The influence of air temperature (T), vapour pressure deficit (vpd), irradiance (Q) and leaf water potential (ψ) on diurnal stomatal movement of coffee plants was examined under field and controlled environmental conditions. Leaves of plants grown under shade had larger stomatal conductance (g) values than plants grown in open sun. Stomatal responses to vpd under constant temperature conditions were very strong, indicating that ambient humidity could play a major role in controlling stomatal aperture. Changes in g as vpd increased probably contributed to observed reductions in the rate of net photosynthesis (Pn), though the effect of vpd on Pn was smaller.

Thirty-two Prosopis accessions were studied and biomass production (dry matter) determined for 27 of them, which were irrigated when the soil moisture tension reached 60, 200, or 500 kPa. Three seasons after transplanting (i.e. after 2½ years) the trees were harvested, weighed, and sub-sampled for moisture content determinations. Little difference was observed in productivity among irrigation treatments. A 20-fold range in biomass productivity occurred among accessions; Prosopis chilensis (0009) from Argentina gave the greatest production of 13.4 t ha−1 a−1. The water use efficiency of US rangeland accessions ranged from 2300–2600 kg H2O kg dry matter−1. P. chilensis (0009) in the driest irrigation treatment had a water use efficiency of 345 kg H2O kg dry matter−1.

The variety Nigerian Synthetic-5 was sown on eight occasions, five in the first season and three in the second, at approximately 15-day intervals from 15 April to 15 June, and on 20 August, 4 September and 23 September. The method of seed bed preparation and time of planting both affected yields, effects that could be related to soil temperature and soil moisture reserve during crop development. Maize planted in August produced the highest yield; heaps and ridges gave the lowest yield at all planting dates, while planting on the flat or in furrows produced the highest yield.

Conservation agriculture (CA) was introduced to farmers in Malawi to address soil degradation, declining crop productivity and the need to adapt to climate variability and change. This research from 2005 to 2014 aimed at analysing the effects of CA on longer-term productivity and profitability compared with conventional systems as practiced in two communities of Central Malawi. CA treatments outyielded conventional ridge tilled control plots in Mwansambo and Zidyana on average by between 22 and 31%, respectively. An economic analysis from 2011 to 2014 found that, on average, income was 50 and 83% greater in CA systems than in conventional systems. The crops were produced with 28 -39 less labour days ha−1 compared with the conventional practice, leading to greater net benefits. Despite the higher returns with CA, there are still challenges with residue retention, weed control, adequate rotations, management of pests and diseases as well as other socio-economic constraints. At the same time, there are opportunities to address these challenges through site-specific and adaptive research using innovation systems approaches.

The growth of two varieties of white yam was analysed from planting in December to harvest in September. Four stages were recognized, viz.: dormancy, rapid growth of vine and root, rapid tuber development accompanied by leaf senescence and tuber maturity followed by reduction in tuber weight. The period of rapid growth coincident with maximum demand for nutrients was early June, suggesting that fertilizer should be applied in mid-May so that it is available in June.

Shoot extension rates and numbers recorded over an 18 month period in Tanzania from three contrasting clones were analysed to determine variation between and within seasons. Clonal differences in base temperatures for shoot extension ranged from 10.3 to 14.5°C, whilst variability in the response of shoot growth rates to temperature could be ascribed to the shoot selection technique employed. Considerable clonal variation in shoot population densities occurred, with maxima ranging from 200 to 1200 shoots m−2. Total active shoot extension, the product of shoot growth rates and population densities, varied between 4 and 35 m m−2 week−1, shoot numbers being the dominant component. The implications of these results are discussed in terms of shoot measurement techniques, clonal selection criteria, yield modelling and harvesting policies.

An experiment at the Kabete Field Station of the University of Nairobi compared maize–bean mixtures with pure stands of the two crops at three plant densities. Although the mixtures gave an apparent yield advantage over pure stands, this could be explained solely by the increased population pressure in the mixtures. The implication of this finding for other published work with cereal–legume mixtures is discussed, and a distinction is drawn between those sites in East Africa where a conclusive yield advantage from mixed cropping has been found and those where any apparent advantage might be explained by the higher population pressure.

The present study documents critical analysis of drought-induced physiological responses in mulberry (Morus spp.) with insights into growth dynamics and leaf productivity. The study was performed for two years in a two-phase experimental design combining both field (experiment no. 1) and glasshouse (experiment no. 2) observations. In field assays, we surveyed 15 mulberry genotypes under two irrigation regimes: well-watered (20 to 24 irrigations in each growing season) and water-limited (irrigated once in a fortnight in each growing season). The genotypes were assessed for variation in key leaf gas exchange characteristics: net photosynthetic rates (Pn), stomatal conductance of CO2 (gs), transpiration rates (E) and instantaneous water use efficiency (WUEi). Leaf yield/plant was considered to determine the tolerance index (TI). Drought stress severely down-regulated leaf-level physiological variables in the susceptible genotypes resulting in poor leaf yield. However, genotypes S-13 and V-1 performed better in terms of leaf gas exchange and proved their superiority over other genotypes in drought tolerance. Conversely, genotypes DD and Bogurai were highly susceptible to drought. Under glasshouse conditions, the combined leaf gas exchange/chlorophyll a fluorescence measurements further dissected out stomatal and non-stomatal restrictions to Pn. As internal/ambient CO2 ratio (Ci/Ca) decreased concurrently with gs in non-irrigated stands, it appeared that greater stomatal limitation to Pn was associated with decreased photo-assimilation and leaf yield production. Further, higher leaf temperature (TL) (>35 °C) and down-regulation of maximum quantum yield of photosystem II (Fv/Fm) were apparent in the susceptible compared to the tolerant genotypes, which indicated chronic photoinhibition due to photo-inactivation of photosystem II centres in the susceptible genotypes. Drought-induced trade-offs in biomass allocation were also highlighted. Overall, our results suggest that greater rooting vigour and leaf hydration status, minimal stomatal inhibition and stabilized photochemistry might play major roles in maintaining higher Pn and associated gas exchange functions in drought-tolerant mulberry genotypes under water stress conditions. The higher leaf yield production in tolerant than susceptible genotypes can be attributed to minimal plasticity in foliar gas exchange traits and better quantitative growth characteristics under low water regimes.

Pearl millet (Pennisetum typhoides) was grown on stored water at Niamey, Niger, using three row spacings (38, 75 and 150 cm), to determine the physiological basis of exploitation and conservation of water by crops during drought Between 18 and 32 days after sowing, roots grew rapidly beneath all crops reaching 140 cm in the narrow spacing, but there were differences between crops in the pattern of growth. Soil cores and trench profiles indicated that plants in wider rows had fewer, deeper roots. Substantial differences in both the amount and pattern of shoot growth were recorded in the different populations. Initially growth was fastest at the narrow spacing but stopped by day 45 and eventually the wide spacing produced most dry matter due mainly to greater survival of tillers. The partitioning of above ground dry matter into vegetative and reproductive fractions was similar at all three spacings and was consistent with figures for comparable crops elsewhere. The important role of tillers is discussed in relation to the development and maintenance of a canopy.

Maize was grown for three years at three levels of nitrogen, 56, 112 and 224 kg. N ha.−1, involving altogether nine different timing and splitting treatments. Measurements were made of grain yield, plant nitrogen status and total-N-uptake, and, in one year, movement of nitrate-N in control plot soils. Where only 56 kg. N ha.−1 was applied, its time of application made very little difference to yield; at higher rates of nitrogen an unsplit application as late as seven weeks was very inefficient, but only at the highest rate did a split application give any appreciable yield increase over an unsplit application to the seed bed. Consideration of the soil nitrate-N data and the long-term pattern of rainfall distribution leads to the conclusion that leaching is unlikely to be a serious problem in the nitrogen nutrition of early-planted maize.

Plants of yam, taro, tannia, cassava and sweet potato were raised under shade or in full sunlight and the effect of shade on leaf chlorophyll and carotenoids was examined to determine and compare the relative shade tolerance and adaptability of the var ious species. All five species of root crops adapted to shade. The chlorophyll concentration was higher, while the chlorophyll a:b ratio, carotenoids per unit chlorophyll and the weight per unit area of leaf were lower in the shade than in the su n in yam, tannia, taro, cassava and sweet potato. All species had larger leaves and more chlorophyll per leaf in the shade. The extent of the changes, however, differed between species. The aroids (taro and tannia) appeared to be shade-tolerant species as their chlorophyll a:b ratios changed less than those of the other species in the shade, suggesting that their light-harvesting systems may be normally adapted to shade conditions. Taro and tannia also adapted to shade by a greater proportional i ncrease in leaf size, a smaller reduction in leaf weight per unit area and a greater proportional increase in chlorophyll and carotenoids per leaf than the other species. Yam compensated for shade by having a large proportional increase in leaf size and a ppeared to be moderately tolerant of shade. Sweet potato and cassava appeared to be the least tolerant of shade of the major tropical root crops.

At various locations in North Ethiopia (Tigray), field experiments were conducted from 2006 to 2009 to assess the crop response to water stress of tef (Eragrostis tef (Zucc.) Trotter) under rainfed, fully irrigated and deficit irrigation conditions. Observed soil water content (SWC), canopy cover (CC), biomass production (B) and final grain yield (Y) were used to calibrate and validate AquaCrop for tef. Data from an experiment in a controlled environment in 2008 were also considered in the calibration process. Simulations of SWC, CC, B and Y were evaluated by determining the index of agreement, the root mean square error, the coefficient of determination and the Nash–Sutcliffe efficiency. The statistical parameters showed an adequate fit between observations and simulations. The model was able to simulate for tef growing under rainfed condition the observed fast drop in SWC and CC when the rains ceased. The overall goodness of fit between the observed and simulated CC and SWC indicated that the thresholds for root zone depletion at which water stress (i) affects canopy development, (ii) induces stomata closure and (iii) triggers early canopy senescence were well selected. The normalised biomass water productivity (WP*) for tef was 14 g m−2 for the local variety and 21 g m−2 for the improved variety, which is a lot smaller than the WP* expected for C4 plants (30–35 g m−2). The results revealed an increase of 27% in reference harvest index (HIo) of tef in response to mild water stress during the yield formation of up to 33%. However, severe water stress causing stomata closure had a negative effect on HIo. Once it is properly calibrated, AquaCrop can provide room to improve the water productivity of tef by developing guidelines for good agricultural management strategies.

Responses of crop yield to water stress are classified on the basis of physiological considerations. Crop growth is sensitive to water stress, particularly because of the physiological effects of stress on the production and maintenance of photosynthetic tissue. Crop yield, depending on the nature of the harvested organ and the origin of its constituents, may be more or less sensitive to water stress than crop growth. In applying this information to irrigation management, there is a need for simple quantitative measures of plant water status. The problem of avoiding water stress during critical ontogenetic stages and, conversely, the possibility of using moderate water stress at certain times to improve yield and the efficiency of water usage, are discussed.

A computer simulation model was developed to investigate strategies for control of the parasitic weed species of Orobanche. The model makes use of data from published literature and predicts infestation levels in a dynamic and deterministic way. It is predicted that sustainable control of the parasite can only be achieved by reducing the soil seed bank to levels of 1000–2000 seeds m−2 and maintaining it at that level in subsequent years. When cultural control methods such as hand weeding, trap/catch cropping, delayed planting, resistant cultivars and solarization were considered individually, a relatively high level of effectiveness was required to contain the soil seed bank. An integrated approach with a selection of appropriate cultural methods is therefore recommended for further testing and validation in the field. The simulations demonstrate the importance of preventing new seeds entering the soil seed bank and that although reducing the soil seed bank may not increase yield for the first few years, it will ultimately increase production.

Rates of leaf development in four groundnut genotypes were found to depend primarily on temperature, although there was a linear relation between the thermal time to produce one leaf and mean leaf water potential below −0.6 MPa. Flower, peg and pod production was analysed in relation to leaf number, since this integrated effects of temperature and water status.

When water was not limited, the ratio of pod number: peg number was about 0.8 for all four genotypes. During drought only one genotype (TMV 2) maintained this value, while for the other genotypes the ratio was approximately 0.15. Genotypes also showed different patterns of development during recovery from drought. TMV 2 maintained relatively high values of partitioning factor throughout the pod-filling period, resulting in the largest harvest index and pod yield. Kadiri 3 achieved the second largest harvest index and pod yield by maintaining production of pegs during drought and only forming pods when stress was relieved.

Farming systems research (FSR) has come to prominence as a part of tropical agricultural research in the past decade or so. The main stimulus was the growing realization that small farmers are ‘economically rational’ and agricultural economists have been the leading agents in developing FSR ideas. Three broad aspects are distinguished: (1) FSR sensu stricto, the deep analysis of farming systems as they exist, which is essentially an academic activity, (2) OFR/FSP (‘on farm research with farming systems perspective’), a practical adjunct to research which seeks to test the socio-economic suitability of research ideas on-farm before recommending extension and (3) NFSD (‘new farming systems development’) which seeks to develop complex, radical change rather than the stepwise change characteristic of OFR/FSP. The technical components of NFSD are probably mostly available but the necessary transdisciplinary, synthetic thinking is not. Research on perennial plants in tropical agriculture has been rather neglected but there are signs of growing concern; they must be an important feature of any NFSD for the wetter areas.

The effect of ‘on-farm’ seed priming – soaking seeds in water before surface-drying and sowing them – was tested for mungbean (Vigna radiata) in 15 irrigated on-station trials and four sets of rainfed, paired-plot, farmer-participatory trials over four contrasting years from 1999 to 2002 in the North West Frontier Province of Pakistan. The optimum soaking time was found to be between six and eight hours; eight hours was used in all the trials. Of the 19 trials, priming was significantly better than non-priming in 14 with a mean yield increase of 56%. In the remaining five trials there was no difference between treatments but in no case was priming worse than not priming. In a subset of 11 on-station trials in which management was considered to be optimal, yield declined in a linear fashion as the date of sowing was delayed. The rate of decline of about 30 kg ha−1 d−1 after 1st June was similar for both non-primed and primed crops, although the latter declined from a higher base. Farmers' yields were proportional to rainfall over the four years and the mean increase in grain yield due to priming in the 39 trials was 30%. Benefits from priming were the result of a combination of faster germination and emergence and more vigorous growth and development, leading to better crop stands and bigger, more productive plants. It was concluded that ‘on-farm’ seed priming is a low-cost, low-risk technology that has the potential to raise mungbean yields substantially thus making it a more attractive crop for farmers.

Growth and interception of Photosynthetically Active Radiation (PAR) in a maize/pigeonpea intercrop and sole maize and sole pigeonpea crops grown in large plots in an operational research watershed at ICRISAT research centre were compared. Growth and yield of the maize crop, in pure stands and in intercrop, were not significantly different. Efficiency of dry matter production, calculated from the relations between dry matter production and cumulative intercepted PAR, was highest for the maize/pigeonpea intercrop, followed by sole maize and sole pigeon-pea, proving the utility of such intercrops in making better use of resources in the Semi-Arid Tropics (SAT).

A review of the outcomes of past attempts at establishing sustainable seed producer groups in Nepal showed that after donor support was withdrawn a lack of marketing skills resulted in the groups no longer producing seed. Learning from this review, when we initiated new attempts at establishing sustainable seed producer groups in Chitwan district, Nepal, we emphasized the strengthening of their marketing and managerial capabilities rather than training in technical issues such as seed quality control. We imparted marketing skills to committee members of farmer groups at an initial training course in Chitwan in 2001. This inspired at least three existing farmer groups in Chitwan, already established for other agricultural activities, to enter into cereal and legume seed production and its marketing. Following their establishment in 2002 we supported them initially by purchasing some of their seed production. This was progressively withdrawn and, after three years, the groups independently marketed all of their substantial seed production. They built up capital reserves mainly from subsidies and by attracting funds from new shareholders with only a small contribution from retained profits that were only about 5% of total turnover. The capital reserves reduced or eliminated the need for loans thus increasing the chances that the enterprises would be sustainable. In contrast, other government-supported groups had practically no cash reserves despite substantial seed sales. By 2010, two of the three groups were still operating and had substantially increased turnover. Shareholders who were also seed producers benefited from being members of the group and from an increased income of 10% by producing seed instead of grain. Our intention in supporting these groups was to promote the scaling out of new rice varieties produced by client-oriented breeding (COB) or identified by participatory varietal selection but most of the seed that was produced was of obsolete varieties. Policies are needed to preferentially promote new varieties by supplying more information about them and increasing the subsidy on their seeds compared with older varieties. Continuing promotion by the organizations that bred them is also desirable but constrained by limited funding for COB.

The effects on yield of varying the planting date and planting pattern of morphologically different cowpea cultivars intercropped with pearl millet were studied in two field trials. The interaction between cowpea cultivars and planting date was highly significant. There was a sharp reduction in cowpea yields with late planting. Millet yields were reduced less when sown simultaneously with early cowpea cultivars than when sown with a late maturing local cultivar. Early maturing cowpea cultivars planted in closely spaced hills had less effect on millet yields than a late maturing cultivar sown in widely spaced hills. An appropriate cowpea cultivar for intercropping with peal millet would be one that was weakly competitive and that yielded both grain and fodder.