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The soils of sub-Saharan Africa are characterized by their poverty in nutrients along with low clay and organic carbon content and low exchange capacity. There is high pressure on land resources with the quick growth of population and demand for food. Maintaining the fertility of cultivated soils and land resources is a challenge. Since the paradigm of "external input" in the 1960s and 1970s, to the latest concept of integrated soil fertility management, most of the approaches remain crop oriented or livestock oriented with less attention to local communities (LC), which are at the heart of land resource management. This chapter suggests a new integrated and holistic approach involving LC for land resources management, including cultivated soils and rangelands. A global framework is proposed for development of management options of land resources with LC. It is a dynamic process of participative management of lands as providers of services for the entire community.

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The effects of cowpea (Vignaunguiculata) and groundnut (Arachis hypogea) on succeeding sorghum yields, soil mineral N and nematode infestation were studied during five cropping seasons (2000 to 2004) in a weakly acid Ultisol of the agronomy research station of Farakô-Balocated in the Guinean zone of Burkina Faso, West Africa. A factorial 5 × 5 design of five crop rotations with five fertilizer treatments in a split-plot arrangement with four replications was used. Sorghum yields were affected by the two factors (rotation with legumes and fertilizer applications) during the four years. But interactions were not observed between the two factors. Monocropping of sorghum produced the lowest yields and legume-sorghum rotations increased sorghum yields by 50% to 300%. Groundnut-sorghum and cowpea-sorghum rotations increased soil mineral N by 36% and 52%, respectively. Crop rotation influenced nematode infestation but the effects on soil and sorghum root infestation differed according to the rotation. The cowpeasorghum rotation increased soil and sorghum root infestationby nematodes while groundnut-sorghum decreesed the nematode population. The soil of the cowpea-sorghum rotation contained 1.5 to 2 times more nematodes than the soil of the monocropping of sorghum. In contrast, the soil of the groundnut-sorghum rotation contained from 17 to 19 times fewer nematodes than that of themonocropping of sorghum. However, nematode infestation did not affect any of the succeeding sorghum yields. It was concluded that the parasitic effect of nematodes was limited by the predominance of positive N-effects on the development of succeeding sorghum.

Biological nitrogen fixation (BNF) by legumes is an indicator of their potential contribution to recycling nitrogen in cropping systems. Many techniques exist for the quantitative measurement of legume BNF. The isotopic dilution (ID) methods are the most accurate but are too expensive, time-consuming and require technical expertise. There is a gap between the simple but less accurate Total Nitrogen Difference (TND) method and the Isotopic Dilution (ID) methods. By measuring the BNF of 11 cowpea (Vigna unguiculata) genotypes, this study aimed to develop a simple model as an improved tool for the quick estimation of BNF. Total N accumulated by traditional genotypes from Burkina Faso varied from 23 to 41 kg ha−1. Approximately 40 to 65% of this was nitrogen derived from the atmosphere (Ndfa) when the TND method was used (Ndfa-TND), while the ID method indicated that 29 to 37% of N accumulated was derived from the atmosphere (Ndfa-ID). The TND method overestimated the BNF of high N-yielding genotypes but underestimated the BNF of low N-yielding genotypes (N-accumulated below 31 kg N ha−1). The relationship between N-accumulated and Ndfa-ID was described by a polynomial regression: Yi = 0.0127 Xi2 - 0.5354 Xi + 17.44, where Yi and Xi represent Ndfa-ID and N-accumulated, respectively (P<0.05, R2 =0.92). The model was validated and could be used for quick estimation of BNF directly from the N accumulated.