Check #1: Evaluate Soils
Basic (Non-Acidic) Soils
With few exceptions, forest soils of the Southeastern US are acidic which means they are below 7.0 pH. One exception is the “black belt” where some prairie-type soils occur in Central Alabama. Otherwise, most forest soils have a pH somewhere between 4.0 and 6.0. All southern pine species are adapted to acidic soils. As the soil pH increases and becomes basic (above 7.0), southern pine species may have difficulty obtaining some nutrients from the soil. Observations of newly planted bareroot loblolly, slash, and longleaf in a heavily limed pecan orchard, revealed a consistent pattern of yellowing, reduced root growth, and increased mortality among newly planted seedlings in basic (above 7.0 pH) soils.
Some sites that were once appropriate for longleaf may be inappropriate owing to changes in soil pH or soil nutrient levels. Sites that have been heavily limed may be basic (>7.0 pH) rather than acidic (< 7.0 pH). Establishing pine trees on basic soils may prove difficult. Likewise, complete planting failures are not uncommon on agricultural sites that were formerly used for tomato production. Southern Forestry Consultants report that some tomato fields in and around Thomasville, GA and Quincy, FL were limed so heavily the soil pH exceeded 8.0. Under these conditions, it may be extremely difficult to establish any pine species.
Furthermore, one of the most frequently used chemicals applied as an herbaceous release over longleaf pine - Oust® or sulfometuron – appears to behave differently based upon soil pH. As pH increases, sulfometuron may become more active. In general, we recommend reducing the rate at which Oust® is applied when pH exceeds 6.0, and Oust® should probably be avoided when pH exceeds 6.5.
Therefore, a good first step is to sample the soil of the old-field or pasture you intend to convert to longleaf pine. If the soil pH exceeds 7.0, you may encounter increased risk of planting failures.
Additionally, sites that have been repeatedly treated with chicken litter may have toxic concentrations of elements that would normally be beneficial to seedling survival and growth. Prior to establishing any pine species on an old field or pasture, have the soils tested for acidity and soil nutrient levels.
Residual Herbicides
While many planting failures that once fell under the category “unexplained” have been tracked back to high soil pH’s, another potential factor in “unexplained” planting failures may be residual herbicides. Most agricultural herbicides decompose fairly rapidly, and are probably not a factor in seedling mortality. Other herbicides may stick around long enough to be picked up by newly planted pine seedlings. A tremendous variety of herbicides are used over the top of agricultural crops, and it is would be very difficult to track down which ones are responsible for increased mortality of pine seedlings. To avoid the possibility of residual herbicides damaging your newly planted tree seedlings, it may be wise to let crop-land lay fallow for one year following peanut or cotton production.
Dry Sites with Excessively Drained Sandy Soil
In most cases, poor sandy soils have become uneconomical to farm given recent commodity prices. Many farmers have been converting their poorer fields to pine trees. In general, longleaf pine is the only species that will grow at an acceptable rate and also produce high quality wood products on these poorer soils.
Some examples of these deep well-drained sands are Lakelands, Troupes, Bigbees, and Kershaws. Luckily, these soils can also be some of the easiest sites to establish longleaf pine. If the site does not have a history of weed competition from Bermuda grass, buffalo grass, crabgrass, or other problematical grasses, then no site preparation may be necessary. Some of the best plantings we have witnessed were either bareroot or container seedlings planted without site preparation. In addition, on these excessively drained sandy soils, it may be unnecessary to apply an herbaceous release the spring following planting.
If competition is expected on the site, then a low rate of Oust®, Oustar®, Arsenal® or another labeled herbicide can usually be applied in a single, banded application. In the absence of late germinants, this should be sufficient. On sites where annual or perennial grasses reappear following the first application, a second application of Arsenal®, Envoy®, or another grass herbicide may be applied as necessary.