As indicated in Step 1 of the series of articles on foliar analyses, mid-summer leaf analyses is the best way to assess the nutritional status of pecan and walnut and to determine the fertilization needs if we want to improve on their nut production. In Step 2, information is provided on how to visual inspection the foliage for signs of nutrient deficiencies and how to interpret the results from chemical analyses of leaves collected in late June to early July. Step 3 will summarize information on correcting nutrient deficiencies.
Most trees must absorb thirteen essential mineral elements from the soil and move them throughout the plant for acceptable growth and nut production. These nutrients are generally divided in the macronutrients usually reported as a percentage of leaf dry weight and the micronutrients usually reported in parts per million (ppm). The macronutrients include nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). The micronutrients include manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), boron (B), and molybdenum (Mo).
Visual Indicators of Deficiencies
Determining nutrient deficiencies from visual symptoms can be difficult because frequently one does not have trees without nutrient deficiencies in the planting to compare to. To save expensive and often unnecessary application of complete fertilizers across the entire orchard, we suggest a grower select a small group of trees near the middle of the orchard to intensively manage without ground covers and relatively high rates of a slow-release fertilizer containing both macro- and micronutrients. These trees become the standard to compare the remaining trees to.
Nutrient deficiencies can result in color and morphological changes in the leaf and leaflets of trees with pinnately compound leaves such as pecan and walnuts (Table 1). A few illustrated guides in color have been published for diagnosing nutrient deficiencies of trees include that by Hacskaylo and others (1969) and by Phares and Finn (1971) for black walnut seedlings (Fig. 1). Other publications give detailed narrative or tabular descriptions for tree responses to deficiencies of a single nutrient such as the articles by Phares and Finn (1969) and Jones (2003). Table 1 is a synthesis of these descriptions and describing changes in coloration and morphology of leaves and leaflets for pecan, walnuts, and other species with pinnately compound leaves in response single element deficiencies.
Elemental Indicators of Deficiencies
Interpretation of nutrient analyses requires development of standards or norms for each nutrient. These standards need to be experimentally determined for each species, when foliage is collected, and possibly the management and geographical region where trees are grown. Ideally, these norms indicate the range over which plants do not exhibit toxicity and are unlikely to exhibit significant increases in growth or nut production with an increase in nutrient availability. Various terms are used in the literature to describe these ranges including normal (Blinn and Bucker 1989) and the sufficiency ranges (Mills and Jones 1996). Other authors have selected to estimate the species critical foliar concentrations for each nutrient usually defined as the concentration below which plants show reduced growth or nut production and are likely to vigorously respond to an application of that nutrient. Ideally, these critical foliar concentrations coincide with the lowest value in the normal or sufficiency range.
Sufficiency ranges for the macro- and micronutrients of nut-bearing northern pecan foliage collected in July have been reported by Reid (2007) and are listed in column 3 of Table 2. Preliminary estimates of the normal or sufficiency ranges have also been reported for seedlings (Phares and Finn 1971), for urban trees (Kopinga and van den Burg 1995), and for forest trees (Mills and Jones 1996) of black walnut. It is unclear if we can use these values to determine sufficiency ranges for walnut nut production.
A quick scan of the literature produced more than 30 publications reporting foliage nutrient values for nut-bearing, forest, or seedlings of pecan and walnuts. To summarize these results, a Microsoft Excel database was created to list the minimum and maximum values for each element as reported in each paper. For publications reporting normal or sufficiency ranges, the endpoints were listed as minimum and maximum values. For publications reporting only critical concentrations, they were listed as minimum values only. Publications reporting results of research studies with multiple treatments, only the minimum and maximum values from treatments that did not differ statistically from the treatment with the best growth or nut production were entered. To obtain preliminary estimates of sufficiency values for walnut, the range of reported values were plotted and ends removed to retain the middle 80 percent of the reported values for each element. These values are reported in Table 2 for pecan orchards and black walnut seedlings, forest trees, and orchards. Comparison of Reid's (2007) reported sufficiency values for northern pecan to estimates using middle 80 percent of published values for all pecans shows reasonable agreement. There is also remarkably good agreement in the estimated normal or sufficiency ranges for black walnut seedlings, forest trees, and nut-bearing trees. Reported nutrient values for walnut seedlings include results of studies with greenhouse-grown seedlings in complete nutrient solutions as well as field-grown seedlings which may explain the wider range of values for seedlings than for values from forest or orchard trees.
Assessing nutrient deficiencies using visual indicators or chemical analyses is somewhat dependent on having only one deficient nutrient. Hacskylo and others (1969) frequently observed very high concentrations for one or more nutrients when growing walnut seedlings in solutions deficient in only one element. Mills and Jones (1996) provided detailed descriptions of potential interactions with addition of a deficient element. DRIS (Diagnosis and Recommendation Integrated System) indices have been develop to look at possible interactions between elements for pecan (Sistrunk 1989) to determine which elements are deficient. Lack of foliar nutrient analyses from high yielding orchards limits development of similar indices for walnut.
Cited Literature
Blinn, C.R.; Bucker, E.R. 1989. Normal foliar nutrient levels in North American forest trees: A summary. Station Bull. 590-1989. Minnesota Agric. Exper. Station. 28 pp.
Hacskaylo, J.; Finn, R.F.; Vimmerstedt, J.P. 1969. Deficiency symptoms of some forest trees. Res. Bull. 1015. Ohio Agric. Res. and Development Center. 68 pp.
Jones, J.B., Jr. 2003. Plant mineral nutrition. In: Agronomic Handbook. Baton Raton, FL: CRC Press: 291-334.
Kopinga, J.; van den Burg, J. 1995. Using soil and foliar analysis to diagnose the nutritional status of urban trees. Journal of Arboriculture 21(1): 17-24 pp.
Mills, H.A.; Jones, J.B., Jr. 1996. Plant Analysis Handbook II. A practical sampling, preparation, analysis, and interpretation guide. Athens, GA: Micromacro Publishing. 422 pp.
Phares, R.E.; Finn, R.F. 1971. Using foliage analysis to help diagnose nutritient deficiencies in black walnut. Annual Report of the Northern Nut Growers Association 62: 98-104.
Reid, W. 2006. Pecan fertilizer recommendations. Kansas Nut Growers Newsletter 45 (4): 19-21.
Sistrunk, L.A. 1989. An improved method of DRIS for determining the nutrient status of pecan with foliar diagnosis. Ph.D. dissertation. Texas A&M University. 156 pp.
Acknowledgments
This article was prepared by J. W. Van Sambeek, USDA Forest Service, with the assistance of William Reid, Kansas State University.
* William Reid is an Assistant professor at the University of Kansas and is an agent at the Kansas Extension Service. He is the author of many books about fruits and nuts.
Dr. Jerry VanSambeek is a research plant physiologist at the USDA Forest Service. He can be reached at jvansambeek@fs.fed.us.
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