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Soil property and class maps for the continent of Africa were so far only available at very generalised scales, with many countries not mapped at all. Thanks to an increasing quantity and availability of soil samples collected at field point locations by various government and/or NGO funded projects, it is now possible to produce detailed pan-African maps of soil nutrients, including micro-nutrients at fine spatial resolutions. In this paper we describe production of a 30 m resolution Soil Information System of the African continent using, to date, the most comprehensive compilation of soil samples ( N ≈ 150 , 000 ) and Earth Observation data. We produced predictions for soil pH, organic carbon (C) and total nitrogen (N), total carbon, effective Cation Exchange Capacity (eCEC), extractable—phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), sodium (Na), iron (Fe), zinc (Zn)—silt, clay and sand, stone content, bulk density and depth to bedrock, at three depths (0, 20 and 50 cm) and using 2-scale 3D Ensemble Machine Learning framework implemented in the mlr (Machine Learning in R) package. As covariate layers we used 250 m resolution (MODIS, PROBA-V and SM2RAIN products), and 30 m resolution (Sentinel-2, Landsat and DTM derivatives) images. Our fivefold spatial Cross-Validation results showed varying accuracy levels ranging from the best performing soil pH (CCC = 0.900) to more poorly predictable extractable phosphorus (CCC = 0.654) and sulphur (CCC = 0.708) and depth to bedrock. Sentinel-2 bands SWIR (B11, B12), NIR (B09, B8A), Landsat SWIR bands, and vertical depth derived from 30 m resolution DTM, were the overall most important 30 m resolution covariates. Climatic data images—SM2RAIN, bioclimatic variables and MODIS Land Surface Temperature—however, remained as the overall most important variables for predicting soil chemical variables at continental scale. This publicly available 30-m Soil Information System of Africa aims at supporting numerous applications, including soil and fertilizer policies and investments, agronomic advice to close yield gaps, environmental programs, or targeting of nutrition interventions.

Purpose The nursery is the production of vigorous seedlings for field transplantation. Fertilization improves the quality of Moringa oleifera in the greenhouse. Thus, the effect of composts amendments on the survival rate and mineral composition of M. oleifera was studied. Methods A randomized complete block (RCB) design comprising fourteen treatments and twelve repetitions (pots referring to as repetitions), was led out in greenhouse. Varying compost receipts (0.1 kg, 0.2 kg, and 0.3 kg) were used and an increasing amount of a chemical fertilizer (NPK: 20:10:10) was added in some treatment at 25 days after sowing. Parameters such as germination rate, survival rate, biomass, and mineral composition of M. oleifera plants were assessed. Results The germination rate was maximal (100%) in the combined treatment PM 1 (0.8 kg of soil + 0.1 kg). A considerable reduction of germination rate and high plantlet mortality were observed in treatments that received chemical fertilizer, although the mineral components’ uptake in young M. oleifera plants was considerably improved. The highest dry root biomass was obtained from the treatments MF 1 (0.8 kg of soil + 0.032 kg each of cow dung, goat, chicken manures + 0.003 kg NPK) and CM 1 (0.8 kg of soil + 0.1 kg of cow dung compost), with, respectively, 0.62 g and 0.59 g per plant. Conclusions All composts types used in this study have appeared as appropriate amendments to improve the M. oleifera production in nursery, through an increase of the vigour and mineral composition of this valuable plant.

In the tropical rain forest zone of Southern Cameroon, shifting cultivation and perennial plantations of cocoa are the main farming systems practiced by small-scale farmers to ensure subsistence food crop production and a small income. This research used scientific modelling tools to produce quantitative information on the evolution of soils under this shifting agricultural system. An analysis of farming system led to the development of a conceptual model of the spatio-temporal dynamics of shifting agriculture, including transition matrices of rotational cycles that guided the sampling strategy for the study of soil evolution under the system. The study of soil variability showed that 30-35% of the total variance of some topsoil (0-20 cm) properties was due to the influence of land use practices. Five soil properties (pH, calcium, available phosphorus, bulk density and organic carbon) that are the most sensitive to these agricultural practices were empirically modelled and linear/quadratic fractional rational functions were successfully fitted to time series soil variables to derive quantitative measures on temporal changes in soil with land use. Data and methods produced are useful for soil quality assessment and spatio-temporal dynamic simulation in order to guide decision-making for sustainable land-use planning and soil resources management.

The Lake Victoria Basin (LVB) is located in the upper reaches of the Nile River Basin and is shared by five East-African countries. The population in the catchment is growing rapidly and the lake is facing several environmental problems. During the past few decades, numerous efforts have been made across the five countries, with the coordination of the Lake Victoria Basin Commission (LVBC) to reduce the loading of reactive nitrogen (Nr) into the lake and Lake Watershed. However, most of the measures envisaged to ensure long-term sustainable N management are not as easily adopted as planned. This paper reports on a review study on N flows and obstacles in achieving sustainable N management in the LVB, with the objectives of improving the understanding of the N cycle and examining the N management practices and policies that can help reduce the loss of Nr in the region. The scientific literature related to a range of N flows, N management obstacles, and options to overcome obstacles has been analyzed using N prospects developed at the global level for their potential applicability across the LVB. The study showed that an unbalanced use of N input is a serious threat to agricultural productivity leading to extreme soil N mining and degradation, with the majority of LVB farms operating within negative N balances and above the safe operating boundary for N in production systems. From the projections in N input as recommended by various stakeholders, there would likely be changes in both current yield and N use efficiency (NUE) values; however, most small-scale farmers will continue to experience low yields, which remains a challenge for food security in the area. These results suggest that scientists as well as those involved in decision-making and policymaking processes should formulate new targets for fertilizer increment to reduce the yield gap for sustainability, focusing on more integrated soil fertility as a package for nutrient management in cropping systems.

Although tree stems act as conduits for greenhouse gases (GHGs) produced in the soil, the magnitudes of tree contributions to total (soil + stem) nitrous oxide (N2O) emissions from tropical rainforests on heavily weathered soils remain unknown. Moreover, soil GHG fluxes are largely understudied in African rainforests, and the effects of land-use change on these gases are identified as an important research gap in the global GHG budget. In this study, we quantified the changes in stem and soil N2O fluxes with forest conversion to cacao agroforestry. Stem and soil N2O fluxes were measured monthly for a year (2017–2018) in four replicate plots per land use at three sites across central and southern Cameroon. Tree stems consistently emitted N2O throughout the measurement period and were positively correlated with soil N2O fluxes. 15N-isotope tracing from soil mineral N to stem-emitted 15N2O and correlations between temporal patterns of stem N2O emissions, soil–air N2O concentration, soil N2O emissions and vapour pressure deficit suggest that N2O emitted by the stems originated predominantly from N2O produced in the soil. Forest conversion to extensively managed, mature (>20 years old) cacao agroforestry had no effect on stem and soil N2O fluxes. The annual total N2O emissions were 1.55 ± 0.20 kg N ha−1 yr−1 from the forest and 1.15 ± 0.10 kg N ha−1 yr−1 from cacao agroforestry, with tree N2O emissions contributing 11 % to 38 % for forests and 8 % to 15 % for cacao agroforestry. These substantial contributions of tree stems to total N2O emissions highlight the importance of including tree-mediated fluxes in ecosystem GHG budgets. Taking into account that our study sites' biophysical characteristics represented two-thirds of the humid rainforests in the Congo Basin, we estimated a total N2O source strength for this region of 0.18 ± 0.05 Tg N2O-N yr−1.

The present study evaluated profitability of some models of cocoa farms and analyzed the relationship between cocoa yield, income and carbon stored in traditional cocoa agroforests to discuss implications of cocoa intensification on carbon emissions in Cameroun. Surveys on establishment, management practices and marketing were conducted in 49 cocoa farms along a gradient of population density, forest cover and market access, and combined with data on carbon stock and trees species inventories. Traditional cocoa farms were stratified according to rehabilitation practices of farms (no rehabilitation, replacing dead/senescent cocoa plants in the farm or extending the farm by adding young plants around the old plots). Results showed that traditional cocoa agroforests are managed under high trees shade and present high carbon stock levels (average of 64 trees/ha of large tree diameter and about 94 tonC/ha). Management is based on an intensive use of family labor and there is little consistency in the use of inputs (as planting material, fertilizers and pesticides). Profitability analysis using net present value indicated that farms rehabilitated by replacement of cocoa trees were more profitable. Intensified systems are more profitable at the various discount rates considered, with up to 50 % cocoa yield increase but with less tree shade (about 40 trees/ha). Structural and productive parameters of the system showed a high variability and it was not possible to assess a clear relationship between carbon stock, yield, and incomes to clearly delineate tradeoffs. Under persistent poverty conditions and with no major intervention to support inputs purchase, suitable designs for intensification pathways should focus on good practices such as shade management, quality of associated trees, use of improved planting materials released by the research.

With increasing concerns raised by climate change, understanding biological processes within cocoa ( Theobroma cacao L.) agroforest (CAF) and fallow systems is a prerequisite for developing actions related to emission reduction in the shifting agricultural landscape of Cameroon. Carbon (C) stocks and accretion were assessed and modeled in various C components (large trees, small trees, dead wood, litter, roots, soil, and total C) of fallow and CAF systems along a 50-year chronosequence. Several functions were empirically fitted to a time series of C stocks. Large tree, soil, and total C stocks were best described by a logistic growth function while that for small trees by a rational quadratic function. The best-fitted functions explained 72–96 % of C stock accumulation over time. Two metrics describing C stock accretion were derived from these functions: the point of maximum C growth and the C growth coefficient (GC). The rate of maximum growth of total C stock was reached after 12–13 years in both fallow and CAF, with maximum GCs of 6.9 and 6.3 Mg C ha −1  year −1 , respectively. Over the 50-year period, the GCs of total C stocks varied between 0.2 and 6.9 Mg C ha −1  year −1 , with quick accumulation within the first decade that then slowed until it levelled off after 45 years. Over a period of about 30 years, both systems sequestered a total of ~200 Mg C ha −1 . This indicates that cocoa agroforests, a main source of income for local populations, can also provide significant climate change mitigation services.

The Intergovernmental Technical Panel on Soils has completed the first State of the World’s Soil Resources report. Globally soil erosion was identified as the gravest threat, leading to deteriorating water quality in developed regions and to lowering of crop yields in many developing regions. We need to increase nitrogen and phosphorus fertilizer use in infertile tropical and semi-tropical soils – the regions where the most food insecure among us are found – while reducing global use of these products overall. Stores of soil organic carbon are critical in the global carbon balance, and national governments must set specific targets to stabilize or ideally increase soil organic carbon stores. Finally the quality of soil information available for policy formulation must be improved – the regional assessments in the SWSR report frequently base their evaluations on studies from the 1990s based on observations made in the 1980s or earlier.