We aimed to assess the potential of the characterization of association among weed species as a tool to understand weed occurrence for further supporting long-term management programs. After a sequence of summer crops, which included irrigated rice and sorghum, the experimental area was submitted to subsoiling, limestone was applied, and ryegrass was planted in the winter season. Six months later, an ACCase-inhibitor herbicide was used to select only non-grassweed species. Field survey was carried out on 100 quadrats with 0.5-m width that were randomly sampled. Plant species were organized in 2 × 2 contingency tables. The results of the calculated chi-squares were compared to the respective tables, and results were presented as a paired chi-square matrix. The species–area curve was also obtained. The relative occurrence of species was determined by its frequency and presented as a wordcloud. The network analysis was obtained by using the Fruchterman–Reingold layout. The hypothesis of plant association aiming survival in arable fields was validated. The methodology of plant association based on the chi-square test was applicable to arable fields, where weed species (usually competitor plant types) occur in clusters. From a practical point of view, preference should be given to herbicides that are efficient on most species within a given cluster.

This special issue brings together a selection of papers that not merely present agronomic research findings, but critically review orientations, methodologies and research practices in agronomy. The focus is on agronomic research as it conducted as component of rural development efforts in the global South or, in short, development-oriented agronomy. Aiming to contribute to development challenges like food security, human welfare and wellbeing, and environmental sustainability, a focus on development-oriented agronomy implies a step beyond a narrow understanding of agronomy as the science of crop production and soil management. Doing development-oriented agronomy forefronts the juggling with productivity enhancing, environmental and social developmental goals entailed when doing agronomy. What is more, development-oriented agronomy generally takes place within a complex environment of (inter)national research and development policy organisations, development donor-funded projects, governmental, NGO and private sector agencies and global professional networks and (public–private) partnerships. Consequently, development-oriented agronomy is a field where debate and contestations over goals and direction, research methodologies and findings of agronomic research are first likely to emerge and become apparent.

Soil nutrient constraints coupled with erratic rainfall have led to poor crop yields and occasionally to crop failure in sole cropping in the Guinea savanna of West Africa. We explored different maize-grain legume diversification and intensification options that can contribute to mitigating risks of crop failure, increase crop productivity under different soil fertility levels, while improving soil fertility due to biological N2-fixation by the legume. There were four relay patterns with cowpea sown first and maize sown at least 2 weeks after sowing (WAS) cowpea; two relay patterns with maize sown first and cowpea sown at least 3 WAS maize in different spatial arrangements. These were compared with groundnut-maize, soybean–maize, fallow-maize and continuous maize rotations in fields high, medium and poor in fertility at a site each in the southern (SGS) and northern (NGS) Guinea savanna of northern Ghana. Legumes grown in the poorly fertile fields relied more on N2-fixation for growth leading to generally larger net N inputs to the soil. Crop yields declined with decreasing soil fertility and were larger in the SGS than in the NGS due to more favourable rainfall and soil fertility. Spatial arrangements of relay intercrops did not have any significant impact on maize and legume grain yields. Sowing maize first followed by a cowpea relay resulted in 0.18–0.26 t ha−1 reduction in cowpea grain yield relative to cowpea sown from the onset. Relaying maize into cowpea led to a 0.29–0.64 t ha−1 reduction in maize grain yield relative to maize sown from the onset in the SGS. In the NGS, a decline of 0.66 and 0.82 t ha−1 in maize grain yield relative to maize sown from the onset was observed due to less rainfall received by the relay maize. Groundnut and soybean induced 0.38–1.01 t ha−1 more grain yield of a subsequent maize relative to continuous maize, and 1.17–1.71 t ha−1 more yield relative to relay maize across both sites. Accumulated crop yields over both years suggest that sowing maize first followed by cowpea relay is a promising ecological intensification option besides the more common legume–maize rotation in the Guinea savanna, as it was comparable with soybean–maize rotation and more productive than the other treatments.

Reduced soil fertility and damage from pests and diseases have contributed to a decline in productivity of cocoa (Theobroma cacao L.) smallholdings in Sulawesi, Indonesia over the last decade. In a trial on a marginal, acidic soil in South Sulawesi, young PBC123 cocoa trees were supplied with compost, mineral fertiliser (NPK fertiliser and urea) or dolomite, alone and in combination. After 20 months, the trees supplied with compost were taller, flowered more profusely and had a five-fold higher dry bean yield than other treatments. Treatments had no impact on incidence of cocoa pod borer, Phytophthora pod rot and vascular streak dieback. All of the trees supplied with compost survived, while the control, mineral-fertiliser- and dolomite-treated trees had a mortality rate of 22–45% and symptoms of interveinal necrosis. Leaf concentrations of N, P and K were within the normal range in all treatments. In the control and mineral fertiliser treatments, leaf concentrations of Ca (0.28–0.30%) and Mg (0.11–0.15%) were deficient, but were higher in trees supplied with compost (0.78–1.21% and 0.26–0.29%, respectively). The Mg/K ratio in soil-exchangeable cations and leaves was increased three-fold by the combined compost/dolomite treatment. Supplying mineral fertiliser alone resulted in 3.3 cmol kg−1 exchangeable Al, compared to 2.2 cmol kg−1 in control soils. Since 10 kg tree−1 year−1 compost was supplied, a rate that is not practical on most cocoa smallholder farms, further investigation of cost-effective applications of organic matter in conjunction with appropriate formulations of inorganic fertilisers is recommended.

Multiflorous spikelets are found in oat Avena sativa L. subsp. nudisativa, which is characterised by elongated rachilla and variable number of florets per spikelet. One of the main factors limiting the exploration of multiflorous spikelets in oats, aiming to produce naked grains, is its variable expressivity. This work aimed to detect the environmental influence on the variable expressivity of multiflorous spikelet formation in oats and to estimate the heritability of this trait by analysing its expression in lower, middle and upper third of the panicle in 94 inbred lines of two crosses each. Two populations of recombinant inbred lines were screened for the spikelet formation in 2 years and sowing dates under field experiments. The results demonstrate that the variable expressivity of the multiflorous spikelet formation was highly influenced by the environmental conditions. The variable expressivity varied according to the genetic background, as well as the panicle third where spikelets were produced. The upper third of the panicle showed greater stability for the multiflorous spikelet formation, which is confirmed by the highest heritability coefficients observed in this third, regardless of the assessed population. Our results provide substantial evidences of the contribution exerted by environmental conditions in multiflorous spikelet formation in oats.

In rainfed lowland rice-based systems, increasing labour scarcity due to off-farm employment is encouraging farmers to switch from transplanting to dry direct seeding (DDS). To assure stable productivity at a level comparable with or superior to transplanting, DDS management must ensure rice seedlings have access to nutrients in order to be competitive with weeds, which must also be suppressed. This paper examined farmer perceptions of DDS using a farmer survey, and used on-farm experiments to examine responses of rainfed lowland rice to integrated nutrient–weed management, based around mechanised DDS. In the survey, weeds were the biggest problem faced by farmers in using DDS (61%). In 90% of cases, farmers reported that weeds had increased under DDS, with most farmers (78%) controlling weeds by hand. All farmers said they would use DDS in the following season (100%), due to labour savings (47%), timeliness of operations, improved productivity, low investment or a combination of these (44%). In on-farm experiments, banding nutrients with the seed at sowing enhanced early dry matter of rice, while early weed dry matter was reduced. Early weed control using ducklings or hand weeding reduced weed competition and increased rice growth, with ducklings providing additional yield benefits over hand weeding. Early increases in seedling vigour of rice, and in weed suppression, carried through to greater dry matter and yield of rice at maturity. Integrated nutrient–weed management in mechanised DDS increased DDS yields, reduced DDS yield variability and contributed to sustainability of DDS rice systems.

Innovation in agronomy by large numbers of smallholder farmers will need to accelerate if global commitments to end hunger are to be achieved in the face of major climate and other global change that are both caused by, and impact, agriculture. Conventional research and development in agronomy have involved a research process that produces technologies, which are then promoted for uptake by large numbers of farmers through extension, with both research and extension phases being more or less participatory. Recent research, including key contributions to this special issue, reveals that the performance of many technology options varies hugely across the geographies over which development programmes operate, depending on social, economic and ecological context. This severely limits the value of attempting to produce recommendations for large areas and numbers of farmers and identifies the need for new ways of supporting innovation that address the real-world heterogeneity of farmer circumstances. Addressing this widespread phenomenon of option by context interaction (OxC) has profound implications for how agronomic research and development are organised. Papers in this special issue show the nature and implications of such interactions and suggest ways in which research and development systems need to respond in order to support locally relevant innovation. It is evident that a paradigm shift is well underway, with researchers embracing new modes of thinking and action required to address OxC interactions, but these also need to be taken up and further developed by extension and change agents in the public and private sector. It is only through continued co-development of methods involving both these constituencies, working closely with farmers that sufficient progress is likely to be made for smallholder farming to keep pace with global demand for food without further damaging the environmental resources upon which production is based.

An extended assumption in maize breeding is that potential yield (Ymax) predicts yield (Y) under stress conditions (here, Ymin), justifying genotypic selection under moderately high-yielding environments. Moreover, it has been postulated that Y tolerance to stress is relatively independent on the main stress factor involved in Y reduction (cross-tolerance). We carried out an analysis of four datasets from Argentine Federated Farmers network (2010/11, 2011/12 and 2012/13, 11 locations and >20 hybrids) and the National Institute of Agricultural Technology (INTA) (12 locations, 13 hybrids). No consistent relation was detected between Ymax and Ymin (r2 < 0.14) in each dataset. Y stability assessed by the coefficient of variation positively related to Ymin (r2 > 0.68 across datasets) but not to Ymax. Depending on the dataset, 40–70% of the hybrids had a varying Y performance (from worse to better) compared with the average of all hybrids, with no consistent advantage of hybrids with high Ymax within the environmental range explored in the dataset. In order to assess the existence of cross-tolerance, INTA environments were divided into two groups: water-limited environments and environments exposed to other(s) type(s) of stress. While a relation was found between average yields (r2 = 0.64) of each hybrid in both environments, there was no relation for Y stability (r2 = 0.07). Taken together, our results suggest that: (i) a high Ymax is not a good indicator of high Y tolerance under stressful conditions; (ii) Y tolerance is related to high Y stability, which may or may not involve a Y penalty under high-yielding environments; (iii) around 50% of the genotypes have Y performance that is not consistently worse or better than the average throughout the range of environments explored and (iv) cross-tolerance to stress is a peculiar trait of some hybrids, but most of the hybrids analysed here do not show cross-tolerance.

In response to the current needs of humanity with regard to food production, environmental disasters and climate change, it is important to define (livestock) production systems and management practices that are both productive and ecologically sustainable. We qualitatively assessed advanced silvopastoral experiences in five ecologically and culturally distinct regions in Chiapas, Mexico, given their ability to provide key services: internal (productivity and productive resiliency) and external (climate change mitigation and biodiversity conservation). We propose 20 indicators that reflect management, resources, use of external inputs, availability of food, commercial products and animal feed and trees in grazing and forest areas. Sets of some indicators form criteria for dependence on external inputs, productive diversification with emphasis on food security, soil conservation, tree cover and landscape connectivity, among others. Indicators and thresholds were adjusted to critical (traffic light) levels, based on field data. Comparing the levels reached by the studied experiences, we found that most of the resulting services go hand in hand; so ‘win–win’ situations are possible to be achieved. The elements and practices that affect both internal and external services were explored. The red light critical points in each production unit were identified so that they could be attended. Experiences that presented higher levels in assessment criteria could serve as examples to enable the improvement of livestock systems under similar conditions. We propose this assessment as a tool for rapid intervention that can be widely applied to livestock systems, from conventional to organic or diversified, because of the criteria used. However, it can be more flexible, as new criteria can be added and thresholds can be adjusted for other types of production systems, always reflecting local and desired conditions. The proposed indicators can be also used as a basis for a quantitative agroecosystem assessment.

Accurate crop varietal identification is the backbone of any high-quality assessment of outcomes and impacts. Sweetpotato (Ipomoea batatas) varieties have important nutritional differences, and there is a strong interest to identify nutritionally superior varieties for dissemination. In agricultural household surveys, such information is often collected based on the farmer's self-report. In this article, we present the results of a data capture experiment on sweet potato varietal identification in southern Ethiopia. Three household-based methods of identifying varietal adoption are tested against the benchmark of DNA fingerprinting: (A) Elicitation from farmers with basic questions for the most widely planted variety; (B) Farmer elicitation on five sweet potato phenotypic attributes by showing a visual-aid protocol; and (C) Enumerator recording observations on five sweet potato phenotypic attributes using a visual-aid protocol and visiting the field. In total, 20% of farmers identified a variety as improved when in fact it was local and 19% identified a variety as local when it was in fact improved. The variety names given by farmers delivered inconsistent and inaccurate varietal identities. Visual-aid protocols employed in methods B and C were better than those in method A, but greatly underestimated the adoption estimates given by the DNA fingerprinting method. Our results suggest that estimating the adoption of improved varieties with methods based on farmer self-reports is questionable and point towards a wider use of DNA fingerprinting in adoption and impact assessments.

Changes in donor priorities have meant that agronomists working in the tropics find themselves in a fundamentally new operational space, one that demands rapid improvements in farmers' livelihoods resulting from the large-scale adoption of new technologies and crop management practices. As a result, on-farm trials in contemporary Agricultural Research for Development (AR4D) are increasingly implemented both to collect data and to spur farmer adoption. We examine the different interpretations and organisational practices of AR4D organisations in this new operational space, and reflect on the usefulness of on-farm trials for agricultural technology scaling. Three case studies are presented to address these questions – two in sub-Saharan Africa and one in South Asia. Each study is considered in light of Science and Technology Studies theory and locates science as a politically situated practice, recognising the tension that scientists face between providing evidence and persuading selected audiences. The case studies show that this tension results in the introduction of several biases that limit the scalability of the technologies under investigation. These include biases at the level of the trial location, host-farmer selection, trial design, management and evaluation. We conclude by discussing how the contemporary political and institutional environment of AR4D produces project beneficiaries and research outcomes on selected farms, but not necessarily impacts at scale.

Climbing bean is the key staple legume crop in the highlands of East and Central Africa. We assessed the impact of interactions between soil fertility characteristics, crop management and socio-economic factors, such as household resource endowment and gender of the farmer, on climbing bean productivity and yield responses to basal P fertiliser in northern Rwanda. Through a combination of detailed characterisations of 12 farms and on-farm demonstration trials at 110 sites, we evaluated variability in grain yields and responses to fertiliser. Grain yields varied between 0.14 and 6.9 t ha−1 with an overall average of 1.69 t ha−1. Household resource endowment and gender of the farmer was strongly associated with climbing bean yield, even though these were partly confounded with Sector. Poorer households and women farmers achieved lower yields than wealthier households and male farmers. Household resource endowment and gender were likely to act as proxies for a range of agronomic and crop management factors that determine crop productivity, such as soil fertility, current and past access to organic manure and mineral fertiliser, access to sufficient quality staking material, ability to conduct crop management operation on time, but we found evidence for only some of these relationships. Poorer households and female farmers grew beans on soils with poorer soil fertility. Moreover, poorer households had a lower density of stakes, while stake density was strongly correlated with yield. Diammonium phosphate (DAP) fertiliser application led to a substantial increase in the average grain yield (0.66 t ha−1), but a large variability in responses implied that its use would be economically worthwhile for roughly half of the farmers. For the sake of targeting agricultural innovations to those households that are most likely to adopt, the Ubudehe household typology – a Rwandan government system of wealth categorisation – could be a useful and easily available tool to structure rural households within regions of Rwanda that are relatively uniform in agro-ecology.

The development of mechanised large-scale farming has led to changes in rice production systems. Increases in time of farming operations often occur under large-scale farming conditions, which can lead to delayed transplanting (DTP). In this study, field experiments were conducted in the late rice-growing season in 2016 and 2017 to compare the growth stages, growing-season temperature and yield attributes between normal transplanting with 15- to 20-day-old seedlings and DTP with 30-day-old seedlings of two rice cultivars. DTP resulted in 6- and 12-day delays in heading stage for both cultivars in 2016 and 2017, respectively. As a consequence, low temperature stress occurred at anthesis under DTP in both years, which led to significantly reduced spikelet filling and grain yield under DTP for both cultivars. These results confirm that DTP can reduce spikelet filling and grain yield due to low temperature stress at anthesis in machine-transplanted late-season rice. This finding highlights that greater efforts should be made to develop high-yielding short-duration rice cultivars to meet the development of mechanised large-scale rice farming.

Our knowledge of melon (Cucumis melo L.) response to salinity stress is limited under field conditions and then the genotype × environment interaction and heritability of agro-morphological traits are poor understood. A field trial (2014/2015) was carried out to evaluate the performance of 17 melon cultivars, including 16 native and one exotic (Galia), under salinity stress. Leaf ion concentrations, agronomic, morphological and fruit quality traits were evaluated and their heritabilities were estimated. The results showed significant effects of salinity stress and genotype on the studied traits except for days to anthesis and peel thickness. Salinity stress also caused significant reductions in fruit weight and leaf K+ concentration, while increasing leaf Na+ and Ca2+ concentrations and total soluble solids. The most salt-tolerant cultivars (‘Sabouni’ and ‘Shahabadi-1’) had higher fruit yield, low leaf Na+ and high leaf K+ concentrations and enhanced K+/Na+ ratio under stress conditions. In general, the heritability estimates were higher under control than under salinity conditions, and the highest heritability was observed for total soluble solids. In addition, fruit weight, number of fruit per plant and leaf Na+ concentration were the strongest predictors of fruit yield, explaining 92% of yield variation under salt stress. These observations suggest that indirect selection based on these traits would be effective in improving fruit production under saline conditions.

In their recent paper ‘On-farm trials for development impact? The organization of research and the scaling of agricultural technologies’, de Roo, Andersson and Krupnik report on three case studies, each undertaken by one of the authors, of projects conducting on-farm research. They reach conclusions on the limitations of the projects themselves and the effects of ‘donor dependency’, and propose a strategy to overcome these issues. However, the description of the philosophy, strategies and conduct of the projects reviewed in the southern African case study is incomplete and misleading, and shows that the case study author did not understand or overlooked important project components. Due to this the conclusions reached, insofar as this case study is concerned, are largely either invalid or already contemplated in the project activities. Here, we describe more fully the philosophy and strategies followed by the series of projects on which the case study was conducted, which were designed to facilitate, through the upscaling of project methodologies, the eventual outscaling and widespread adoption of more sustainable farming systems by smallholder farmers in eastern and southern Africa. We propose these methodologies as a valid comprehensive approach to the organization of agricultural research for development for the successful development, scaling-up and scaling-out of agricultural technologies.

The extent to which coffee agroforestry systems provide ecosystem services depends on local context and management practices. There is a paucity of information about how and why farmers manage their coffee farms in the way that they do and the local knowledge that underpins this. The present research documents local agro-ecological knowledge from a coffee growing region within the vicinity of the Aberdare Forest Reserve in Central Kenya. Knowledge was acquired from over 60 coffee farmers in a purposive sample, using a knowledge-based systems approach, and tested with a stratified random sample of 125 farmers using an attribute ranking survey. Farmers had varying degrees of explanatory knowledge about how trees affected provisioning and regulating ecosystem services. Trees were described as suitable or unsuitable for growing with coffee according to tree attributes such as crown density and spread, root depth and spread, growth rate and their economic benefit. Farmers were concerned that too high a level of shade and competition for water and nutrients would decrease coffee yields, but they were also interested in diversifying production from their coffee farms to include fruits, timber, firewood and other tree products as a response to fluctuating coffee prices. A range of trees were maintained in coffee plots and along their boundaries but most were at very low abundances. Promoting tree diversity rather than focussing on one or two high value exotic species represents a change of approach for extension systems, the coffee industry and farmers alike, but is important if the coffee dominated landscapes of the region are to retain their tree species richness and the resilience this confers.

Berseem clover (Trifolium alexandrinum L.) is an important forage legume and is the primary winter forage crop in Pakistan. There are significant gaps in yield potential among varieties of berseem clover, as well as yields obtained at research stations and on-farm. To address this problem a survey of farmers was undertaken in the districts of Kasur and Okara, Punjab, Pakistan to determine the level of knowledge and understanding of berseem forage cultivation and seed production. The study comprised 44% smallholder (<3 ha), 26% medium (3–5 ha) and 30% large farmers (>5 ha) with average age of 42 years. Most farmers had little or no knowledge of the role of seed quality, inoculation with rhizobium, pollination, fertiliser use, irrigation management and the importance of forage nutritional value in improving livestock productivity. Most farmers (56%) had received no input from the government or private sector to improve forage production, relying instead on traditional knowledge. Knowledge of the importance of land preparation (95%), sowing rate (98%) and insect and pest management (75%) was higher than seed selection and fertilisation. Adoption of improved varieties (3%) and production technologies (14%) was low due to various constraints including ignorance, high cost of inputs, lack of availability of inputs in the market and a perceived high level of financial risk. Almost 100% of the respondents agreed that seed of improved varieties was a pre-requisite for higher forage and seed production as well as essential to start village-based forage seed enterprises.

Overaged full-sun cacao plantations and the need for sustainable production systems call for combining rehabilitation of plantations with the establishment of agroforestry. We tested the effect of drastic rehabilitation pruning of old cacao tree stock and the introduction of both high- and low-diversity agroforestry on survival, growth and yield of T. cacao in a commercial plantation in peninsular Malaysia over a period of 5 years. We further determined the incidence of pests and diseases of cacao pods and assessed the performance of the whole system for smallholder farmers, including yields of by-crops. Rehabilitation pruning negatively affected cacao tree development and short-term yield. No more effects of pruning on cacao yield were observed starting in the third year on in the monoculture and starting in the fourth year on in low-diversity agroforestry. We found similar cacao tree development and yield in the low-diversity agroforestry and a common practice monoculture, suggesting that the implementation of agroforestry is a commercially feasible strategy, due to additional income generated through timber production. Reduced cacao tree development and yield in the high-diversity agroforestry were compensated by additional harvests of cassava and banana compared to monoculture. Incidence of cocoa pod borer (Conopomorpha cramerella) was lower in the agroforestry systems, especially the high-diversity system, while the incidence of black pod disease (Phytophthora spp.) did not differ between agroforestry and monoculture. The findings highlight the potential of agroforestry to reconcile ecologically sustainable land use with natural, cost-effective pest management. While pruning needs to be done with timing and disease pressure in mind to minimize short-term yield losses, this measure proved to be a feasible strategy for establishing agroforestry on extant plantations.

Little is known about the adaptability of mamey sapote (Pouteria sapota) to acidic soils high in aluminum (Al). A 2 year field study was conducted to determine the effects of various levels of soil Al on dry matter production, stem diameter and nutrient concentration in tissues of four cultivars of mamey sapote. Soil Al treatments were statistically different for all variables measured in the study. Cultivars and the year × cultivar interaction were not significant; therefore, results were averaged over cultivars and years. Increasing soil Al concentration from 3.5 to 7.8 cmol kg−1 resulted in an increase in total dry weight, but higher soil Al concentrations resulted in dry weight and stem diameter reductions. Increments in soil Al resulted in a significant reduction in the concentration of leaf, stem and root calcium. The Al concentration in leaf and stem tissues was not significantly affected with increments in soil Al, but there was a significant decline in the concentration of Al in root tissue suggesting that mamey sapote may exclude Al from roots.