Variability in Soil Properties Along an Udalf Toposequence in the Humid Forest Zone of Nigeria

Abstract

Uniform soil management without any knowledge of the variability of soil properties could result in some parts of an agricultural field receiving insufficient inputs, while other parts receive an excess. Profile soil samples were collected and analyzed for some physico-chemical properties along an Udalf toposequence and their variability assessed. Soil pH was consistently least variable along the toposequence and at all depths. Highly variable properties on the upper slope (crest) included Ca, Mg, Na, K, and P; on the middle slope (hill slope) they were K, organic C, N, silt and clay; and on the foot slope (valley floor) they were Mg, organic C, available P, EA, silt and clay. Moderately variable properties were: C. electrical conductivity (EC), effective cation exchange capacity (ECEC), bulk density, clay, gravimetric moisture, volume wetness and degree of saturation on the upper slope; Mg, Na, EC, and ECEC, base saturation, sand, bulk density, gravimetric moisture and volume wetness on the middle slope; and on the foot slope Ca, N, EC, ECEC, base saturation, bulk density, gravimetric moisture, volume wetness and degree of saturation were moderately variable. The use of bulk samples randomly collected to determine soil properties should be minimized. Large soil sample sizes are needed for soil property studies along the toposequence, as most properties varied from highly to moderately variable. Uniform soil management along the toposequence should be avoided.