| Abstract: | Two expert programs, soil fertility capability classification (SFCC) and ACID4, were used to assess fertility of some soils in the highland region of Rwanda. Soils were grouped with respect to altitude, rainfall and parent material into three agro-ecological zones. Soils in Zone 3 with high rainfall, low altitude and underlain by quartzite-schists complex were lower in pertility and more acidic than their counterparts in Zones 1 and 2. N, P and K were generally deficient. Ca and Mg were considered as borderline cases and are expected to fall below acceptable levels after few years of cultivation. The SFCC identified clayey topsoils (> 35% clay), acidic (Al saturation between 10 and 60%) and low K reserves (exchangeable K < 0.2 mEq (100 g)−1) as the dominant fertility class. Crop residue management, agroforestry and green manure systems are recommended in addition to P and K fertilization to alleviate nutrient deficiency problems. Soil acidity was associated with exchangeable Al and Al saturation was > 50% at pH <5.2. Base saturation was negatively correlated with Al saturation and positively related to Ca+Mg. Therefore liming to supply Ca and Mg may reduce exchangeable Al, improve ECEC and nutrient retention. Lime requirement ranged from 0 to 6 t CaCO3 ha−1 and was directly proportional to exchangeable Al (r = 0.95**) and inversely related to pH (fr = −0.73**). Results from lime prediction equation, estimated lime requirement (Y) = 1.332×Al−0.11, computed for soils in the region concurred with those of other workers. |
