AGGREGATE STABILITY OF NKPOLOGU SANDY LOAM SOIL UNDER DIFFERENT SOIL AND CROP MANAGEMENT SYSTEMS
A study was conducted in the runoff plots at the University of Nigeria Nsukka Teaching and Research Farm, in 2010 and 2011 to monitor the changes in aggregate stability, and some selected physicochemical properties of Nkpologu sandy loam soil under different cover and soil management systems. The management systems were bare fallow (BF), grass fallow (GF), legume (CE), groundnut (GN), sorghum (SM), and cassava (CA) cultivation. Following the characterization of the soil of the study site, three samplings were carried out at five- month interval marking the end of first cropping season, and the start and end of the second cropping season respectively. There was no change in soil texture due to treatments. The soil was acidic throughout the period of the study with pH values ranging from 5.1 (under BF) to 5.5 (under GF) in 2010 and from 4.8 (BF) to 6.1 (SM) in 2011. The aggregate stability (AS), mean weight diameter (MWD), water dispersible silt (WDSi), bulk density (BD), total porosity (TP), macroporosity (MACP), aggregate size distributions (> 2 mm, 1- 0.5 mm and < 0.25 mm) and Ksat showed significant (P =0.05) changes under different cover management practices. The Ksat varied (CV = 52%) significantly (P< 0.05) under the different cover management practices over the sampling period. Generally, the highest values for Ksat, AS and MWD were obtained in the first sampling period whereas the lowest values were obtained in the last sampling period. There were significant effects (P<0.05) of cover management systems on AS, MWD and Ksat. The highest values for AS, MWD and aggregate size fraction > 2 mm (80.3, 2.22 and 55.6 % respectively) were obtained under GF whereas the highest Ksat(16.8cm/hr) was obtained under GN. The lowest values for these parameters throughout the sampling periods were obtained under BF. The preponderance of aggregates < 0.5 mm under BF showed that raindrop impact and other agents broke down macroaggregates into microaggregates. The interaction of cover management and sampling period was not significant (P<0.05) for the structural and hydraulic parameters determined. The cover treatments generally increased organic matter (O.M.) content compared with the BF. Soil pH increases with increasing O.M. content and vice versa. The Fe and Al oxides were significantly (P<0.05) affected by the different cover and soil management systems. The concentration of Fe oxides was high relative to the concentration of Al oxides. The O.M. had significant (P<0.05) correlation with two aggregate size ranges; 1-0.5mm (r = – 0.276* at P<0.05) and 0.5-0.25mm (r = – 0.245*at P <0.05) and Fe oxides. The cover management systems affected the infiltration characteristics measured. The highest infiltration rates (1,317 mm h-1) and cumulative infiltration (72,390 mm) were obtained under the GF and CE respectively whereas the lowest values; 287 mmh-1 (infiltration rate) and 14,455 mm (cumulative infiltration) were obtained under the BF.
The study has shown that cover and soil management systems affected the organic matter content, soil pH, Fe and Al oxides, infiltration characteristics, aggregate stability and structural properties of the Nkpologu sandy loam soil differently over time. Continuous addition of organic manure is encouraged. Legume and other crop fallows which protect the soil and guarantee regular additions of organic materials are ecologically sound components of sustainable management of Nkpologu sandy loam soil for improved agricultural productions.