectively for soybean, 68 and 27 cmolc kg−1 respectively for cowpea, and 52 and 10 cmolc kg−1 respectively for maize. Nutrient and excess cation concentrations were also measured in 13 soybean and eight cowpea lines grown in replicated field trials at Fashola in the derived savanna zone and Shika in the northern Guinea savanna zone of Nigeria to assess the variation within these species. Maize, mucuna and lablab were included at these sites. The results are discussed in the context of soil nutrient depletion due to removal of nutrient elements in harvested seed and stover. The contribution of seed and stover removal to the proton (H+) budget and acidification of the soil is also discussed. It is estimated that the quantity of lime required to neutralize the acidity resulting from the removal of 1 t seed is 28 kg for soybean, 14 kg for cowpea and 5 kg for maize. The corresponding values for stover were soybean 35, cowpea 24 and maize 26 kg lime t−1 stover. Given the soil pH buffer capacity at the Ibadan site for the surface 16 cm, the yields obtained and assuming that seed and crop residues are removed, carbon cycle acidification would lead to a fall of 1 pH unit after 75 crops for soybean, 114 crops for cowpea and 68 crops for maize. The inclusion of legumes in cropping systems to increase N supply, and the use of P fertilizer to maximize N-fixation by legumes will raise production, but will inevitably accelerate removal of alkalinity and nutrients in harvested products, and the consequent decline in soil fertility. The data presented in this paper can be used in estimating the lime and fertilizer nutrients needed to maintain soil fertility and sustain yields.

Climate change and land use change are two forces influencing the hydrology of watersheds and their ability to provide ecosystem services, such as clean and well-regulated streamflow and control of soil erosion and sediment yield. The Soil Water Assessment Tool, SWAT, a distributed, watershed-scale hydrological model was used with 18 scenarios of rainfall, temperature and infiltration capacity of land surface to investigate the spatial distribution of watershed services over the 3587 km2 Nyando basin in Western Kenya and how it is affected by these two forces. The total annual water yield varied over the 50 sub-basins from 35 to 600 mm while the annual sediment yield ranged from 0 to 104 tons ha−1. Temperature change had a relatively minor effect on streamflow and sediment yield compared to change in rainfall and land surface condition. Improvements in land surface condition that result in higher infiltration are an effective adaptation strategy to moderate the effects of climate change on supply of watershed services. Spatial heterogeneity in response to climate and land use change is large, and hence it is necessary to understand it if interventions to modify hydrology or adapt to climate change are to be effective.

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.

Ground-based radiometric measurements in the red and infrared bands were used to monitor the growth and development of wheat under irrigated and stressed conditions throughout the 1987–88 and 1988–89 growth cycles. Spectral data were correlated with plant height, leaf area index, total fresh and total dry biomass, plant water content and grain yield. The radiance ratio (R) and normalized difference vegetation index (NDVI) were highly and linearly correlated with yield, establishing the potential which remote sensing has for predicting grain yield. The correlation for R and NDVI was at a maximum between 75 and 104 days after sowing, corresponding with maximum green crop canopy cover. The differences in spectral response over time between irrigated and unirrigated crops allowed detection of water stress effects on the crop, indicating that a hand-held radiometer can be used to collect spectral data which can supply information on wheat growth and development.

Efectos de lafalta de agua en el trigo

Over a period of seven years farmers participated in trials in which common vetch (Vicia sativa (V)) or chickling (Lathyrus sativus (C)) replaced the fallow in a barley (Hordeum vulgare)–fallow rotation (F) or were introduced into continuous barley cropping (B) – giving a total of four rotations, B–F, B–B, B–V and B–C. Trials on 4 ha, 2 ha per phase of each rotation, were replicated on 6–8 farms. Some vetch and chickling crops were grazed in spring. Mean seven-year dry matter yields were 2.91 t ha−1 for B–F, 4.82 t for B–B, 5.02 t for B–C and 5.32 t for B–V; total crude protein outputs were twice as high from rotations including legumes; and the B–V rotation yielded most metabolizable energy. Realizing the benefit, farmers started to adopt vetch. In 1991 three farmers were growing vetch on 7 ha but by 1997 174 farmers in 15 villages were growing vetch on 420 ha. Forage legumes will not, however, become more widely grown until inexpensive and efficient mechanized methods of harvesting the mature crop are available in order to avoid the high cost of hand labour. Drought and cold tolerance, early maturation and high harvest index may also enhance farmers' interest in forage legumes.

The aim of this work was to assess the effects of N levels and intercropping of two common bean (Phaseolus vulgaris) varieties (Carioca and Rio Tibagi) with maize (Zea mays) on accumulated N, grain yield and biomass of both crops, and nodulation of common bean inoculated or not with Rhizobium. Two field experiments were conducted simultaneously: common bean–maize intercropping and common bean in sole cropping. Intercropping increased common bean nodulation and biomass, mainly with Rhizobium, but mineral N was deleterious to nodulation. Inoculation also increased the Carioca cultivar yield most in sole cropping (+72%), but N levels did not affect common bean yield in either cultivar. Although intercropping reduced maize grain yield by 17%, the equivalent yield increased by 31%, whilst Rhizobium increased it by 11%. Despite the reduction of maize yield in intercropping, this system was shown to be more economically viable, in particular when common bean was inoculated with Rhizobium.

Various intercrops were examined in an alternate row pattern with pigeonpea or sorghum on both Alfisol (red soil) and Vertisol (black soil). The slow-establishing and later-maturing pigeonpea combined well with earlier cereals and legumes to give very large yield advantages as measured by the Land Equivalent Ratio. In the pigeonpea/cereal combinations, the earlier the cereal the bigger the yield advantage tended to be, attributed to improved use of resources over time as the difference in maturity periods of the component crops increased. Sorghum was generally more competitive than pigeonpea and intercropping advantages tended to be less. But even where there was little difference in maturity periods of the component crops, both sorghum/legume and sorghum/cereal combinations gave substantial and statistically significant advantages, suggesting that improved ‘spatial’ use of resources was also important.

Effects of moisture stress during different stages of cotton development were examined in two experiments when temperatures were mild and evapotranspiration less than 6 mm./day. Two varieties of upland cotton, Acala 4–42 and Deltapine Smoothleaf, were affected similarly. Moisture stress at the beginning of flowering reduced growth rate and the numbers of flowers and bolls. During the second half of the flowering period it reduced the percentage of boll retention, boll number, boll weight, seed index, lint index and lint length. Stress during boll development had similar effects and caused earlier maturity. Lint yield was reduced significantly by moisture stress during each of the periods but tensile strength of lint was not affected. Three irrigations, if properly timed so that no appreciable moisture stress occurred, were sufficient for high yields and good quality of lint, and the first could be postponed until after flowering began without any loss in yield.

Because of shortages of oxen for mouldboard ploughing, delayed planting of maize is common in Mangwende, Zimbabwe and reduces grain yield by 32%. On-farm experiments over four years tested the possibility of using a ripper tine, with atrazine herbicide, to allow smallholders to plant maize earlier. Compared to mouldboard ploughing, tine cultivation increased grain yield at 13 out of 18 sites. All these sites had less than 240 mm of rainfall in January (which coincided with crop anthesis) and long term rainfall records suggest tine cultivation should raise yields in two out of three years. Handweeding and atrazine treatments gave similar grain yields when used with tine cultivation, provided weeds were controlled within 14 days of crop emergence. Tine cultivation was economic at sites where the yield was greater than that with the mouldboard plough. The farmers could manage the combination of tine and atrazine use on a field scale.

Gas exchange, leaf carbon isotope discrimination, growth, yield and beverage quality were evaluated for two Coffea arabica cultivars (Catuai and Mundo Novo), grafted on to C. canephora and C. congensis progenies growing in open fields. During the years 1994 to 1997, grafting resulted in an average increase in bean yield of 151 and 89% for Catuai and Mundo Novo respectively. As analysed by sensory analyses and by the ratio between the mono-isomers and di-isomers of caffeoylquinic acid, beverage quality of the C. arabica was not altered by grafting. Shoot growth was significantly greater in grafted plants, showing an increase of 52% in total leaf area compared with the non-grafted plants. Under conditions of water excess in the soil there was little difference in the transpiration and stomatal conductance rates between the grafted and non-grafted plants, but the net photosynthesis was higher in grafted plants. With an accentuated water deficit in the soil in the dry period, the grafted plants showed significantly higher transpiration and stomatal conductance rates than the non-grafted plants, and similar values to those of C. canephora. Carbon isotope discrimination was greater in the grafted plants, suggesting greater root hydraulic conductance. The results suggest that the better performance of the grafted plants during the dry period was due to the greater capacity of the root system of C. canephora to provide water to the shoot thereby maintaining greater gas exchange in the leaves and consequently a greater carbon gain.

Experiments to assess the yield and economic performance of a maize-groundnut rotation compared with continuous maize (both when inorganic fertilizer was applied to maize and when not), were conducted under management by smallholder farmers in Zimbabwe over six years. The experiment was planted on-station near Harare and at six smallholder sites in northeast Zimbabwe, predominantly on sandy soils. Fertilizer rates and practices were those used by farmers, as described in surveys. On-farm grain yields from continuous maize without fertilizer were generally in the range 0.5–0.8 t ha−1 over five years. Maize yield responses to inorganic fertilizer on smallholder farms were highly variable, but moderate (up to 29 kg grain per kg N) with adequate rainfall. With no inorganic fertilizer applied to maize, the on-station groundnut crop (producing 0.260–0.355 t ha−1 shelled grain) almost doubled the grain yield of the following maize crop (in 1995–96), increasing output from 2.46 t ha−1 to 4.61 t ha−1. Where inorganic fertilizer was applied to maize, the rotation produced even more additional maize grain (an increase of 2.93 t ha−1). Up to 0.50 t ha−1 extra grain was obtained in the second year of maize following groundnut (1996–97). With inorganic fertilizer, groundnut improved the grain yield of following maize crops at only two of five on-farm sites. Without fertilizer, the groundnut rotation increased maize grain yields at five on-farm sites by an average of only 0.28 t ha−1. For the on-station groundnut and two subsequent years with maize, discounted net benefits (DNBs) over cash costs (seed and fertilizer) were greater for the rotation than for continuous maize, irrespective of whether or not inorganic fertilizer was applied. When labour costs were added, continuous maize plus fertilizer showed better returns than did the rotation, while the returns for the rotation and continuous maize without fertilizer were almost the same. On-farm the rotation was far less profitable. At only two sites, DNBs over cash costs were higher for the rotation whereas DNBs over all costs (including labour valued at a local casual-worker wage) were always negative or close to zero. At three sites, it was far more profitable to grow continuous maize, especially with fertilizer. These findings of low groundnut yield, marginal to zero profitability, and high labour cost of groundnut-maize rotations, support and explain the general trend by smallholder farmers to reduce groundnut area in Zimbabwe.

Assimilate storage in vegetative organs is an essential buffer for the source–sink imbalances that inevitably occur in perennial plants. In contrast to temperate trees, little information is available on such storage in tropical perennials, and almost none for Cocos nucifera. This paper describes the chemical nature, quantity and distribution of carbohydrate reserves in coconut plants grown in an environment favourable to production. The study was carried out on the island of Santo (Republic of Vanuatu, Southern Pacific) on twelve 17-year-old adult plants, representative of a large population, which were felled and characterized for root, trunk and crown dry matter, and contents of soluble sugars and starch. Roots were divided into three diameter classes and distal/proximal portions, the trunk into three axial and three or four radial zones, and the crown into petiole, rachis and leaflets for various leaf ages. The aggregate reserve pool size was compared with estimates of incremental demand for assimilates for growth and fruit production. Plants contained little starch but large quantities of sucrose were found, mainly located in the trunk. Less sucrose was present in roots and little in leaf blades. Large glucose and fructose pools were found in leaves, near the apex of the trunk and in the terminal portions of large roots. Aggregate soluble and non-soluble sugar pools were about equivalent to six months of copra production or 51 days of crop growth. More studies are needed on the dynamics of these sugars to evaluate their physiological role, particularly with regards to stress periods and fluctuating demand for fruit filling.

As a result of continued fiscal challenges from the late 1980s to date, the government of Uganda liberalized and decentralized the provision of veterinary services. As a result, many actors are involved in providing veterinary services without adequate regulation and supervision. With the resurgence of infectious diseases, and increased economic and health risks, especially to the rural poor, there is the need to understand relational patterns of actors to ensure good governance, and address emerging and re-emerging risks of animal diseases. A participatory mapping tool called Process Net-Map was used to identify relevant actors and assess their influence in the delivery of clinical and preventive veterinary services in both pastoral and intensive livestock production systems. The tool also served to elicit governance challenges in veterinary service delivery. The results reveal that important social relations in veterinary service delivery include the following: (1) Cooperation between private veterinarians and paraprofessionals as well as private veterinarians and government veterinarians in intensive production systems; and (2) cooperation between NGOs, government veterinarians and community-based animal health workers in pastoral areas. Staff absenteeism, insufficient and unpredictable budgets, weak legislation, exclusion of technical staff from the decision-making process and policy illogicality were identified as major governance problems of veterinary service delivery. The paper concludes that given the existing fiscal challenges, the key to improving animal service delivery in Uganda is getting priorities, policies and institutions right.

Precipitation in Western Nigeria is principally from thunderstorms with sharp, high-intensity rainfall peaks. The time of occurrence of the peak intensity period in a rainstorm has an influence on whether or not runoff occurs in smaller storms. Runoff and soil loss on bare, cultivated Iwo soil are closely related to an EI30 erosivity index, modified by the time-position of the peak intensity. The soil erodibility factor in the universal soil-loss equation could be reasonably estimated from easily measured soil parameters.

As part of a programme to improve production of the main food crops of Northern Nigeria, trials were carried out to investigate the effect of nitrogen and phosphate fertilizer on the grain yield of sorghum. Five fertilizer response areas have been defined and estimates have been made of the most profitable combinations and levels of phosphorus and nitrogen to use in each area. Fertilizers produced the greatest increase in yield in the two response areas which cover the north of the country.

The possible use of tropical forage legumes in pastures based on Brachiaria decumbens and Andropogon gayanus pastures was tested on farms in the humid tropics region of Pucallpa, Perú. The pastures were established by farmers using manual labour. They were associated with maize in some cases and were normally grown without fertilizers. The pastures were established in areas where fallow regrowth was felled and burnt. These pastures, with grass-alone controls, were incorporated by farmers into their normal paddock rotation and were grazed by dual-purpose cows. Despite the variable terrain and soil conditions, all the pastures established and persisted well. Over a four year period under grazing, the legume contribution to the forage averaged 21% and ranged between 1 and 66%. Desmodium ovalifolium was the dominant legume in paddocks that were not burnt, whereas in pastures regularly burnt to control weeds it tended to disappear and Stylosanthes guianensis was the main legume present. It is concluded that where farmers ensure the maintenance of adequate levels of forage, grass-legume mixtures are a viable and persistent option even if the pasture is occasionally burnt.

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.

Increasing transplanting costs in southeast Asia have encouraged farmers to adopt labour-saving crop establishment techniques for rice, such as wet seeding. This practice has been accompanied by an increase in weed problems and a shift in the dominant species to grassy weeds. Other problems are encountered with wet seeding but weeds are the most severe and most widespread constraint. It is impossible to produce rice economically without a well-planned weed control programme. The problems caused by weeds in wet-seeded rice and ways of controlling them by preventive, ecological, managerial, physical and chemical means are discussed in this paper. Herbicides are the most cost-effective weed control method in wet-seeded rice but there is a need to reduce the almost total reliance on them for weed control; cultural practices need to be integrated with judicious herbicide use. Worldwide concerns over environmental issues also need to be addressed.

Control de malezas en el arroz de siembra húmeda

Smallholders' acceptance of innovations depends largely on the approach used to take their needs and constraints into account. The adoption of integrated pest management (IPM) strategies by smallholders can lead to a reduction in pesticide use in cotton, as soon as the recommended cropping practices are adapted to local conditions and associated with a threshold-based use of chemicals. To achieve this goal, farmers need to be trained on the biological basis of IPM. To ensure effective and rational implementation of IPM by farmers, it is essential to overcome constraints associated with pest scouting, identifying and preserving beneficial insects, and gaining access to the right inputs on time. In the current African context, where the extension system is sometimes in very poor shape, participatory methods fostered by the ‘farmer field school’ concept could enable farmers to implement an integrated approach to pest management, while keeping researchers informed about farmers' needs and constraints. Our paper is an attempt to use such a participatory method as a tool to explore farmers' needs and constraints when smallholders are asked to adopt an integrated approach to cotton pest management.

Sustainable intensification (SI) of agriculture is the predominant objective for agricultural research and extension worldwide. Researchers and policymakers consider SI to be essential to avoid global hunger, improve human nutrition and reduce rural poverty while avoiding all manner of environmental disasters. To achieve these global public goods requires a large number of rural households – ‘small farmers’ – in less developed countries to improve their agriculture. Household size and farm size from 11,789 households in 15 countries from sub-Saharan Africa were used to calculate an intensification benefit index (IBI) that reflects how much a household will benefit if intensification occurs. IBI is defined as the increase in personal daily income (cents/person/day) as returns to land (dollars/hectare/year) increase. Actual net farm income from 160 rural households in each of three countries was compared with their IBI values to explore the gap between potential intensification and current smallholder farm performance. Fifty percent of all households had IBI values less than 0.075 cents/dollar, 70% less than 0.125 cents/dollar and 90% less than 0.225 cents/dollar. Returns of $1000/ha/year would result in fewer than 15% of households crossing a $2/person/day poverty line; $2500/ha/year would be required to lift 50% of the sample above the line; and even with $4000/ha/year, more than 30% of households would remain below the line. Since mean net returns from three sub-sampled sites were only $78, $83 and $424/ha/year the gap between potential- and actual performance is large but, theoretically, amenable to closure through adoption of improved technologies. However, surveys have shown that the available technologies would struggle to bridge the gap completely for rural households with small farms. For many small farms, the gains from adopting improved technologies are unlikely by themselves to lift them out of poverty and so might not be as attractive as scientists would wish.