Soil Profile Characteristics of a 25-Year-Old Windrowed Loblolly Pine Plantation in Louisiana
Windrowing site preparation, the raking and piling of long rows of logging debris, has been reported to displace surface soil, redistribute nutrients, and reduce volume growth of southern pine forests. Many of these studies have reported short-term results, and there are few long-term studies of the effects of windrowing on soil properties and pine growth. A 16.2 hectare tract on Sacul fine sandy loam (clayey, mixed, thermic Aquic Hapludult) in Jackson Parish in northern Louisiana was windrowed in 1975. The objective of this study is to compare soil physical and chemical properties from scraped areas between windrows with that from windrow pile soils, 25 years after windrowing. Surface, subsurface, and subsoil horizons were sampled from 13 soil profiles within inter-row (scraped) and windrow (piled) positions. Thickness of the 0, A, and E horizons, as well as depth to the Bt horizon, were measured in these profiles. Comparisons were made on the following properties for each horizon on each of the two site positions: organic matter, pH, available phosphorus, and exchangeable calcium, magnesium, potassium, and sodium. Bulk density was measured for windrow and inter-row position surface and subsurface soils. Pore space and air-filled volume were calculated using bulk density and water content, Mean bulk density of windrow surface soils was 1.18 g cm-3, as compared with 1.53 g cm-3 for inter-row surface soils. Inter-row subsurface bulk density was also significantly greater than that for windrow positions. Inter-row soils at both depths had significantly less pore space and air-filled volume than that of the windrow positions. In contrast to physical properties on the site, there were no significant differences in surface or subsurface soil chemical properties. Site index (base 50 years) of loblolly pine growing between the windrows was the same (97 feet) as that growing on a non-windrowed part of the tract. Although surface and subsurface soils between windrows were significantly compacted, this compaction does not appear to have limited loblolly pine growth. After 25 years, there was little evidence of nutrient redistribution. The effectiveness of windrowing in reducing woody competition during early stand development may be a more important factor influencing growth.