Measurements indicate that the tea crop—which consists of young shoots—is sink-limited and that the plucking of immature shoots, essential for quality tea, is a major factor limiting yields of the crop. The importance of this aspect in selecting for high-yielding plant material is discussed.

Farmer participation in agricultural research can improve the efficiency and impact of the research. This functional component of participatory research includes the identification of traits that guide crop breeders' work. Participatory research can also lead to farmer empowerment, although when carried out by research organizations, direct empowerment is often limited to relatively few farmers. Farmer empowerment is, therefore, best carried out by development organizations whose longer-term interaction with farmers is likely to ensure that greater numbers of farmers benefit. Hence, research organizations ought to focus on the functional components of participatory research along with the empowerment of intermediate/partner organizations rather than the direct empowerment of large numbers of farmers.

Variation in time from sowing to flowering (f) was examined for 44 cultivars of soyabean, mungbean, black gram, ricebean, cowpea, chickpea, lentil and barley, when grown in up to 21 diverse environments obtained by making one or more sowings at each of six locations spanning tropical, sub-tropical and temperate climates in Australia. The utility of simple linear models, relating rate of development (l/f) towards flowering to mean photoperiod and temperature prevailing between sowing and flowering, was evaluated. The models were highly efficient, explaining most (86.7%) of the variation observed across species, cultivars and environments. They were particularly efficient in describing responses where cultivars were relatively well-adapted, in agronomic terms, and least efficient where cultivars were exposed to unfavourable temperature and, to a lesser extent, photoperiod. Opportunities for exploiting the models in applied crop improvement include their use in interpretation of G × E interaction, genotypic characterization and selection of parental genotypes, selection of test environments, designing screening procedures, and more efficiently matching genotypes to target environments. The main strengths of these linear, additive rate models in crop improvement are their wide applicability across species and genotypes, their relative simplicity, and the requirement for few genotype-specific response parameters. Their main weakness is their lack of precision in describing responses when plants are exposed to unfavourable photothermal extremes, albeit in circumstances that are sometimes unrealistic for cropping those particular genotypes.

Predicciones del tiempo que ha de transcurrir hanta la floración. VI.

This paper documents the yield gains attributable to the breeding and distribution of new cocoa varieties in Ghana, using data from a 2002 survey of 192 fields in the country's key cocoa producing regions. We find that planting the more recently-released varieties is associated with at least 42% higher yields, and that genetic improvement accounts for much but not all of the observed correlation between tree age and cocoa yield. Fertilizer use is also very important, being associated with 19% higher cocoa yield per 50 kg bag of fertilizer. We find no evidence that varieties differ in their response to fertilizer, pesticide use or labour, and no evidence of a decline in the yield advantage of new varieties over the 17-year age span observed in the sample.

Since shading often occurs under normal growing conditions in various cropping systems (for example, intercropping, alley cropping), field experiments were carried out to determine the effects of shading on stomatal density, leaf size, leaf dry matter, and leaf lamina thickness in the major tropical root and tuber crops, tannia (Xanthosoma sagittifolium), sweet potato (Ipomoea batatas), yam (Dioscorea esculenta), cassava (Manihot esculenta), and taro (Colocasia esculenta). Shading decreased stomatal density in the lower epidermis of tannia, sweet potato, yam and cassava, and in the upper epidermis also in tannia and sweet potato; the upper epidermis of yam and cassava were devoid of stomata. In contrast to the other species, taro under shade had an increased stomatal density in both the upper and lower epidermis, a finding which was confirmed in subsequent pot experiments. This response of taro was postulated as a possible manifestation of greater shade adaptation by the species.

For all the species, shading generally resulted in the production of larger (in terms of surface area) but thinner leaves, with a decreased dry matter concentration. For the two species (yam and cassava) that had stomata only on the lower epidermis, normal sun-grown plants had about twice as many stomata per unit area of lower epidermis than did corresponding plants of the other three species. The agronomic and physiological significance of the findings are discussed.

Two groundnut varieties, the small-seeded, early-maturing Natal Common and the large-seeded, late maturing ‘pops’-susceptible Makulu Red, were cultivated in nutrient solution, Application of calcium, labelled with 45Ca, to the roots and the fruit-medium respectively, showed that both varieties absorbed most of their seed-Ca from the fruit-medium. The translocation of calcium from the shells to the nuts was greater in the small-seeded variety Natal Common, which showed less susceptibility to ‘pops’. Calcium absorbed by pods and gynophores also migrated to a certain extent into the vegetative parts.

Most farming systems in semi-arid West Africa rely on organic matter recycling for maintaining soil fertility. The cycling of biomass through ruminant livestock into dung (faeces) and urine that fertilize the soil has long been an important factor in t he nutrient cycling processes of these integrated, mixed crop/livestock systems. While dung greatly improves soil properties and crop yields, little is known about the effects of urine on soil chemical properties and the impact of dung and urine on crop p roduction. An average voiding of sheep urine applied to a sandy, siliceous soil in the Republic of Niger increased soil pH, available phosphorus and ammonium levels dramatically in the upper 10–15 cm of soil, especially during the first week following application. Losses of applied urine nitrogen via volatilization were in the order of 30–50%. A four-year field trial was conducted on the same soil type to evaluate the effects on pearl millet and weed yields of corralling cattle o r sheep overnight on cropland (dung plus urine application) for one, two or three nights, every one, two or three years versus the effects of applying only dung at the same application rates and intervals achieved with corralling. The main results of this field trial were that (1) urine had large positive effects on millet grain, threshed panicle, leaf, stem and weed yields, (2) sheep dung was more effective than cattle dung in increasing yield, (3) two nights of dung application was adequate for maximum yield and (4) the positive effects of dung and urine on yield lasted two to three cropping seasons after application.

Weeds are major constraints to wider adoption of wet seeded rice. Two split-plot experiments on water management during crop establishment of wet seeded rice were conducted in the dry and wet seasons of 1994 to quantify crop stand establishment and weed suppression by herbicides and rice genotypes. The latter consisted of five previously identified hypoxic-tolerant lines and three standard cultivars, sown at approximately 300 seeds m−2. The tested hypoxic-tolerant genotypes had superior seedling growth, but not higher crop stand establishment than the standard ones. Genotypes that had superior crop stand establishment or faster seedling growth did not necessarily give better weed suppression. Genotypes with high tillering ability were more competitive against weeds. Echinochloa glabrescens dominated the weed flora, especially in farmers' practice and anaerobic seeding (seeding into soft mud), followed by flooding at 7 d after seeding (DAS). The relative proportion of Monochoria vaginalis increased in anaerobic seeding with flooding 3 DAS and seeding into standing water. Pretilachlor + fenclorim effectively controlled weeds in farmers' practice and anaerobic seedings, and 2,4-D in water seeding. Without herbicide, water seeding and anaerobic seeding flooded 3 DAS reduced dry weed weight by 73–88% compared with farmers' practice. Anaerobic seeding with flooding 7 DAS controlled weeds effectively when the weed pressure was low (dry season, about 136 g m−2 of weed biomass in plots without herbicide) but not when weed pressure was high (wet season, 513 g m−2). Water seeding could not sustain high rice yields due to low crop stand population caused by flotation of seedlings. Anaerobic seeding with flooding 3 DAS allowed genotypes to sustain high yield and increased water productivity (rice production per unit volume of water used in the field) without having to use herbicide or with only half of the recommended herbicide rate. The correct water management during the crop establishment stage may effectively lower the economic and possible runoff costs of herbicides without reduction in yield or water productivity.

Rainfed agriculture in sub-Saharan Africa (SSA) is the mainstay of the continent's food and feed production. Nearly 90% of staple food and feed production comes from, and will continue to come from, rainfed agriculture (Rosegrant et al., 2002). In spite of this, investment in this vital production system, and hence its productivity, has stagnated. There are many complex and interrelated issues that contribute to this state of affairs. The outcomes of lack of investment and low production of rainfed agriculture reinforce each other leading to poverty traps and increased vulnerability of livelihoods to climatic and other shocks (World Bank, 2000). This has become well recognized and an emerging political will, both within and outside SSA, to support increased investment in rainfed agriculture appears to be gaining momentum (Sanchez et al, 2009).

The use in analysis of variance of six different ways of calculating the Land Equivalent Ratio (LER) was assessed. Criteria used are (1) normality of the residuals of LER values after fitting block and treatment effects, (2) precision of comparisons arising from the analysis of variance, and (3) possible bias in the means. These were examined in detail for data from one experiment and consistency of the results was investigated for seven other sets of data. Separate standardization in each block had no advantages over using the same standardization in all blocks. The use of many different divisors can lead to problems in the statistical analysis of LERs.

The tubers of yam, principally those of Dioscorea rotundata (white Guinea yam) and D. alata (water or greater yam), are important staple foods and sources of carbohydrate in West Africa. Yams are grown in diverse environments – from the high-rainfall forest zone on the coast to the seasonally arid savannas of West Africa, that is in situations in which the duration and the timing of the onset of the growing season vary appreciably. Dormancy in both underground and aerial tubers of the Dioscoreaceae is an important adaptive mechanism that helps to maintain organoleptic quality during storage and also ensures that tubers germinate at the start of the growing season. Plant breeders are especially keen to manipulate the duration of the dormant period in order to synchronize growth periods and, therefore, to produce more than one generation per year. The control of tuber dormancy, however, is poorly understood. This review examines critically those factors that affect tuber initiation, dormancy and sprouting, and makes recommendations for future priorities in research.

Pearl millet (Pennisetum glaucum L.) is an important grain crop for millions of poor farmers and consumers in the semi-arid region of West Africa. During the past 40 years, much research on pearl millet production practices and adoption in this region has been conducted, but an attempt to summarize these results has not been previously completed and these research results are not readily available to many West African scientists. This review was completed to address this need and integrate knowledge, and at the same time identify research needs for the future and extension priorities for semi-arid West African agro-ecological zones. Research has shown that selection of improved varieties and cropping systems, appropriate cultural practices, and recommended integrated soil, nutrient, residue and pest management can greatly increase grain and stover yields of pearl millet. However, adoption by farmers has been minimal due to limited profitability, high risk and labour demand, limited input supply, market availability and appropriate public policy. This review has 196 articles included as in-text citations (Table 1) compared to 149 articles in the reference list, indicating that only one in four articles integrated two or more topics in the research. The obvious conclusion is that most of the past research has not addressed the ‘system’ but rather one or two management practices. In addition, most studies have interpreted responses in terms of yield without addressing other important considerations for farmer adoption. Recent conservation agriculture research moves closer to addressing the larger integrative types of research needed. Such research is complex and requires sustained funding for field and laboratory activities, but also for computer simulation modelling and economic assessment.

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.

A modified technique for measurement of nitrogen fixation by blue green algae and Azolla sp. using intact, moist soil cores was developed for use in field studies in which chemical fertilizers, blue green algae and Azolla biofertilizers had been used in association with a rice crop. This method involves collection of fresh and moist soil cores (0–30 mm) using a soil auger, incubation with 10% acetylene in airtight glass vials under field conditions for three hours, and measurement of the ethylene produced using a gas chromatograph. Experiments carried out over a period of three consecutive years revealed that the estimates of nitrogen fixation were comparable with data of other researchers obtained through the use of soil water columns, sophisticated chambers and automated sampling devices. This simplified technique, therefore, can provide rapid and reliable measurements of nitrogen fixation in field experiments.

In experiments with transplanted rice, the first row next to the unplanted alley consistently gave significantly higher grain yields than the centre rows. The increase was progressively higher as the width of the unplanted alley between plots was increased up to 100 cm., but where the increase was very large, yields of the second outermost row were significantly decreased. No evidence was found that border effects reach beyond the second outermost row. Varieties that differed in tillering capacity, plant height, or both responded differently to the unplanted borders.

The effects of three shade densities, NPK fertilizers and fertilizer-pest/disease relationship on Amazon cocoa (Theobroma cacao L.) over a 20-year period are reported. Yields equivalent to the mean yield from the unfertilized plots were achieved in about 3, 4 and 6 years in fertilized plots under the no shade (S0), medium shade (S1) and heavy shade (S2) treatments, respectively. There were three growth phases, each characterized by a different yield trend. No appreciable changes in the exchangeable Ca and Mg were observed during the experiments, but K dropped to 68% of its initial value while the available P of the unfertilized and the S0 plots fell by 38%. Fertilizer recommendations for P and K should take account of overhead shade. The effect of N application was often negative. No direct relationship was observed between fertilizer treatment and the incidence of pest/blackpod/swollen shoot virus (SSV) disease of cocoa. SSV infection was greatest under S0. Cocoa farms in Ghana cannot maintain high yields (above 1000 kg dry cocoa ha−1) beyond 15 years of intensive cropping.

Participatory varietal selection in a development project in western India showed that the rice (Oryza sativa) variety Kalinga III was highly preferred by farmers. The spatial diffusion of this variety from three villages (two project and one non-project) was studied. Seed of Kalinga III had spread from the three villages in 1994 to 41 villages by 1996 and is estimated to have reached over 100 widely distributed villages by 1997. Farmer-to-farmer spread was as high from the non-project case study village that received no further seed from the project, possibly because farmers are more likely to spread seed of a new variety to other farmers when they have no assured supply. Project interventions used key villages, informal-sector seed merchants, and Non-Government Organizations in the spread of seed. The project also collaborated with Rajasthan State Agricultural University and Kalinga III has been proposed for release in that state. A financial analysis revealed the very high internal rates of return that are possible from investment in participatory varietal selection.

A computer crop simulation model of the growth and development of maize was validated using data sets obtained from field experiments run at various sites in the mid-altitude maize zone of central Malawi between 1989 and 1992. The model was used to provide information concerning management options such as the timing and quantity of nitrogen fertilizer applications and to quantify the weather-related risks of maize production in the region. It was linked to a Geographic Information System to provide information at a regional level that could ultimately be of value to policy makers and research and extension personnel.

Continuous rice–wheat (RW) cropping with intensive tillage has resulted in land degradation and inefficient use of water in Indo-Gangetic Plains (IGP) of South Asia. Replacement of rice with less water requiring crops such as soybean in RW system and identification of effective strategies for tillage management could result in sustainable cropping system in IGP. A field experiment was conducted for five years on an annual soybean–wheat (SW) rotation in the northwest IGP of India to evaluate effect of tillage, raised bed planting and straw mulch on yield, soil properties, water use efficiency (WUE) and profitability. In soybean, straw mulch reduced soil temperature at seeding depth by about 2.5 °C compared with no mulch. Straw mulch also resulted in slightly reduced water use and slightly higher WUE relative to their respective unmulched treatments. During wheat emergence, raised beds resulted in higher soil temperature by 1.6 °C compared with flat treatments. Bulk density and cumulative infiltration were greater in no-tillage compared with conventional tillage. Soil organic carbon in surface layer increased significantly after five years of experimentation. Soybean and wheat yields were similar under different treatments during all the years of experimentation. Soybean and wheat planted on raised beds recorded about 17% and 23% higher WUE, respectively, than in flat layout. The net returns from SW system were greater in no-tillage and permanent raised beds than with conventional tillage. Both no-tillage and permanent raised bed technologies can be adopted for sustainable crop production in SW rotation in northwest IGP. However, more studies are required representing different soil types and climate conditions for making recommendations for other regions of IGP.

We analyse the adoption of an Integrated Food-Energy System (IFES) in southern Malawi. The IFES combined the improved cookstove (chitetezo mbaula in Chichewa), designed to reduce demand for fuelwood, with the pigeonpea variety Mthawajuni, which increased both food supply and supply of fuelwood from pigeonpea stems. Adoption of the improved cookstove was found to be higher among households that were better off and where women had greater control over decision-making. However, adoption of the IFES was not associated with reduced demand for fuelwood from forests and hills or reduced frequency of collection. IFES adopters might have high fuelwood consumption because they were better off, but fuelwood consumption in better-off households did not differ significantly between IFES adopters and non-adopters. Pigeonpea increased food supply for adopter households, including children aged less than five years. Consequently, the IFES has had mixed results, improving food supply but not reducing demand for fuelwood. Households ranked early maturity, fuelwood and yield as the three most important reasons for preferring Mthawajuni over other varieties of pigeonpea. The plant breeding programme for pigeonpea in Malawi should evaluate improved varieties not only for earliness and grain yield but also for the production of fuelwood. Improved varieties with desirable market traits have had limited success in the absence of reliable markets and price incentives.