The interaction of land use and seasonal microclimatic events could explain the differences in soil quality characteristics which mediate biological and physical processes of the soil under low input land use systems (plough plus harrow, strip/heap tillage, manual clearing/no till). It is hypothesised that in a humid tropical Alfisol, low input system involving reduced tillage methods, and mineral fertilizer and/or livestock manure use, would support a higher density of microbial biomass, soil aggregation, organic C and total N and hence improvement in soil quality. The dynamics of biotic and abiotic soil properties as affected by methods of seedbed preparation characterised by manural input and microclimatic transitions from wet to dry season was studied in a maize field in a tropical rain forest Alfisol in Akure, a humid rain forest zone of Nigeria. Each year, trials were carried out during the rainy (April-July) and late (September-December) seasons of 2001 and 2002. Methods of seedbed preparation involving plough plus harrow, strip/heap tillage and no tillage, and addition of different gradients of manures (mineral N and/or plant debris and live stock litter) were imposed on the soil at the site of the experiment (of comparable physical properties of bulk density and texture). Among the treatments, there were significant differences in the values of water holding capacity, aggregate stability (macro-aggregation), concentrations of microbial biomass, organic C, total and mineral N and CEC. In the rainy and late season trials, the strip/heap tillage and the no till treatments improved aggregate stability (as measured by the percent ages of aggregates between 2 and 10 mm of soil) and water holding capacity over plough+harrow. For example, in the rainy season trial, under treatments involving strip/heap tillage and the no till alone and in combination with livestock manuring and residue retention, the values of aggregates between 2 and 10 mm range from (110-116; 113-119 g/kg) and water holding capacity (0.11-0.14; 0.12-0.15 g/g) over plough+harrow (107.3 g/kg; 0.11 g/g). Similar trends were found in the values of soil microbial biomass C (377, 353; 547, 490 g/g dry soil), soil organic C (3.8, 4.3; 5.2, 5.5 g/g) and total N (2.9, 2.3; 2.9, 3.0 mg/g) for strip/heap and no till treatments compared to plough+harrow (327.6 g/g dry soil; 3.4 g/g; 2.8 mg/g). Although the %C microbial to C organic ratio (an indicator of the utilisation of organic carbon by the microbesin terms of organic matter turn over rate) was stable for all treatments, its magnitude was not constant but increased with increases in soil C concentration. The values of microbial biomass carbon to organic carbon (Cmic: Corg) ratio were higher under ploughing and heap tillage combined with mineral N (0.096, 0.099) than in no-till treatment (0.083) in the rainy season trial. Similar trends were obtained in the magnitudes of this parameter in the late season trial. Microbial biomass correlated positively with both soil organic C ( y=0.393 c-6.7; r2=0.99; P< 0.05)
