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Improved forages of genus Brachiaria and Panicum grasses were introduced to men and women farmers in western Kenya and southern Ethiopia. To provide an understanding of the social and demographic characteristics of farming systems, a household survey was implemented in 2018/2019. In 2020, a complementary qualitative study was conducted to understand: i) gender dynamics in accessing forage planting materials: ii) role of forage trait preferences, and: iii) how the introduction of forage varieties influences gender relations in households. Forage seed/splits were accessed through women’s groups. In Kenya, men and women were advised to source more forage seeds from private seed companies for scaling. In Ethiopia, men prioritized ‘fast regrowth’ and women ‘nutritious biomass’ traits; in Kenya, men prioritized ‘nutritious biomass’ and women ‘how fast forage splits could be established’ traits. Sale of the forage cuttings appeared to provide marketing opprtunities that were promising for women, who were able to control the income generated. The introduction of improved forages, which are grown close to homesteads, reduced the time men and boys spent in grazing livestock while increasing time women and girls spent in harvesting fodder. Following gender sensitivity training provided alongside forage introductions, Ethiopian men reported being involved in forage harvesting, chopping and feeding against prevailing norms while the Kenyan women took on greater decision-making roles. These positive outcomes in gender equity suggest that the integration of gender and forage technology trainings can secure significant gains not only for women, but also for the men in the households.

Dairy development provides substantial potential economic opportunities for smallholder farmers in East Africa, but productivity is constrained by the scarcity of quantity and quality feed. Ruminant livestock production is also associated with negative environmental impacts, including greenhouse gas (GHG) emissions, air pollution, high water consumption, land-use change, and loss of biodiversity. Improved livestock feeding and forages have been highlighted as key entry point to sustainable intensification, increasing food security, and decreasing environmental trade-offs including GHG emission intensities. In this perspective article, we argue that farming systems approaches are essential to understand the multiple roles and impacts of forages in smallholder livelihoods. First, we outline the unique position of forages in crop-livestock systems and systemic obstacles to adoption that call for multidisciplinary thinking. Second, we discuss the importance of matching forage technologies with agroecological and socioeconomic contexts and niches, and systems agronomy that is required. Third, we demonstrate the usefulness of farming systems modeling to estimate multidimensional impacts of forages and for reducing agro-environmental trade-offs. We conclude that improved forages in East Africa are at a crossroads: if adopted by farmers at scale, they can be a cornerstone of pathways toward sustainable livestock systems in East Africa.

Livestock productivity in East Africa, and especially in Tanzania, remains persistently low, while greenhouse gas (GHG) emission intensities are among the highest worldwide. This mixed methods study aims to explore sustainable livestock intensification options that reduce agro-environmental trade-offs across different smallholder farming systems in Northern Tanzania. A smallholder livestock systems typology was constructed, and representative farms simulated with a whole farm multi-objective optimization model. Livestock contributed more than 90% of on-farm GHG emissions, and DAIRY had the lowest GHG emission intensity (2.1 kg CO2e kg−1 milk). All livestock systems had alternative options available to reduce agro-environmental trade-offs, including reducing ruminant numbers, replacing local cattle with improved dairy breeds, improving feeding through on-farm forage cultivation, and minimizing crop residue feeding. Three obstacles to adoption of these technologies became apparent: they require a skillful re-organization of the entire production system, result in loss of some multi-functionality of livestock, and incur higher production risks. Sustainable livestock intensification can be a key building block to Tanzania's climate-smart agriculture portfolio, providing synergies between productivity and income increases, and climate change mitigation as co-benefit. A better understanding of the institutional settings, incentives and coordination between stakeholders is needed to sustainably transform the livestock sector.

Heat stress is a global issue constraining pig productivity, and it is likely to intensify under future climate change. Technological advances in earth observation have made tools available that enable identification and mapping livestock species that are at risk of exposure to heat stress due to climate change. Here, we present a methodology to map the current and likely future heat stress risk in pigs using R software by combining the effects of temperature and relative humidity. We applied the method to growing-finishing pigs in Uganda. We mapped monthly heat stress risk and quantified the number of pigs exposed to heat stress using 18 global circulation models and projected impacts in the 2050s. Results show that more than 800 000 pigs in Uganda will be affected by heat stress in the future. The results can feed into evidence-based policy, planning and targeted resource allocation in the livestock sector.

Livestock are critical for incomes, livelihoods, nutrition and ecosystems management throughout the global South. Livestock production and the consumption of livestock-based foods such as meat, cheese, and milk is, however, under global scrutiny for its contribution to global warming, deforestation, biodiversity loss, water use, pollution, and land/soil degradation. This paper argues that, although the environmental footprint of livestock production presents a real threat to planetary sustainability, also in the global south, this is highly contextual. Under certain context-specific management regimes livestock can deliver multiple benefits for people and planet. We provide evidence that a move toward sustainable intensification of livestock production is possible and could mitigate negative environmental impacts and even provide critical ecosystem services, such as improved soil health, carbon sequestration, and enhanced biodiversity on farms. The use of cultivated forages, many improved through selection or breeding and including grasses, legumes and trees, in integrated crop-tree-livestock systems is proposed as a stepping stone toward agroecological transformation. We introduce cultivated forages, explain their multi-functionality and provide an overview of where and to what extent the forages have been applied and how this has benefited people and the planet alike. We then examine their potential to contribute to the 13 principles of agroecology and find that integrating cultivated forages in mixed crop-tree-livestock systems follows a wide range of agroecological principles and increases the sustainability of livestock production across the globe. More research is, however, needed at the food system scale to fully understand the role of forages in the sociological and process aspects of agroecology. We make the case for further genetic improvement of cultivated forages and strong multi-disciplinary systems research to strengthen our understanding of the multidimensional impacts of forages and for managing agro-environmental trade-offs. We finish with a call for action, for the agroecological and livestock research and development communities to improve communication and join hands for a sustainable agri-food system transformation., Frontiers in Sustainable Food Systems, 5, ISSN:2571-581X

The gap between milk demand and domestic supply in Tanzania is large and projected to widen. Meeting such demand through local production of affordable milk presents an opportunity to improve the welfare of producers and market agents through the income and employment generated along the value chain (VC). Efforts to maximize milk yields, production and profitability need to be balanced with long-term sustainability. We combined environmental and economic ex-ante impact assessments of four intervention scenarios for two production systems in the Tanzanian dairy VC using the CLEANED model and an economic feasibility analysis. Intervention scenarios propose increases in milk production through (i) animal genetic improvement, (ii) improved feed, (iii) improved animal health and (iv) a package combining all interventions. Results show that economically feasible farm-level productivity increases of up to 140% go hand-in-hand with increased resource-use efficiency and up to 50% reduction in greenhouse gas (GHG) emission intensities. Absolute increases in water, land and nitrogen requirements in mixed crop-livestock systems call for careful management of stocks and quality of these resources. An overall rise in GHG emissions is expected, with a maximum of 53% increase associated with an 89% increase in milk supply at VC level. The CLEANED tool proved effective to evaluate livestock interventions that improve incomes and food security with minimal environmental footprint. Here, our simulations suggest that due to current low productivity, the greatest efficiency gains in combination with relatively low increases in total GHG emissions can be made in the extensive agro-pastoral dairy systems, which represent the majority of herds.

Scarcity of quantity and quality feed has been a key constraint to productivity of smallholder crop-livestock systems. Tropical forages include a variety of annual and perennial grasses, herbaceous and dual-purpose legumes, and multipurpose trees and shrubs. They have been promoted in Sub-Saharan Africa (SSA) for increasing livestock productivity and household income through higher quantity and quality of herbage, while contributing to soil improvement and higher food crop yields. For the first time, we quantitatively reviewed 72 experimental studies from across SSA to take stock of geographical distribution and forage technology focus of past research; quantify magnitudes of multidimensional impacts of forage technologies; and present variability in forage agronomy data. Improved forage technologies were classified into four groups: (i) germplasm, (ii) management, (iii) cropping system integration, and (iv) feeding regime. Mean weighted response ratios were calculated from 780 pairs of observations for 13 indicators across the five impact dimensions. Improved forage germplasm had on average 2.6 times higher herbage productivity than local controls, with strongest effect in grasses. Feeding regimes with improved leguminous forages increased milk yield by on average 39%, dry matter intake by 25%, and manure production by 24%. When forage technologies were integrated with food crops, soil loss was almost halved, soil organic carbon increased on average by 10%, and grain and stover yields by 60% and 33%, respectively. This study demonstrates the central role improved forages could play in sustainable intensification of crop-livestock systems in SSA. It highlights the need for multidisciplinary and systems-level approaches and studies to quantify synergies and tradeoffs between impact dimensions. Further research is needed to explain forage agronomic yield variability, unraveling interactions between genotype, on-farm environmental conditions, and management factors. Results from this review can inform development programs, prioritizing technologies proven successful for dissemination and indicating magnitudes of expected impacts.

South East Asia's agricultural landscape is rapidly transitioning from subsistence to intensive and market-oriented production, often with negative impacts on soil fertility. Ensuring that this transition is conducted in a sustainable way is critical, especially for the poorest who rely exclusively on natural resources that are of limited quality and quantity. This study aims to evaluate sustainable intensification options for smallholder ethnic minority farmers of the Lao uplands. Following a systematic selection of case study crop-livestock farms with different degrees of diversification and market orientation, we adopted a detailed nutrient flow approach to quantify nitrogen (N) and phosphorus (P) balances at farm level using a whole farm modelling tool. This was then used to simulate alternative sustainable intensification options relative to the baseline and their impact on farm performance and N and P cycling. Irrespective of the intensification level, nutrient balances were negative on all farms, with net nutrient removal between −34 and −130 kg N ha−1y−1 and between −9 and −20 kg P ha−1y−1. The positive effect of the sustainable intensification options on selected system performance variables was up to 15 times higher when its baseline value was low, i.e. when potential for improvement was high. Compared to the baseline (rice and maize monocropping systems), fallow plots during the dry season and low level of residues recycling, all intensification options increased land productivity and N balance by at least 12% on each farm, whereas the P balances were negatively impacted. The positive effects on the N balances might not be sufficient to reverse nutrient depletion, and additional nutrient inputs would be necessary. Four management principles are key to ensure a smooth transition from subsistence to intensive production: no residue burning, stay diverse, integrate livestock and use small amounts of P mineral fertilizer. If combined with efficient and integrative agricultural extension, seed systems and market development, these basic principles could be the key success factor for a sustainable development of the Lao uplands.

CONTEXT The Greater Mekong Subregion has been undergoing rapid agricultural transformation over the last decades, as traditional diverse subsistence-oriented agriculture is evolving towards intensified commercial production systems. Negative environmental impacts often include deforestation, nutrient pollution, and greenhouse gas (GHG) emissions. OBJECTIVE This study aims to explore the potential of crop-livestock integration to mitigate trade-offs between economic and environmental impacts of smallholder farming systems at different stages of agricultural transition and degrees of agricultural diversity across the Greater Mekong Subregion. METHODS We chose a ‘middle ground’ between detailed modeling of few, representative farming systems and modeling of large household populations. 24 low and high diversity farms were selected in Laos (Xieng Khouang province), Cambodia (Ratanakiri province) and Vietnam (Central Highlands) from a survey dataset of 1300 households. These farming systems were simulated with the whole-farm bio-economic and multi-objective optimization model FarmDESIGN, calculating operating profit, GHG emissions and nitrogen (N) balance. Two optimizations (‘business as usual’ vs. ‘crop-livestock integration’) were performed, generating ‘solution spaces’ or alternative configurations aiming to maximize profitability, keep farm N balanced and minimize GHG emissions. RESULTS AND CONCLUSIONS Agricultural systems across the sites differed in their production orientation and management practices, representing various stages of agricultural transition. Nitrogen balances varied between sites, being negative in Ratanakiri (average − 20.5 kg N ha−1 y−1) and Xieng Khouang (−36.5 kg N ha−1 y−1) and positive in the Central Highlands (73 kg N ha−1 y−1). Negative balances point to unsustainable mining of nutrients due to sale of cash crops without sufficient inputs, and positive balances to the risk of environmental contamination. Total GHG emissions ranged from 0.52–8.12 t CO2e ha−1 and were not significantly impacted by stage of agricultural transformation or agricultural diversity. GHG sources in Ratanakiri and Xieng Khouang were determined by crop residue burning while in Central Highlands fertilizer and livestock were main emitters. High diversity farms obtained higher operating profits (10,379 USD y−1) than low diversity farms (4584 USD y−1). Crop-livestock integration, a combination of measures including introduction of improved forages grasses, manure recycling and residue feeding, and reduction of residue burning, resulted in larger ‘solution spaces’, thus providing farmers with more options to mitigate agro-environmental trade-offs. SIGNIFICANCE These findings underline the potential of crop-livestock integration to support sustainable intensification pathways in the Greater Mekong region. Public and private investment in further research and extension is needed to develop and scal, Agricultural Systems, 195, ISSN:0308-521X

Agriculture is a global contributor to greenhouse gas emissions, causing climate change. Soil organic carbon (SOC) sequestration is seen as a pathway to climate change mitigation. But, long-term data on the actual contribution of tropical soils to SOC sequestration are largely absent. To contribute to filling this knowledge gap, we measured SOC in the top 15 cm over 12 years in two agronomic long-term trials in Western Kenya. These trials include various levels – from absence to full adoption – of two widely promoted sustainable agricultural management practices: Integrated Soil Fertility Management (ISFM; i.e. improved varieties, mineral fertilizer and organic matter/manure incorporation) and Conservation Agriculture (CA; improved varieties, mineral fertilizer, zero-tillage and crop residues retention). None of the tested ISFM and CA treatments turned out successful in sequestering SOC long-term. Instead, SOC decreased significantly over time in the vast majority of treatments. Expressed as annual averages, losses ranged between 0.11 and 0.37 t C ha−1 yr−1 in the CA long-term trial and 0.21 and 0.96 t C ha−1 yr−1 in the ISFM long-term trial. Long-term application of mineral N and P fertilizer did not mitigate SOC losses in both trials. Adopting zero-tillage and residue retention alone (as part of CA) could avoid SOC losses of on average 0.13 t C ha−1 yr−1, while this was 0.26 t C ha−1 yr−1 in response to mere inclusion of manure as part of ISFM. However, cross-site comparison disclosed that initial SOC levels of the two trials were different, probably as a result of varying land use history. Such initial soil status was responsible for the bulk of the SOC losses and less so the various tested agronomic management practices. This means, while ISFM and CA in the humid tropical agro-ecosystem of Western Kenya contribute to climate change mitigation by reducing SOC losses, they do not help offsetting anthropogenic greenhouse gas emissions elsewhere.

Rwanda's agricultural sector is facing severe challenges of increasing environmental degradation, resulting in declining productivity. The problem is likely to be further aggravated by the growing population pressure. A viable pathway is climate smart agriculture, aiming at the triple win of improving food security and climate change adaptation, while contributing to mitigation if possible. The Government of Rwanda has initiated ambitious policies and programs aiming at low emission agricultural development. Crop focused policies include the Crop Intensification Program (CIP) which facilitates access to inorganic fertilizer and improved seeds. In the livestock subsector, zero-grazing and improved livestock feeding are encouraged, and the Girinka program provides poor farm households with a crossbred dairy cow. In this study, we aimed at assessing the potential impact of these policy programs on food availability and greenhouse gas (GHG) emissions of 884 households across different agro-ecologies and farming systems in Rwanda. Household level calculations were used to assess the contribution of current crops, livestock and off-farm activities to food availability and GHG emissions. Across all sites, 46% of households were below the 2500 kcal MAE − 1 yr − 1 line, with lower food availability in the Southern and Eastern Rwanda. Consumed and sold food crops were the mainstay of food availability, contributing between 81.2% (low FA class) to 53.1% (high FA class). Livestock and off-farm income were the most important pathways to higher FA. Baseline GHG emissions were low, ranging between 395 and 1506 kg CO 2 e hh − 1 yr − 1 per site, and livestock related emissions from enteric fermentation (47.6–48.9%) and manure (26.7–31.8%) were the largest contributors to total GHG emissions across sites and FA classes. GHG emissions increased with FA, with 50% of the total GHG being emitted by 22% of the households with the highest FA scores. Scenario assessment of the three policy options showed strong differences in potential impacts: Girinka only reached one third of the household population, but acted highly pro-poor by decreasing the households below the 2500 kcal MAE − 1 yr − 1 line from 46% to 35%. However, Girinka also increased GHG by 1174 kg CO 2 e hh − 1 yr − 1 , and can therefore not be considered climate-smart. Improved livestock feeding was the least equitable strategy, decreasing food insufficient households by only 3%. However, it increased median FA by 755 kcal MAE − 1 yr − 1 at a small GHG increase (50 kg CO 2 e hh − 1 yr − 1 ). Therefore, it is a promising option to reach the CSA triple win. Crop and soil improvement resulted in the smallest increase in median FA (FA by 322 kcal MAE − 1 yr − 1 ), and decreasing the proportion of households below 2500 kcal MAE − 1 yr − 1 by 6%. This came only at minimal increase in GHG emissions (23 kg CO 2 e hh − 1 yr − 1 ). All policy programs had different potential impacts and trade-offs on different sections of the farm household population. Quick calculations like the ones presented in this study can assist in policy dialogue and stakeholder engagement to better select and prioritize policies and development programs, despite the complexity of its impacts and trade-offs.

Despite considerable development investment, food insecurity remains prevalent throughout East and West Africa. The concept of ‘sustainable intensification’ of agricultural production has been promoted as a means to meet growing food needs in these regions. However, inadequate attention has been given to assessing whether benefits from intensification would be realized by farm households considering highly diverse resource endowments, household and farm characteristics, and agroecological contexts. In this study, we apply a simple energy-based index of food availability to 1800 households from research sites in 7 countries in East and West Africa to assess the food availability status of each of these households and to quantify the contribution of different on- and off-farm activities to food availability. We estimate the effects of two production intensification strategies on food availability: increased cereal crop production from crop-based options, and increased production of key livestock products from livestock-based options. These two options are contrasted with a third strategy: increased off-farm income for each household from broader socioeconomic-based options. Using sensitivity analysis, each strategy is tested against baseline values via incremental production increases. Baseline results exhibit considerable diversity within and across sites in household food availability status and livelihood strategies. Interventions represented in the crop and livestock options may primarily benefit food-adequate and marginally food-inadequate households, and have little impact on the most food-inadequate households. The analysis questions what production intensification can realistically achieve for East and West African smallholders, and how intensification strategies must be augmented with transformational strategies to reach the poorest households.

Phosphorus (P) is an essential nutrient but is commonly limiting for food production in tropical and subtropical maize cropping. The efficiency of P fertiliser uptake is often low (5–30%) for various site-specific reasons and so identifying the drivers of P efficiency for different systems is important. We conducted a sensitivity analysis on the parameters of a well-established cropping systems model (APSIM) for a wide range of soil, crop and management factors to understand their influence on yield. The analysis was conducted for two contrasting maize cropping systems: (a) a high-input, large-scale commercial system in subtropical Queensland, Australia and (b) a low-input, small-holder system in tropical, western Kenya. In Queensland, yield was most sensitive to available P and mineral N supply, and the sensitivity of both increased with in-crop rainfall. Available P was also the most important parameter in Western Kenya, but N supply had much weaker influence due to higher levels of organic matter. Parameters controlling P sorption were more important than other soil parameters at both sites irrespective of seasonal conditions. In conclusion, these results suggest that efforts to improve efficiency of P use by plants need to account for interactions between water and N supply in environments where these are limiting. They also highlight a potential constraint to modelling of these systems as some of the most influential parameters are difficult to measure directly.

Dairy development provides substantial economic opportunities for smallholder crop-livestock farmers in East Africa, but productivity is constrained by scarcity of quantity and quality feed. Livestock is also associated with negative environmental impacts, including greenhouse gas (GHG) emissions, air pollution, high water consumption, loss of biodiversity and land degradation. Improved livestock feeding has been proposed as a triple-win strategy towards achieving climate-smart agriculture, increasing food security and climate change adaptation, and decreasing GHG intensities. Improved tropical forages include a wide variety of sown or planted annual and perennial grasses, herbaceous or dual-purpose legumes and shrubs developed for increasing productivity of grazed and cut-and-carry fed livestock. This thesis aims to explore potential impacts and trade-offs associated with the implementation of improved livestock feeding and forage technologies at farm scale, across a diversity of smallholder crop-livestock systems in East Africa. We first quantitatively reviewed 73 published studies to take stock of evidence on agronomic, livestock, environmental and economic impacts of tropical forage technologies in Sub-Saharan Africa. We then introduced a relatively simple approach to quantify feeding systems and feed gaps in data-scarce smallholder systems. Based on this, household-level impacts and trade-offs of improved livestock feeding and forages were explored in Tanzania and Rwanda, considering productivity, environmental and livelihood dimensions. To do so, a combination of approaches and methods was employed, including coupled livestock and economic modeling, bio-economic farming systems modeling and multi-objective optimization, multi-variate statistics, on-farm monitoring and measurements, semi-structured interviews, participatory validation and expert knowledge. Results from this thesis confirmed the considerable feed gaps in metabolizable energy and crude protein. Feed gap here is defined as the difference between livestock feed demand for an attainable milk production level (attainable feed demand) and actual feed supply at individual herd level. The literature review revealed that higher herbage production and quality of improved forage technologies resulted in an average 35% milk and 24% manure increase and 60% higher associated food crop yields while almost halving soil loss. In Lushoto in Tanzania, predicted adoption rates for improved livestock feeding and poverty reduction among households with improved dairy cows were likely to be higher compared to households with only local cows. Methane emissions intensity declined with adoption of improved livestock feeding strategies. Across Rwanda, livestock production was among the most important pathways to higher food availability. Total baseline GHG emissions were low, with enteric fermentation and manure emissions contributing 74 – 81%. Scenario assessment of three policy options showed that Girinka program (providing a crossbred cow to a poor households) strongly increased food availability of the poorest section of the household population at a high GHG cost, while improved livestock feeding had less impact on food availability but at an only small GHG increase. In Babati in Tanzania, emission intensity was lowest for the dairy farming system (2.1 kg CO2e kg-1 milk) when compared to three other smallholder livestock types, with lowest trade-offs with household income, and carbon and nitrogen balances. Available options to reduce agro-environmental trade-offs included reducing ruminant numbers, replacing local cattle with improved dairy breeds, improve feeding through on-farm forage cultivation to reach higher milk production levels, and reducing crop residue feeding to leave them on the field. However, adoption of these technologies require a skillful re-organization of the entire production system, resulting in loss of some multi-functionality of livestock, and incur higher production risks. In conclusion, we argue that pathways to sustainable intensification of livestock in East Africa are needed, which can also unlock new financing avenues. Improved forages can play a key role as they deliver multiple productivity, economic and environmental benefits when skillfully integrated in smallholder cropping and farming systems. Livestock feeding and forages are thus at multiple crossroads: at a point where crucial decisions regarding future pathways are taken, where productivity and environmental impacts meet, and where scientific disciplines including agronomy, soil and animal science intersect. Results from this thesis aim to inform policy makers, project designers, investors, donors and other decision-makers on prioritizing options towards low emission livestock development. Suggestions and recommendations for future research include next-level forage agronomy, further multi-disciplinary and systems-level trade-off analysis, and quantification of technology contributions to national-level climate and land restoration policy targets.

The widespread promotion of conservation agriculture (CA) in regions with weathered soils prone to phosphorus (P) deficiency merits explicit consideration of its effect on P availability. A long-term CA field trial located on an acid, weathered soil in western Kenya was evaluated for effects of reduced tillage and residue retention on P availability. Reduced tillage and residues were hypothesized to increase soil aggregation, and as a result, reduce P sorption potential, increase labile and organic P (Po), and stimulate phosphatase activities. After 9 years (18 cropping seasons), residue management had no effect on soil aggregate mean weight diameter (MWD), soil P fractions, or phosphatase potential activities. However, reduced tillage increased soil MWD and labile soil P stocks at 0–15 cm depth. Total P was greater at 0–15 cm depth under reduced tillage, but not for 0–30 cm depth, indicating stratification of P under reduced tillage. Increases in total P at 0–15 cm depth were correlated with maximum P sorption (Pmax sorption), whereas labile P increased with MWD and Po stocks. Reduced tillage also decreased pH and increased Pmax sorption, but these properties were not correlated. Despite a positive association of MWD and Po, weak or no changes were observed for Po and phosphatase activities, nor were there management effects on soil C stocks. Low residue retention rates (2 t maize residue yr−1) and relatively small improvements in soil structure due to reduced tillage were likely insufficient to yield changes in Po. Fertilizer P inputs at recommended rates (60 kg P ha−1 per season) may have also muted treatment effects on organic P cycling, though phosphatase activities were positively correlated with inorganic P fractions. The reduced tillage component of CA offers some improvements in P availability in weathered soils of western Kenya. However, relatively low soil available P across treatments suggests that CA with P fertilization may not be an optimal P management strategy for weathered soils in this region.

Forage-based livestock production plays a key role in national and regional economies, for food security and poverty alleviation, but is considered a major contributor to agricultural GHG emissions. While demand for livestock products is predicted to increase, there is political and societal pressure both to reduce environmental impacts and to convert some of the pasture area to alternative uses, such as crop production and environmental conservation. Thus, it is essential to develop approaches for sustainable intensification of livestock systems to mitigate GHG emissions, addressing biophysical, socio-economic and policy challenges. This paper highlights the potential of improved tropical forages, linked with policy incentives, to enhance livestock production, while reducing its environmental footprint. Emphasis is on crop-livestock systems. We give examples for sustainable intensification to mitigate GHG emissions, based on improved forages in Brazil and Colombia, and suggest future perspectives. Resumen

Conservation agriculture is widely promoted for soil conservation and crop productivity increase, although rigorous empirical evidence from sub-Saharan Africa is still limited. This study aimed to quantify the medium-term impact of tillage (conventional and reduced) and crop residue management (retention and removal) on soil and crop performance in a maize–soybean rotation. A replicated field trial was started in sub-humid Western Kenya in 2003, and measurements were taken from 2005 to 2008. Conventional tillage negatively affected soil aggregate stability when compared to reduced tillage, as indicated by lower mean weight diameter values upon wet sieving at 0–15 cm (PT < 0.001). This suggests increased susceptibility to slaking and soil erosion. Tillage and residue management alone did not affect soil C contents after 11 cropping seasons, but when residue was incorporated by tillage, soil C was higher at 15–30 cm (PT*R = 0.037). Lack of treatment effects on the C content of different aggregate fractions indicated that reduced tillage and/or residue retention did not increase physical C protection. The weak residue effect on aggregate stability and soil C may be attributed to insufficient residue retention. Soybean grain yields tended to be suppressed under reduced tillage without residue retention, especially in wet seasons (PT*R = 0.070). Consequently, future research should establish, for different climatic zones and soil types, the critical minimum residue retention levels for soil conservation and crop productivity.

International audience; The increased use of grain-based feed for livestock during the last two decades has contributed, along with other factors, to a rise in grain prices that has reduced human food security. This circumstance argues for feeding more forages to livestock, particularly in the tropics where many livestock are reared on small farms. Efforts to accomplish this end, referred to as the ‘LivestockPlus’ approach, intensify in sustainable ways the management of grasses, shrubs, trees, and animals. By decoupling the human food and livestock feed systems, these efforts would increase the resilience of the global food system. Effective LivestockPlus approaches take one of two forms: (1) simple improvements such as new forage varieties and animal management practices that spread from farmer to farmer by word of mouth, or (2) complex sets of new practices that integrate forage production more closely into farms’ other agricultural activities and agroecologies.

Soil macrofauna such as earthworms and termites are involved in key ecosystem functions and thus considered important for sustainable intensification of crop production. However, their contribution to tropical soil quality and crop performance, as well as relations with agricultural management (e.g., Conservation Agriculture), are not well understood. This study aimed to quantify soil macrofauna and its impact on soil aggregation, soil carbon and crop yields in a maize–soybean system under tropical sub-humid conditions. A field trial was established in Western Kenya in 2003 with tillage and residue retention as independent factors. A macrofauna exclusion experiment was superimposed in 2005 through regular insecticide applications, and measurements were taken from 2005 to 2012. Termites were the most abundant macrofauna group comprising 61% of total macrofauna numbers followed by ants (20%), while few earthworms were present (5%). Insecticide application significantly reduced termites (by 86 and 62%) and earthworms (by 100 and 88%) at 0–15 and 15–30 cm soil depth respectively. Termite diversity was low, with all species belonging to the family of Macrotermitinae which feed on wood, leaf litter and dead/dry grass. Seven years of macrofauna exclusion did not affect soil aggregation or carbon contents, which might be explained by the low residue retention and the nesting and feeding behavior of the dominant termites present. Macrofauna exclusion resulted in 34% higher maize grain yield and 22% higher soybean grain yield, indicating that pest damage – probably including termites – overruled any potentially beneficial impact of soil macrofauna. Results contrast with previous studies on the effects of termites on plant growth, which were mostly conducted in (semi-) arid regions. Future research should contribute to sustainable management strategies that reduce detrimental impact due to dominance of potential pest species while conserving soil macrofauna diversity and their beneficial functions in agroecosystems.

Earthworms can increase nitrous oxide (N2O) emissions, particularly in no-tillage systems where earthworms are abundant. Here, we study the effect of residue incorporation depth on earthworm-induced N2O emissions. We hypothesized that cumulative N2O emissions decrease with residue incorporation depth, because (i) increased water filled pore space (WFPS) in deeper soil layers leads to higher denitrification rates as well as more complete denitrification; and (ii) the longer upward diffusion path increases N2O reduction to N2. Two 84-day laboratory mesocosm experiments were conducted. First, we manually incorporated maize (Zea mays L.) residue at different soil depths (incorporation experiment). Second, 13 C-enriched maize residue was applied to the soil surface and anecic species Lumbricus terrestris (L.) and epigeic species Lumbricus rubellus (Hoffmeister) were confined to different soil depths (earthworm experiment). Residue incorporation depth affected cumulative N2O emissions in both experiments (P < 0.001). In the incorporation experiment, N2O emissions decreased from 4.91 mg N2O– Nk g 1 soil (surface application) to 2.71 mg N2O– Nk g 1 soil (40–50 cm incorporation). In the earthworm experiment, N2O emissions from L. terrestris decreased from 3.87 mg N2O– Nk g 1 soil (confined to 0–10 cm) to 2.01 mg N2O– Nk g 1 soil (confined to 0–30 cm). Both experimental setups resulted in dissimilar WFPS profiles that affected N2O dynamics. We also found significant differences in residue C recovery in soil organic matter between L. terrestris (28–41%) and L. rubellus (56%). We conclude that (i) N2O emissions decrease with residue incorporation depth, although this effect was complicated by dissimilar WFPS profiles; and (ii) larger residue C incorporation by L. rubellus than L. terrestris indicates that earthworm species differ in their C stabilization potential. Our findings underline the importance of studying earthworm diversity in the context of greenhouse gas emissions from agro-ecosystems.