Nigeria comprises some of the most densely inhabited areas of semi-arid West Africa (Harris, 2000). As a result, the soils of this region have been cultivated for long periods. Plant
Table 21.1 Main Characteristics of Study Sites
On Kj Kj
Case Study Kano Region
Soil type Ferrugineous tropical soils, sandy, poor water holding capacity (WHC) and low-nutrient organic matter content Farming Smallholder farming:
systems Intensive: permanent annual or biannual cultivation (cropping intensity >60%) Less intensive: shrub/short-bush fallow regime (30% to 60%) Extensive: long-bush fallow and uncultivated areas (<30%) Farming Low-input systems practice Cattle manure
Study sites Futchimiram, Borno State:
Low-intensity agropastoral CP: 5-year cycle of grazing and millet cropping
Makueni District Kenya
Ferralsols naturally low in P
Annual or multiple cropping
Andrha Pradesh and Karnataka States
Alfisols and vertisols
Smallholder farming Integration among livestock, crops, and trees
Short in livestock Cattle manure
Very little fertilizer Tillage Crop residue management Soil fertility treatment Darjani Lingampally
Large mixed dryland farming
Tucuma, Catamarca, and Cordoba Provinces
Grazed prairie Row cropping
Inorganic fertilizers No tillage
Tucuman province: graze prairie and row cropping o o h fkan n,
n toi n
Kaska, Yobe State:
Low-intensity agropastoral CP: 7-year cycle of grazing and millet-cowpea cropping
Dagaceri, Jigawa State:
Intensive agropastoral (legumes and grains) CP: shrub with short-bush fallowing
Tumbau, Kano close-settlement Athi Kamunyuni zone (CSZ): Highly intensive agricultural CP: crop and livestock production system with intercropping of legumes, intensive manuring, and inorganic fertilizer Millet, sorghum, groundnut, sesame, cowpea
Open forest savannahs Grasslands
Large farmers using irrigation
Small mixed dryland farming Mixed crop and livestock
Small, mixed dryland farming
Maize and pulses Millet, cowpea, sorghum
graze prairie and row cropping
Large agrodiversity, between 8 to 10 crops: paddy, sorghum, maize, millet, groundnut, coconut, cotton, etc.
Grass, woodland system
Maize, sunflower, wheat, and soybean
Far rmi ng Sy
Note: CP = current practices.
On Gj production is limited by rainfall and nutrients (Breman and De Wit, 1983). The economy and infrastructure of northern Nigeria are not suited to high external inputs or fertilizers, and thus smallholder farming units operate as low-input systems. Legumes such as cowpeas are used to provide nitrogen inputs.
CENTURY was run for several practices at four sites: Futchimiram, Kaska, Dagaceri, and Tumbau for the last 50 to 60 years with alternate cycles of grazing and cropping (Table 21.1). Land degradation is a problem at all sites. Current practices (CP) were compared with continuous cultivation (CC), additions of inorganic fertilizer (IF), farmyard manure (FYM), plant residues (PR), and retained plant residues and grazing (NG). The predicted annual change in soil carbon for the various scenarios is presented in Figure 21.1.
The modeling exercise of the farming systems in the Nigerian case studies shows that soil carbon stocks can be increased from a low base with a variety of technologies and practices already available to farmers (Figure 21.1). The total amount of carbon that can be sequestered with the use of legumes, fallow periods, farmyard manure, and retention of plant residues varied between 0.1 to 0.3 metric tons C ha-1 year-1. Figures for CS were slightly higher when trees were introduced. The use of inorganic fertilizers caused no change or loss of soil carbon. Continuous cultivation (reduced fallows) caused small carbon losses each year when no additional organic inputs were provided. However, when a cropping practice is accumulating significant amounts of carbon, fallowing will decrease the CS potential. Despite the intensification of the current systems, the levels of carbon were maintained. The main conclusion from these systems is that CS can only be achieved by increasing organic inputs into the soil.
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