Bulletin no. 102 BLUEBERRY FERTILIZATION Transplanting Blueberries may be planted any time during dormancy from early December through March in most areas of the Southeast. Each planting hole should receive about 1 /4 to Generally, 600 plants per acre (6' x 12' spacing) is practiced. Machine harvesting requires about 725 plants per acre on a 5' by 12' spacing. Pick-your-own operations require an approximately 8' x 14' spacing and about 400 plants per acre. Fertilization Blueberry plants are sensitive to both soil salts from poor water. quality and excessive fertilization. Nutritionally, nitrogen is generally viewed as the most limiting factor in blueberry productivity. Research has indicated that mature plantings at 600 plants per acre on mineral soils will require between 60-90 pounds per acre of dry, surface-applied actual nitrogen (N) for maintenance of top productivity. The research literature available regarding use of water-soluble fertilizers, indicates that for fruit trees and small fruit crops,. used with drip irrigation systems, approximately 1/2 to 2/3 as much water-soluble fertilizer is normally required to achieve equivalent or even higher yields as compared to conventional surface-applied fertilizers. This is because uniform moisture and readily available water soluble plant nutrients provide an ideal nutritional environment for plant growth. Considerable nitrogen is lost via microbial processes and significant amounts of phosphorus and potash pare rendered unavailable by soil colloids, where surface-applied conventional fertilizers are used. Drip feeding, often called "fert.igation" provides small. amounts of plant food constantly over the entire growing season, and little loss or tie-up occurs. Assuming a 5096 rate using water-solubles, a mature stand of blueberries will require approximately 5-7 pounclsof 27-9-18, 5-6 pounds of 30-10-10, or 7-9 pounds of 20-20-20 per acre per week during the growing season from mid-March through mid-September. A general rate of 5-6 pounds per acre per week of any of the TotalGro blueberry formulations will provide adequate nutrition where plant age is-incertain. Rates of between 1-5 pounds per acre per week provided satisfactory growth in 1987 field trials with TotalGro. BLUEBERRY FERTILIZATION The TotalGro 27-9-18 formula is a true 3-1-2 plant food as recommended by Texas A&M and other universities for production of rabbiteye blueberries. This formula has t;0 percent of its nitrogen in the urea and ammoniacal form, has a high acidifying potential, and contains 0.30 percent chelated iron. It contains a .balanced blend of chelated micronutrients and sulfur designed to provide optimum nutrition for drip-fed blueberries. Our 27-9-18 formula is a general, all-purpose product, intended for general feeding and in any situation calling for extra potash. It may be used throughout the growing season.
The 20-20-20 formula is designed primarily for use in blueberry propagation and in container production, and in the field where a soil or tissue test specifically requires a 1-1-1 type plant food. It is not intended for continual use on field-grown plants, but is useful in improving P 6-K. The 30-10-10 formula is a 3-1-1 ratio plant food designed for use during post-harvest growth flushes, and in any situation where the soil or tissue test calls for additional nitrogen, or where the potash supply is high. All TotalGro blueberry formulas possess high acid potentials, with the 27-9-18 having a potential acidity (PA) of 720 pounds per ton, the 20-20-20 providing 550 pounds per ton, and the 30-10-10 providing 1010 pounds per ton. Table 1 outlines suggested fertilization rates using TotalGro blueberry plant foods on a 600 plant per acre operation, feeding from mid-March through mid-September. These rates are based upon our present knowledge of blueberry nutrition using water-soluble fertilizers, and are subject to change as new information becomes -available. Nitrogen System for Blueberries The nitrate reductase system is poorly developed in rabbiteye blueberry plants, thus blueberries grow best where the nitrogen supply is predominately ammoniacal in basis. BLUEBERRY FERTILIZATION Since urea conversion proceeds to the NH4 stage and stops at this point under acidic soii conditions, we can assume that incorporated urea will be essentially converted to ammoniacal.. nitrogen. Desirable characteristics of a blueberry plant food include high urea and/or ammoniacal-nitrogen content, high acid-forming potential, low salt index and adequate micronutrient supplies, especially for iron. All of our TotaiGro blueberry formulas meet these-criteria. Feeding blueberries at very high rates of nitrate nitrogen will cause iron precipitation leading to iron chlorosis (yellowing), as well as nitrogen starvation. In addition, use of high nitrate materials may exert a direct osmotic effects from the nitrate salt ion itself. Never use calcium or sodium nitrate for blueberry fertilization! Monitorinq Blueberry Nutrition Alterations in your routine fertility program should never be made without soil or plant tissue tests.. Examine plants frequently for signs of leaf yellowing or burning-_. This may be indicative of changes in soil pH or salt build-up, or aeration problems. Many blueberry soils tend to be low in magnE ium. Since addition of dolomitic lime will not only raise the magnesium level, but will also increase pH, lime is not recommended normally. Fortunately, magnesium can be easily supplied through your irrigation system in the form of Epsom Salts (magnesium sulfate). Have your water tested first to see if adequate magnesium might be present in your water supply. If not, it can be added through your watering system. Generally, where a soil test shows a calcium:magnesium ratio greater than 8:1, blueberries will probably respond to applications of magnesium. Be cautious of soil test reports that recommend high rates of potash application. Excessive potash cannot be easily removed once applied, and may be sufficiently high: to induce a chronic magnesium deficiency in blueberry plants. Blueberries are not heavy users of potash. Tissue testing, i .e., chemical analysis of leaf blades, is an excellent means of monitoring the nutrition of blueberries. Most. growers take samples at mid-season before harvest, and possibly a second sampling in August. Visual symptoms in rabbiteye blueberries usually occur when the following critical levels occur in blueberry leaves taken in mid-season: TABLE 1. SUGGESTED FERTILIZATION RATES FOR RABBITEYE BLUEBERRIES PLANTED AT 600 PER ACRE Rates assume Weekly irrigation for 25 weeks from mid-March through mid-September BLUEBERRY FERTILIZATION Nitrogen (N) - - - - less than 1.40 to 1.50 percent Potassium (K) - - - - less than 0.35 to 0.40 percent Iron and Manganese (Fe E Mn) - - - - less than 40 to 50 parts per million TotalGro provides soil and plant testing free of charge to its customers for monitoring nutrition through the growing season. Water tests can be obtained through TotalGro Technical Services Department at a nominal charge.
Propagation of Blueberries
Various mixes have been found suitable for rooting blueberries. Root development is usually best in mixes containing 25-50% peat and perlite in a 1:1 mix; peat and sand in a 1:1 mix; peat, bark and sand at 1:1:1; or peat, sand and perlite at 1:1:1 or 2:1:1. Less root development occurs where cuttings are grown in coarse sand rather than mixtures of sand plus peat. Plants can be fertilized weekly after cuttings have rooted and are well-established usually in May or June. Use 20-20-20 at about 50-75 parts per million as nitrogen. Plants can be grown in the propagation bed until winter, then transplanted into the nursery or containers. Good results are usually obtained by transplanting rooted hardwood cuttings into 1 gallon containers in late July. Grow in 50% shade and water frequently for several weeks,
BLUEBERRY FERTILIZATION Irriqation and Water Quality During the first several years after transplanting to the field, blueberries have very shallow root systems.
Plantings may require between 1 to 1 3/4 inches of water per week during the growing season to promote vigorous growth. Supplemental watering of young plants will promote uniform growth and bring plants into earlier production. Irrigation of mature producing plants during the dry periods prior to harvest will minimize fruit drop and result in larger, juicier berries and higher yields. Irrigation during postharvest months in August and September will increase fruit bud formation for the next season. It is wise to test your water source before making a large investment Jn a blueberry operation. The most important considerations in evaluating water quality for blueberry culture include alkalinity,total calcium, magnesium, sodium and total soluble salts (electrical conductivity). Water pH has little or no effect upon blueberry growth. The combined effects of alkalinity and levels of calcium, magnesium and sodium, are the factors that alter soil pH. Some waters have sufficient dissolved lime that application of only 12 inches of water per acre per year will add more than a ton of agricultural lime per acre! Excessive sodium in water can not only increase soil pH, but may also destroy soil structure to the point that drainage is impaired, leading to aeration-related nutritional problems. In addition, blueberries are highly sensitive to sodium accumulation in tissues. Sodium can exert a direct toxic effect on blueberry growth, and can inhibit potassium uptake as well. Irrigation water should be tested once every 1-2 years, and more frequently where the water quality has been known to show seasonal fluxes. The TotalGro Diagnostic Laboratory can provide a complete irrigation water audit and recommendations at a nominal fee. We recommend tissue testing once or twice during the growing season, and soil testing every 3 years or when new ground is to be planted. Material Compiled by Samuel P. Faulkner, PhD TotalGro Technical Services Department 1-800-433-3055
(Outside Louisiana) 1-318-435-7587 (In Louisiana) |