Issue link: http://read.dmtmag.com/i/132109
Optimizing Production Optimizing apple nutrition PART IV: Soil and tissue analyses provide basis for precise fertilizer application. by Richard Lehnert P recision nutrition management is slowly coming to the world of annual crop production, where some field crop growers are using GPS technology and soil testing to gridmap their fields. Computer-controlled equipment then matches fertilizer application to soil test results, patch by patch. On that score, fruit growers may be considered behind. But fruit growers grow crops and have tools to make precise nutrient application. Before planting, soil testing allows fruit growers to make adjustments in soil pH and nutrients. Once planted, perennial crops stay in place for several years, allowing orchardists to fine-tune fertility treatments, matching nutrition to soil capacity, tree age, and variety. Tissue testing, which is not widely used in row crop production, has been well developed for orchardists. And fertigation—applying fertilizer in small amounts with water—offers the promise of delivering the right amount of nutrients to the root zone at the right time. Foliar application also makes it feasible to make adjustments throughout the growing season and achieve optimal results. At Cornell University, Dr. Lailiang Cheng has been working on orchard nutrient management. Growers need to test their soil and make the needed amendments before and at planting time. From then on, they should rely on leaf analysis. Orchardists who take the trouble to collect and prepare representative samples of fruit leaves and have them analyzed can know precisely where their trees stand and can go about adjusting their nutritional status. Cheng spoke to about 200 apple growers during Cornell's Precision Apple Management Summit earlier this year. About five years ago, Cheng did some basic work to determine exactly what apple trees need in the way of nutrients, when they need them, and what they do with the nutrients they take in. By growing Lailiang Cheng trees in acid-washed sand and using fertigation, he could control nutrient supply. Working with Gala/M.26 trees trained in tall spindle in their sixth leaf at a density equivalent to 1,125 trees per acre, he adjusted the crop load to 8.2 fruits per square centimeter of trunk cross-sectional area. What trees need At several key developmental stages during the growing season, the trees were dug up, divided into roots, shoots, leaves, and fruit, and the dry matter in each was measured. He found that each tree accumulated about ten pounds of dry matter per year. The tree put 72.2 percent of that into fruit, 17.3 percent into shoots and leaves, and 10.5 percent into trunk and roots. Fruit yield was 41.3 pounds per tree, or 1,100 bushels per acre. Chemical analysis showed the mineral content of a year's production of wood and fruit on one acre was as follows: Nitrogen: 50 pounds; phosphorus: 8.5 pounds; potassium: 90 pounds; calcium: 36 pounds; magnesium: 11 pounds; sulfur: 4.0 pounds; boron: 0.23 pounds; zinc: 0.15 pound; copper: 0.12 pound; manganese: 0.46 pound; iron: 0.37 pound. The remaining dry matter—about 10,000 pounds—is made up of the primary constituent elements of carbohydrate—carbon, hydrogen, and oxygen, which are taken up from air and water. From these numbers, Cheng calculated the tree nutrient requirements in relation to yield. Since fruit leaves the orchard, the nutrients in the fruit need to be replaced in the fertility program. Leaf analysis Now Accepting Contracts for Spring 2014 and 2015! We have over 50 years of experience in the nursery business and are now taking growing contracts for: Ultima™ Gala, Banning Red Fuji, Auvil Early Fuji,® Honeycrisp,™ Granny Smith, & Many Others. Red Fuji Banning to 10 Taking orders for benchgrafts. be 7 pears to ap 8 ier than days earl Fujis! r late othe June 2013 GOOD FRUIT GROWER + (- ) ,- !( - #!! While these basic numbers are helpful, the best approach to knowing what your orchard needs is through leaf analysis. "The first step in evaluating the nutritional status of orchards is to compare results of leaf analysis with a set of standard values," Cheng said (see Table 1). Samples should be carefully prepared. They should be taken in late July or early August, from healthy limbs at about eye level (not from water sprouts). Take about 50 leaves from trees that are similar in age, variety, vigor, etc. If some trees are quite different, they may need to be sampled separately. "In most cases, the content of elements such as nitrogen, phosphorus, potassium, calcium, magnesium, and boron is not affected appreciably by washing leaf samples prior to drying," he said. "Surface contamination by dust, soil, pesticide sprays, or foliar nutritional sprays, however, may result in significantly higher levels of iron, manganese, zinc, and copper." He recommends that leaves be washed in a mild detergent solution, rinsed three times in distilled water, washed quickly so as not to soak the leaves, then drained and placed in paper bags for drying. The goal in fertilizing apple trees with nitrogen is to have a relatively high nitrogen status early in the season to promote rapid canopy development and early fruit growth, Cheng said. Then, as the season progresses, nitrogen status should decline gradually to help fruit quality (color and firmness) and wood maturity to assure cold hardiness. Orchards typically need from 50 to 80 pounds of nitrogen per acre per year. Part of that comes from the natural decomposition of organic matter in the soil. Each 1 percent of organic matter contributes 12 pounds of nitrogen per acre per year. Organic matter breaks down as soil warms, peaking about 90 days after bud break, too late for early growth. For early growth, trees depend on applications of nitrogen made in early spring or the previous fall. A good way is to apply nitrogen as a foliar spray in the fall, using about 25 pounds of urea in 100 gallons of water. The nitrogen will be taken up and stored to support spring growth. Urea, at a rate of about 40 pounds per acre, sprayed on fallen leaves in fall or spring, has been shown to greatly reduce apple scab inocula on the orchard floor, where primary scab infections begin the next spring. This nitrogen will also become available for early season tree growth. When nitrogen levels are too high, fruit color development is delayed. Red color is reduced about 5 percent for each 0.1 percent increase in leaf nitrogen, Cheng said. Golden Delicious fruit shows a similar reduction in color as leaf nitrogen increases. www.goodfruit.com