Abstract
The objective of this study was to determine, at a farm level, the spatial variability of organic carbon stock (CS) at different depths on a field of 1 soil type in long-term (13-year) crop production under no-tillage. The crop rotation comprised soybean [Glycine max (L.) Merr.] alternating with maize (Zea mays L.) in the summer season. For the winter season, wheat (Triticum aestivum L.) was cropped in rotation with black oat (Avena sativa L.), a cover crop. The 12.5-ha field was sampled at a density of 6.25 samples/ha. Within the coarse grid, 2 dense grids with 20-, 10-, and 5-m spacing were established. Soil samples were collected at all grid nodes and analysed for soil organic carbon and bulk density. The CS at 0–0.05, 0.05–0.10, and 0.10–0.20 m was corrected for equal soil mass. Geostatistics was used for the estimation of spatial distribution of CS at 3 soil depths. We found that CS variation was low to medium (CV 6.7–19.4%). The variograms of CS at all depths were best fitted by spherical models and showed ranges of 120 m, except at 0–0.05 m (range 109 m). At 0–0.20 m depth, CS was 15.2–24.5 t/ha (CV 8.2%, range 120 m). The use of geostatistics reveals a powerful tool for the spatial estimation of CS at depth of a Rhodic Ferralsol under no-tillage, and demonstrated CS variation on a 12.5-ha area, even though soil and crop management were the same for >10 years.
Published Version
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