Abstract
Light textured soils are often characterized as acid to depth that results in low productivity levels. In an effort to address this constraint a four year study was undertaken that evaluated the productivity of Gamba grass ( Andropogon gayanus) and Stylosanthes ( Stylosanthes guianensis) (Stylo) to grow on these soils. In addition, Gamba grass treatments received either no nitrogen fertilizer (Gamba) or a total 287 kg N ha − 1 as either KNO 3 (Gamba NO 3) or (NH 4) 2SO 4 (Gamba NH 4). Average annual dry matter production levels for the Gamba, Gamba NO 3 and Gamba NH 4 were 11.9, 22.5, and 26.6 t ha − 1 whilst that of the Stylo treatment was 6.9 t ha − 1 . However, the net annual acid addition rates associated with the export of biomass ranged from 5.1–13.3 kmol H + ha − 1 yr − 1 . Rapid acidification of the soil profile was observed to depths > 110 cm in all treatments regardless of the tempering influence of nitrate based fertilizers. Soil organic carbon levels over the study period showed a 6 fold increase at > 30 cm from the initial values, suggesting significant carbon sequestration. Whilst the study demonstrates the positive impact of a grass or legume ley in producing forage for livestock in a cut and carry system under rainfed conditions in Northeast Thailand, along with positive contributions to soil organic carbon sequestration, a precautionary approach should be adopted. Significant accelerated soil acidification has occurred to depths > 110 cm that brings into question the sustainability of these systems on these soil types.
Published Version
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