SUMMARYCowpea (Vigna unguiculata L. Walp) is the most important food grain legume in Africa. Cowpea is nodulated by rhizobium bacteria in almost all soils of the tropics, but studies performed in the 1970s and 1980s in Nigeria suggested only modest responses of grain yield in the field to inoculation of selected rhizobium strains. More recently, experiments performed in Brazil have shown that cowpea responded to inoculation of rhizobium selected locally and grain yields increased by up to 30%. We tested some of the Brazilian strains on cowpea at a site in northern Mozambique and at several sites in Northern Ghana. At all sites phosphorus fertilizer (26 kg P ha−1) was added to all plots. At the site in Mozambique despite considerable damage to the crop by the parasitic yellow witchweed (Alectra vogelii), grain yields were more than doubled by inoculation of one of the Brazilian strains and reached 1.4 Mg ha−1. In on-station experiments conducted in 2012 in June and August in northern Ghana using the local cowpea variety Padi-Tuya as the test crop, nodule weight at 35 days after planting (dap) tripled with rhizobium strain BR 3299 (530 mg plant−1) in August with the other inoculants (BR 3267 and a mixture of BR 3267 and BR 3299) also increased nodule weight to over 300 mg plant−1. In the first on-station experiment, grain yields were doubled by the inoculation of any of the three rhizobium strains, and in the second experiment, significant increases in grain yield ranged from 39% to 57% and reached over 2.0 Mg ha−1. Similar increases in nodulation and grain yield due to inoculation were observed in 22 on-farm trials. Nitrogen fertilizer application promoted vegetative growth but did not increase grain yield and nodulation. Inoculating cowpea with highly effective rhizobium strains can therefore enhance grain yield of smallholder farmers in Africa.

Groundnut yields obtained by farmers in northern Ghana are generally low due to low soil fertility resulting from continuous cropping coupled with low use of external inputs. There is therefore the need to use systems’ internal resources such as biological nitrogen fixation efficiently to enhance crop production. This on-station experiment investigated nodulation and pod yield responses of three groundnut varieties, namely Obolo, Oboshie and Samnut 22 to inoculation with rhizobium inoculants of exotic strains, namely Bradyrhizobium yuanmingense (BR 3267) and USDA 3456 in combination with 0 kg P ha−1, 15 kg P ha−1 and 30 kg P ha−1. Combined application of 30 kg P ha−1 and BR 3267 increased the nodule numbers in Obolo, Oboshie and Samnut 22 by 144%, 188% and 56%, respectively compared to their uninoculated counterparts. Inoculation with BR 3267 produced the highest pod yield in all the three varieties with yields increasing from 13 to 40% over that of the uninoculated treatments, with BR 3267-inoculated Samnut 22 giving the highest yield of 2013 kg ha−1. P fertilizer and rhizobium inoculant also had a significant interactive influence on the pod yield of groundnut. Combined application of 30 kg P ha−1 and rhizobium inoculation increased the groundnut yield by 64 to 68%. The study observed a positive interaction between the rhizobium strains and P fertilizer.

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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