Cassava is the major staple in the African Humid Tropics. Many countries rely on cassava to cover basic calorific and protein needs (cassava leaves), yet cassava yields in SSA are globally the lowest (6-12 Mg/ha) and appear stagnant. Major reasons are choice of poor soils, assuming cassava performs on poor soils and low nutrient supply to attain a larger portion of the cassava yield potential (90Mg/ha). The combination of growing cassava on poor soils and low fertilizer use limit farmers’ yields and incomes, affects consumer prices, and hampers improved livelihoods. Cassava, including roots and aboveground biomass, requires 6.2kg N, 1kg P, and 5.3kg K per ton DM, thus a total of 165–25–145 kg/ha N-P-K attain 50% of the current potential yield (45Mg/ha fresh roots). Such nutrient amounts are unlikely supplied by the soil, making nutrient supply along with the choice of suitable soils crucial factors in achieving higher cassava yields. Current cassava systems rely almost entirely on soil supplies and thus are exploiting the natural resource base not only for cassava but for all crops in a cropping cycle. Cassava specifically due to its slow early growth and relatively late canopy closure exposes the soil to a high risk of erosion and compaction, thus aggravating negative effects on soil quality and nutrient stocks. The proposed research will be conducted in strategically selected sites representing major cassava growing agro-ecologies in each country. Within agro-ecologies sites are allocated across major landscape features to reflect major farming portions of the landscape and to cover sufficient variability across the farming landscape. This will generate information to model whole landscape partial nutrient balances and flows. Considering that in the target countries cassava has undergone strong expansion of the cropped area and is still expanding the obtained data will further help to better place cassava in the agricultural landscapes to increase profitability and reduce negative environmental impact. There are no recent cassava fertilizer response curves. Nutrient(s) limiting cassava production have not been determined. Eliminating deficiencies will lead to substantial yield increases. Depending on the nutrient(s) most limiting, productivity and profitability increases may be possible at low cost and risk. IITA will determine most limiting nutrient(s) and elaborate quantities required to recommend optimal nutrient composition and quantities, comprising blends eliminating deficiencies of sulfur, magnesium, zinc, boron. Fertilizer alone is unlikely to sustainably intensify root crop production. Soil organic matter is crucial for nutrient retention, physical stability and biological functions required for crop production. Organic matter (OM) additions and interactions with fertilizer will be evaluated. Animal manure, a common source of OM is not readily available in the humid tropics. Therefore other sources of OM, such as biomass, biochar and crop residues are focal aspects in soil management. Cassava, if correctly managed and supplied with nutrients is a crop that can produce more biomass than most other crops. Leaf litter production alone exceeds 5 Mg/ha DM per year not including the canopy still existing at the final harvest. Cassava root harvest index is around 50% and a certain portion of stems is removed to plant new fields. Targeting root yields of 25 Mg/ha this activity will ultimately provide around 20 to 25 Mg/ha fresh biomass to the soil at around 30% dry matter content However, compared to cereals and grain legumes more biomass remains on the fields after cassava. Thus buildup of OM is more likely possible with a cassava crop than with short term cereals and legumes. Many root crops are grown in intensively tilled soil, a feature than may facilitate harvest yet has potentially negative effects on OM. Recent results from Nigeria comparing ridged with flat soil cultivation of cassava shows rather small yield increments and significant interactions with maize intercropping. This activity will therefore as well look into the tillage requirements versus the OM buildup with a view on the opportunity to move cassava cultivation in the direction towards minimum or zero tillage systems that are known to permit OM build up. Organic matter input quality is an issue in the humid tropics and manure is not readily available due to low stocking rates of livestock which is likely due to insufficient feed stock year-round and poorly performing races of goat and sheep. This activity will not look into livestock integration yet will be able to draw on experiences collected in RTB projects on livestock integration in root & tuber systems. In the long term such collaboration may close the manure gap and offer opportunities for better crop residue utilization, higher incomes, improved nutrition and high quality inputs for soil fertility management. This activity fits under WLE because Humidtropics does not conduct commodity research and RTB does not conduct beyond commodity specific issues. Focus of this activity is on Integrated Soil Fertility Management across landscape positions for a commodity that is already covering a substantial proportion of the agricultural land in Humid SSA and is expanding as climate change worsens growing conditions for other crops. Humidtropics and RTB have formal agreements on collaborating and collocating research -these two CRPS will be close partners in this activity to cover the commodity specific aspects (RTB) and the larger cropping systems and livelihood strategy aspects (Humidtropics). Partnerships and NARS engagement: IITA will involve the NARS of the target countries such as INERA in DR Congo, the Agricultural Research and Development Institute in Tanzania and the Zambia Agriculture Research Institute (ZARI). Currently IITA has ongoing collaboration with these NARS and is involved in capacity development of young researchers. Further, IITA has an ongoing south – south collaboration with IPNI (Philippines) investigating cassava nutrient manager expert systems to develop site specific fertilizer recommendations for cassava. Soil carbon and plant nutrient analysis are supported by a collaborative agreement with the Katholieke Universiteit Leuven, Belgium (KUL) using advanced analytical technologies.