Comparative study of soil properties under various cultivation regimes of different crops

Establishment of cover crops is an effective way to reverse the soil fertility decline, which can be caused by a range of inappropriate traditional agriculture practices, particularly tillage and inorganic fertiliser application. In this study, soil properties were assessed under various cultivation regimes of different crops, including legumes, grass, and nursery natural rubber (NR) trees (Hevea brasiliensis Muell. Arg.), in southern Vietnam. The crops studied had all been growing for 7 years commencing in 1999, on light-textured Acrisols. Soils under the cultivation regime of creeping legumes including 'Calopogonium caeruleum', 'Pueraria phaseoloides', and 'Stylosanthes gracilis' had significantly higher carbon (C) and nitrogen (N) concentrations and porosity than soils under the other management types studied. Soils under 'Brachiaria ruziziensis' and 'P. phaseoloides' had the highest aggregate stability. Cultivation regimes with tillage, field traffic, and inorganic fertilisers applied to nursery NR trees increased phosphorus (P) availability, but this was accompanied by increased soil compaction and reductions in most of the other soil properties analysed. Relative to the nursery NR cultivation, creeping-legume cultivation increased soil C concentration (by 95%), soil pHH2O (by 19%), macro-aggregates (by 29%), and porosity (by 8%). From principal component analysis, three soil properties - soil organic carbon (SOC), porosity, and P availability - were selected as key indicators suitable for the evaluation of the effects of cultivation on soils. Establishment of 'C. caeruleum' and 'B. ruziziensis' was most effective in improving soil C content, and soil porosity was significantly higher under 'C. caeruleum' and 'P. phaseoloides'. These findings suggest that each cover crop had its own dominant agro-characteristics and that selection of a cover crop to either improve soil fertility or reduce compaction should be considered by farmers in this region.