Towards understanding factors that govern fertilizer response in casave: lessons from East Africa

Information on fertilizer response in cassava in Africa is scarce. We conducted a series of on-farm and on-station trials in two consecutive years to quantify yield responses of cassava to mineral fertilizer in Kenya and Uganda and to evaluate factors governing the responses. Average unfertilized yields ranged from 4.2 to 25.7 t ha-1 between sites and years. Mineral fertilizer use increased yields significantly, but response to fertilizer was highly variable (-0.2 to 15.3 t ha-1). Average yield response per kg applied nutrient was 37, 168 and 45 and 106, 482 and 128 kg fresh yield per kg of applied N, P and K, respectively in 2004 and 2005. Fertilizer response was governed by soil fertility, rainfall and weed management, but was not influenced by variety, pest and disease pressure and harvest age. Relative N and K yields were positively correlated to SOC and exchangeable K, while response to fertilizer decreased on more fertile soils. Still, fertilizer response varied widely on low fertility soils (e.g. on soils wit

Yield gaps, nutrient use efficiencies and response to fertilisers by maize across heterogeneous smallholder farms of western Kenya

The need to promote fertiliser use by African smallholder farmers to counteract the current decline in per capita food production is widely recognised. But soil heterogeneity results in variable responses of crops to fertilisers within single farms. We used existing databases on maize production under farmer (F-M) and researcher management (R-M) to analyse the effect of soil heterogeneity on the different components of nutrient use efficiency by maize growing on smallholder farms in western Kenya: nutrient availability, capture and conversion efficiencies and crop biomass partitioning. Subsequently, we used the simple model QUEFTS to calculate nutrient recovery efficiencies from the R-M plots and to calculate attainable yields with and without fertilisers based on measured soil properties across heterogeneous farms. The yield gap of maize between F-M and R-M varied from 0.5 to 3 t grain ha-1 season-1 across field types and localities. Poor fields under R-M yielded better than F-M, even without fertilisers. Such differences, of up to 1.1 t ha-1 greater yields under R-M conditions are attributable to improved agronomic management and germplasm. The relative response of maize to N-P-K fertilisers tended to decrease with increasing soil quality (soil C and extractable P), from a maximum of 4.4-fold to -0.5- fold relative to the control. Soil heterogeneity affected resource use efficiencies mainly through effects on the efficiency of resource capture. Apparent recovery efficiencies varied between 0 and 70% for N, 0 and 15% for P, and 0 to 52% for K. Resource conversion efficiencies were less variable across fields and localities, with average values of 97 kg DM kg-1 N, 558 kg DM kg-1 P and 111 kg DM kg-1 K taken up. Using measured soil chemical properties QUEFTS over-estimated observed yields under F-M, indicating that variable crop performance within and across farms cannot be ascribed solely to soil nutrient availability. For the R-M plots QUEFTS predicted positive crop responses to application of 30 kg P ha-1 and 30 kg P ha-1 + 90 kg N ha-1 for a wide range of soil qualities, indicating that there is room to improve current crop productivity through fertiliser use. To ensure their efficient use in sub-Saharan Africa mineral fertilisers should be: (1) targeted to specific niches of soil fertility within heterogeneous farms; and (2) go hand-in-hand with the implementation of agronomic measures to improve their capture and utilisation

Is conservation agriculture a climate-smart option for smallholders in sub-Saharan Africa?

Sub-Saharan Africa (SSA) faces the challenge of developing a climate-smart agriculture (CSA) that simultaneously ensures food security, mitigation and adaption to climate change (CC). Conservation agriculture (CA) is widely promoted in SSA and is considered as a way to meet these CSA objectives. The objective of the study was to assess whether CA in SSA contributes to the three pillars of CSA, seeking evidence from the peer-reviewed literature that compares the performances of CA and conventional tillage-based (CT) cropping systems. The positive yield responses to CA compared to CT are widely documented in SSA. The positive effects on soil fertility result in increased yield in the long term. Yield impacts in the shorter term are variable and depend to a great extent on the climatic context. CA responds better under low and/or erratic rainfall conditions, mainly due to the mulching effect on soil water conservation. This suggests the potential of CA as a cropping strategy to adapt to more variable rainfall in the future as predicted in many regions of SSA. However, an increase in yield does not necessarily translate into an increase in farm income. The economic impact of CA is highly dependent on the socioeconomic context. The potential of CA to mitigate CC remains unclear. Retention of crop residues as mulch may not always translate into soil carbon sequestration. Further studies on the impact of CA on soils' greenhouse gases emissions are needed. In conclusion, the ability of CA to contribute to CSA is very site- and farm-specific, and lies to a great extent in its capacity of retaining crop residues as mulch on the soil surface. (Texte intégral

Influence of planting basins on selected soil quality parameters and sorghum yield along an agro-ecological gradient in South Eastern Zimbabwe

Planting basins are an important soil and water conservation technology. This study evaluated the effects of basins on soil organic carbon (SOC) stocks, aggregate stability (Ima), bulk density, soil moisture retention and sorghum yield in agro-ecological regions III, IV and V of Chipinge district. The experiment consisted of three treatments; namely planting basins (basins) with goat manure and inorganic fertilizer application, hand hoeing with similar fertility amendments (FP+) and hand hoeing without fertility amendments (FP). It was hypothesized that planting basins with fertility amendments would improve the selected soil quality parameters and sorghum yield. Only planting basins significantly (p˂0.05) improved soil quality parameters in the 0-15 cm depth and bulk density, Ima, SOC stocks ranged from 1356 to 1451 kg/m3; 314 to 450 and 14.18 to 25.55 Mg ha-1 respectively. Planting basins significantly increased (p<0.05) sorghum yield relative to hand-hoeing practices (FP+ and FP) with average grain yield of 2.68, 1.72 and 1.32 t ha-1 in agro-ecological regions III, IV and V, respectively. When compared to FP+ and FP, basins increased grain yield by >130% in all the 3 agro-ecological regions. The hypothesis was accepted and it was concluded that basins improve soil properties and sorghum grain yield in agro-ecological regions III, IV and V. Considering the soil and crop productivity benefits highlighted in this study, there is a strong justification for the widespread promotion and adoption of planting basins in semi-arid agro-ecological regions of Zimbabwe

Timescales of transformational climate change adaptation in sub-Saharan African agriculture

Climate change is projected to constitute a significant threat to food security if no adaptation actions are taken. Transformation of agricultural systems, for example switching crop types or moving out of agriculture, is projected to be necessary in some cases. However, little attention has been paid to the timing of these transformations. Here, we develop a temporal uncertainty framework using the CMIP5 ensemble to assess when and where cultivation of key crops in sub-Saharan Africa becomes unviable. We report potential transformational changes for all major crops during the twenty-first century, as climates shift and areas become unsuitable. For most crops, however, transformation is limited to small pockets (<15% of area), and only for beans, maize and banana is transformation more widespread (â 1/430% area for maize and banana, 60% for beans). We envisage three overlapping adaptation phases to enable projected transformational changes: an incremental adaptation phase focused on improvements to crops and management, a preparatory phase that establishes appropriate policies and enabling environments, and a transformational adaptation phase in which farmers substitute crops, explore alternative livelihoods strategies, or relocate. To best align policies with production triggers for no-regret actions, monitoring capacities to track farming systems as well as climate are needed

Longitudinal analysis of household types and livelihood trajectories in Oaxaca, Mexico

In Mexico, a political shift to fit into neoliberal directives since the 80s has brought several consequences to rural households and their trajectories. This study focused on the relation between drivers of change and household trajectory. The study was carried out in Santa Catarina Tayata, in the state of Oaxaca, Mexico. 44 household heads were interviewed to recall their production system and economic activities at significant moments. The results were summarized as variables describing the socio-economic and agronomic situation of households over three decades: 1988-1997, 1998-2007, and 2008-2017. Household types were identified for each decade. Three household types were distinguishable in the first two decades, and five in the last decade. Drivers of change such as international markets, land tenure, government support, and migration were connected to household trajectories. Results showed that household type diversity increased, while half of the households changed types at one point according to different strategies. Changes in land tenure in the study area in the early 2000s were attributable to the PROCEDE national program, which acted to lift restrictions on land tenure, facilitating the buying and selling of land. The implementation of PROCEDE resulted in fewer households relying on borrowed or rented land while allowing others to expand their land and form a new household type. A migration process enabled some households to invest in land or animal production as a “step up” strategy. The majority of households that received agriculture-related subsidies tended to engage solely in agricultural activities. Half of the households that did not benefit from subsidies engaged in off-farm to diversify their income, suggesting that the type of governmental support can have an impact on farming activities. Household types that had more animal production or larger areas did not tend to engage in off-farm activities because of high demands for labor in their production systems. This type of study can be used to monitor policy impact and households’ strategic responses, to arrive at better articulation of policy objectives and policy impact while considering household type diversity.</p

Back to the people:The role of community-based responses in shaping landscape trajectories in Oaxaca, Mexico

Land use change results from top-down drivers, such as policies, trade, and migration. Land use change may also result from community-based responses. In Mexico, rural communities govern most of the country's forests. This study aimed to assess how socio-economic and biophysical factors affected the landscape trajectories of rural communities in southern Mexico. It also aimed at evaluating the role of communities in landscape change. Land use change of 63 rural communities was analyzed for the years 1987 and 2017. Four land uses were distinguished: forest, shrubland, agriculture, and bare soil. Five groups of communities were identified according to their socio-economic and biophysical factors. Two groups located in areas with high slopes and elevated marginalization index values showed deforestation patterns. Two other groups, consisting of more than half of the municipalities assessed, showed reforestation trends. The final group did not reveal major changes in land use. Two municipalities with reforestation trends were selected for an in-depth analysis of how community-based responses impacted natural resource management and conservation. Through local assemblies, the population voted for regulations that increased the forest area and reduced the bare soil. There was no evidence that these regulations affected croplands. These results show how a combination of socio-economic and biophysical factors can affect landscape change, but it also shows the often overlooked role of communities as a relevant bottom-up driver of change.</p

The importance of the traditional milpa in food security and nutritional self-sufficiency in the highlands of Oaxaca, Mexico

Around 30% of global food is produced by smallholder farmers, yet they constitute the most food-insecure group. In Mexico, food self-sufficiency is declining. Rural policies in the country have stimulated the production of cash crops to the detriment of the traditional intercropping system, the milpa. Such a decline may have negative consequences for the food security of subsistence farmers. This study aimed to assess changes in nutritional self-sufficiency over the last 30 years and the role of milpa systems in food security for two communities in the highlands of Oaxaca, Mexico. The study used satellite images, censuses, and field data to estimate food production. Three cropping systems, monoculture of maize, monoculture of common bean, and the milpa were compared in terms of nutrients and vitamins produced. Furthermore, a household typology was developed for each community to contrast nutritional self-sufficiency levels between the different household types. Results showed that the milpa produced more volume of food per area compared to the other systems. The milpa also produced all the nutrients and vitamins (except for B12) required to feed at least 2 persons ha-1. Monocultures of maize lacked vitamins A, B9, B12, and C, and the common bean lacked vitamins A, B12, and C. While farmers recognized the importance of the milpa, they preferred monocultures due to the reduced labor demands of this system. Households that obtained most of their income from off-farm activities had the lowest nutritional self-sufficiency. Enhancing nutritional self-sufficiency through crop diversification has the potential to not only improve the nutrition of subsistence farmers, but also to enhance ecosystem service provision, promote biodiversity conservation and restoration, and improve resilience to climate change.</p