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In rural sub-Saharan Africa, where malnutrition in all its forms is rife, the greatest gap between the availability of foods and the foods needed for a nutritious diet are faced during the ‘hunger season’. We investigated what rural households in Northern Ghana would need to grow to ensure year-round availability of a nutrient adequate diet or the income required to fulfil their dietary needs. We applied linear programming to model different scenarios and interventions. Our results provide three major insights. First, considering seasonality is crucial in nutrition-sensitive farming. Ensuring a nutritious diet year-round requires enhanced availability of vegetables and fruits throughout the year. Second, although staple crops do not provide the full range of essential nutrients, increasing their yields allows for a reduction of field size, freeing up space for the production of other foods belonging to a nutritious diet, such as vegetables. Third, small farms are unable to produce sufficient food to cover their needs. They depend on income both from agriculture and other sources, and the availability of types of foods on markets to meet their dietary needs. Our study shows the value of modelling the range of dietary effects from agricultural interventions in a specific context, using a local feasible nutritious diet as a starting point and taking seasonality into account.

In Tanzania, diets are dominated by starchy staple crops such as maize, levels of malnutrition are high and largely attributed to lack of dietary diversity. We employed fuzzy cognitive mapping to understand the current soybean, maize and chicken value chains, to highlight stakeholder relationships and to identify entry points for value chain integration to support nutritious diets in Tanzania. The fuzzy cognitive maps were constructed based on information gathered during household interviews with 569 farming households, followed by a participatory workshop with 54 stakeholders involved in the three value chains. We found that the soybean, maize and chicken value chains were interconnected, particularly at the level of the smallholder farming systems and at processing facilities. Smallholder farming households were part of one or more value chains. Chicken feed is an important entry point for integrating the three value chains, as maize and soybean meal are the main sources of energy and protein for chicken. Unlike maize, the utilization of soybean in chicken feed is limited, mainly due to inadequate quality of processing of soybean grain into meal. As a result, the soybean grain produced by smallholders is mainly exported to neighbouring countries for further processing, and soybean meal is imported at relatively high prices. Enhancing local sourcing and adequate processing of soybean, coupled with strengthening the integration of smallholder farmers with other soybean, maize and chicken value chain actors offers an important opportunity to improve access to nutritious diets for local people. Our method revealed the importance of interlinkages that integrate the value chains into a network within domestic markets.

Most food in sub-Saharan Africa is produced on small farms. Using large datasets from household surveys conducted across many countries, we find that the majority of farms are less than 1 ha, much smaller than previous estimates. Farms are larger in farming systems in drier climates. Through a detailed analysis of food self-sufficiency, food and nutrition security, and income among households from divergent farming systems in Ethiopia, Ghana, Mali, Malawi, Tanzania and Uganda, we reveal marked contrasts in food security and household incomes. In the south of Mali, where cotton is an important cash crop, almost all households are food secure, and almost half earn a living income. Yet, in a similar agroecological environment in northern Ghana, only 10% of households are food secure and none earn a living income. Surprisingly, the extent of food insecurity and poverty is almost as great in densely-populated locations in the Ethiopian and Tanzanian highlands that are characterised by much better soils and two cropping seasons a year. Where populations are less dense, such as in South-west Uganda, a larger proportion of the households are food self-sufficient and poverty is less prevalent. In densely-populated Central Malawi, a combination of a single cropping season a year and small farms results in a strong incidence of food insecurity and poverty. These examples reveal a strong interplay between population density, farm size, market access, and agroecological potential on food security and household incomes. Within each location, farm size is a major determinant of food self-sufficiency and a household’s ability to rise above the living income threshold. Closing yield gaps strongly increases the proportion of households that are food self-sufficient. Yet in four of the locations (Ethiopia, Tanzania, Ghana and Malawi), land is so constraining that only 42–53% of households achieve food self-sufficiency, and even when yield gaps are closed only a small proportion of households can achieve a living income. While farming remains of central importance to household food security and income, our results help to explain why off-farm employment is a must for many. We discuss these results in relation to sub-Saharan Africa’s increasing population, likely agricultural expansion, and agriculture’s role in future economic development.

The world is challenged to meet the food demand of a growing population, especially in developing countries. Given the ambitious plans to scale up agroforestry in Africa, an improved understanding of the effect of agroforestry practices on the already challenged food security of rural households is crucial. The present study was undertaken to assess how on-farm trees impacted food security in addition to other household income sources in Rwanda. In each of the six agroecologies of Rwanda, a stratified sampling procedure was used where two administrative cells (4th formal administrative level) were selected in which households were randomly selected for interviews. A survey including 399 farmers was conducted and farmers were grouped in three types of agroforestry practice (i) low practitioners (LAP) represented by the first tertile, (ii) medium practitioners (MAP) represented by the second tertile and (iii) high practitioners (HAP) represented by the third tertile of households in terms of tree number. Asset values, household income sources, crop production, farm size, crop yield, and food security (food energy needs) were quantified among the types of agroforestry practice. A larger proportion of HAP households had access to adequate quantity and diversity of food when compared with MAP and LAP households. Food security probability was higher for households with more resources, including land, trees and livestock, coinciding with an increased crop and livestock income. We found no difference in asset endowment among types of agroforestry practices, while farmers in agroecologies with smaller farms (0.42 ha to 0.66 ha) had more on-farm trees (212 to 358 trees per household) than farms in agroecologies with larger farms (0.96 ha to 1.23 ha) which had 49 to 129 trees per household, probably due to differences in biophysical conditions. A positive association between tree density and food security was found in two out of six agroecologies. The proportion of income that came from tree products was high (> 20%) for a small fraction of farmers (12%), with the more food insecure households relying more on income from tree products than households with better food security status. Thus, tree income can be percieved as a “safety net” for the poorest households.

The extreme poverty line is the most commonly used benchmark for poverty, set at US$ 1.90 by the World Bank. Another benchmark, based on the Anker living wage methodology, is the remuneration received for a standard work week necessary for a worker to meet his/her family’s basic needs in a particular place. The living wage concept has been used extensively to address incomes of plantation workers producing agricultural commodities for international markets. More recently intense discussion has emerged concerning the ‘living income’ of smallholder farmers who produce commodities for international supply chains on their own land. In this article we propose a simple method that can be used in all types of development projects to benchmark a rural ‘living income’. We launch the Living Income Methodology, as adapted from the Living Wage Methodology, to estimate the living income for rural households. In any given location this requires about one week of fieldwork. We express it per adult equivalent per day (AE/day) and data collection is focused on rural households and their immediate surroundings. Our three case studies showed that in 2017 in Lushoto District, rural Tanzania, the living income was US$ PPP 4.04/AE/day, in Isingiro District, rural Uganda, 3.82 and in Sidama Zone, rural Ethiopia, 3.60. In all cases, the extreme poverty line of US$ PPP 1.90 per capita per day is insufficient to meet the basic human rights for a decent living in low-income countries. The Living Income Methodology provides a transparent local benchmark that can be used to assess development opportunities of rural households, by employers in rural areas, including farmers hiring in labour, while respecting basic human rights on a decent living. It can be used to reflect on progress of rural households in low-income countries on their aspired path out of poverty. It further provides a meaningful benchmark to measure progress on Sustainable Development Goal 1, eliminating poverty, and 2, zero hunger and sustainable food systems, allowing for consideration of the local context.

Achieving SDG2 (zero hunger) in a situation of rapid global population growth requires a continued focus on food production. Farming not merely needs to sustainably produce nutritious diets, but should also provide livelihoods for farmers, while retaining natural ecosystems and services. Rather than focusing on production principles, this article explores the interrelations between farms and farming systems in the global food system. Evaluating farming systems around the world, we reveal a bewildering diversity. While family farms predominate, these range in size from less than 0.1 ha to more than 10,000 ha, and from hand hoe use to machine-based cultivation, enabling one person to plant more than 500 ha in a day. Yet, farming in different parts of the world is highly interdependent, not least because prices paid for farm produce are largely determined by global markets. Furthermore, the economic viability of farming is a problem, globally. We highlight trends in major regions of the world and explore possible trajectories for the future and ask: Who are the farmers of the future? Changing patterns of land ownership, rental and exchange mean that the concept of ‘what is a farm’ becomes increasingly fluid. Next to declining employment and rural depopulation, we also foresee more environmentally-friendly, less external input dependent, regionalised production systems. This may require the reversal of a global trend towards increasing specialisation to a recoupling of arable and livestock farming, not least for the resilience it provides. It might also require a slow-down or reversal of the widespread trend of scale enlargement in agriculture. Next to this trend of scale enlargement, small farms persist in Asia: consolidation of farms proceeds at a snail’s pace in South-east Asia and 70% of farms in India are ‘ultra-small’ – less than 0.05 ha. Also in Africa, where we find smallholder farms are much smaller than often assumed (< 1 ha), farming households are often food insecure. A raft of pro-poor policies and investments are needed to stimulate small-scale agriculture as part of a broader focus on rural development to address persistent poverty and hunger. Smallholder farms will remain an important source of food and income, and a social safety net in absence of alternative livelihood security. But with limited possibilities for smallholders to ‘step-up’, the agricultural engine of growth appears to be broken. Smallholder agriculture cannot deliver the rate of economic growth currently assumed by many policy initiatives in Africa.

Soil nutrient management proves critical to increase maize yield under both current and projected climatic conditions. The yield benefits from nutrient management are further enhanced given an early maize planting date. [ABSTRACT FROM AUTHOR]

Despite continuing economic growth, Uganda faces persistent challenges to achieve food security. The effectiveness of policy and development strategies to help rural households achieve food security must improve. We present a novel approach to relate spatial patterns of food security to livelihood strategies, including the contribution of on- and off-farm activities to household food availability. Data from 1927 households from the World Bank Living Standards Measurement Study were used to estimate the calorific contribution of livelihood activities to food availability. Consumption of crops produced on-farm contributed most to food availability for households with limited food availability, yet the majority of these households were not food self-sufficient. Off-farm and market-oriented on-farm activities were more important for households with greater food availability. Overall, off-farm income was important in the north, while market-oriented on-farm activities were important in western and central Uganda. Food availability patterns largely matched patterns of agroecological conditions and market access, with households doing worst in Uganda’s drier and remote northeast. Less food-secure households depended more on short-cycle food crops as compared with better-off households, who focused more on plantation (cash) crops, although this varied among regions. Targeting interventions to improve food security should consider such differences in enterprise choice and include options to improve household market access and off-farm income opportunities.

Boosting smallholder food production can potentially improve children’s nutrition in rural Sub-Saharan Africa through a production-own consumption pathway and an income-food purchase pathway. Rigorously designed studies are needed to provide evidence for nutrition impact, but are often difficult to implement in agricultural projects. Within the framework of a large agricultural development project supporting legume production (N2Africa), we studied the potential to improve children’s dietary diversity by comparing N2Africa and non-N2Africa households in a cross-sectional quasi-experimental design, followed by structural equation modelling (SEM) and focus group discussions in rural Ghana and Kenya. Comparing N2Africa and non-N2Africa households, we found that participating in N2Africa was not associated with improved dietary diversity of children. However, for soybean, SEM indicated a relatively good fit to the posteriori model in Kenya but not in Ghana, and in Kenya only the production-own consumption pathway was fully supported, with no effect through the income-food purchase pathway. Results are possibly related to differences in the food environment between the two countries, related to attribution of positive characteristics to soybean, the variety of local soybean-based dishes, being a new crop or not, women’s involvement in soybean cultivation, the presence of markets, and being treated as a food or cash crop. These findings confirm the importance of the food environment for translation of enhanced crop production into improved human nutrition. This study also shows that in a situation where rigorous study designs cannot be implemented, SEM is a useful option to analyse whether agriculture projects have the potential to improve nutrition.

The demand for chicken meat and eggs exceeds what can be produced in Tanzania, largely due to low productivity of the sector. Feed quantity and quality are the major factors determining the potential production and productivity of chickens. The present study explored the yield gap in chicken production in Tanzania and analyses the potential of increased chicken production as a result of closing the feed gaps. The study focused on feed aspects limiting dual-purpose chicken production in semi-intensive and intensive systems. A total of 101 farmers were interviewed using a semistructured questionnaire and the amount of feed provided to chickens per day was quantified. Feed was sampled for laboratory analysis and physical assessments were made of weights of chicken bodies and eggs. The results were compared with the recommendations for improved dual-purpose crossbred chickens, exotic layers, and broilers. The results show that the feeds were offered in insufficient quantity compared with the recommendations for laying hens (125 g/chicken unit/d). Indigenous chickens were fed 111 and 67 while the improved crossbred chickens were fed 118 and 119 g/chicken unit/d under semi-intensive and intensive systems, respectively. Most feeds fed to dual-purpose chickens were of low nutritional quality, particularly lacking in crude protein and essential amino acids in both rearing systems and breeds. Maize bran, sunflower seedcake, and fishmeal were the main sources of energy and protein in the study area. The study findings show that the important feed ingredients: protein sources, essential amino acids, and premixes were expensive, and were not included in formulating compound feeds by most chicken farmers. Of all 101 respondents interviewed, only one was aware of aflatoxin contamination and its effects on animal and human health. All feed samples contained a detectable concentration of aflatoxins and 16% of them exceeded the allowed toxicity thresholds (>20 µg/kg). We highlight the need for a stronger focus on feeding strategies and ensuring the availability of suitable and safe feed formulations.

The poultry industry in Tanzania has grown steadily over the past decade. We surveyed 121 chicken farming households along an intensification gradient from backyard to semi-intensive and intensive production systems based on rearing system and assumed purpose and poultry breed in the Iringa region. About 30% of households had more than one breed and/or rearing system combination. The subdivision of poultry systems was refined by adding the size of the flocks to highlight variation in scale of operations. On this basis we distinguished 3 main types: 1) subsistence small-scale free-range chicken production; 2) market-oriented small to medium scale semi-intensive and 3) small to medium-large scale intensive systems. ‘Intensification’ involves the transition from keeping indigenous chickens to improved dual-purpose and exotic breeds driven by greater productivity and potential for income generation. The more intensive the production system, the more the intensity and diversity of diseases identified by farmers as their main problem, which was partly attributed to the greater sensitivity of the improved breeds, poor veterinary measures, and the high chicken density facilitating disease spread. Based on the survey we constructed a problem tree to classify the underlying constraints and their interrelations, and to identify common root causes, based on which we propose practical solutions to improve chicken production. Development of medium-large scale systems is particularly constrained by a limited supply of 1-day-old chicks and theft. By contrast, intensification of small-scale systems is constrained by limited access to quality feed, vaccines and medicines, capital, and lack of a reliable market, partly due to the absence of farmer organization. These constraints can be addressed through formation of producer groups and promotion of outgrower and enterprise development models. Enterprise development appears to be the most promising business model for smallholder chicken farmers given that it allows farmers more freedom in decision-making and management while strengthening linkages with input suppliers and output markets to ensure a viable and profitable business.

Despite abundant land and favourable climatic conditions, Mozambique remains food insecure. We investigated the diversity, constraints and opportunities to increase smallholder productivity and achieve food self-sufficiency in maize-based farming systems in two Posts in central Mozambique. We identified four farm types in each village based on cultivated area and labour. Farm type 1 cultivated relatively large areas, owned cattle and hired in labour. Farm type 2 cultivated moderate areas and both hired in and hired out labour. Farms of type 3a and 3b cultivated the smallest areas. Farm type 3a shared labour while Farm type 3b only hired out labour. For each farm type, we calculated land and labour productivities of maize, sunflower and sesame and assessed maize self-sufficiency. Access to labour during weeding was the main constraint. The hiring out of labour by small farms caused severe reductions in both land and labour productivity. Yield reductions on these farms were due to delayed weeding in own fields. In one Post, Farm type 3b was not maize self-sufficient. Labour quality was probably impaired by excess alcohol consumption among the poorer farmers (both men and women). Our results showed that production can be increased based on current agricultural practices. Farmers did not cultivate all of their land, suggesting that lack of labour constrained intensification by smallholder farmers.

Family farms are defined by two criteria: the importance of family labour and the transfer of ownership, land tenure or management to the next generation. Most farms across the globe are family farms, and they vary in size from <1ha to >10,000ha. Trends in farm size (small farms getting smaller and large farms getting larger) are not directly related to farm ownership and do not necessarily impact global food security. Rather, both the causes and effects of farm size trends depend on the availability of farm resources and off-farm employment opportunities. Similarly, environmental sustainability, though impacted by agriculture, cannot be linked directly to family ownership or farm size. To address issues related to environment, social conditions and food security, focus should not be on the preservation of family farms but on transformations to strive for environmental, social and economic sustainability of farming in all its shapes and forms.

A diet containing insufficient micronutrients can harm human health. Maps that pinpoint areas of Africa associated with micronutrient-poor grains now offer a way to target interventions that tackle such deficiencies.

•The conference attracted 600 participants from 65 countries.•There is a need to understand and adopt a global food systems approach.•Concern was expressed on the lack of data on all aspects of food systems.•We summarise the main conclusions of discussions at the conference.

Resource use and management are major determinants of the food self-sufficiency of smallholder farmers in sub-Saharan Africa. A study was conducted in Rwanda in two contrasting agro-ecological zones (Central plateau and Buberuka) to characterise farms, quantify their resource flows, and evaluate the effect of resource management on food self-sufficiency. The Simbi and Kageyo sectors were selected as the representatives of agro-ecological zones and two villages were selected within each sector. Wealth ranking, focus group discussions and formal survey techniques were used. Farms were classified into resource groups (RGs) that differed with regards to socio-economic and food self-sufficiency status. Soils were more fertile in Kageyo (Buberuka) than in Simbi (Central plateau). In both sites 67 % or more of the households were classified in the poorest category who cultivated less than 0.2 ha and experienced 4–5 months of food deficit each year. The partial N balance was more negative in Kageyo (−35.87 kg N ha−1year−1) while the P balance was negative in close fields and outfields but positive in homefields (0.43 kg P ha−1year−1). Calorie and protein availability were insufficient in RG1 (poor resource group) and RG2 (moderate resource group) farms in Simbi and RG1 (poor resource group) in Kageyo. Boundary line analysis indicated that poor soil C contents led to 0.6–0.8 t ha−1less yield with respect to the attainable yield in better fields in RG 2. Closing the maize yield gap would result in doubling the energy and protein intake in Simbi. In such complex agricultural systems, there is a need to apply an integrated and multi-dimensional approach to understand differences among farms, identify limitations to food production and explore realistic options to ensure sustainable agricultural production and food self-sufficiency.

The article focuses on an experiment conducted in Zimbabwe on the effect of nutrient fertilizers in different types of soil for producing maize. Topics discussed include applying multi nutrient fertilizers lead to the growth of maize production on depleted soils, negative effect of applying nutrient fertilizers in sandy and clay soil, and the benefit of combined application of nutrient fertilizer and manure.

We studied the process of assessment and adoption of 10 grain- and green-manure legumes by smallholder maize farmers differing in resource endowment in Chisepo, central Malawi. The legumes had been promoted with the farmers from 1998 to 2004, primarily as a way to diversify food production and maintain the fertility of their soils. Farmers (n= 136) were surveyed in 2004 at the end of the period of promotion to assess the degree of awareness and uptake of the legumes and the reasons for adoption. A follow-up survey was conducted in 2007 among a broader sample of Chisepo farmers (n= 84) to measure the persistence of adoption. An Analytic Hierarchy Process (AHP) was used in 2004 to create scales of priority and as a tool to compare predicted with actual legume uptake. Actual adoption of food grain legumes reflected predictions by the AHP but it over-predicted uptake of the non-food legumes. The AHP helped us understand how farmer perceptions and needs influence adoption, as well as limitations with the legumes. Suitability for food was the most important criterion that farmers identified for adoption, followed by contribution to soil fertility and suppression of weeds. Over 75 % of the farmers surveyed in 2004 were aware of most of the legumes. Frequent use of the grain legumes was reported in 2004 (79 % for CG7 groundnut, 77 % for soyabean and 47 % for pigeonpea) by both the better-resourced (wealthier) and less-well-resourced (poorer) farm households. Awareness rose to over 90 % of farmers surveyed in 2007 but adoption fell somewhat to 67 % for soyabean, 57 % for CG7 groundnut and 43 % with pigeonpea among the wealthier farmers, while Bambara groundnut rose to 38 %. Fifty-two percent of poorer farmers reported adoption of CG7, 46 % soyabean, 35 % Bambara groundnut and 27 % pigeonpea in 2007. There was greater uptake by the wealthier farmers than those with fewer resources. Overall, although the legumes were promoted for maintenance of soil fertility, farmers were largely interested in and mainly adopted those legumes they considered most useful for food diversity and security, and with potential for market sale. Only a few wealthier farmers used mucuna and tephrosia among the green manure legumes. Improving the food value of vigorous and productive multi-purpose legumes, particularly mucuna, may help raise the farmers’ interest, with secondary benefits for soil fertility.

Agriculture faces many challenges. In both public discourse and the scientific literature debates about the future are increasing framed in terms of ‘alternative’ versus ‘conventional’ agriculture. In this paper we critically examine this framing, and seek to understand how the term conventional has been and is being used. We argue that the category conventional agriculture has little analytical purchase, and that its use is part of a strategy of homogenising, normalising and othering. In effect, the term conventional agriculture has been weaponised. This helps explain the sterile and unproductive nature of much debate about future agricultures. A more productive approach is to focus on where and how different farming systems can contribute to the sustainability of agriculture.

Emerging trends of a changing and increasingly variable climate have introduced new livelihood challenges in rain-fed smallholder agricultural systems that predominate in Sub-Saharan Africa (SSA). The capacity of local farming communities and their institutions to respond to the new and emerging impacts of climate change is often constrained by lack of access to information and improved technologies, as well as poor support mechanisms to promote assimilation of new knowledge. This threatens to heighten vulnerability of the majority of SSA's rural communities who are already facing severe problems of food insecurity and a declining soil resource base. In this paper we use two case studies from Wenchi district in Ghana and Makoni in Zimbabwe to communicate how participatory action research (PAR) methodology, characterised by iterative planning–action–reflection cycles, was coupled with a new concept of field-based farmer learning centres to build adaptive capacity of smallholder farmers to climate change. The study was part of a University of Zimbabwe—led project supported under the Climate Change Adaptation in Africa (CCAA) programme to explore the state of resilience in African smallholder farming. The PAR and learning centre processes enabled communities, local leaders, and extension agents and researchers to establish the, hither to, imperceptible link between poor soil fertility and rising institutional challenges within communities. Institutional conflicts related to land tenure and sharecropping arrangements between migrant farmers and native landowners were addressed in Ghana, while local institutions supporting traditional social safety net mechanisms were revitalized in Zimbabwe. In both cases, it was apparent that farmers faced multiple stresses, at the core of which were poor and declining soil fertility and weakening local institutions. The worsening rainfall distribution and increasing cases of drought are broadening the scope for vulnerability, often driving competing claims and conflicts. PAR was successfully used as an entry point, empowering communities to self-mobilize and self-organize to co-learn and experiment with integrated soil fertility management (ISFM) technologies and other improved farming practices. They realised opportunities for achieving high crop yields and generate surpluses in good years. Strengthening local institutional capacity to revitalise community safety nets proved an essential ingredient for enhancing adaptive capacity of smallholders to climatic shocks. The PAR process was a major driver of effective partnerships among community members, extension, policy makers and researchers, but ensuing success generated a new set of social challenges that could not be addressed within the short timescale of the project. We conclude that PAR was a suitable mechanism for supporting self-organization and co-learning processes among smallholder farmers and their service providers, enabling them to use ISFM technologies and strengthen their local institutions around natural resource management. This revealed the scope for building adaptive capacity of these communities against climate change and variability.

The deliberate planting of fast‐growing N2–fixing legume monoculture species in rotation with cereal crops can be an important source of N for soil fertility replenishment. We hypothesized that mixed‐species fallows have a higher potential of giving long‐term residual benefits in terms of biomass, nutrients, and quality of residuals leading to long‐term nutrient supply to postfallow maize (Zea maysL.) crops. To test these hypotheses, two experiments were established in farmers' fields on very fine Kandiudalfic Eutrudox soils with monoculture and mixed‐species fallows. Treatments included: sesbania [Sesbania sesban(L.) Merr.], crotalaria (Crotalaria grahamianaWight and Arn.), pigeonpea [Cajanus cajan(L.) Millsp.], siratro [Macroptilium atropurpureum(DC.) Urb.], and calliandra (Calliandra calothyrsusMeissn.) as monoculture‐species fallow and mixture fallows of sesbania + crotalaria, sesbania + pigeonpea, sesbania + siratro, or sesbania + calliandra compared with continuous maize cropping with or without N fertilizer, and natural weed fallow. Total aboveground biomass ranged from 4.1 to 20.5 Mg ha−1for monoculture and 7.8 to 23.3 Mg ha−1for mixed‐species fallows. Recyclable fallow biomass N ranged from 70 to 313 kg ha−1and there was a positive interaction in some mixtures leading to increased N accumulation. Postfallow maize yields for fallows over five cropping seasons were 161–272% or 61–103% higher when compared with continuous maize without or with N fertilizer, respectively. Long‐term postfallow effects on maize yield were linearly related to the amount of recycled fallow N yield. Thus, choice of fallow species to mix should be primarily driven by a better risk management strategy and an increased basket of multiple products and services.

In November 2014 I suffered a major stroke and was unable to work. I recently began to ‘wake up’ and have been able to re-engage with literature and discussions on agricultural development and climate change. I am surprised how familiar I am with much of the debate, but disappointed that major issues receive little attention – such as the impacts of climate change on smallholder agriculture, conservation of biodiversity and the need for reform of global financial institutions. In this short ‘perspective’, I comment on issues where there has been little academic attention over the past seven years and new issues that have arisen such as animal-free foods and artificial intelligence. I conclude by suggesting where attention needs to be focused. I expect this to be my final contribution to the literature.

The release of mineral-N in soil from plant residues is regulated by their ‘quality’ or chemical composition. Legume materials used by farmers in southern Africa are often in the form of litter with N concentration <2%. We investigated the decomposition of Sesbania sesbanand Acacia angustissimalitter in the field using litterbags, and N mineralization of a range of legume materials using a leaching tube incubation method in the laboratory. The mass loss of the litter could be described using a modified exponential decay model: Y= (Y0−Q)e−kt+ Q. The relative decomposition constants for Sesbaniaand Acacialitter were 0.053 and 0.039 d−1, respectively. The % N mineralized from fresh Sesbaniaprunings was 55% compared with only 27% for the Sesbanialitter after 120 days of incubation under leaching conditions. During the same period, fresh prunings of Acaciareleased only 12% of the added N while Acacialitter released 9%. Despite the large differences in N concentration between Acaciaprunings and its litter, the total mineralized N was similar, as mineralization from prunings was depressed by the highly active polyphenols. While N supply may be poor, these slow decomposing litter materials are potentially useful for maintaining soil organic matter in smallholder farms. In two field experiments with contrasting soil texture, Sesbania, Acaciaand Cajanusproduced large amounts of biomass (>5 Mg ha−1) and improved N cycling significantly (>150 kg N ha−1) on the clay loam soil, but adapted poorly on the sandier soil. There was a rapid N accumulation in the topsoil at the beginning of the rains in plots where large amounts of Sesbaniaor Acaciabiomass had been incorporated. Despite the wide differences in resource quality between these two, there was virtually no difference in N availability in the field as this was, among other factors, confounded by the quantity of N added. A substantial amount of the nitrate was leached to greater than 0.4 m depth within a three-week period. Also, the incidence of pests in the first season, and drought in the second season resulted in poor nitrogen use efficiency. Our measurements of gaseous N losses in the field confirmed that N2O emissions were <0.5 kg N ha−1. As we had measurements of all major N flows, we were able to construct overall N budgets for the improved fallow – maize rotation systems. These budgets indicated that, in a normal rainfall season with no major pest problems, reducing nitrate leaching would be the single largest challenge to increased N recovery of added organic N in the light textured soils.

With recent advances in rhizobial phylogeny, questions are being asked as to how an ecological framework can be developed so that rhizobial classification and diversity could have greater practical applications in enhancing agricultural productivity in tropical ecosystems. Using the results of studies on tropical rhizobia which nodulate agroforestry tree legumes, three ecological aspects of rhizobial biodiversity were used to illustrate how its potential can be exploited. The results showed that legumes nodulate with diverse rhizobial types, thus contributing to the success of legumes in colonising a wide range of environments. There was an apparent shift in the relative dominance of rhizobia populations by different rhizobial types as soil pH changed. The Rhizobium tropici-type rhizobia were predominant under acidic conditions, Mesorhizobiumspp. at intermediate pH and Sinorhizobiumspp. under alkaline conditions. The R. tropici-type rhizobia were the most effective symbiotic group on all the host legumes. However, strains of Sinorhizobiumspp. were as effective as the R. tropicitypes in N2-fixation on Gliricidia sepium, Calliandra calothyrsusand Leucaena leucocephala; while Mesorhizobiumstrains were equally as effective as the R. tropicitypes on Sesbania sesban. Classification of rhizobia based on phenotypic properties showed a broad correlation with groupings based on 16S rRNA sequence analysis, although a few variant strains nested with the dominant groups in most of the clusters. Some of the phenotypic characters that differentiated different rhizobial groups are highlighted and a case is made for the need to standardise this method.

The rotation of crops with planted N2–fixing legumes (improved fallows) is a promising agroforestry innovation for replenishing soil fertility in the tropics. We postulated that woody and herbaceous legumes with different rooting and growth patterns could be mixed in improved fallows to maximize utilization of belowground growth resources. We used a method of injecting a solution of 15N‐labeled (NH4)2SO4into soil at 0.15‐ and 1.0‐m depths to measure soil mineral N acquisition by sesbania [Sesbania sesban(L) Merr], crotalaria [Crotalaria grahamianaWight and Arn.], and the understory herbaceous legume siratro [Macroptilium atropurpureum(DC.) Urb.] grown in mixed stands on a Kandiudalfic Eutrudox soil in western Kenya. Crotalaria had the highest root length in the topsoil. Sesbania on the other hand had nearly half its total root length below 0.3 m at 0.3‐ to 1.5‐m depth; sesbania took up more added 15N than crotalaria and siratro from the 1.0‐m depth. Mixed sesbania and crotalaria stands, as compared with growing species in monocultures, increased root length at the 0.3‐ to 1.2‐m depth. Sesbania mixed with siratro was more effective than sesbania mixed with crotalaria in uptake of 15N at 1.0‐m depth but not at 0.15‐m depth. At 2 mo after injection, the 15N was concentrated immediately below the injection point with little lateral movement. This confirmed the utility of the methodology in determining temporal N uptake for species in mixed stands. Our results suggest that opportunities exist for enhanced subsoil N retrieval through the mixing of leguminous species, which can influence root distribution and increase rooting in the subsoil.

The rotation of crops with planted, N2‐fixing legumes is a promising agroforestry innovation for replenishing soil fertility in the tropics. We postulated that woody and herbaceous legumes with different growth and rooting patterns could be mixed to optimize above‐ and belowground resource capture. The objective of this study was to evaluate the effect of species interactions on resource utilization by legumes grown in mixtures on a Kandiudalfic Eutrudox in western Kenya. Four woody legume shrubs—pigeonpea [Cajanus cajan(L.) Millsp.], sesbania [Sesbania sesban(L.) Merr.], crotalaria (Crotalaria grahamianaWight and Arn.), and tephrosia (Tephrosia vogeliiHook F.)—grown in monoculture and mixed stands were evaluated for light interception, soil N and water uptake, and biomass production. Siratro [Macroptilium atropurpureum(DC.) Urb.] and groundnut (Arachis hypogaeaL.) were undersown in woody legume stands. Total aboveground biomass production ranged from 9 to 13 Mg ha−1for monoculture and 8 to 15 Mg ha−1for mixtures of woody legumes. Total N in woody‐legume stands ranged from 100 to 178 kg N ha−1. Biomass and plant N were not significantly different among woody‐legume treatments. However, undersowing siratro as a supplement increased stand productivity and recycled biomass N. Species complementarity in topsoil and subsoil utilization of mineral N was observed in crotalaria + sesbania and pigeonpea + tephrosia mixed stands. Dense soil cover created by siratro led to better conservation of soil water. Results indicated that the tested mixtures provide a better risk management strategy through compensatory growth potential. Greatest opportunities for intensifying resource utilization appear to exist through undersowing a creeping legume with an open‐canopy woody legume.

Advances in our understanding of the management of organic resources are reviewed in relation to management of N demands for crop growth in smallholder agriculture in the tropics. In most tropical countries, organic residues represent an important source of nutrients for crop growth whereas they represent unavoidable but problematic wastes in many developed countries. Sources of N for cropping systems are N$_2$-fixation by legumes or mineral N fertilizers; recycling of organic resources can improve the overall efficiency of N use within the cropping system. Approaches to manipulating the timing of N availability in the soil in relation to the strength and timing of crop N demand are discussed. A framework is presented, focused around the capture efficiency of N by crops, which links systems of N excess to systems of N limitation in relation to N use and potential N losses.

Inputs of organic materials play a central role in the productivity of many tropical farming systems by providing nutrients through decomposition and substrate for synthesis of soil organic matter (SOM). The organic inputs in many tropical farming systems such as crop residues, manures, and natural fallows are currently of low quality and insufficient quantity to maintain soil fertility hence there is need to find alternative or supplementary sources of nutrients. Knowledge gained over the past decade on the role of organic resource quality in influencing soil nutrient availability patterns (Synchrony Principle) and SOM maintenance (SOM Principle) provides a strong scientific basis on which to develop management tools. This scientific information must be linked with farmer knowledge and circumstances to provide a realistic approach to soil fertility and SOM management in the tropics. A decision tree has been developed for testing hypotheses about the resource quality parameters that affect nitrogen release patterns and rates. The decision tree is linked to an Organic Resource Database (ORD) with detailed information on the resource quality of agroforestry trees and leguminous cover crops providing a systematic means of selecting organic resources for soil fertility management. The decision tree has also been translated into a practical field guide for use with farmers in evaluating organic materials. The longer-term effects of organic inputs on SOM might also be addressed through the decision tree and database. It is generally believed that materials good for short-term soil fertility will not build or maintain SOM; if true then it is difficult to imagine practical means of maintaining SOM in the African context where short-term fertility issues will take precedence over longer-term maintenance of SOM.

Sustainable intensification has been proposed as a pathway to achieve food security and reduce environmental impacts of agriculture by focusing on narrowing yield gaps on existing agricultural land while improving resource use efficiencies. There is a general consensus that regions with large yield gaps can benefit most from sustainable intensification but it remains unclear how sustainable this is for farmers given their current resource constraints and livelihood strategies. Here, we draw upon three contrasting case studies, for which detailed data at field and farm levels were available for yield gap decomposition, to assess how sustainable intensification of crops (at field level) works out at farm level using environmental and socio-economic indicators. Although there is large potential for future intensification (more output with more input) of cereal production in southern Ethiopia, current input use in these farming systems is not economically and environmentally sustainable at farm level. The same is true for rice production in Central Luzon where sustainable intensification (more output with less input) can help to narrow yield gaps and improve N use efficiency (NUE) but it is not profitable due to the heavy reliance on costly hired labour. Trade-offs between yield gap closure and labour productivity were also observed in the aforementioned farming systems. Arable farms in the Netherlands exhibit small yield gaps as well as higher economic performance, NUE and N surplus compared to those observed in Southern Ethiopia and Central Luzon. For improving environmental sustainability, these farms require increases in resource-use efficiency and a reduction of the environmental impacts through a lower use of inputs (same output with less input). We conclude that public investments conducive for innovation and profitable farming are essential to make technologies accessible and affordable for farmers and to ensure that yield gaps can be narrowed and sustainability objectives served at the farm level.

The 4th Global Food Security conference highlighted four major developments: the shift from food security to food systems; a focus on diets and consumption patterns; the importance of unknown futures and inherent uncertainties and risks; and the central role of multi-level connections between local- and global-oriented research. These shifts highlight the importance for research to contribute to dialogue and collective intelligence through evidence-based brokerage, and to move beyond polarization of debates. These shifts also call for the involvement of scientists in multi-stakeholder arrangements to strengthen innovation and learning at different levels, and for their participation in foresight studies to help navigate plausible futures. Delegates discussed five scientific challenges to be addressed through both research investments and by improving science-policy interfaces.

Deleterious effects of heavy metals on soil microorganisms are reviewed in relation to the complexities involved in their study. There is strong evidence that soil microbes are more sensitive to heavy metals than animals or crop plants. Decisions concerning limits considered to be ‘safe’ in terms of protection of soil microorganisms or soil microbial processes from metal toxicity depend on the organisms considered and value judgements as to their importance. At present there is a large discrepancy in actual concentrations of heavy metals that are allowed to accumulate in agricultural soils between different countries. The approach of attempting to achieve zero accumulation of heavy metals in soils is undoubtedly the most conservative, but will severely restrict the recycling of sewage sludges to agricultural land.

Summary This paper reviews the evidence for impacts of metals on the growth of selected plants and on the effects of metals on soil microbial activity and soil fertility in the long-term. Less is known about adverse long-term effects of metals on soil microorganisms than on crop yields and metal uptake. This is not surprising, since the effects of metals added to soils in sewage sludge are difficult to assess, and few long-term experiments exist. Controlled field experiments with sewage sludges exist in the UK, Sweden, Germany and the USA and the data presented here are from these long-term field experiments only. Microbial activity and populations of cyanobacteria,Rhizobium leguminosarum bv.trifolii, mycorrhizae and the total microbial biomass have been adversely affected by metal concentrations which, in some cases, are below the European Community's maximum allowable concentration limits for metals in sludge-treated soils. For example, N2-fixation by free living heterotrophic bacteria was found to be inhibited at soil metal concentrations of (mg kg-1): 127 Zn, 37 Cu, 21 Ni, 3.4 Cd, 52 Cr and 71 Pb. N2-fixation by free-living cyanobacteria was reduced by 50% at metal concentrations of (mg kg-1): 114 Zn, 33 Cu, 17 Ni, 2.9 Cd, 80 Cr and 40 Pb.Rhizobium leguminosarum bv.trifolii numbers decreased by several orders of magnitude at soil metal concentrations of (mg kg-1): 130–200 Zn, 27–48 Cu, 11–15 Ni, and 0.8–1.0 Cd. Soil texture and pH were found to influence the concentrations at which toxicity occurred to both microorganisms and plants. Higher pH, and increased contents of clay and organic carbon reduced metal toxicity considerably. The evidence suggests that adverse effects on soil microbial parameters were generally found at surpringly modest concentrations of metals in soils. It is concluded that prevention of adverse effects on soil microbial processes and ultimately soil fertility, should be a factor which influences soil protection legislation.

Collaborative research utilizing field trials and whole farm crop simulation enables adaptation of Australian wheat crop practices. Novel varieties sown earlier enable a longer growing season, which facilitates wheat yield increases despite an increasingly challenging climate.

The article presents a research which examines the optimization of phosphorus (P) and manure application in maize-soybean rotations in Zimbabwe. It notes that production of soybean in the country is limited because farmers pay little attention to the crop and prefer to use fertilizer to the previous crop in the rotation. According to the research, the combined application of P fertilizer and manure to maize is more productive and economic under poor soil fertility conditions.

National food security in countries of sub-Saharan Africa requires an abundant supply of cheap and nutritious food for the burgeoning population. At the same time agriculture is a major contributor to the balance of payments for African economies. So agricultural production in Africa needs to increase strongly to meet the demands of both national and international markets. Yet fragmentation of land due to population pressure in rural areas, and the low prices farmers are paid for their produce, mean that in many rural areas in sub-Saharan Africa the farms are already too small to provide food security or a living income for the household. There is a high dependency on off-farm income and little incentive to intensify production. Thus rural households are often ‘reluctant’ farmers, lacking resources or the economic incentives to invest in agriculture. The conundrum that must be addressed is how to provide cheap, nutritious food to feed the growing urban and rural populations while creating incentives to stimulate increased agricultural production. This will require major transformations of the smallholder farming systems alongside creation of alternative employment.

Sustainable development goal 2 (SDG 2) challenges the world to connect food production and consumption in a way that matches local contexts and enables everyone to enjoy a healthy diet that is produced sustainably and contributes to the other SDGs. We identify a Missing Middle between food production and consumption, and between globally defined goals and local implementation practices that may hinder progress towards SDG 2. Examples of this Missing Middle and how it can be bridged demonstrate that key challenges should be addressed in a more integrated manner for more effective action on SDG 2. We encourage actors in food provisioning to start addressing the Missing Middle by collaborating with relevant stakeholders in specified cases.

Rhizobia were isolated from root nodules of three tree legumes inoculated with dilution series of two tropical soils. The diversity of the isolates obtained from different soil dilutions was assessed by PCR-RFLP analysis of the internally transcribed spacer (ITS) region between the 16S and 23S rRNA genes. In both soils there was a strong effect of dilution on the genetic diversity of the populations with apparent diversity decreasing with increasing dilution.

Resource quality (in particular N. lignin and polyphenol concentrations) is a major factor in regulating decomposition and N mineralization from organic materials. Simple decision trees have been constructed which allow translation of chemical Parameters into tests readily applied in the field. This allows discussion of the potential uses of organic resources with field extension agents and farmers in relation to their decomposition and N release. ©2000 Pubhshed by Elsevier Science B.V. All rights reserved.

Describes the success of a Filipino farmer in providing total self-sufficiency for a family of 13 by growing the azolla plant. Doubles mass every 3-5 days; Fixes nitrogen; Provides animal food, methane and fertilizer; Weed suppressant; Human food; Future outlook.

The article offers information on the simulation model called PALMSIM to quantify the potential yield palm oil to meet demands. It mentions that the model stimulates the yield by estimating solar radiation in high rainfall environments of Malaysia and Indonesia by estimating fresh fruit bunches (FFB). A study was conducted to analyze efficacy of the model which concludes that the model is efficient in selecting potential crop sites along with quantifying the effect of water stress on yield.