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Alnus acuminata Kunth. (alnus) is widely used in agroforestry systems across the globe and is believed to provide multiple ecosystem services; however, evidence is lacking in agroforestry literature to support the perceived benefits, particularly in Rwanda. To understand carbon sequestration potential and other benefits of alnus, a household survey, tree inventory and destructive sampling were conducted in north-western Rwanda. Over 75% of the respondents had alnus trees in their farms. The trees provide stakes for climbing beans, firewood and timber. They also improve soil fertility and control soil erosion. Farmers had between 130 and 161 alnus trees per hectare with an average height of 7.7 ± 0.59 m and diameter at breast height of 16.3 ± 1.39 cm. The largest biomass proportion was found in stems (70.5%) while branches and leaves stock about 16.5 and 13% of the total biomass, respectively. At farm level, aboveground biomass of alnus trees was estimated to be 27.2 ± 0.7 Mg ha−1 representing 13.6 Mg of carbon (C) per hectare. Biomass carbon increased with tree size, from 7.1 ± 0.2 Mg C ha−1 in 3 years old trees to 34.4 ± 2.2 Mg C ha−1 in 10 years old trees. The converse was observed with elevation; biomass carbon decreased with increasing elevation from 21.4 ± 1.29 Mg C ha−1 at low (2011–2110 m) to 9.6 ± 0.75 Mg C ha−1 in the high elevation (> 2510 m). In conclusion, alnus agroforestry significantly contributes to carbon sequestration, although the magnitude of these benefits varies with tree age and elevation. Planting alnus trees on farms can meet local needs for stakes for climbing beans, wood and soil fertility improvement, as well as the global need for regulation of climate change.

Smallholder maize growers are experiencing significant yield gaps due to sub-optimal agricultural practices. Adequate agricultural inputs, particularly nutrient amendments and best management practices, are essential to reverse this trend. There is a need to understand the cause of variations in maize yield, provide reliable early estimates of yields, and make necessary recommendations for fertilizer applications. Maize yield prediction and estimates of yield gaps using objective and spatial analytical tools could provide accurate and objective information that underpin decision support. A study was conducted in Rwanda at Nyakiliba sector and Gashora sector located in Birunga and Central Bugesera agro-ecological zones, with the objectives of (1) determining factors influencing maize yield, (2) predicting maize yield (using the Normalized Difference Vegetation Index (NDVI) approach), and (3) assessing the maize yield gaps and the impact on food security. Maize grain yield was significantly higher at Nyakiliba (1.74 t ha−1) than at Gashora (0.6 t ha−1). NDVI values correlated positively with maize grain yield at both sites (R2 = 0.50 to 0.65) and soil fertility indicators (R2 = 0.55 to 0.70). Maize yield was highest at 40 kg P ha−1 and response to N fertilizer was adequately simulated at Nyakiliba (R2 = 0.85, maximum yield 3.3 t ha−1). Yield gap was 4.6 t ha−1 in Nyakiliba and 5.1 t ha−1 in Gashora. Soil variables were more important determinants of social class than family size. Knowledge that low nutrient inputs are a major cause of yield gaps in Rwanda should prioritize increasing the rate of fertilizer use in these agricultural systems.

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.

Wheat (Triticum aestivum L.) is an important East Africa highland crop but yields are low. Information is scarce for optimization of fertilizer use. Research was conducted to determine yield response functions for N, P and K, and to diagnose Mg–S–Zn–B deficiencies. The average grain yield increase in Rwanda due to N application was 1.5 Mg ha−1 with a mean economically optimal rate (EOR) of 68 kg ha−1 N. In Kenya and Tanzania, yield was increased by 29% with EOR N for two SY but unaffected by N rate for four other SY which on average had 50% of the soil organic C (SOC) as the N-responsive SY. Yield was increased, on average, with application of P and K by 0.47 and 0.23 Mg ha−1, respectively, at EOR in Rwanda but effects were inconsistent for other SY where soil test K was higher than in Rwanda. Application of Mg–S–Zn–B resulted in 0.46 Mg ha−1 more yield in Rwanda but did not affect yield at other SY where the average soil test values for these nutrients was 35% higher than in Rwanda. If the financially constrained farmer opts to apply the affordable fertilizer to twice as much land at 50% EOR compared with 100% EOR, the mean yield increase is reduced by 27% but production and PCR are increased by 43 and 72%, respectively. Nutrient effects were relatively consistent and positive in Rwanda, but less and less inconsistent elsewhere with generally less SOC, more K–Mg–S–Zn–B availability, and often lower yields.

In the sub-humid parts of East Africa, high population density and pressure on land have led farmers to integrate multipurpose trees on farm. Although mixing trees and crops generates numerous benefits (e.g., fuelwood, timber), it often reduces crop yields. Whereas the effects of mature trees on crops are well studied in semi-arid parklands, there are only few studies for the sub-humid environment. The effects of mature Alnus acuminata (Kunth) and Markhamia lutea (Seem.) on crops were studied on-farm for four seasons in the sub-humid environment of northern Rwanda. Five sampling points for A. acuminata and M. lutea were: (i) 1 m from tree trunk without maize, (ii) 3 m from tree trunk without maize, (iii) 1 m from tree trunk with maize, (iv) 3 m from tree trunk with maize and (v) sole maize away from any tree. Nutrient availability and uptake, soil water, air temperature, solar radiation, crop growth and yields were measured. The APSIM-maize module was used to assess the sensitivity of maize yields to changes in these variables. Nutrients availability was higher under A. acuminata compared with M. lutea, because of higher litter fall but maize nutrient uptake increased only under A. acuminata 3 m from tree trunk during a wetter season. None of tree species affected water availability for maize in the topsoil. Photosynthetically active radiation (PAR), total solar radiation and day air temperature were reduced by both tree species. Maize crop at 1 m and 3 m from the tree trunk was shorter in height but had the same number and size of leaves when compared to sole maize plots. Crop yield was generally reduced more at 1 m than at 3 m from the tree trunk. A positive interaction between A. acuminata and maize was only apparent at 3 m from the tree in one of the four seasons following higher litter fall, suggesting that the negative effect of shade was offset by extra N input during that season. In a modelled scenario under low N fertilization, larger N input from trees could compensate for yield loss caused by reduction in radiation and temperature in about 60% of the seasons. Our findings suggest that adequate pruning and high leaf litter recycling can reduce the negative effect of shade in low intensity farming systems.

Experiences in smallholder contexts indicate frequent mismatches between technologies introduced and needs of farmers who must make complex decisions in reallocating their limited resources under highly risky ecological and market contexts. This study proposes a cost- and time-effective, easy-to-implement approach to identify farmers’ priorities and critical intervention areas, and presents its application in guiding an agroforestry strategy in Rwanda. It was found that different tree species have distinctive enabling vs. constraining conditions under different agroecological contexts in the perspective of smallholder farmers. Tree species preferred by farmers were not necessarily widely adopted if multitudes of conditions were not enabling. The essential conditions for sustainable adoption include: quality materials/inputs are available; technologies are compatible with existing local farming systems; they are resilient to climate risks/resistant to pests-diseases; management is not complicated; and, there is guaranteed access to markets. The results show that there will not be a silver bullet national strategy to scale up agroforestry. Instead a matrix kind of strategies -to promote enabling conditions and address constraining conditions for priority species in specific agroecologies- will be required. The proposed concept should be further refined for wider agricultural technology transfer debates to break the myths of low uptakes by smallholders.

Densely populated rural areas in the East African Highlands have faced significant intensification challenges under extreme population pressure on their land and ecosystems. Sustainable agricultural intensification, in the context of increasing cropping intensities, is a prerequisite for deliberate land management strategies that deliver multiple ecosystem goods (food, energy, income sources, etc.) and services (especially improving soil conditions) on the same land, as well as system resilience, if adopted at scale. Tree based ecosystem approaches (TBEAs) are among such multi-functional land management strategies. Knowledge on the multi-functionality of TBEAs and on their scaling up, however, remains severely limited due to several methodological challenges. This study aims at offering an analytical perspective to view multi-functional TBEAs as an integral part of sustainable agricultural intensification. The study proposes a conceptual framework to guide the analysis of socio-economic data and applies it to cross-site analysis of TBEAs in extremely densely populated Rwanda. Heterogeneous TBEAs were identified across Rwanda’s different agro-ecological zones to meet locally-specific smallholders’ needs for a set of ecosystem goods and services on the same land. The sustained adoption of TBEAs would be guaranteed if farmers subjectively recognize their compatibility and synergy with sustainable intensification of existing farming systems, supported by favorable institutional conditions.

Nutrient-balance assessments are valuable tools for both planning and monitoring the implementation of sustainable integrated soil fertility management strategies. The aim of this study was to assess nutrient flows as affected by cropping systems and production niche in soils of Cyabayaga watershed. yabayaga watershed is located in Nyagatare district, Eastern province of Rwanda. Production niches considered are homestead fields, remote hillside fields and wetland fields. Partial nutrient (N, P and K) flows were collected through a survey using MonQi structured questionnaire, administrated to a random sample of 35 farmers. There was nitrogen (N) and Potassium (K) negative balances (– 67.5 kg N ha-1 season-1 and – 7.7 kg K ha-1 season-1 respectively) whereas phosphorous (P) balance was positive (17.4 kg P ha-1 season-1). N, P and K balances were negative in bean, maize-bean, cassava, groundnut, maize, onion, sorghum and tomato and positive in rice, banana and banana-bean. Highest amount of nutrients were significantly allocated in wetland fields while allocation of nutrients in homestead fields and remote hillside fields was almost the same. Groundnut and maize plots were experiencing highest negative nutrients balance (e.g. N balance in groundnut plot was – 40.6 N ha-1 season-1). N and K balance were positive in rice and banana plots; whilst P balance was positive in banana, bean, maize, rice and tomato plots. Partial nutrients flow and balance from this study show that nutrient depletion is a problem in the study area. A special attention should be put to fertility management and alternative solution for less fertile soil (uplands in particular), especially for farm that have reduced land size. From this respect, conservation agriculture is the main farm management which could be recommended.

The growing need to intensify smallholder farming systems to enhance food security for a rapidly growing population in sub-Saharan Africa constitutes a major sustainability challenge. Intensification of agriculture has often resulted in degraded, highly vulnerable, exhausted and unproductive soils. Even though smallholder farming systems are heterogeneous and dynamic, conventional approaches to improving soil management have focused on promoting one or two technologies, informed by coarse-resolution assessments, rather than tailoring technologies to context. This has resulted in technologies that have been promoted not being locally adapted. The research reported here explores the extent to which farmers' indicators of soil quality vary with land degradation status and gender and can be used in selecting locally appropriate land restoration practices. Knowledge was elicited from 150 smallholder farmers across a land degradation gradient in Rwanda through combined use of a systematic knowledge-based systems approach (AKT5), and a participatory knowledge sharing method for indicators of soil quality (InPaC-S). Data were analysed using R software through frequency statistics, ‘ggplot’-generated bar plots and Chi-square tests of independence. Farmers described 12 indicators of soil quality with a mean of five per farmer. The four most frequently mentioned were: soil colour (96%), indicator plants (90%), crop vigour (71%) and soil texture (67%). Farmers' knowledge about 10 out of 12 indicators varied with land degradation status (p