Use of biochar (B) and poultry manure (PM) as soil amendments can improve the productivity and sustainability of tropical agriculture. Our fieldwork is the first research on the agronomic use of B and PM for the growth of cocoyam in sandy soil of the humid tropics. In this study, the effects of B, PM and their mixture were investigated on soil properties, mineral and nutrient concentrations, growth, and corm and cormel yields of cocoyam during the 2017 and 2018 cropping seasons. The experiment consisted of 4 × 2 factorial combinations of B (0, 10, 20, and 30 Mg ha−1) and PM (0 and 7.5 Mg ha−1). In both years, the application of B and PM either alone or in combination improved soil physical and chemical properties, plant nutritional status, growth, and corm and cormel yields of cocoyam. The combination of 30 Mg ha−1 B and 7.5 Mg ha−1 PM (B30 + PM7.5) gave the highest corm and cormel yields of cocoyam. Pooled over the 2 years, application of B at 30 Mg ha−1 and PM at 7.5 Mg ha−1 (B30 + PM7.5) significantly increased corm yield of cocoyam by 47 and 66%, respectively, when compared with sole PM at 7.5 Mg ha−1 and B at 30 Mg ha−1. Lowest corm and cormel yields were obtained for the unmanure control. The combination of 30 Mg ha−1 B and 7.5 Mg ha−1 PM is recommended for soil fertility management and cocoyam production in the rainforest agroecology of SW Nigeria.

Land Equivalent Ratio (LER) and cowpea growth attributes were used to evaluate three different maize cultivars for intercropping with cowpea, a low canopy crop. The relatively short maize cultivar (Kewesoke) with erect upper leaves transmitted the most light to cowpeas, followed by a liguleless erect-leaf type and then a floppy-leaf type. The more the transmitted light, the greater were the growth and yields of associated cowpeas.

Due to escalating costs of imported fertilizers, there is renewed interest in the use of local nutrient resources in managing soil fertility in Kenya. We tested the effect of two organic materials, farmyard manure (FYM) and Tithonia diversifolia (tithonia), and an inorganic N fertilizer, urea, when applied alone or in combination with three inorganic P sources, triple superphosphate (TSP), Minjingu phosphate rock (MPR) and Busumbu phosphate rock (BPR), on maize yields and financial benefits. The study was conducted for three consecutive seasons, from March 2007 to August 2008 in western Kenya. FYM and tithonia were applied to supply 20 kg P ha−1 in treatments where they were used either alone or in combination with the inorganic P sources while 40 kg P ha−1 was from the inorganic P sources in the combination. Where urea was used, the inorganic P sources were applied at 60 kg P ha−1. When applied in combination with urea, MPR was a better P source for maize than TSP or BPR. However, when applied in combination with FYM or tithonia, TSP was the best P source. Treatments including tithonia were more effective in increasing maize yields than those without it with a similar total P application rate. The agronomic effectiveness of tithonia did not, however, translate to economic attractiveness, mainly due to very high labour costs associated with its use. FYM when applied alone at 20 kg P ha−1 was the only treatment that exceeded a benefit:cost ratio of 2 and, therefore, the most likely, of the tested technologies to be adopted by farmers.

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.

Yields of rainfed barley (Hordeum vulgare) for feed and forage in small-ruminant production systems in low-rainfall areas of North Africa and West Asia are limited by low and erratic water availability. Therefore, the testing of conservation farming techniques, effective in dryland systems elsewhere, is often suggested. Seven-year results from a typical site in northern Syria showed that zero-till (direct-drill) systems with cereal residue retention may marginally enhance soil moisture status, but the yield effect on barley, either monocropped or rotated with vetch (Vicia sativa), was small and non-significant. In the vetch–barley rotation, a small and fairly consistent benefit to vetch was observed, amounting to a 20% yield increase in vetch hay. Given smallholders' strong preference for barley and reluctance to grow vetch as an alternate crop, there is little in this result to encourage the promotion of zero-till conservation techniques in these farming systems.

Root rots are one of the main biotic constraints to common bean (Phaseolus vulgaris L.) production, causing losses estimated at 221 000 metric tons a year in sub-Saharan Africa. Until recently, root rots in Ugandan common bean agroecologies were mostly caused by Pythium and Fusarium spp., especially in high altitude areas. But now, severe root rots are observed in low and medium altitude agroecologies characterized by dry and warm conditions. The objective of our study was therefore to ascertain the current prevalence and incidence of common bean root rot diseases in Ugandan common bean agroecologies. Our results show that root rots were present in all seven agroecologies surveyed. Overall, the most rampant root rot was southern blight caused by Sclerotium rolfsii Sacc., followed by root rots caused by Fusarium spp., Pythium spp. and Rhizoctonia solani, respectively. Our study clearly showed the influence of environmental conditions on the prevalence and incidence of common bean root rots. While Fusarium and Pythium root rots are favoured under low air temperature and high air humidity in highland areas, high incidence of southern blight is favoured by warm and moist conditions of lowland areas. The prevalence and incidence of common bean root rots was mapped, providing a reliable baseline for future studies. Similarly, hotspots identified for common bean root rots will be a very useful resource for evaluation of germplasm and breeding lines for resistance to root rots.

Farmers in the southern Kilimanjaro region of Tanzania have a strong preference for maize as their staple crop and have resisted attempts to introduce sorghum as an alternative in spite of the high drought risk associated with maize production. This paper presents the results of a seven-year period of field experiments to assess the benefits of a modified cropping system for maize, which aims to reduce drought risk through rainwater harvesting. In-situ, microcatchment and macrocatchment rainwater harvesting systems were tested against the local practice of flat cultivation as control. All were managed according to local extension recommendations, and the benefits were measured in terms of grain yield. In-situ rainwater harvesting provided no benefit. Microcatchment rainwater harvesting resulted in increased yield per unit area cultivated. On a total system area basis (i.e. including the uncropped catchment), however, production decreases were observed. A cost-benefit analysis, however, does show a benefit in the short rainy season. Macrocatchment rainwater harvesting provided increases in grain yield in both the short and the long rainy seasons.

Yields of sweet potato tips varied from 10 to 16 t/ha in weight and 61 to 352/m2 in number, whilst yields of marketable roots varied from 1 to 16 t/ha. Cultivar differences in dry matter, fibre, ash, vitamin B2 and oxalate were also observed. The tips appeared to provide an excellent source of vitamin B2 which is important for Asian diets deficient in this vitamin. Application of 120 kg N/ha gave higher tip yields than no nitrogen, primarily due to increases in their number and size. Among the leaf types evaluated, Kinangkong (a fine leaf cultivar) produced the highest yield, and had the highest amount of protein, lowest oxalate, and fairly high dry matter, which makes it a very desirable leafy vegetable.

Microcomputer-based simulation models are increasingly being recommended as multipurpose tools for agricultural research. Use of a model should be conditioned by an evaluation of its performance and understanding of its limitations. This paper evaluates the responses of the process-oriented growth model for dry bean (Phaseolus vulgaris), BEANGRO V1.01, with an emphasis on the factors related to cultivar differences for production in tropical environments. Simulations of seed yield from beans grown under conditions of a known water deficit showed good agreement with observed data. The qualitative response to plant population resembled that of a field trial, and the model showed the expected linear relation between days to maturity and seed yield. Overall, the results suggest that BEANGRO has utility for certain types of agronomic studies, but that improvements are possible, particularly with respect to prediction of phenology.

Since the Green Revolution, the public-sector's agricultural research strategy for increasing food crop productivity has been explicitly based on the premise that technology can cross political and agro-climatic boundaries, primarily through the ‘training and visit’ system of extension (also known as ‘transfer of technology’ and the ‘pipeline’ model). Today, a different strategy is emerging. Efforts to develop the necessary institutional capacity for more client-oriented participatory research, particularly in plant breeding, are now a central part of the public-sector agricultural research strategy. Greater use of participatory and gender-analysis approaches in agricultural research has significant conceptual and methodological implications for impact assessment and institutional learning.

The first ever on-farm soil fertility research in the rainfed lowland rice (Oryza sativa) fields of Sukumaland, in northwest Tanzania, was carried out between 1990 and 1996 in response to farmers' complaints about declining rice yields. From diagnosis to extension, the research approach followed that of the International Maize and Wheat Improvement Center (CIMMYT). In 1990/91, rice yields in the Maswa district increased sharply when nitrogen at a rate of 30 kg ha−1 in the form of urea was broadcast in flooded rice fields at tillering. Similar research was subsequently conducted in other parts of Sukumaland to evaluate this type of low-dose nitrogen application under varying circumstances. In 1995/96, higher doses of nitrogen (60 and 120 kg ha−1) and a high dose of phosphorus (17.5 kg ha−1) were applied for comparison in Sengerema district. Between 1990 and 1996, the average increase in rice yield from the application of 30 kg N ha−1 varied between 463 and 986 kg ha−1. In 1995/96, the same application of N was more economical than both 60 and 120 kg N ha−1, and no phosphorus deficiency was found. The deteriorating ratio between the price of rice at the farm gate and that of urea, however, threatens the adoption of this technology by farmers. Adaptability analysis showed that the relatively small differences in response per field (environment) in all years did not justify a need for multiple different extension messages. Until more detailed recommendations can be made, therefore, a single dose of 30 kg N ha−1, in the form of urea, applied to rice at tillering is recommended for the whole of Sukumaland to reverse the decline in yields. Further on-farm research should concentrate on improving the efficiency of nitrogen fertilization and on determining the optimum rates of other major nutrients to refine this initial recommendation.

Considerable variation in seedling vigour was observed among 36 maize populations; genotypic variances were generally high for emergence percentage (E%), emergence index (EI), dry-matter accumulation and relative growth rate (RGR). Broadsense heritability values and environmental variances indicated that E% and EI would be more reliable indices for seedling vigour than emergence rate index (ERI). The expression of growth rate (GR) was influenced more by the environment than the genetic constitution of seedlings; GR was not therefore an effective indicator for seedling vigour, and RGR would be preferred because it was more heritable and less influenced by the environment.

Erosion changes soil properties, removes nutrients and alters crop yields. A knowledge of these impacts on soil productivity is needed for economic analyses of erosion and conservation. Based on a United Nations Food and Agriculture Organization experimental design to monitor these changes, results are reported from four research sites in southern Brazil on Ferralsols and Cambisols, enabling the construction of erosion–yield–time and nutrient loss relationships. Plot experiments ran for up to seven years of natural erosion, followed by one or two years of maize cropping. A remarkably consistent composite erosion–yield relationship in logarithmic form was found, showing a sharp yield decline with initial soil loss. Soil ‘resilience’ was identified through erosion–time relationships, ‘sensitivity’ through erosion–yield equations. As erosion progressed, losses of nutrients, especially of organic carbon and calcium, were significant. In situ changes in soil properties were far less marked. Together with measured yield reductions caused by cumulative erosion, these results enabled the modelling of changes in soil productivity over time with respect to both soil quality and impact on yields. A production ‘half-life’ of between one and 39 years according to soil type and level of erosion was also identified.

Several methods of measuring and estimating the available-water capacity of soils with varying degrees of accuracy are described. The errors associated with the use of the different techniques on a wide range of soils have been calculated and suggestions are made regarding the choice of method for particular circumstances.

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

Three cultivars of Coffea arabica, Catuaí Vermelho IAC 81, Icatu Amarelo IAC 2944 and Obatã IAC 1669–20, were evaluated in relation to leaf gas exchange and potential photochemical efficiency of photosystem II under field conditions on clear and cloudy days in the wet season in southeast Brazil. Independent of levels of irradiance, leaf water potential (υleaf) values were always higher than the minimum required to affect daily net photosynthesis (PN). PN, stomatal conductance (gs), leaf transpiration (E) and the index of photochemical efficiency (Fv/Fm) declined on a clear day in all cultivars. The depression of leaf gas exchange and Fv/Fm (specially around midday) caused a strong decrease (about 70 %) in daily carbon gain on a clear day. Under cloudless conditions, gs and PN were correlated with the air vapour pressure deficit (VPDair), but not with photosynthetic photon flux density (PPFD) values. On a cloudy day, the daily carbon gain was barely limited by PPFD below 800 μmol m−2 s−1, the Fv/Fm values showed a slight decrease around midday, and gs and PN were positively correlated with PPFD but not with VPDair. By contrast, irrespective of the contrasting irradiance conditions during the day, PN and E were correlated with gs.

The results of two tea irrigation experiments conducted independently in southern Tanzania and Malawi, where severe annual droughts of similar duration occur, were compared. There were marked differences in the dry season yield distributions between the two sites. These could be attributed to the adverse effects of large saturation deficits on plant water status and rates of shoot extension in Malawi. The implications for tea irrigation in particular and for irrigation agronomy experiments in general are discussed. The need to include detailed descriptions of the environment in which experiments are conducted is stressed.

A reconnaissance survey and participatory varietal selection trials (PVS) were conducted in four major pearl millet-growing countries of the Sahel between 2001 and 2003. The studies aimed to identify farmers' preferences in improved pearl millet varieties, increase awareness, test new varieties and enhance farmers' access to the improved varieties. Farmers selected five out of 10 tested varieties, with preferred characteristics, namely, maturity cycles of 80–90 d in the Sahel and 90–100 d in the Sudanian agro-ecozones, acceptable grain yield, compact and long (30–100 cm) panicles, a large number of tillers with panicles, adaptation and an acceptable taste. Farmers indicated that their local varieties were of superior adaptation and taste. They mentioned that hindrances to uptake and sustained use of improved varieties were due to lack of awareness, traditional values, seed unavailability, early maturity, bird damage and lack of fertilizer. The strong genotype × environment interactions in the Sahel suggests that breeding should be directed towards producing varieties adapted to specific zones rather than for wide adaptation. Notably, since farmers often cultivate pearl millet without any soil amendments, it may be advisable to disseminate varieties as a package (with fertilizer and agronomic instructions) rather than as varieties alone in a PVS programme, in order to achieve the full potential of improved varieties. The PVS trials are synergistic to plant breeding in identifying varieties suitable for harsh environments, which are difficult to duplicate in the research station. However, in the absence of formal distribution seed systems in the trial countries, village- or community-based seed production of varieties selected by farmers appears critical to the sustainable adoption of selected varieties.

The north eastern region (NER) of India receives a high amount of rainfall (2450 mm) both in terms of intensity and frequency. Most of the precipitation goes waste because of improper conservation measures and inadequate rainwater harvesting. Growing a second crop during winter (rabi) season on hill slopes and uplands without moisture conservation measure is almost impossible. A simple and very low-cost technique of in situ soil moisture conservation in maize (Zea mays L.)–toria (Brassica campestris L.) system has been developed using residue of preceding rainy season maize crop and mulching with locally available weed biomass Ambrosia artemisiifolia. Six residue mulching combinations tested were viz. control, Maize stalk cover (MSC), MSC + Ambrosia sp. 5 t/ha, MSC + Ambrosia sp. 10 t/ha, MSC + farmyard manure (FYM) 10 t/ha and MSC + Ambrosia sp. 5 t/ha + poultry manure 5 t/ha under zero tillage (ZT) and conventional tillage (CT) systems. Results showed that in situ residue retention of preceding maize crop along with green biomass of Ambrosia sp., applied before sowing of toria, maintained optimum soil moisture for good growth and higher yield of toria. The soil moisture content was consistently higher under residue mulched plots than that under control. All the residue mulching measures recorded higher crop yield for maize and toria than those observed under residue removal (control). The productivity of toria was enhanced by about 99%, only due to retention of MSC as mulch. Mulching with MSC + Ambrosia sp. 5 t/ha + poultry manure 5 t/ha recorded the highest seed yield of toria (four-year average: 641 kg/ha), which was 228% and 64% higher than no mulching (control) and MSC alone. MSC + FYM 10 t/ha (568.3 t/ha) and MSC + Ambrosia sp. 10 t/ha (517.4 t/ha) were found equally effective and produced significantly higher toria yield than that of control. MSC + Ambrosia mulch 10 t/ha gave the highest net returns and B:C ratio of the maize–toria system. The overall B:C ratios were better under ZT than CT. Thus, the study indicated that the integrated management of crop residues and weed biomass (Ambrosia sp.) under ZT created favourable soil moisture to support double cropping with high yield in hill eco-system of northeastern Indian Himalayas.

Yield and growth records from an oil palm planting density experiment, comparing 56, 110, 148 and 186 palms ha−1, and a progeny experiment, planted at 115 and 143 palms ha−1, were used to estimate the partitioning of assimilates into those used for structural dry matter (DM) production, and those used for growth and maintenance respiration.

Gross photosynthetic assimilation (A) for closed canopies was estimated from absorbed photosynthetically active radiation (PAR), derived from actual sunshine hours, and the assimilation-light response curve, to be 128 t CH2O ha−1 year−1. A for non-closed canopies was calculated by correcting for the degree of light transmission, which in turn was estimated from recorded leaf area index values (L), i.e. the total leaf area per unit ground area.

Forty-eight percent of gross assimilation was used for DM production, about half of this being lost in growth respiration. The remaining 52% was lost in maintenance respiration. These losses appeared to level off before crown expansion was completed, and since trunk biomass continued to increase, maintenance respiration per unit biomass (R) decreased with age.

An increase in planting density reduced the assimilates available for bunch DM, had little effect on those for vegetative growth, but strongly reduced maintenance respiration and, since biomass was little affected, reduced R. Assimilates for bunch DM ha−1 reached a maximum at L = 5.6.

The observed trends in R as a function of palm age and planting density merit further study.