Converting Agricultural Lands to Forestry Plantations
Each year ArborGen produces enough seedlings for reforestation on a wide array of sites to cover approximately 600,000 acres, primarily in the Southeastern United States. Most of these sites are classified as cutovers, where all of the timber has been harvested to make way for a new stand. Quite often, however, former agricultural crop fields and livestock pastures are converted to forestland, and this practice is known as afforestation.
Years of traffic by farm equipment and animals can cause compaction forming what is commonly referred to as a plow-pan or a hard-pan. The surface layer and the initial soil horizon is usually friable, and if a tree were planted 8-10 inches below the soil surface, you might not even detect the hard pan. The plow-pan is often 12-15 inches below the soil surface and limits the amount of root system development and nutrition availability for a newly planted seedling. Many times landowners plant former productive crop fields, only to be disappointed in tree growth two to three years later due to the seedlings inability to thrive in its new environment from soil compaction. Common symptoms include thinning of the crowns and poor coloration of the foliage.
Before planting seedlings, an operation known as subsoiling, breaking up the ground before planting, should be performed to shatter the compaction pan associated with past agricultural practices. Subsoiling before forestry plantation establishment is strongly recommended for all sites formerly cultivated or pastured, which usually always has problems with soil compaction or a plow-pan (Zobel and Talbert 1984). Many studies have shown that subsoiling improves plant development and vigor (Gregory and Davey, 1977). Subsoiling minimizes soil compaction issues and allows new seedling roots to proliferate to greater depths. One other key benefit of subsoiling is that it prevents surface water runoff, improving soil moisture in the newly established forest plantation (Zobel and Talbert 1984). Soil penetrometers, found at forestry suppliers, are extremely easy to use and are an invaluable tool to test for soil compaction before and after subsoiling. One such tool that is affordable and user-friendly is the Agratronix Soil Compaction Tester. A dial is situated so that the user can quickly and easily assess compaction levels inherent to the planting site.
If former agricultural sites are to be machine planted, the mechanical planter is usually equipped with a “shank” that can be adjusted to a depth that will rip or shatter the plow-pan. The seedling is then placed right behind the ripper in a soil medium where the compaction has been alleviated for better root growth potential. If hand planting is the only option, then subsoiling in the desired transect across the field with a farm tractor before planting is essential. Then the hand planting crew can easily follow the ripped line and place the seedlings at the desired stocking level. Either method of planting following subsoiling ensures the newly planted seedling will attain adequate root growth potential.
Finally, an equally important and easy task to complete before establishing forestry plantations on former agriculture sites is to perform a soil pH test. It is not uncommon for former agriculture sites to have a higher than desired soil pH for most forest trees. Former pasturelands are usually limed, raising the soil pH to higher than desired levels for southern yellow pine. The soil pH range for loblolly pine, for example, is from 4.5 – 7.0, but is most productive and is more tolerant to herbicides at 5.2 – 6.2. University county extension agencies provide directions on how to conduct soil testing and can also analyze results with minimal costs. Always consult with herbicide specialists before treating sites with chemicals both before and after plantation establishment.
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