No single factor influences the ultimate success of a field nursery more than soil. Unlike container nurseries, field nurseries depend on native soil characteristics such as soil texture, drainage, profile, and slope to be suitable for production of perennial crops. Most nurseries in North Carolina are located on a clay loam, loam, or sandy loam soil.
Since some soil will be sold with field-grown nursery stock, consideration should be given to whether a field soil will produce a root ball with soil cohesive enough to remain around the roots. Generally, root balls with sandy soil fall apart during handling. Soils should be relatively free of rocks to facilitate digging when planting, as well as deep enough to allow digging a root ball. The American Standards for Nursery Stock (Ansi Z 60.1) establishes standard diameters for harvesting root balls according to the size of the plant (Figure 1). The American Standards also require standard depths based on the diameter of the root ball, which are generally 60 to 75 percent of the root ball diameter depending on the stem caliper of the plant. For example, a 1-inch caliper dogwood requires a root ball diameter of 18 inches and a depth of 13.5 inches.
North Carolina Cooperative Extension Service agents, State Extension specialists, Natural Resources Conservation Service field representatives, and the North Carolina Soil Testing Laboratory personnel can provide assistance in determining the feasibility of soil and site characteristics for production of nursery stock.
Field-grown nursery stock is harvested by extracting the root system and soil by one of two methods. With the traditional balled and burlap method a root ball is hand-dug, then burlap is pinned with pinning nails and tied with twine to pull the burlap tightly around the root ball to hold the soil in place around the roots. However, machine digging with a tree spade has become the standard harvesting technique. Tree spades are equipped with three or four hydraulic blades that extract a cone of soil and roots, which are placed in a wire basket lined with burlap and secured using pinning nails and twine. Mechanical diggers and burlap-lined wire baskets have made harvesting nursery stock in sandy soils more successful. Although mechanical harvesting is possible in less cohesive soil, it is still important for soil to be retained around the roots (Figure 2).
Soil drainage is another factor you must consider when selecting a site. Avoid soils that have poor internal drainage or that are subject to flooding. Nursery stock that has been flooded is often weakened and predisposed to increased disease and insect problems. Fields being considered for nursery stock production should have a minimum of 8 to 10 inches well-drained profile. A soil probe can be used to determine the soil profile.
Mottled yellow, grey, or blue soil or a sour-smelling soil indicates poor drainage and a standing water table at some time during the year. Soils with mottled characteristics are often saturated during winter months. These soils are not suitable for most nursery stock production. Annual field crops are not as likely to be affected by high winter water tables as perennial field grown nursery stock, which will be in production for three to five years. If the high water table is only seasonal, preparing ridged planting rows can alleviate some of the effects. Even sandy soils can have poor drainage if they are underlain by an impervious B-Horizon often found in many North Carolina fields. At the other extreme, deep sandy soils have relatively little water holding capacity and generally require an irrigation system to ensure successful field production.
Slope is another important consideration. Many major North Carolina field nurseries are located in flat, nonflooding river bottoms. These bottom lands are generally close to irrigation water, flat enough to allow easy working with equipment, and relatively rock free. However, properly located upland soils with these same characteristics can make excellent nursery sites, as long as the slope is not too great, topsoil too thin, or erosion too severe.
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