No abstract

The impact of intensive forest management practices on soil physical properties was examined by collecting intact, 7.6‐cm diameter soil core samples to a depth of 30 cm before harvest, after harvest, and after site preparation in plots established in primary skid trails and areas receiving whole‐tree and conventional tree‐length harvesting treatments. Site preparation for all plots was shear, burn, chop, and bed. Harvesting increased bulk density and decreased aeration porosity in all sampled areas. Significant changes in these properties were detected to the 30‐cm depth in the skid trail plots. However, significant changes in the whole‐tree and tree‐length plots were limited to the upper 15 cm of soil. Harvesting also significantly decreased saturated hydraulic conductivity to a depth of 8 cm in the skid trail plots and 15 cm in the tree‐length plots but had no significant effect in the whole‐tree plots. Bedding proved to be effective in offsetting soil compaction in the whole‐tree and tree‐length plots by forming a new soil surface, 19 cm in height, over the surface which was trafficked during harvest. Bedding may not be as effective in the skid trail plots because the soil found at the original surface under the bed was compacted to the extent that root growth may be inhibited.

The impact of intensive forest management practices on soil bulk density, aeration porosity, and saturated hydraulic conductivity was examined to a depth of 0.3 m before harvest, after harvest, and after site preparation. Harvesting caused significant changes in soil physical properties to an average depth of 0.17 m in whole tree harvest plots and 0.22 m in skid trail plots. Disking was effective in restoring soil physical properties to preharvest levels in the upper 0.07 to 0.12 m of soil. Soil compaction in chop/burn plots may result in reduced root growth because of mechanical impedance, reduced aeration, or both.

Phosphorus‐retention capacities in the surface horizons of 42 forest soils of the US Southeastern Coastal Plain were determined from the adsorption maximum of the Langmuir isotherm and by saturation with 2,500 µg P/g soil. Both indices were closely correlated (r = 0.986) although on the average the saturation method gave retention capacities two to three times greater than those derived from the Langmuir equation. Range in retention capacities were from 0 to 1,288 µg P/g soil from the concentrated solution. Spodosols generally had the lowest retention capacities although there was considerable overlap between soil orders.Several soil properties (% clay, % silt, pH, loss on ignition) were significantly correlated with P retention but partial correlation analysis showed that, except for pH and to a lesser extent clay, the relationship was indirect through association with extractable Al. Extractable Al and Fe provided the best indices of P retention. The most successful of the extractants of Al for predicting P retention (r = 0.934) was 1N NH4OAc (pH 4.8), while 0.3M (NH4)2C2O4 (pH 3.2) was the most successful of the extractants of Fe (r = 0.903) for predicting P retention.Multiple regression analysis of P retention on exchangeable, amorphous, and crystalline forms of Al and Fe showed that on a per unit weight basis, the order of activity in P retention was exchangeable > amorphous > crystalline with apparently little distinction between Al and Fe within these categories. The greater contribution of Al than Fe to P retention in these soils was primarily a function of the greater amount of Al than Fe in the active forms.

Soil tests were evaluated as methods for predicting height growth or increased height growth due to P fertilization of Pinus elliottii var. elliottii Engelm. on acid Coastal Plain soils. Growth and response parameters were obtained from field and greenhouse trials fertilized at time of planting with N and P. Field trials were measured 1, 3, and 5 years after planting and the greenhouse trial, which involved unfertilized soils collected from the field trials, was measured 1 and 2 years after planting.The amounts of P extracted by H2O or NH4OAc (pH 4.8) were the most closely correlated with height growth and response to P fertilization after 1 year of growth in both the greenhouse and field. The effectiveness of these methods declined after longer growth periods. Methods which extracted larger amounts of P—0.5M NaHCO3; 0.05N HCl + 0.025N H2SO4; 0.03N NH4F + 0.025N HCl—were more effective predictors of response to P fertilization over growth periods of 3 and 5 years in the field. Phosphorus extracted by 0.03N NH4F + 0.025N HCl was the most closely correlated with response recorded after 5 years (r2 = 0.778).Concentrations of P in the tops of greenhouse‐grown pine seedlings after both 1 and 2 years growth were most closely related to P removed by the stronger extractants. The r2 values for the relationships between soil test values and both concentrations of P in seedling tops after 2 years and in foliage of field trees at age 4 were almost identical.