This version is distributed under a non-commencial no derivatives Creative Commons (CC-BY-NC-ND) user license, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited and not used for commercial purposes. Further, the restriction applies that if you remix, transform, or build upon the material, you may not distribute the modified material.Please cite this publication as follows: 1.9 and 8.4 kg at an HI of 0.65 were required to produce 1000 kg of storage roots dry matter. 26The corresponding optimal NPK supply ratios are 6.0 -1.0 -4.2 and 5.3 -1.0 -4.2. Nutrient 27 use efficiencies decreased above yields of 77-93% of the maximum. Evaluation of the 28 performance of blanket fertiliser rates recommended by national research services for cassava 29 production resulted in average benefit:cost ratios of 2.4±0.9, which will be unattractive to 30 many farmers compared to 3.8±1.1 for the balanced fertiliser rates. The indigenous soil supply 31 of nutrients revealed that, at balanced nutrition, K was the most limiting nutrient to achieve 32 storage roots yields up to 8 Mg dry matter ha -1 at most sites, whereas N and P were needed at 33 greater yields. Dry weight of storage roots measured on the control plots in our researcher 34 managed experiment ranged from 5.6 to 12.2 Mg ha -1 , and were larger than the average

Background and aims Enhanced understanding of plant and nutrient interactions is key to improving yields. We adapted the model for QUantitative Evaluation of the Fertility of Tropical Soils (QUEFTS) to assess cassava yield response to soil and fertilizer nutrients in West Africa. Methods Data from on-station and farmer's field experiments across Togo and Ghana were used. Results Soil nutrient supply ranged from 86 to 177, 18-24 and 70-104 kg ha −1 of N, P and K, respectively, and induced variable cassava responses to fertilizer application. Considering harvest (HI) in deriving the physiological nutrient use efficiencies for maximum dilution (PhEmax) and for maximum accumulation (PhEmin), which are key QUEFTS parameters, improved model predictions with reduction in normalized root mean square error from 32 to 13% at Davié (Southern Togo) and from 18 to 13% at Kumasi (Southern Ghana). Model overestimated yields in Nyankpala (Northern Ghana) where drought stress reduced yields. Estimated PhEmin and PhEmax at HI of 0.50 were 41 and 96 kg kg −1 N, 232 and 589 kg kg −1 P, and 34 and 160 kg kg −1 K. Conclusions QUEFTS can be used for site-specific estimates of cassava yield responses to fertilizers under rain-fed conditions in West Africa, provided that yield is primarily constrained by N, P and K supplies, and not by drought or other nutrients.

This chapter explores alternatives of nutrient supply and management for high nutrient use efficiency. It establishes that fertilizer use optimization is within the framework of integrated soil fertility management with recommended fertilizer rates adjusted according to soil property information and the use of complementary practices in sub-Sahara Africa.

This chapter describes soil nutrient management, including fertilizer use in Ghana, then suggests fertilizer use and recommendations. The chapter then discusses fertilizer use integrated with other practices, then diagnose nutrient deficiencies in the region. Further, the chapter provides information on optimizing fertilizer use and fertilizer use optimization tools for Ghana. Finally, the chapter explores how to adjust fertilizer rates for other practices and soil test information, and enumerates targeted crops and cropping systems by agroecological zone.

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