Short term effects of tillage-mulch practices under sorghum and soybean on organic carbon and eutrophic status of a degraded ultisol in southeastern Nigeria

a key indicator of soil quality as organic carbon needs to be enhanced in the highly weathered soils predominant in southeastern nigeria through appropriate tillage-mulch practices and cropping systems. we subjected a degraded typic paleustult (sandy loam) at nsukka to no-till (nt) and conventional tillage (ct) and bare fallow (b) and mulch cover (m). this was duplicated with one sole-cropped to sorghum and the other to soybean as separate crop treatments during 2006 and 2007 growing seasons. the ct resulted in higher available p (pav) (under soybean) and cation exchange capacity (cec) (under both crops) than the nt. mulch gave lower pav under sorghum and vice versa under soybean. exchangeable ca was lowered while exchangeable acidity was enhanced with mulch under soybean. overall, soil organic carbon and exchangeable mg, na and acidity were enhanced under soybean relative to sorghum; the reverse was the case for pav. however, the soil's cec indicated comparable values in both cropping systems. our results suggest that cropping 'ct with m' soil to soybean could be a promising agronomic combination for enhancing the soc and fertility status of the soil.