Microaggregate stability and sesquioxides content of degraded ultisol under different soil and crop management practices in nsukka, southeastern nigeria

Evaluating microaggregate stability and sesquioxides content of degraded Ultisol is important for sustainable management and productivity of the soils and our agroecosystem. A research was conducted in the runoff plots at the University of Nigeria Nsukka Teaching and Research Farm, in 2010 and 2011 to evaluate changes in microaggregate stability, and sesquioxides contents of Nkpologu sandy loam soil under different cover and soil management practices. The management practices were bare fallow (BF), grass fallow (GF), legume (CE), groundnut (GN), sorghum (SM), and cassava (CA) cultivation. Soil samples for analysis were taken at 0-20 cm depth at the end of each cropping season and five-month interval. There were significant effect (p<0.05) of soil and cover management on the sesquioxides (Fe2O3 and Al2O3) and the organic matter (O.M.) contents. Fe2O3 recorded the lowest value (5.88%) under the BF while the highest value (10.18%) was recorded under SM. However, the lowest value (0.265%) of Al2O3 was recorded under GN, and the highest value (0.345%) was recorded under CA. Although, the soil and cover management practices did not have significant effect (p<0.05) on the microggregate stability indices; water dispersible silt (WDSi) and clay (WDC), clay flocculation index (CFI), dispersion ratio (DR), aggregated silt and clay (ASC), and clay dispersion index (CDI) measured, there were traces of variability (CV 16-31%) in the microaggregate stability indices under the different soil and cover management practices. The most varied index was WDSi (CV 30.8%) while the least varied index was DR (CV 16%).Both Fe2O3 and O.M. had significant high positive correlation with DR (0.6658; 0.7615) and CDI (0.6068; 0.5360), but significant high negative correlation with ASC (-0.7675; -0.6918) and CFI (0.6068; -0.5360) respectively. However, while Fe2O3 had significant high positive correlation with WDC, O.M. content had a poor positive correlation with WDC. On the other hand, Al2O3 had poor correlation with all the microaggregate stability indices studied. The sesquioxides and O.M. had similar but opposite correlation coefficients with CDI and CFI respectively. It was clear that O.M. and Fe2O3 played major role in the microaggregation of the soil studied. A continuous vegetative cover management practices and adequate crop residue management were recommended for this soil, due to its fragile nature to minimize further structural degradation and further leaching of the basic cations in the soil which affects the sesquioxides and O.M. contents.