Soil organic carbon (SOC) management for sustainable productivity of cropping and agro-forestry systems in Eastern and Southern Africa

Abstract

In Eastern and Southern Africa, the shifting from the no-external input agriculture (shifting cultivation through slash and bum) to intensified agricultural systems has resulted in widespread agro-ecosystems with high soil organic carbon and nutrient depletion. This is quite evident in farming systems with reduced fallow period or those that practice continuous cropping without or with little inputs. Long-term experiments indicate that losses of up to 0.69 t carbon ha-1 yr-1 in the soil surface layers are common. Such losses are commonly reported by farmers engaged in participatory community-based research development projects. This calls for judicious strategies for recapitalization or replacement of these depletions. Such strategies include direct SOC replenishment through addition of organic materials, notably manures, wastes, residues and plant litter; biomass transfer; incorporation of improved fallows in the farming systems. Indirect contribution to SOM replenishment or recapitalization may be achieved through inorganic fertilizations and amendments; legume integration in the production system; and combined inorganic and organic inputs. Research is required to identify inputs that help meet both nutrients availability while contributing to SOC build up at the same time.

Soil Fertility Status and Its Determining Factors in Tanzania

“…Generally, there seems to be a consensus that the soils in Tanzania and the neighboring countries are not very fertile. The relevance of soil organic carbon management and appropriate fallowing systems such as agroforestry have been pointed out since as critical for sustaining agricultural production (Kimaro et al, 2008;Nandwa, 2001). In the present study, the regional trend in soil fertility with respect to the soil mineralogical and chemical properties was investigated.…”

The Impacts of Household Land Use and Socio Economic Factors on the Soil Fertility of Smallholder Farms in the Highlands of Kenya

“…In contrast, in Madzuu P levels ranged from 6.0 to 12.7 mg kg -1 (Table 2). Olsen P values of less than 15 mg P kg −1 when SC is less than 15 mg kg -1 and less than 10 mg P kg −1 for all Ferralsols, irrespective SC levels, are considered limiting (Nandwa, 2001) <<Please Insert Table 2>> 3.2 Principal components analysis of soil properties…”

“…In Madzuu, except for pasture, which is usually located near the homestead, soil fertility status among land use types was not strikingly different and was generally low (Cochrane et al, 1995 andNandwa, 2001). Between farms and between fields within farms variances were about equal.…”

“…Unlike Madzuu, in Embu most soil sampled had relatively high values for the different soil fertility indicators (Cochrane et al, 1985, Nandwa, 2001. Differences in soil fertility among land uses were generally small, though food crop fields were significantly lower in SC.…”

Effect of plant biomass, manure and inorganic fertilizer on maize yield in the central Highlands of Kenya

“…One of the approaches is the integrated nutrient management that combines use of organic inputs with chemical fertiliser. The beneficial effects of combined organic and inorganic sources on soil fertility, crop yields, and maintenance of soil organic matter have repeatedly been shown in field trials (Nandwa, 2003;Vanlauwe et al, 2002), yet there are no predictive guidelines for their management, such as those that exist for inorganic fertiliser. The success of combined nutrient management depends on several factors that include the types and quantities of organic materials available, and the rates and proportions at which the two nutrient sources are combined.…”