BEGINNING AN ORCHARD NUTRITION PROGRAM: DETERMINING NUTRITIONAL STATUS FOR APPLE AND PEACH

Stephen S. Miller, Research Horticulturist
USDA-ARS, Appalachian Fruit Research Station
Kearneysville, West Virginia 25430

A well-designed nutrition/fertilizer program will optimize tree performance and help prevent over or under application of nutrients. A nutrition program for fruit trees is built on information collected during the growing season. Early spring or late fall, when ground fertilizers are traditionally applied, is not the time to begin developing a good nutrition program. In recent years, determining the nutritional status of the orchard and maintaining optimum nutrition has been relegated to "last place" on the list of cultural practices by some apple and peach growers. While it is true that trees throughout the mid-Atlantic region generally do not show nutrient deficiency or toxicity symptoms, a number of orchards "live" on the edge of good nutritional status and would benefit from the application of fertilizers. Conversely, application of fertilizer nutrients above what the tree can utilize is wasteful and serves no purpose in attaining maximum yields. In fact, such applications might lead to groundwater contamination. With their deep and expansive root systems, apple and peach trees are capable of absorbing nutrients from large volumes of soil, unlike most annual crops that have a rather limited root system and, therefore, depend on fertilizer applications for maximum yields.

Fruit quality (Fig. 1a, Fig. 1b) is closely associated with optimum nutrient levels and some nutrients, such as potassium, calcium, and boron, have a significant impact on the quality and storage ability of fruits. If you don’t know where your trees stand on the nutrition scale, you may be sacrificing optimum production of high quality fruits.

There are several approaches to assess the nutritional status of your orchard:

Observation - Beginning in early spring when trees leaf-out, and continuing until harvest, periodically examine trees for signs of nutritional problems. Record your observations, good or bad, for later comparison with the results of soil and foliar analyses. A single tree, an individual limb, or small group of trees that show a similar symptom may not be indicative of a general nutritional problem, but may suggest some other malady such as herbicide injury, mechanical damage, or a pest problem. Record the crop load for blocks of trees of the same cultivar sometime after June drop. I use a system based on a percentage of what the tree could carry if it were carrying a full (100%) crop. For example, in 1998 I would rate many ‘York’ blocks in the Eastern Panhandle at 50 to 60% of a full crop load. This information will be useful when interpreting your foliar analysis and making decisions regarding fertilizer applications.

Poor shoot growth may indicate a lack of nitrogen (N). Nitrogen deficient trees will have light green or pale-yellow foliage that generally appears over the entire tree (Sprague, 1964). Nitrogen is a mobile element (readily translocated from older leaves to younger leaves) and deficiency symptoms may appear first in the older leaves.  Leaves on N deficient peach trees may show red to purple spots that die and drop from affected leaves. This "shot-hole" symptom should not be confused with X-disease that has tufts of green leaves at the end of shoot growth. Excess vegetative growth may suggest that N levels are abnormally high and additional N fertilization is unwarranted. Remember that young non-bearing trees should make more growth than mature bearing trees.

Phosphorous (P) is another major element that is mobile and will exhibit symptoms generally over the entire tree canopy. Apple and peach seldom exhibit P deficiency since they are efficient in extracting P from low soil P levels. A purple color on leaf veins, leaf petioles, and young shoots throughout the canopy in the early season that disappears later may indicate P problems. The young expanding leaves on P deficient trees may be abnormally dark green.

Like P, potassium (K) deficiencies are not common. If deficiencies occur, symptoms will be seen on older leaves first since K is a mobile element. Marginal scorching and an upward curling of the leaf margins (stone fruits) may suggest K deficiencies. Apple and peach use large quantities of K since the fruit levels are high.

In the mid-Atlantic region, symptoms of magnesium (Mg) deficiency (Fig.2) can be seen in some seasons, especially when heavy rains occur in the middle of the growing season or excessive irrigation is applied. Trees low in Mg may have interveinal chlorosis on older leaves that appears in a herringbone pattern. The base of the leaf petiole may exhibit an inverted V-shaped green area. Symptoms of a physiological disorder in ‘Golden Delicious’, "necrotic leaf blotch (NLB)" can be misinterpreted as Mg deficiency. The randomly distributed irregular necrotic spots distinguish NLB in the early stages over the leaf surface. Later, the entire leaf blade turns a very bright yellow color, except for the necrotic spots (Fig. 3), and affected leaves drop. Normally, only 20 to 30% of the leaves on a tree will be affected by NLB. Heavy application of K can result in reduced Mg levels.

Manganese (Mn) deficiency is rather uncommon, but Mn toxicity does occur. The Delicious cultivar is quite susceptible to excess Mn. Symptoms occur on the bark as raised pimples. These enlarge and crack and lead to a rough, scaly bark. If the outer bark is removed, small dark circular dead areas can be seen throughout the inner bark (Fig. 4). This physiological disorder is known as "internal bark necrosis (IBN)" or more commonly "apple measles" since the bark symptoms resemble human measles. Manganese toxicity is associated with low soil pH and low calcium and/or boron. Over the years, Mn toxicity has been common in the mid-Atlantic region primarily because of low soil pH.

In the past decade zinc (Zn) and copper (Cu) deficiencies have become more common, primarily because fewer Zn and Cu based fungicides are used in the orchard. Because these elements are immobile, deficiency symptoms will first appear in the younger terminal leaves. If leaves are stunted, misshapen, and/or elongated, and there is terminal dieback or reduced terminal growth with small, elongated leaves (rosetting) you may suspect Zn or Cu deficiencies. This small, elongated leaf condition is also a symptom of glyphosate herbicide injury (Fig. 5), so care should be exercised in diagnosing these symptoms.

Low levels of calcium (Ca) and boron (B) are seldom expressed as shoot or leaf symptoms but appear in the fruit as physiological disorders such as cork spot or bitter pit. Both nutrients are immobile, thus foliar symptoms appear first in the young terminal leaves. Boron deficiency can lead to terminal dieback and a necrotic bark condition. Chronic poor fruit set may be an indication of low B. Peaches are highly sensitive to excess B.

In addition to tree observations, take note of fruit quality during the growing season. Small fruit size may be a result of low N. Poor color on red cultivars can be an indication of low K levels. Low calcium in apple can be observed about 8 weeks before harvest as sunken areas on the fruit surface (cork spot) which turn dark and remain firm (Fig. 6). Cutting the fruit tissue reveals a corky tissue beneath. Dark sunken areas that appear on apple just before harvest or after a short period in storage, a condition known as bitter pit (Fig. 7), may also be an indication of low calcium. Bitter pit is generally confined to the calyx end of the fruit and occurs near the surface. Fruit cracking (not to be confused with "Stayman cracking") may be a result of low B. Low B can also lead to corking in the flesh of apples.

Good observation is a valuable and necessary part of any nutrient-management program, but observation alone should not be relied upon to develop your program. A periodic, planned and organized sampling of soil and foliage is necessary to make the best decisions for the orchard’s nutrition/fertilizer needs. Only through these diagnostic tools can moderately low nutrient levels and nutrient imbalances be detected. It is often these minor differences that separate high, quality production from average production.

Soil Sampling – Soil analysis should be considered an essential tool in establishing a new orchard. Practical adjustments in soil pH, P, K, and Mg can best be made before trees are planted. Soil analysis in established orchards has some limitations and research has shown that results may correlate poorly with leaf-tissue analysis and tree responses. Nonetheless, a good soil sample can reveal much about the relative levels of Ca, P, K, and Mg in the soil as well as the need for lime. The greatest value in sampling soil in established orchards lies in the pH determination and the lime requirement. Soil acidity has a significant impact on the availability of nutrients. At soil pH values below 6.0 many of the essential major elements (N, P, K, Ca, Mg, and S) are less available. A good example in the mid-Atlantic region is Ca. Many of the soils in this region have very high Ca levels but soil pH levels of 5.0 to 5.5. Under these conditions Ca availability to the tree is significantly limited. It is recommended that soil analysis be conducted at least once every three years. In blocks with previous problems, such as low pH, a soil analysis every year or two may be advised, at least until the problem is corrected.

A soil analysis also provides other information that can be of value in developing your nutrition/fertilizer program – a measure of the soil’s lime requirement and the soil cation exchange capacity or CEC. Lime requirement tells you the amount of agricultural limestone, or equivalent liming material, to raise the soil pH to a desired value. Cation exchange capacity is simply the sum total of exchangeable cations (Ca++, K+, Mg++, etc.) that a soil can absorb. In general, soils with low CEC values (< 5) require more fertilizer than those with high (>20) CEC values to provide the same nutrient availability. Most soils in the mid-Atlantic region will have a CEC between 5 and 20 milliequivalents per 100 grams of soil.

Care should be exercised in collecting an orchard soil sample so it is as representative as possible of the orchard soil profile where the trees are growing. Remember that a soil analysis is no better than the sample collected. A shovel can be used to collect the sample, but a soil probe or soil auger specifically designed to collect a small core of soil is best and well worth the small investment especially if many samples will be collected. However, in rocky soils a shovel may be easier to use. The area collected per sample should be limited to a maximum of 10 acres. Avoid unusual spots in the designated sample area such as low ground with poor drainage, eroded areas, or similar areas that are uncharacteristic. If an area of the orchard appears to have a specific problem, collect a sample from the problem area and a second sample from an adjacent area where the trees exhibit normal growth. Also, use a soil survey map to ensure that only one soil type is collected per sample.

The best time to collect soil samples for orchard crops is mid-July through mid-August, however, since soil nutrient levels change slowly, this sample can be collected almost anytime that is convenient (future samples should be collected during the same time period). A representative sample consists of several sub-samples collected from several locations within a block and mixed together to provide the final composite sample for testing. The number of sub-samples to collect depends on the size of the area being sampled: for areas of an acre or less, 7 to 10 sub-samples is sufficient; for plots as large as 10 acres, 20 to 25 sub-samples should be collected; for all other plots collect a minimum of 15 sub-samples. Remove the organic debris from the top inch of soil and collect a soil core or sample from the top 1 to 8 inch depth. It is recommended that a second sample be collected and submitted for analysis from the same site representing the 8 to 16 inch depth but this is not essential unless severe subsoil problems are suspected. Collect the sub-samples at random from representative areas within the designated orchard area. Crisscrossing through the orchard from one end to the other is a good technique. Collect the sub-samples only from within the tree rows under the tree canopy about midway between the trunk and the drip line of the canopy, not in the drive middles between the rows. Mix the sub-samples thoroughly, remove large stones, pieces of root tissue and other foreign material, and air-dry the sample (Do not oven dry soil samples as this may alter the test results). When the sample is dry send all, or a portion as directed, to your soil testing laboratory along with the requested information on site history and/or past lime/fertilizer applications. Most land-grant universities are equipped to accept and perform routine soil analyses. The charge varies by state.

Foliar Tissue Sampling - Research has demonstrated that leaf-tissue (foliar) analysis provides the most reliable information on nutrient needs for the orchard. A soil analysis only indicates what is available but a foliar analysis shows what the tree has actually absorbed. Observation and soil analysis are of little value in identifying minor deficiencies or nutrient excesses when visual symptoms are absent. Foliar analysis, however, can detect shortages or excess nutrient levels in the absence of symptoms and when performed on a yearly basis can reveal trends that can help avoid future problems. Occasionally soil and foliar analyses offer opposing recommendations. In this case, follow the recommendations from the foliar analysis.

Levels of some leaf nutrients increase during the early part of the growing season while others decrease. The levels of most elements stabilize when vegetative growth slows. For the mid-Atlantic region the best time to collect leaves for a foliar analysis is from July 13 to August 15. Standards used to interpret the results of a foliar analysis are based on this time period and leaves collected at other times cannot be compared to the standards. Most foliar analyses provide results on N, P, K, Ca, and Mg in percent dry matter and Mn, Fe, Cu, B, and Zn in parts per million. As with soil samples, the accuracy of a foliar analysis is only as good as the sample submitted.

A foliar sample should consist of about 50-100 mature leaves collected from the mid-section of the current season terminal shoot growth on several trees in the area you desire to sample. Select trees of one variety at random, similar to the procedure for collecting soil samples, that are representative of trees in the block. Collect leaves from the periphery of the tree at 5 to 7 feet above ground level (or at a height that represents the majority of foliage for young trees or high density trees). Collect only 1 or 2 leaves from each terminal and sample at least 4 to 5 terminals per tree. Do not collect spur leaves or shaded leaves as these will not be representative of the standards. Collect only healthy and undamaged leaves and only one variety per sample; mixing leaves collected from more than one variety will not be representative of any one of the varieties. Retain the leaf petiole as part of the leaf sample. To remove the leaf blade and petiole from the shoot together pull downward toward the base of the shoot (Fig. 8). The leaf with attached petiole should detach cleanly from the shoot, leaving the axillary bud in place.

Contamination from dusts or spray residues can affect the results of a foliar analysis. Avoid collecting leaf samples soon after a cover spray application. Leaf samples can be washed to remove contaminates, but care must be exercised to avoid further contamination or extraction of some nutrients. Since most growers are not equipped to properly wash leaves, leaf washing is discouraged by most analytical labs. To properly wash leaves rinse in a 0.1% mild detergent solution (most common household detergents will do) and then rinse in three separate changes of distilled water. Do not use regular tap water as it may contain iron or salts that will affect the results. Remove the leaves, shake to remove excess water, and lay on paper towels in a clean environment to dry. Do not allow the leaves to soak in the detergent solution or rinse water. Once leaves have dried, place in paper bags, secure the top, and allow to air dry. In the summer, drying will be complete in several weeks if placed in a warm, low humidity environment. When thoroughly dry, crush the leaves while still in their original bag and, if necessary transfer the dry leaf material to the container supplied by the analytical lab and send for analysis.

Additional Reading and References on Soil and Foliar Sampling and Nutrition:

Childers, N.F. 1966. Fruit Nutrition. Horticultural Publications, Gainesville, FL.

Hogmire, H.W., Jr. (Ed.). 1995. Mid-Atlantic Orchard Monitoring Guide. Cornell Coop. Extension, NRAES-75.

Pennsylvania Tree Fruit Production Guide, 1998-1999. 1998. Penn State Agric. Expt. Stat. Publication, University Park, PA.

Sprague, H.B. (Ed.). 1964. Hunger Signs in Crops. David Mckay Co., New York, NY.

Stiles, W.C. and W. Shaw Reid. 1991. Orchard Nutrition Management. Cornell Cooperative Extension Bulletin 219.

Westwood, M.N. 1978. Temperate-Zone Pomology. W. H. Freeman and Co., San Francisco, CA.

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