Soil Fertility in Africa Is at Stake

Abstract

Soil fertility in Africa is under pressure as an increasing number of fanners attempt to make a living based on what the land can offer to growing plants. Studies in Africa from about 1989 have focused on different spatial scales, i.e., subcontinental, subnational, and farm. This chapter reviews the results obtained at these three levels and compares methodologies and implications. For N, annual depletion was recorded at all levels at rates of 22 kg ha-1 (sub-Saharan Africa), 112 kg ha" 1 (Kisii District, Kenya), and 71 kg ha~' (average for 26 farms in Kisii, Kakamega, and Embu Districts). If the soil nutrient balance is to become a suitable land quality indicator for wider use as a policy instrument, increased sophistication is required, including data on soil nutrient stocks and availability. The advantage of the nutrient balance approach over traditional rate-response research on fertilizers is that it includes all possible nutrient flows at the spatial scales discussed. A drawback, however, is the lack of hard data on flows that are difficult to measure (leaching, gaseous losses, and erosion), and the fact that the balance comprises several inputs minus the sum of several outputs. Nonetheless, the message comes out clearly that improved soil nutrient management is crucial for maintaining and improving soil productivity in Africa. Soil fertility is not a static feature. On the contrary, it changes constantly and its direction (accumulation or depletion) is determined by the interplay between physical, chemical, biological, and anthropogenic processes. This dynamism also is reflected in terminology such as nutrient cycles, budgets, or balances, referring to inputs and outputs in natural ecosystems and managed agroecosystems, to which nutrients are added and from which nutrients are removed. As the world

Fertility Status of Soils under Different Land uses at Wujiraba Watershed, North-Western Highlands of Ethiopia

“…Organic carbon was highly significantly (P ≤ 0.001) and strongly positively correlated (r = 0.86, 0.77, 0.73 and 0.7) with total N, Zn, Fe and Ca, respectively in this study (Table 5) which might be due to all of them sourced from OM. As per the classification rate suggested by Tekalign [61], the OC for forest land qualified as high while grazing and cultivated lands medium and low status, respectively for the study area.…”

White Lupin (Lupinus albus L. cv. Amiga) Increases Solubility of Minjingu Phosphate Rock, Phosphorus Balances and Maize Yields in Njoro Kenya

“…These include the form of native soil P, the type of P applied to soil, and soil reaction (Kogbe and Adediran, 2003). The higher grain yields in second year were partly as a result of elevated available P content in soil due to residual effect of MPR (Buresh et al, 1997) and subsequent uptake by maize. Key: Means in a column followed by the same letter (for maize) are not significantly different at P<0.05, using the Tukey mean separation procedure.…”

Weed control under conservation agriculture in dryland smallholder farming systems of southern Africa. A review

“…Since 2004, there has been a major push by researchers, non-governmental, and donor organizations to extend CA to smallholder farming systems in southern Africa (Sims et al 2012b;Thierfelder et al 2014;Wall et al 2014). Soils in southern Africa are affected by parent soil material of granitic origin, which is low in fertility (Smaling and Janssen 1997), low use of chemical and organic inputs (Mafongoya et al 2006), and unsustainable land use practices (Wall et al 2014). Soil degradation from conventional tillage practices emphasizes the importance of systems that increase soil organic matter content and improve soil structure (Johansen et al 2012;Tittonell et al 2012).…”