Cassava (Manihot esculenta Crantz) has generally been reported to possess hypostomatal leaves. Several cultivars have now been found to possess clusters of functional stomata around the veins on the upper leaf surface and two cultivars (M Col 88 and M Col 90) have significant numbers of stomata (83–140 mm−2) dispersed over the entire upper leaf surface. Stomatal density on the lower leaf surface ranged from 322–553 mm−2 among cultivars, with a relative stomatal area of 3.4–6.1%. The CO2 uptake by the upper leaf surface (27% of total) and the transpiration loss (32% of total) corresponded closely to the ratio of relative stomatal areas on the upper and lower leaf surface of cv. M Col 88.

Herding and farming environments in sub-Saharan Africa are described briefly. The relative importance of crops and livestock is described for each environment. A matrix of crop-livestock interactions is defined for each environment and the reasons for each type of relation are noted. Farming systems are defined as segregated or completely integrated, according to the degree of crop-livestock integration on the farm. Points at which farming systems research (FSR) might be undertaken to improve interactions between crops and livestock are noted for both systems.

Yields of pearl millet were significantly increased when grown after legume crops such as groundnut (22·6%), cowpea (24·2%) or pigeonpea (12·1%) instead of after pearl millet. A previous crop of short-duration mung did not affect the yield of pearl millet. Benefits from previous crops of groundnut and cowpea were equivalent to about 60 kg N/ha applied to a pearl millet crop following a previous crop of pearl millet.

Sequential sowings were carried out at Dodoma, Tanzania, to examine the effect of changing climatic parameters on the growth and yield of bambara groundnut (Vigna subterranea). Sowings took place on 4 January, 4 February and 4 March 1994; 4 and 24 January, and 13 February 1995; 4 and 21 January, and 7 February 1996. Rainfall during the crop life cycle varied from 163 to 611 mm, mean photoperiod from 11.82 to 12.09 h d−1 and mean temperature from 22.6 to 24.4 °C. In 1994, the highest pod yields were achieved at the earliest sowing date, with a maximum of 2.87 and 1.42 t ha−1 for the red- and cream-seeded landraces, representing pod harvest indices of 0.56 and 0.34 respectively. A 30-d delay in sowing caused >60% reduction in pod yield, and a further 30-d delay resulted in no pods at all. Similarly, in 1995 successive delays in sowing caused dramatic yield declines, and the maximum yield was much lower, at 0.44 t ha−1. In 1996 there was no significant difference in pod yields between the two early sowing dates for the red-seeded landrace and yields were again lower than in 1994 with a maximum of 1.02 t ha−1. Differences in dry matter production between sowings and years were attributed mainly to differences in the amount and distribution of rainfall and to declining temperatures towards the end of the season; however, partitioning to pods was remarkably consistent across sowings.

If corn-soyabean intercrops are to replace corn grown alone, maintenance of yield and improvements in forage quality are important. Total yields and inter-crop competition in corn-soyabean intercropping experiments have been discussed previously (Putnam et al., 1985). In Part II yield composition, components and protein content are presented for intercrops of varying planting patterns and corn densities. Most intercrop patterns produced more forage than sole crops compared at the same yield ratio of corn-soyabean as in the intercrop harvested mixture. At high plant density ear yields in the intercrop were increased while in sole crops they were reduced or unaffected. The increase was a result of an increased number of ears, weight per ear and kernel, and number of kernels per row in the intercrops. Increases in crude protein content over sole crop corn of 11–51% were shown for the various intercrop treatments. Crude protein yields in the intercrops were greater than either sole crop in 1981 and greater than corn and similar to soyabean in 1982, and greater than the crude protein yields expected from an equal planted area of sole crop corn and soyabean in both years. Intercrop forage quality was improved over sole corn both by the addition of protein from soyabean pods and an increased ear: stover ratio of the intercropped corn.

At a field site in central India, four populations of groundnut (Arachis hypogaea L.) were grown on stored water to investigate how the production of shoot and root dry matter is related to transpired water and intercepted radiation. Throughout the season, total dry matter was closely related to transpiration (slope = 3.0 mg dry matter g−1 water) and the amount of radiation intercepted by foliage (slope = 0.74 g dry matter MJ−1 radiation intercepted). Accumulated transpiration increased linearly with intercepted radiation at 0.37 kg water MJ−1 in the sparser stands. In the densest spacing, the initial slope of the relation at 0.28 kg MJ−1 decreased later in the season because water deficits curtailed growth without a concomitant reduction in the interception of radiation.

At Hyderabad, India, stands of pearl millet were grown after the monsoon (a) with no irrigation after establishment and (b) with irrigation as needed to avoid stress. Increases of dry matter and leaf area were determined by regular harvesting. The interception of radiation by the foliage, uptake of water from the soil and stomatal conductance were monitored. Before anthesis at 42 days after sowing (DAS), the rate of dry matter production and the transpiration rate in the unirrigated stand were about 80% of the corresponding rates for the irrigated control, mainly because of a smaller stomatal conductance from 30 DAS. After anthesis, the unirrigated stand grew little and used only 10% of the water transpired by the control. This large difference was partitioned between loss of leaf area and smaller stomatal conductance in the ratio of approximately 2:1. Radiation intercepted by foliage in the irrigated stand produced 2.0 g of dry matter per MJ compared with 2.5 g MJ−1 for the same variety growing in the monsoon, a difference consistent with a smaller stomatal conductance in drier air.

Time to flowering of mung bean crops varies appreciably depending on the genotype, and the daylengths and temperatures prevailing during the period after sowing. Relatively little is known about the precise nature and inheritance of flowering responses to photoperiod and temperature. The combined effects of variations in these two factors on time to flowering were therefore evaluated in controlled environment studies on six genotypes and four F1 hybrids. The responses were examined for conformity with hypothesized linear models from which inferences might be made of the genetic control of flowering. The analyses suggest that all the genotypes and F1s tested were quantitative short day plants, with the possible exception of one line which may be day neutral. The analyses further suggest that time to flowering was influenced by four genotype-specific attributes: minimum time to flowering, critical photoperiod (Pc), responsiveness to photoperiod longer than Pc, and responsiveness to temperature. Among the genotypes tested, different values were observed for each attribute. In most instances, the values for the F1s were closer to one or other parent, indicating dominance rather than additive genetic effects. We conclude that, with several levels each, the four attributes provide the potential for a diversity of flowering response types within mung bean. Further, it should prove possible to manipulate the mung bean germplasm to obtain novel combinations of attributes, and thus to breed genotypes adapted to photothermal regimes not previously considered suitable for the crop.

Thirteen cultivars of cassava were planted, widely spaced, and harvested after two, three, five and seven months. Differences in root yield after seven months were caused by variations in rate of root bulking, and were not associated with differences in onset of root bulking, which occurred during the second month of growth in all varieties that produced thickened roots.

Intended to test broad hypotheses and arrive at unifying conclusions, meta-analysis is the process of extracting, assembling, and analyzing large quantities of data from multiple publications to increase statistical power and uncover explanatory patterns. This paper describes the ways in which meta-analysis has been applied to support claims and counter-claims regarding two topics widely debated in agricultural research, namely organic agriculture (OA) and conservation agriculture (CA). We describe the origins of debate for each topic and assess prominent meta-analyses considering data-selection criteria, research question framing, and the interpretation and extrapolation of meta-analytical results. Meta-analyses of OA and CA are also examined in the context of the political economy of development-oriented agricultural research. Does size matter? We suggest that it does, although somewhat ironically. While meta-analysis aims to pool all relevant studies and generate comprehensive databases from which broad insights can be drawn, our case studies suggest that the organization of many meta-analyses may affect the generalizability and usefulness of research results. The politicized nature of debates over OA and CA also appear to affect the divergent ways in which meta-analytical results may be interpreted and extrapolated in struggles over the legitimacy of both practices. Rather than resolving scientific contestation, these factors appear to contribute to the ongoing debate. Meta-analysis is nonetheless becoming increasingly popular with agricultural researchers attracted by the power for the statistical inference offered by large datasets. This paper consequently offers three suggestions for how scientists and readers of scientific literature can more carefully evaluate meta-analyses. First, the ways in which papers and data are collected should be critically assessed. Second, the justification of research questions, framing of farming systems, and the scales at which research results are extrapolated and discussed should be carefully evaluated. Third, when applied to strongly politicized topics situated in an arena of scientific debate, as is the case with OA and CA, more conservative interpretations of meta-analytical results that recognize the socially and politically embedded nature of agricultural research is are needed.

Modern maize varieties have been bred for drought tolerance and early maturity, to assist farmers in avoiding or escaping the effects of moisture stress in drought-prone areas. This study evaluates the prospects for widespread adoption of these modern maize varieties as a climate change adaptation strategy for smallholder farmers. Data are from a detailed household survey completed in four rural villages in Southern Malawi between May and July 2010. The empirical analysis involves estimation of an ordered logit regression model because the dependent variable is categorical, with one category for nonadoption (has never grown modern maize varieties) and three categories for the duration of growing a modern maize variety among adopters (this year only, 2 to 5 years and 6 years or more). The empirical findings indicate a positive association between a farmer's perception of drought risk and the adoption and continued use of modern maize. Regression results also show that farmers that value the traits of early maturity and drought tolerance are more likely to adopt modern maize varieties. There is evidence of some disadoption among farmers dissatisfied with maize genotype performance, in terms of poor storability and yield under drought conditions. Finally, the study highlights the urgent need for maize breeders interested in sustained use of modern varieties to simultaneously address robust drought tolerance, early maturity and storability. This underscores the importance of cognizance of local farmer preferences in crop breeding efforts.

Surveys and on-farm trials are frequently used to facilitate farmer participation in agricultural research. This paper reports on a less common method-farmer involvement in on-station trials. Thirty-nine farmers were invited to multipurpose-tree screening trials in Burundi. Three different methods were used to determine which species the farmers wanted to test on their own farms. Private interviews and voting by a show of hands in plenary sessions gave very similar results whereas focus group interviews produced different and contradictory results. Researchers also learned what criteria farmers used to evaluate trees and the reasons for their choices. A supplementary survey of farmers’ preferences for trees grown on their own farms confirmed the findings and more clearly defined their criteria. In this survey, farmers used a local board game, Bao, to rate tree species across criteria they considered important. Overall, the visit to the trials and follow-up survey proved to be a useful and cost-effective method for getting farmer input and applying it in the screening process.

La participación de los agricultores en la selección de especies de árboles

Seed inoculation with Bacillus polymyxa markedly increased the yields of rice and chickpea crops, while Pseudomonas striata caused a greater impact on crop production when used with rock phosphate or super-phosphate in a wheat crop. The effect of the phospho-microbe inoculants was greater in phosphorus-deficient soils.

Mixed tree and food crop farming systems are being developed in the humid tropics. They offer one solution to the problems caused by population pressure and de-forestation, since they can provide a satisfactory income to the subsistence farmer, while adequately protecting the environment In seeking to develop optimal systems, examples and information can be drawn from traditional mixed cropping systems, from taungya systems of forestation, and from other systems developed within the commodity cropping sector. However, the full potential of mixtures involving perennials and food crops can only be realised within the limitations of local socio-economic and political circumstances.

Understanding farm diversity is essential to delineate recommendation domains for new technologies, but diversity is a subjective concept, and can be described differently depending on the way it is perceived. Historically, new technologies have been targeted primarily based on agro-ecological conditions, largely ignoring socioeconomic conditions. Based on 273 farm households' surveys in Ethiopia, we compare two approaches for the delineation of farm type recommendation domains for crop and livestock technologies: one based on expert knowledge and one based on statistical methods. The expert-based typology used a simple discriminant key for stakeholders in the field to define four farm types based on Tropical Livestock Unit, total cultivated surface and the ratio of these two indicators. This simple key took only a few minutes to make inferences about the potential of adoption of crop and livestock technologies. The PCA-HC analysis included a greater number of variables describing the farm (land use, household size, cattle, fertilizer, off-farm work, hiring labour, production). This analysis emphasized the multi-dimensional potential of such a statistical approach and, in principle, its usefulness to grasp the full complexity of farming systems to identify their needs in crop and livestock technologies. A sub-sampling approach was used to test the impact of data selection on the diversity represented in the statistical approach. Our results show that diversity structure is significantly impacted according to the choice of a sub-sample of 15 of the 20 variables available. This paper shows the complementarity of the two approaches and demonstrates the influence of data selection within large baseline data sets on the total diversity represented in the clusters identified.

Low soil pH and associated soil infertility problems are considered to be amongst the major challenges to barley production in the highlands of Ethiopia. In response to this, an experiment was conducted at low soil pH (< 5 H2O) site on the effects of different levels of lime and phosphorus (P) fertilizer on soil pH, exchangeable aluminium (Al3+), grain yield and yield components of barley during 2010 and 2011 cropping seasons. The experiment comprised factorial combinations of five lime rates (0, 0.55, 1.1, 1.65 and 2.2 t ha−1) and four P rates (0, 10, 20 and 30 kg ha−1) in a randomized complete block design in three replications. The amount of lime that was applied at each level was calculated on the basis of Al3+. Results of soil analysis after 2 years of liming showed that liming significantly (P < 0.05) increased soil pH, and markedly reduced exchangeable Al3+. Liming at the rate of 0.55, 1.1, 1.65 and 2.2 t ha−1 decreased Al3+ by 0.88, 1.11, 1.20 and 1.19 mill equivalents per 100 g of soil, and increased soil pH by 0.48, 0.71, 0.85 and 1.1 units, respectively. Amongst the liming treatments, liming at the rate of 1.65 and 2.2 t ha−1 gave significantly (P < 0.05) the highest grain yield and yield components of barley. However, grain yield obtained by applications of 1.65 and 2.2 t ha−1 lime was statistically comparable. By additions of 10, 20 and 30 kg P ha−1, grain yield of barley increased by about 29, 55 and 66% as compared to control (without P). During 2010, however, the combined applications 1.65 t ha−1 lime and 30 kg P ha−1 gave 133% more grain yields of barley relative to control (without P and lime). Therefore, sustainable barley production on acid soils in the central highlands of Ethiopia should entail combined applications of both lime and P fertilizer.

Low concentrations of phosphorous were added to the floodwater of submerged rice in an attempt to regulate algal growth, so as to increase floodwater O2 concentration and plant survival during submergence for up to 12 days. Increasing the phosphorus concentration of the floodwater by 1 ppm increased algal growth by at least 4-fold based on chlorophyll concentrations, and increased floodwater O2 concentrations to over twice air saturation. However, additions of phosphorus reduced rice plant survival during submergence by up to 35%. The adverse effects of a high phosphorus concentration in the floodwater were mainly attributed to competition between the algae and the submerged rice for CO2 and, perhaps, light. The importance of photosynthesis during the submergence of rice was supported by the results of experiments in which floodwater CO2 concentration was manipulated by altering pH. The survival of an intolerant rice cultivar during submergence increased from 0 to 17 and 62% at pH 8, 7 and 5 respectively, while floodwater CO2 concentrations at these pHs would have increased from 0.02 to 0.3 and 1.0 mol m−3 respectively. The results were used to question the importance of floodwater O2 concentrations above anoxia for submergence tolerance of rice.

A study was conducted to determine the population sizes of indigenous pigeonpea (Cajanus cajan)-nodulating rhizobia and responses of the crop to rhizobial inoculation in soils under smallholder management. Rhizobia populations were determined in 21 soils from three different agro-ecological regions of Zimbabwe using the plant infection most-probable-number technique. Pigeonpea response to rhizobial inoculation was tested in five soils representative of low, medium and high rhizobia populations. Pigeonpea rhizobia ranged from undetectable to 121 cells per g soil compared with 16 to 159 cells per g soil for cowpea (Vigna unguiculata) which was used for reference. Soils with high cowpea rhizobia counts had relatively low counts of pigeonpea rhizobia and vice versa, showing that the two legumes associate with different subgroups of rhizobia. Poor soil organic matter, low soil moisture at sampling, low pH and low clay content of the soils had a significant negative effect on rhizobial counts. Organic matter appeared critical for maintenance of high populations of indigenous rhizobia in the mostly sandy soils sampled. Lack of pigeonpea response to inoculation in all the soils tested despite the low initial rhizobial populations could be the result of within-season proliferation of indigenous populations which are competitive and effective. There was evidence of rapid build-up of pigeonpea-compatible rhizobia within one growing season when the crop was first introduced. It was concluded that effective pigeonpea rhizobia occur in many arable soils of Zimbabwe. However, to fully exploit biological nitrogen fixation and maximize yields of pigeonpea, highly efficient, adapted and competitive indigenous rhizobial isolates must be identified and evaluated.

Long-term in situ soil and water conservation experiments are rare in sub-Saharan Africa, particularly in Eastern Africa. A long-term experiment was conducted (2005–2013) on a Vertisol to quantify the impacts of resource-conserving agriculture (RCA) on runoff, soil loss, soil fertility and crop productivity and economic profitability in northern Ethiopia. Two RCA practices were developed from traditional furrow tillage practices: (i) derdero+ (DER+) and terwah+ (TER+). DER+ is a furrow and permanent raised bed planting system, tilled once at planting time by refreshing the furrow and 30% of crop residue is retained. TER+ is ploughed once at planting, furrows are made at 1.5 m intervals and 30% crop residue is retained. The third treatment was a conventional tillage (CT) with a minimum of three tillage operations and complete removal of crop residues. Wheat, teff, barley and grass pea crops were grown in rotation. Runoff, and soil and nutrient loss were measured in plastic sheet-lined collector trenches. Significantly different (P < 0.05) runoff coefficients (%) and soil losses (t ha−1) averaged over 9 yrs were 14 and 3, 22 and 11 and 30 and 17 for DER+, TER+ and CT, respectively. Significant improvements in crop yield and gross margin were observed after a period of three years of cropping This study demonstrated that RCA systems in semi-arid agro-ecosystems constitute a field rainwater conservation and soil fertility improvement strategy that enhances crop productivity and economic profitability. Adoption of RCA systems (DER+ and TER+) in the study area requires further work to improve smallholder farmers’ awareness on benefits, to guarantee high standards during implementation and to design appropriate weed management strategies.