Resource-poor farmers who are living in the harsh environments of the West African Sahel (WAS) depend on subsistence orientated, low-input farming systems for meeting their livelihood needs.These largely extractive farming systems have resulted in nutrient depletion, soil fertility decline, low productivity and land degradation.A study conducted over 25 years in Niger, aimed to evaluate the long-term effects of organic and mineral fertilizers, cropping systems (CS) of millet and cowpea on crop productivity.The traditional millet/cowpea intercrop system without P fertilizer (TrM/C) was compared with four improved CS receiving P fertilizer: sole millet (MM), millet/cowpea intercrop (M/C), millet-cowpea rotation (M-C), and M/C and rotation with cowpea (M/C-C).Nitrogen fertilizer (N) and the residues of millet (CR) were applied alone or in combination in all five cropping systems.CR were always applied as mulch.The traditional system (TrM/C) produced the lowest millet grain yields (GY) (0.02-0.43 t/ha).All the four improved CS (MM, M/C, M-C and M/C-C) increased GY compared with the traditional system (TrM/C).The M/C and MM systems increased millet GY 3 and 3.3 times compared with the TrM/C, respectively.The M/C-C and M-C systems produced 4 and 4.2 times more GY than that of the TrM/C system, respectively.The lowest revenue was obtained with the TrM/C system.Except for the TrM/C, the revenue of the MM system was lower compared with combined cultivation of millet and cowpea.Compared with the TrM/C system, M/C and M/C-C provided 2 times more revenue.By providing 2.4 times more revenue than the TrM/C system, the M-C system was the most productive system.Cowpea provided from 54% and 56% of the revenue in M/C-C and M-C system, respectively.Soil organic carbon decreased in all the CS from 46% to 63% compared with the soil kept under natural vegetation fallow.The improved CS increased soil P from 3.4 to 4 times.Over the 25 years of cropping, the highest millet yields were obtained with the lower levels of rainfall indicating the role of nutrients in the system.The four improved systems maintained millet yields over the 25 years of cropping.By improving water and nutrient use efficiency, integrated management of mineral fertilizers, CR and cowpea affected more crop productivity than the rainfall.We concluded that cereal-legume based cropping systems treated with small doses of mineral fertilizers and CR could be used for sustainable management of soil fertility in low-input farming systems.

Joint application of mineral and organic fertilizers and incorporation of legumes into cropping systems, known as integrated soil fertility management (ISFM), has improved short-term crop productivity in sub-Saharan Africa. Little research exists, however, on the effectiveness of long-term ISFM in improving soil quality and productivity. This study determined the long-term effects of different ISFM treatments on soil chemical properties and OM dynamics up to 20 cm soil depth at a long-term research site at Saria, Burkina Faso. The ISFM treatments applied from 1960 to 2008 included broadcasted fertilizer (100 kg ha(-1) 14-23-14 (NPK) with 50 kg ha(-1) urea; and NPK with an additional 50 kg ha(-1) urea and 50 kg ha(-1) KCl) supplemented with crop residue retention, and with manure application at 5000 or 40000 kg ha(-1). In addition, continuous cropping of Sorghum bicolor (sorghum) was compared to yearly rotation between sorghum and Vigna unguiculata (cowpea). The large manure rate (40,000 kg ha (-1)) supplement was most effective in buffering fertilizer-application-induced pH decline and increasing grain yield, soil carbon (C), nitrogen (N), and phosphorus (P) concentrations (p < 0.05). Manure application also enhanced the microbial cycling and retention of C and N microbial byproducts compared to other fertilizer treatments, as indicated by C and N X-ray Absorption Near Edge Structure (XANES) spectroscopies. Legume-cereal cropping led to increased abundance of C and N functional groups indicative of reduced OM breakdown compared to the continuous cropping system. Supplemental application of manure with mineral fertilizers under mixed cereal-legume cropping was found to be most effective in improving long-term soil fertility and crop productivity in the Sahel.

It is widely believed that limited access of small scale farmers to agricultural credit is one of the key causes of rural poverty and a major constraint to adoption of innovations in Sub-Saharan Africa. Since the early 1960s, many strategies to access agricultural credits have been implemented with success. This study assessed the effects of warrantage, a community-based micro credit system, on poor small resource farmers’ income and livelihoods of the semi-arid area of Burkina Faso. Two broad socio economic surveys were conducted among 1040 farmers and 440 household heads. Data were collected from 58 inventory credit warehouses and 36 input shops established in the study areas. The results showed that the warrantage system is dominated by women farmers (who produce 60% of the stored harvests) and appears as the main source of agricultural credit. The profit (up to 140%) provided allows farmers to purchase external inputs such as inorganic fertilizers. This resulted in higher crop productivity and a substantial increase of farmers’ income which in turn improve farmers’ livelihood. Key words: Inventory credit system, mineral fertilizer, staple crop production, small farmers.

Soil carbon in the form of organic matter is a key component of the soil ecosystem structure. In most parts of West Africa agro-ecosystems (except the forest zone), the soils are inherently low in SOC content due to low organic matter additions, and accelerated degradation. The rapid turnover rates of organic material is as a result of high soil temperatures and fauna activity particularly termites. The SOC levels rapidly decline with continuous cultivation. For the sandy soils, average annual losses may be as high as 4.7% whereas with sandy loam soils, losses are lower, with an average of 2.0%. To maintain food production for a rapidly growing population, application of mineral fertilizers and the effective recycling of organic amendments such as crop residues and manures are essential especially in the smallholder farming systems that rely predominantly on organic residues to maintain soil fertility. The efficiency of fertilizer use is likely to be high where the organic matter content of the soil is also high. In unhealthy or depleted soils, crops use fertilizer supplied nutrients inefficiently. Where soils are highly degraded, crops hardly respond to fertilizer applications. When SOM levels are restored, fertilizer can help maintain the revolving fund of nutrients in the soil by increasing crop yields and, consequently, the amount of residues returned to the soil. Crop yields can be increased by 20–70 kg ha 1 for wheat, 10–50 kg ha 1 for rice, and 30–300 kg ha 1 for maize with every 1Mg ha 1 increase in soil organic carbon pool in the root zone. There is need to increase crop biomass at farm level and future research should therefore focus on improvement of nutrient use efficiency in order to increase crop biomass.

Our study on soil N dynamics was conducted in the rainy season of 2005 and 2006. It focused on the effects of soil managements with sole and combined applications of mineral and organic fertilizers in the long-term experiment conducted since 1993 in the Niamey Center of the International Crop Research Institute for the Semi-Arid Tropics, Niger. Treatments were established with each three input levels of chemical fertilizer as urea and SSP, pearl millet residue, and cattle manure. The lowest and highest levels were focused in our study. Treatments with 2700 kg ha(-1) of applied crop residue showed high total N in the soil surface (< 30 cm), but did not show any change in the deeper layer (> 30 cm) or seasonal changes. Phosphate-buffer extractable organic nitrogen (PEON) as an indicator to estimate available N in the soil was not affected by the different treatments; however, similar seasonal changes were identified in all treatments. PEON in soil surface was high right before the rainy season began, then gradually decreased with increasing rainfall and remained at approx. 10 mg kg-1 until the end of the season. In deeper layer, leaching was identified after heavy rainfall but at least 5 mg kg(-1) of PEON remained during the season. Inorganic N (NO3-N plus NH4-N) increased in the soil surface right after fertilizer application but its effect disappeared in a few weeks. The 'Birch effect' affected the fluctuations of PEON and inorganic N at the start of rains in the Sahel region of Niger. (C) 2017 Elsevier B.V. All rights reserved.

Crop production in sub-Sahara Africa is constrained by low soil phosphorus (P) content. A study was conducted in western Kenya to explore alternative P inputs and ways of optimizing their effectiveness and profitability. A field experiment established in 2007 studied the effects of Minjingu phosphate rock (MPR) and triple superphosphate (TSP) on maize, common beans and soybean yield. MPR and TSP were applied seasonally at a rate of 0, 12.5, 25 and 50 kg P ha−1 either alone or in combination. Application of P, irrespective of amount, resulted in significantly higher grain yield and total biomass for maize, common beans and soybean compared with the 0 P treatment. Applying P at 12.5 kg ha−1 resulted in significantly (ρ ≤ 0.05) lower maize, common beans and soybean grain yields than all the other P rates. On the other hand, application of P at 25 kg ha−1 resulted in similar yields to the higher P application rates. Relative agronomic effectiveness of MPR was similar for both maize and soybeans in most seasons, confirming that MPR has high potential for direct application in these soils. Switching from no application to P applied at 12.5 and also 25 kg P ha−1 attracts a marginal rate of return of at least 200 %. Switching from 25 kg P ha−1 to any of the other options attracted MRR < 200 %. This implies that adoption of either MPR or TSP by farmers in western Kenya is profitable for maize and soybeans production, given that MRRs were above 100 % minimum acceptable rate of return which is a requirement for farmers to change from one technology to another.

Fire and overgrazing reduce aboveground biomass, leading to land degradation and potential impacts on soil organic carbon (SOC) and total nitrogen (TN) dynamics. However, empirical data are lacking on how prescribed burning and livestock exclusion impact SOC in the long-term. Here we analyse the effects of 19 years of prescribed annual burning and livestock exclusion on tree density, SOC and TN concentrations in the Sudanian savanna ecoregion at two sites (Tiogo and Laba) in Burkina Faso. Results revealed that neither livestock exclusion nor prescribed burning had significant impact on SOC and TN concentrations. The results at both sites indicate that 19 years of livestock and fire exclusion did not result in a significant increase in tree density compared to grazing and annual prescribed burning. The overall mean (± SEM) of SOC stocks in the 0–50 cm depth increment in the unburnt (53.5 ± 4.7 Mg C ha−1) and annually burnt (56.4 ± 4.3 Mg C ha−1) plots at Tiogo were not statistically different. Similarly, at Laba there was no significant difference between the corresponding figures in the unburnt (37.9 ± 2.6 Mg ha−1) and in the annually burnt plots (38.6 ± 1.9 Mg ha−1). Increases in belowground inputs from root turnover may have countered changes in aboveground biomass, resulting in no net change in SOC and TN. We conclude that, contrary to our expectation and current policy recommendations, restricting burning or grazing did not result in increase in SOC stocks in this dry savanna ecosystem.

Microdosing, the point-source application of a reduced fertilizer rate within 10 days of sowing, has increased short-term crop yields across the Sahel and is being actively scaled up as an agronomic practice. However, there is no information on the long-term effects of the technique upon soil fertility. To rectify this, this study used soil samples from the International Crop Research Institute for the Semi-Arid Tropics in Sadore, Niger, to assess the effects of 16 years of a reduced fertilizer rate of 15 kg N and 4.4 kg P ha−1 compared to unfertilized soil and a recommended rate of 30 kg N and 13.2 kg P ha−1 upon millet yield trend, soil chemical properties, and soil organic matter quality. The interaction of fertilizer with crop residue and manure amendments at 300, 900, and 2700 kg ha−1 was also assessed. Compared to unfertilized soil, the reduced fertilizer rate improved yield by 116 % but did not increase total N or available P. The recommended rate doubled available P and increased total N by 27 %, but resulted in slightly lower pH compared to the reduced rate. Yield trends were negative for both fertilizer treatments, indicating mineral fertilizer alone is not sustainable at Sadore. Crop residue or manure addition at 2700 kg ha−1 with fertilizer did not improve SOC but buffered pH by 0.3 units, provided nutrients beyond N and P, and changed the forms C and N functional groups in soil organic matter.

Sustainable farming practices are required to address the persistent problems of land degradation and declining crop productivity in Sub-Saharan Africa. Approaches such as reducing tillage and retaining crop residues as mulch are potential entry points for smallholder farmers to move towards sustainability. In this study, we assessed the impact of reduced tillage (RT) compared with conventional tillage (CT), each combined with crop residue reapplication, on soil quality indicators and crop yields under an 8-year trial in western Kenya. Our results indicate that RT combined with crop residue reapplication enhanced soil physical quality through increased macroaggregate (>2000µm) proportions and mean weight diameter. Similarly, lower respiratory quotient values indicate that soil microbes under RT have better substrate-use efficiency than those under CT. Nevertheless, soil organic carbon (C), potentially mineralisable C, microbial biomass C and mineral nitrogen contents were all higher under CT with crop residue incorporated into the soil. Maize grain yield and aboveground biomass were also higher under CT. Thus, despite RT showing potential to improve soil physical properties, CT performed better. A stepwise approach is proposed towards the practice of conservation agriculture under resource-constrained smallholder farming conditions, starting with increased biomass production to provide crop residue for soil cover, followed by RT approaches.

The production of pearl millet [Pennisetumn glaucum (L.) R. Br.] in the low fertility sandy soils of the Sahel region of northern sub-Saharan Africa requires careful management. An experiment was established in 1993 at the Niamey Center of the International Crops Research Institute for the Semi-Arid Tropics, Niger. The objectives were to (i)determine the effect of long-term applications of fertilizer, crop residue, cattle manure, and combinations of these on changes in grain yield (GY) and total dry matter (TDM) of pearl millet; (ii) determine the effect of management on nitrogen application efficiency (NAE) and nitrogen use efficiency (NUE), using data from 1998 and also from 2005 and 2006. Fertilizer use showed significant positive effects on GY and TDM from 1998 to 2006. The positive effects of organic matter appeared rather later, that is, around 8 yr after the start of the experiment. The GY and TDM were strongly affected by N and P but not K. From 1998 to 2000, N-fertilizer strongly affected GY and TDM, but TDM increased gradually with the total amount N application, including N from organic matter. Nitrogen uptake by pearl millet was similar among treatments except for control in 2005, but in 2006 was higher in the treatments that combined fertilizer and organic matter. The NAE in combined applications of fertilizer and crop residue, and NUE in the treatments with residue showed higher trends than other treatments. This suggested that residue had more potential than cattle manure to enhance the effect of fertilizer.

Rapid disappearance of crop residue used as soil surface cover in conservation tillage systems reduces the envisaged soil cover benefits. This study was conducted in a conservation tillage experiment, established in 2003 in Nyabeda, western Kenya, to (1) characterize crop residue disappearance during crop growth, and (2) assess termite activity and characteristics of soil (carbon concentration and aggregate stability) in termite-molded sheetings and mound soil. Loss of surface-placed residue in the presence of macrofauna (defined as >1 mm) was up to 83 % in 3.5 months, compared to 33 % in the absence of macrofauna. Overall, residue loss was up to 34 % higher for buried than surface-placed residue. Termite sheetings had, depending on the cropping system, 11–26 and 25–42 % higher (P < 0.01) carbon than bulk soil (0–5 cm depth) and termite mound soil, respectively. Mound soil had 68 % of the soil as water stable macroaggregates (i.e., >250 µm) compared to 57 and 53 % for bulk soil and termite sheetings, respectively. Also, large and small macroaggregates were elevated under conservation tillage compared to conventional-tillage for continuous maize and maize–soybean rotation systems. We conclude that termites can affect soil carbon and its distribution considerably through their sheetings and strategies to supplement residue under ‘sustained attack’ by soil fauna are needed if a specific soil cover rate is to be maintained in conservation tillage.

Agriculture in Sub-Saharan Africa (SSA) is experiencing climate change-related effects that call for integrated regional assessments, yet capacity for these assessments has been low. The Agricultural Model Intercomparison and Improvement Project (AgMIP) is advancing research on integrated regional assessments of climate change that include climate, crop, and economic modeling and analysis. Through AgMIP, regional integrated assessments are increasingly gaining momentum in SSA, and multi-institutional regional research teams (RRTs) centered in East, West, and Southern Africa are generating new information on climate change impacts and adaptation in selected agricultural systems. The research in Africa is organized into four RRTs and a coordination team. Each of the RRTs in SSA is composed of scientists from the Consultative Group of International Agricultural Research (CGIAR) institutions, National Agriculture Research institutes (NARs), and universities consisting of experts in crop and economic modeling, climate, and information technology. Stakeholder involvement to inform specific agricultural systems to be evaluated, key outputs, and the representative agricultural pathways (RAPs), is undertaken at two levels: regional and national, in order to contribute to decisionmaking at these levels. Capacity building for integrated assessment (IA) is a key component that is undertaken continuously through interaction with experts in regional and SSA-wide workshops, and through joint creation of tools. Many students and research affiliates have been identified and entrained as part of capacity building in IA. Bi-monthly updates on scholarly publications in climate change in Africa also serve as a vehicle for knowledge-sharing. With 60 scientists already trained and actively engaged in IA and over 80 getting monthly briefs on the latest information on climate change, a climate-informed community of experts is gradually taking shape in SSA.