This study examined the influence of organic residue quality and N fertilizer on aggregate‐associated soil organic matter (SOM) in maize (Zea mays L.) cropping systems of southern Ghana. Six residue treatments of differing quality [Crotalaria juncea L., Leucaena leucocephala (Lam.) de Wit, maize stover, sawdust, cattle manure, and a control with no residues added] were applied at 4 Mg C ha−1 yr−1 both with and without fertilizer N additions (120 kg N ha−1 season−1). Soils (0–15 cm) were sampled 3 yr after study implementation and wet sieved into four aggregate size classes (8000–2000, 2000–250, 250–53, and <53 μm). Small macroaggregates (2000–250 μm) were further separated into coarse particulate organic matter (>250 μm), microaggregates within macroaggregates (53–250 μm), and macroaggregate‐occluded silt and clay (<53 μm). Nitrogen fertilizer additions reduced aggregate stability, as was evident from a 40% increase in the weight of the silt and clay fraction (P = 0.014) as well as a decrease in microaggregates across all residue types (P = 0.019). Fertilizer similarly affected C and N storage within these aggregate fractions, while the effects of residue quality were largely insignificant. Our results suggest that fertilizer effects on soil aggregation may have important implications for long‐term SOM dynamics.

Deadwood is a large global carbon store with its store size partially determined by biotic decay. Microbial wood decay rates are known to respond to changing temperature and precipitation. Termites are also important decomposers in the tropics but are less well studied. An understanding of their climate sensitivities is needed to estimate climate change effects on wood carbon pools. Using data from 133 sites spanning six continents, we found that termite wood discovery and consumption were highly sensitive to temperature (with decay increasing >6.8 times per 10°C increase in temperature)—even more so than microbes. Termite decay effects were greatest in tropical seasonal forests, tropical savannas, and subtropical deserts. With tropicalization (i.e., warming shifts to tropical climates), termite wood decay will likely increase as termites access more of Earth’s surface.

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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C assava (Manihot esculenta Crantz) is an important crop of smallholder farmers in Tanzania, Kenya and Ghana (Harvest Choice, 2011). In Ghana, cassava is second to maize in terms of production area and an important cash crop (MOFA, 2010; FAO, 2015). In Tanzania and in Western and Coastal Kenya, cassava is second to maize in importance as a food crop (Mwango'mbe et al., 2013). However, mean cassava fresh storage root yield was estimated to be 13.5, 6.2 and 14.4 Mg ha-1 for Kenya, Tanzania and Ghana, respectively (FAOSTAT, 2017) while cassava yield has reached 80 Mg ha-1 (FAO, 2013). Pests and diseases, the use of poor cultural practices, and low soil fertility status are among causal factors for low cassava yields (Harvest Choice, 2011; Ezui et al., 2016). Several studies have shown that the soil nutrient balance is negative due to nutrient removal at harvest, minimal or no use of fertilizers, and soil erosion (Asadu and Nweke, 1999; Shekiffu, 2011; Fermont 2009). Few soil fertility studies have been conducted in cassava production in Tanzania, Kenya and Ghana and very few farmers apply fertilizer to cassava (