Clay and silt dispersion in relation to some physicochemical properties of derived savanna soils under two tillage management practices in southeastern Nigeria

Abstract

Monitoring clay dispersion in tillage-managed soils is important to avoid its negative impact on the soil. We studied clay dispersion in tilled (T) and untilled (NT) managed systems in five different soils from five locations. The aim was to compare the water-dispersible clay (WDC) generated with the T and NT practices and relate them to the measured soil properties. Soil samples were collected from 0–20 cm depth from T and NT of each location for analyses. The soils are acid and low in soil organic carbon (SOC), CEC and cations. WDC varied from 50 to 130 g kg⁻¹ in the soils. In all the locations except one, WDC was higher in T than NT, while higher dispersion ratio (DR) was obtained in T for three out of the five soils. The potential shrink-swell hazard of the soils was in the moderate to severe classes, while two of the soils were in the very severe shrink-swell potential class. WDC correlated significantly with exchangeable acidity and pH (r=0.77*; −0.60*), respectively. Also the DR had a negative relationship with the Ca/Mg ratio (r=−0.60*). DR negatively correlated significantly (r=–0.69*) with mean-weight diameter (MWD). The SOC positively correlated with water-stable aggregates (WSA) >2.00 mm (r=0.71*). Again the SOC was found to relate significantly with WSA sizes 0.50–0.25 mm, WSA<0.25 and the soil bulk density. These relationships between WDC, SOC and exchangeable acidity including the pH have further demonstrated the significant role that SOC can play in the stability of these soils. The net negative charge of the soil also was shown to play a very significant role in clay dispersion. It is therefore recommended that in these tropical soils with high WDC, higher application levels of organic matter should always be applied to the soil not only to improve fertility but to maintain ideal soil aggregates with less water-disperseve potential.