Soil Fertility Variability in Relation to the Yields of Maize and Soybean Under Intensifying Cropping Systems in the Tropical Savannas of Northeastern Nigeria

In northeast Nigeria, there are compound and bush fields which are variable in soil fertility. This variability influences the efficiency of resource use to increase crop yields on the fields. To address this variability, some soil fertility parameters in 0–15 cm depth soil samples from farmer’s compound (64) and bush (73) fields in southern Guinea savanna (SGS), northern Guinea savanna (NGS), and Sudan savanna (SS) zones were related to soybean and maize yields. Sand and silt contents significantly influenced soybean yields in compound fields in SGS and maize yields in compound fields in NGS. Clay content had significant effect on soybean yield in compound fields in SGS and bush fields in NGS. Soil pH (range 5.23–8.03) was a significant parameter of soybean in bush fields in SGS and total nitrogen (range 0.14–4.90 g kg–1) in bush fields in NGS. Organic C (range 2.2–23.6 g kg–1) significantly influenced soybean yields in bush fields in SGS and maize yields in bush fields in SS. Available P (range 0.30–11.30 mg kg–1) and exchangeable K (range 0.15–1.79 cmol kg–1) were important variables for soybean yields in compound fields in SGS and for maize yields in bush fields in SS. Available phosphorus was also related to soybean yield in bush fields in NGS. Organic carbon and available P were deficient in some of the fields and were three times determinants of soybean or maize yields. The addition of organic inputs and phosphorus and the rotation of maize and soybean, but targeted to the specific fields, are recommended.