Low levels of phosphorus limit the yield of pearl millet (Pennisetum glaucum) grown on acid sandy soils of the West African Sahel. The application of phosphorus and the recycling of millet residues produces large increases in the total dry matter and grain yields of millet but little is known about the effects of these amendments on the by-products of millet fields which include weeds and millet leaves at harvest. Phosphorus applied at 13 kg ha−1 as single superphosphate and millet residues applied at 500 or 2000 kg ha−1 as a mulch or as the ash from 2000 kg millet residues ha−1 that had been burned, increased dry matter yields of millet leaves and weeds leading to large increments in the total in vitro metabolizable energy harvested per unit area. These increases in dry matter production were only accompanied by minor decreases in the concentration of crude protein. The increased availability of millet by-products should be taken into account when evaluating the effects of phosphorus and crop residue application on the economy and sustainability of agro-pastoral farming systems in the West African Sahel.

Four experiments were conducted in southern Taiwan to evaluate the yield and economic benefits of management practices aimed at alleviating the effects of high temperature and heavy rain on tomato production. Following tropical storms, waterlogging caused wilting which was more evident in tomatoes grown in beds 20 cm in height than in those grown in raised beds 40 cm in height. This indication of crop water stress induced by flooding was quantified by measurement of the difference between canopy surface and air temperature at a specified saturation vapour pressure deficit. Canopy heating was less on the raised beds, especially when straddled by rain shelters. Nevertheless, waterlogging stress for the low-bed treatment did not result in loss of stand. In crops which experienced heavy rain, application of a synthetic fruit-set hormone enhanced fruit numbers as did the simple transparent polyethylene rain shelters. While planting on raised beds was without yield benefit the use of fruit-set hormone improved yield by at least 10 t ha−1. A further 4–6 t ha−1 yield was gained through the additional use of rain shelters. Partial budget analysis showed positive returns to the use of fruit-set hormone (US$6600 ha−1) but, unless rain shelters could be constructed with cheaper frame material or used for two tomato crops throughout the summer, their use would be uneconomical. Using existing frame material, net returns to rainshelters reached US$8000 ha−1. The likelihood of high temperatures, tropical storms and typhoons will influence economic returns to summer tomato production. Data from this study may be subjected to economic analyses using values for inputs and tomato prices from other countries with similar climatic conditions.

In a field experiment, microbiological and chemical amelioration of a highly deteriorated alkaline soil (pH 10.6, exchangeable sodium percentage 95) was undertaken during 1989–92 using two reclamation technologies: namely, growing Karnal grass (Leptochloa fusca) as a first crop in the absence of any amendment (biological reclamation) or applying gypsum as a chemical amendment for different cropping sequences. After ten months average dehydrogenase activity, used as a measure of catabolic activity of micro-organisms under anaerobic conditions, was 49.5 μg triphenylformazan (TPF) per g soil in treatments where the soil was reclaimed by growing Karnal grass, compared with 26.8 μg TPF by applying 50% of the estimated requirement of gypsum. After three years of reclamation, average dehydrogenase activity was 118.7 μg TPF per g soil with Karnal grass and 96.1 μg TPF with gypsum. After three years average microbial biomass carbon was 28% greater in the gypsum treatments (206.5 mg per kg soil) compared with Karnal grass treatments (161.7 mg). However, at this stage the ratio between average dehydrogenase activity and microbial biomass carbon was greater with Karnal grass (0.77) than in gypsum treatments (0.47). The microbiological properties changed more than the chemical properties of alkali soil as the time period advanced. After three years of reclamation, the average pH of the alkali soil dropped from 10.6 to 9.45 and the average exchangeable sodium percentage was reduced from 95 to 47.5. The increase in total organic carbon was 64% and in available nitrogen about 38% compared with the original soil. Higher microbial biomass carbon in gypsum treatments corresponded with lower exchangeable sodium percentage, higher availability of nitrogen and potassium and greater total yield of sensitive winter clovers.

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.

Shoot dry matter yield, shoot nitrogen yield and amount of nitrogen derived from fixation are collated for chickpea (Cicer arietinum L.) cv. ILC482 and lentil (Lens culinaris Medic.) cv. ILL8 grown at the ICARDA research station Tel Hadya, Syria over a period of 17 years. Regression analyses of shoot nitrogen yield on shoot dry matter and of the amount of nitrogen fixed on shoot nitrogen yield were undertaken for both species. The intercepts for both analyses with lentil were not significantly different from zero, so the slopes of the lines represented the concentration of nitrogen in the plant tissue (20.6 g kg−1 dry matter) and the proportion of nitrogen derived from fixation 0.75. Data for other cultivars of lentil grown at Tel Hadya and at four other locations in Syria fell within the 95% confidence limits of the original analyses. The intercept of the regression of shoot nitrogen yield on shoot dry matter yield for chickpea grown at Tel Hadya was not significantly different from zero, so the concentration of nitrogen in the plant tissue was constant (17.8 g kg−1 dry matter). The proportion of nitrogen derived from fixation increased asymptotically as the shoot nitrogen yield increased. Data for other cultivars of chickpea grown in different locations were generally similar to those for cv. ILC482 grown at Tel Hadya. It is proposed that generalized relationships between shoot nitrogen yield and shoot dry matter yield, and between amount of nitrogen fixed and shoot nitrogen yield can be established for lentil and chickpea grown in the West Asia–North Africa region. Consequently the amounts of nitrogen fixed by the two crops could be predicted from a knowledge of dry matter production alone.

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 use of tropical grass–legume mixtures containing the grasses Brachiaria decumbens or Andropogon gayanus associated with a mixture of several herbaceous legumes was tested on farms in the rainforest area of Pucallpa, Peru. Pastures were established by farmers using manual labour and without fertilizer in previously deforested areas covered with secondary growth. The pastures, together with their grass-alone control, were incorporated by farmers into the normal paddock rotation, and were grazed by dual-purpose cattle of mixed breeding. Cows were milked once daily by hand and with their calves at foot. Following a training period, farmers kept records of milk yields. Frequent and unannounced visits at milking time by the research team were used to verify milk yields and to annotate events such as calving, drying out, sales and others. Across farms and years, grass–legume mixtures significantly outyielded grass-alone pastures by 9%. Milk yields on the mixed pastures were examined further by stepwise regression. A positive and significant effect of the proportion of crossbred cows in the herd was established, whereas soil quality (evaluated by the percentage of aluminium saturation) had a negative impact on milk yields. Two of the farms, which for different circumstances had poorer than average animal and pasture management, also had a significantly negative effect on milk yield. The interactions between animal and pasture management, and regional infrastructure are discussed. It is concluded that grass–legume mixtures increased milk yields on farms. Nevertheless, it is also hypothesized that they may have a more restricted niche than anticipated and that their adoption may be highly sensitive to the overall economic context of the region.

Advanced genotypes of common bean (Phaseolus vulgaris L.) were tested on-station and on-farm to evaluate their performance and acceptability under farmers' circumstances. Farmers were given seed of the genotypes to plant a minimum area of 100 m2 to be grown as a sole crop or intercropped with sorghum according to their preference. Yield, seed colour, taste, maturity time, disease reaction, growth habit and many other bean characteristics were assessed by farmers. The promising genotypes were higher yielding than the farmers' genotypes in most testing sites. Pairwise ranking of the genotypes showed that in export-oriented western Hararghe, white pea bean (navy bean) type Awash-1 and food bean G-2816 were preferred. In eastern Hararghe GLP ×92 and G-2816 were highly preferred but white pea beans were not preferred. Genotypes in advanced observation nurseries were also evaluated by the farmers and some of the genotypes have been promoted for further testing in yield trials. Selection criteria have been proposed by the farmers in each region. Future breeding and selection of genotypes will incorporate the proposed selection criteria and priorities of the two regions.

The strengths and weaknesses of the evolving techniques used by researchers in Bolivia to evaluate potato germplasm with farmers are assessed. When detailed knowledge of farmers' criteria is required, questionnaires or forms are most appropriate; otherwise techniques from participatory rural appraisal could be used. Initially, when evaluating large numbers of clones, scientists' and farmers' choices tended to coincide, although subsequently they diverged. This suggested that it may be more efficient to involve farmers later in the selection process, ensuring that an interesting amount of diversity still exists, and work to improve breeders' knowledge of farmers' criteria. Integration between social scientists and breeders was less than ideal at the start of the study, reducing the impact of farmer evaluations on the breeding programme.

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.

Two shrub species, Atriplex halimus L. and Salsola vermiculata L., are considered useful for rehabilitation of degraded rangelands in west Asia and north Africa. They can be established from direct seeding and are capable of self-sowing. In this study, seed storage at different temperatures and the influence of fruiting bracts on seed germination were examined for the two species during two seasons. Fruits (utricles) were stored at 20–22°C (room temperature), 0°C or −22°C. Germination tests were carried out after 33, 56, 90, 152, 272 and 397 d in storage in the first season and after 44, 76, 104, 170, 288 and 412 d in the second season. Seeds were germinated in their fruiting bracts or after bract removal. Bract removal significantly improved seed germination of both shrubs regardless of storage temperature. For S. vermiculata the increase in germination was in the range of 1.3- to 14.7-fold compared with values for the intact fruit in Season 1 and 0.5 to 3.8 in Season 2. Similarly the ranges for A. halimus were 0.5- to 4.2-fold and 0.7- to 5.3-fold in the two seasons respectively. The effect of cold storage was greater on Salsola than on Atriplex. The reduction of the storage temperature from 21°C to 0°C and −22°C increased the longevity of S. vermiculata seeds by 2.8–46.6 times in Season 1 and by 2.9–2.6 times in Season 2. There was little or no effect on the longevity of A. halimus. A leachate prepared by soaking fruiting bracts from S. vermiculata significantly depressed germination (p < 0.01), the effect being greater on Salsola seeds (20% reduction) than on Atriplex seeds (8% reduction). A leachate from A. halimus produced a slight but non-significant reduction in germination.

A series of grazed and cut experiments were conducted in Bali and North Sulawesi, Indonesia, between 1992 and 1994, to evaluate a range of selected forages for both intensive and extensive ruminant production under mature, tall coconuts. Yield, botanical composition and persistence of grass–legume mixtures were assessed under regular grazing and cutting regimes.

In North Sulawesi, total dry matter yields of most grass–legume treatments were relatively stable over the two-year period but yields of legume components within treatments declined sharply. In Bali, the grazed plots maintained stable yield and legume components over the experimental period but yield and legume components of cut plots declined sharply. Paspalum malacophyllum and Setaria sphacelata cv. Splenda were productive and persistent grasses and formed weed-free swards but did not combine well with prostrate legumes. The erect growth habit of these grasses may limit their suitability in coconut production systems by impeding nut collection. The prostrate species Brachiaria humidicola and Stenotaphrum secundatum were slightly less productive but equally weed-free and persistent, and established rapidly from cuttings. S. secundatum also formed stable associations with prostrate legumes under grazing. Arachis pintoi cv. Amarillo and A. glabrata CPI 93483 were the most persistent of a range of prostrate legumes. The tree legume, Calliandra calothyrsus, showed promise as a productive cut-and-carry species.

This study applies systems simulation to characterize determinants of sustainability of a hillside farm in the upper Cauca River watershed of Colombia. A farm model linked to process-level crop models was used to simulate a set of farm scenarios. Susta inability, expressed as the probability of farm continuation, was estimated for each scenario based on replicated simulation with stochastic weather and price inputs. Hypotheses about determinants of sustainability were tested by sensitivity analysis. Res ults identify cropping system, area under cultivation, consumption requirements and crop prices as important determinants of sustainability. The study highlights the impacts of price variability and spatial diversification on farm risk and the results sug gest ways to enhance the sustainability of the farm. The methodology was useful for integrating the diverse biophysical and economic factors that affect farm sustainability.

Employing data from an intercropping field experiment which measured the yields achieved by a surviving crop when the other crop failed at 0, 6 or 10 weeks after sowing, the use of a simple computer model to study the long-term yield effects of compensation in intercropping is described. Assuming different probabilities of crop failure for one or both of the crops, the model provided a comparison of long-term intercrop and sole crop yields from intercropping systems of oat–mustard, mustard–bean and oat–bean. It showed that if failure was restricted to only one of the crop species, intercropping suffered less yield decline with increasing probability of failure than did sole cropping only if there was a sufficiently high yield of the surviving crop. However, in the more realistic situation where each crop was subjected to the possibility of failure, this decline in yield was less in intercropping than sole cropping for all three combinations because poor yields when one species was the surviving crop were offset by good yields when the other species was the survivor. Mustard–oat and mustard–bean gave no yield advantage in the absence of failure (Land Equivalent Ratios less than 1) but they outyielded sole cropping for failure probabilities above about 5% and 15%, respectively. All combinations gave large intercropping advantages at high probabilities of failure. Oat–bean always had a strong yield advantage, even with no failure.

The model is very simplistic but it illustrates the potential for modelling long-term effects from field data. Limitations of the model are discussed and it is emphasized that these can be overcome if information to make the underlying assumptions more realistic is available.

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.

The agroclimatic potential of the forest–savanna transition zone of Nigeria for the cultivation of sorghum (Sorghum bicolor) was investigated. Five phenological stages of the crop formed the basic unit of time for the investigation. Selected agroclimatological thermal and moisture indices were measured daily and processed into ten-day (decadal) averages for the 1993 and 1994 cropping seasons. The thermal indices, temperature and photoperiods were optimal for sorghum growth but, on the basis of the distribution of rainfall and actual water availability in relation to the crop's water consumption, the moisture indices were above optimum. However by relating effective water availability to the indices of moisture adequacy for the growth of the crop, it was found that the agroclimatological moisture indices were optimum during the moisture sensitive stages. A comparison of the vegetative growth and grain yield of sorghum in the study area and elsewhere in the savanna region confirmed the agroclimatic potential of the forest–savanna transition zone for sorghum production.

The potential of pigeonpea (Cajanus cajan (L.) Millsp.) as a simultaneous fallow component in cropping systems is unique in that, being a shrubby grain legume, it combines food production with ease of establishment, fast growth and high biomass productivity. A study was carried out under on-farm conditions at three different sites in southern Bénin, West Africa over two years to evaluate the biomass productivity and recycled nutrients of a local pigeonpea cultivar, managed as annual hedgerows. Pigeonpea was sown between a standard cassava–maize intercrop and compared with two other agroforestry systems and annual intercrops with and without mineral fertilizer. The number of cuts taken at a height of 1 m was doubled from two in 1991–92 to four in the 1992–93 season, leading to an increase in total cut dry matter by a factor of eight (1908 g m−2) and cut leaf dry matter by a factor of fourteen (1317 g m−2) in 1992–93. There were no trade-offs in subsequent dry grain (9.5 g m−2) and firewood yields (96.2 g m−2) for cutting hedges earlier and more often during the second year, despite much lower precipitation. In pigeonpea recycled nutrients, N, P, Ca, Mg and K, increased proportionally to cut dry matter yields. Yield increases over two years with pigeonpea were highest among all evaluated cropping systems for maize (+150%) and significant for cassava (+66%). Pigeonpea as a simultaneous fallow component in cassava–maize intercropping, can help to sustain moderate yields of maize and cassava, provided that insects, nematodes and diseases do not lower its high biomass productivity with continued cropping after two years.

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 two-year study considered the effect of pod harvesting intervals of 3, 5, 7, 9, 11 or 20 weeks after pod set (WAPS) on the relationship between the physical condition of the pods, seed maturation and quality in fluted pumpkin (Telfairia occidentalis). Pod characteristics, such as the intensity of bloom wax on the pod and stiffness of the pod ridges, showed perfect linearity and correlation with the age of the pod, whereas changes in seed quality factors – germination, dry matter, oil and protein concentrations were curvilinearly associated with the time of pod harvest. Thus, seed quality factors increased steadily up to nine WAPS then declined. The point at nine WAPS defined as physiological maturity for fluted pumpkin seed and approximate visible indications of this point in the field were fairly stiff pod ridge condition and fading of bloom wax.

Four weeding systems were evaluated for three seasons on sandy soils in a semi-arid area of Zimbabwe. Inter-row weeding with a plough with body (mouldboard breast) attached, produced a ridge and furrow landform. This confers the advantage of increased water retention associated with ridging without the additional investment in labour and equipment needed when ridges are made pre-planting with a ridging plough. Mid-season ridging by plough with body attached achieved more efficient weed control than the common farmer practices of using a cultivator or plough without the body. In terms of crop water use efficiency and grain yield, weeding with the plough and body performed at least as well as any existing farmer practices. Productivity, in terms of grain yield per hour worked, was considerably higher following weeding with the plough and body compared with alternative systems.