Soil Fertility

Conduct soil tests to determine soil fertility. The number of soil tests required per field will vary with the size and uniformity of the field. Take at least one soil test for each change in field texture, color, and drainage characteristics. The soil pH and nutrient content may vary considerably, thus requiring varied amendment practices. It is important to take soil tests well in advance of any cultivation, because it takes time to conduct the tests, evaluate the results, and plan the most economical and effective program for crop production. Certain practices such as liming and applying superphosphate should be completed before planting so that these materials can be thoroughly mixed with the top 6 to 8 inches of soil during normal soil preparation practices. Soil test results will indicate if other soil nutrients are required as pre-plant adjustments. In clay loam soils of the upper piedmont and mountains, where phosphorus (P) and potash (potassium, K ) tend to remain high once adequate levels are established, nitrogen may be the only required yearly addition. Currently, ammonium nitrate (33-0-0) and urea (46-0-0) are the most popular soluble fertilizers. In some regions of the state, yearly P application is also warranted. In those instances, di-ammonium phosphate (18-46-0) is often used as a nitrogen and phosphorus source.

Best management practices for fertilizer applications focus on water quality and nutrient runoff as well as maximizing growth of nursery stock. During field preparation, incorporate fertilizer at 50 pounds of nitrogen per acre; this practice reduces runoff potential and usually meets the nitrogen requirements of new plants during the first year. Other nutrients as recommended by soil tests should be incorporated before planting. In subsequent years, surface application of nitrogen is based on an amount of nitrogen per plant rather than pounds of nitrogen per acre. Place fertilizer within the root zone as a side dress at the rate of 0.25 to 0.5 ounce of nitrogen per plant rather than previous recommendations of 100 to 200 pounds of nitrogen per acre. Doing so maximizes growth with a minimum amount of fertilizer. If supplemental fertilizer is required the first year for fall-transplanted plants, each plant should receive 0.25 to 0.5 ounce of nitrogen before bud break. The second year each plant should receive 0.5 to 1.0 ounce distributed in split applications: the first two-thirds of the total amount should be applied before bud break, and the second application should be applied by mid-June. The third and following years each plant should receive 1.0 to 2.0 ounces in split applications as described for the second year. Slower-growing cultivars or species should be fertilized at the lower application rates, whereas vigorous plants will have increased growth if the higher application rate is used. Rates greater than those recommended have not proven to be warranted and, in fact, have reduced growth and can contribute to nutrient runoff and water quality impacts. Recently, slow-release fertilizers developed specifically for field use have been introduced. Although they are more expensive, one application may last the entire growing season. (For more details about rates of fertilization for field nurseries, refer to the North Carolina Agricultural Chemicals Manual, Fertilizer Use Section entitled “Fertilizer Suggestions for Nursery Crops.”)