A collaboration between

Acknowledgments

Acknowledgments

Funding provided by:

Guidelines and Webpage Design:

Daniel Geisseler, Ph.D.; UCCE Specialist in Nutrient Management; Department of Land, Air and Water Resources, University of California, Davis

Patricia Lazicki, Department of Land, Air and Water Resources, University of California, Davis

Reviewers:

Franz J.A. Niederholzer, Ph.D.; Farm Advisor Orchard Systems; University of California Cooperative Extension Sutter-Yuba Counties

Katherine Pope, Ph.D.; Farm Advisor Orchard Systems; University of California Cooperative Extension Yolo County

William R. Horwath, Ph.D.; Professor of Soil Biogeochemistry and James G. Boswell Endowed Chair in Soil Science; Department of Land, Air and Water Resources, University of California, Davis

Support:

Moradi A. Barzin, Ph.D.; Senior Environmental Scientist FREP, California Department of Food and Agriculture

Amadou Ba, Ph.D.; Branch Chief Feed, Fertilizer, and Livestock Drugs Regulatory Services, California Department of Food and Agriculture

Amrith Gunasekara, Ph.D.; Science Advisor to the Secretary; California Department of Food and Agriculture

Last Update: September, 2015

Additional Information:

Prune and Plum Nitrogen Uptake and Partitioning

Prune and Plum Production in California

California Fertilization Guidelines

Prune and Plum

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Young
Trees

Dormancy
Winter

Bloom
Spring

Fruit Development
Summer

Post-Harvest
Fall

Nitrogen (N)

Leaf Analysis

Leaf Analysis N

In orchards, leaf analyses are more reliable for the diagnosis of nutrient deficiencies than soil analyses. Leaf analyses allow growers to evaluate their fertilization program.

The critical values presented in the table are conservative; they represent the minimum concentrations necessary for optimal growth ^[N25]. Leaf concentrations greater than 2.8-3.0% indicate over-fertilization. Visual observations of tree vigor, crop load and leaf color may also be used to interpret test results.

If the test shows adequate leaf N, no N is needed until mid-April of the following year, at which point the rate may be decided based on the crop load. If the test N is low or marginal, a soil N application several weeks after petal fall may be needed, regardless of crop load ^[N24]. To correct an N deficiency mid-season, foliar urea sprays can be used (see Foliar N). An in-season soil application may also be used, but should be very light since stone fruit trees take up little N in fall and excess N may be leached with winter rains ^[N25].

Leaf critical nutrient values from nonbearing spur leaves of French prune sampled in July ^[N33].
Critical
nutrient level

The values in the table refer to a tree. In contrast, the results from leaf analyses refer to the average of all trees sampled in the orchard with some trees being below and others above the average. To minimize the risk of some trees in the orchard being deficient, the lower limit of the adequate range may be increased to 2.4-2.5% N may be more appropriate (Niederholzer, personal communication).

The critical values for N and P are also valid for Japanese plums ^[N1]. If prunes are produced for the fresh market the lower end of the optimal N range should be used, because of the importance of early maturity ^[N8].

N to Young Trees

N Fertilization of Young Trees

Application Rate

Mode of Application

Fertilizer Type

Time of Application

Soil Applied N

Soil Applied Nitrogen

Application Rate

Nitrate in the Irrigation Water

Mode of Application

Fertilizer Type

Time of Application

Very little soil N is taken up during dormancy and before bud swelling. While N is needed for flowering it is recycled from the perennial parts of the tree rather than taken up from the soil for immediate use ^[N35]. The majority of N uptake occurs during the period of rapid shoot growth, with about 60-70% of the total N requirement being taken up by June ^[N6]. The N taken up during the late summer supports flowering the following spring ^[N35]. Uptake slows during fall through leaf drop, and is essentially zero through winter ^[N22]. For this reason N fertilizers should not be applied after leaf drop, in winter or in spring before bud break as they have a high risk of being leached out before the crop can use them.

Based on the seasonal uptake pattern, the first N application in spring is best done around mid-April, before rapid uptake is beginning. Exceptions are marginal or N-deficient orchards where some N should be applied a few weeks after petal fall ^[N24].

Multiple small applications are more efficient than large applications; Niederholzer ^[N23] recommends not more than 20-30% of the annual fertilizer budget should be added per application. A general rule in a healthy orchard with adequate tree vigor is that one-third of the annual N requirement may be applied in spring (March or April), with the remaining two thirds applied in mid-to late summer (June, July and August). Where tree vigor is low, a relatively greater proportion should be applied in spring, and the remainder applied in summer ^[N22]. Applications after harvest should be small and applied well before leaf fall, so that the N can be taken up and stored in the tree's woody parts ^[N21,N25].

Foliar N

Phosphorus (P₂O₅)

Soil Test

Soil Analysis

Soil analyses have not been shown to be a reliable means of determining prune response to fertilizers, and the University of California has not developed critical values for soil analysis ^[P9]. However, soil analyses may be useful to monitor trends in nutrient availability over the years.

Soil analyses are also useful prior to orchard establishment to determine pH and identify potential problems, i.e. salinity, the presence of toxic ions such as boron or chloride, and the presence of limiting layers ^[P9].

Soil Sampling and Analysis

Interpretation of Test Results

Leaf Analysis

In orchards, leaf analyses are more reliable for the diagnosis of nutrient deficiencies than soil analyses. Leaf analyses allow growers to evaluate their fertilization program.

Sampling Procedure

Interpretation of Results

P to Young Trees

Soil Applied P

Soil Applied Phosphorus

Phosphorus deficiency has rarely been observed in stone fruit orchards in California ^[P5]. There are currently no University of California recommendations for P fertilization of prune and plum orchards. Soil and leaf analyses can be used to monitor the P status of an orchard over the years to ensure that the P availability is adequate (see Soil P Test and Leaf P Analysis).

Application Rate

Mode of Application

Fertilizer Type

Time of Application

Potassium (K₂O)

Soil Test

Leaf Analysis

In orchards, leaf analyses are more reliable for the diagnosis of nutrient deficiencies than soil analyses. Leaf analyses allow growers to evaluate their fertilization program.

Sampling Procedure

Interpretation of Results

May Leaf Interpretation

K to Young Trees

Soil Applied K

Soil Applied K - In-Season

A heavy crop of prunes must accumulate a lot of K, meaning that severe deficiencies may develop quickly even on soils with normal K concentrations ^[K19,K27]. Ensuring that sufficient K is available during fruit development involves good irrigation management, fruit thinning in heavy crop years and a consistent supply of in-season K. Although K- deficiency is less of a problem on plums than on prunes, recommended rates and methods of deficiency correction are similar ^[K18].

Common prune K fertilization strategies ^[K7].
K
fertilization strategies
¹⁾ Fertigation with KCl can be risky, as chloride may burn the roots ^[K7].

Application Rate

Prunes remove an estimated 23 lbs K₂O per dry ton harvested per acre. Assuming that 50% of the fertilizer applied is plant available, about 100 lbs of potassium sulfate fertilizer (0-0-50) per acre would be needed to replace K removed by each ton of yield ^{[K2,K24,K28,K32]}. A common recommendation for K applied by fertigation to mature, heavily cropped prune trees is 150 lbs K₂O/acre as K₂SO₄ or KCl ^[K7]. Since more of the K applied through drip systems is plant available, the application rate can be reduced when fertigation is used compared to when dry fertilizer is banded in fall (240-250 lbs K₂O/acre) ^[K7].

Fruit is the driver of K uptake, so in years where crop load is light (for example, if hot spring weather reduced fruit set) in-season K can be reduced^[K7,K24,K32]. If prunes are being grown for the fresh market, the K requirement will be lower because of the lighter crop load ^[K5].

Soil properties can affect K availability. Higher rates may be required for heavy soils, where more K is held on soil surfaces, compared to lighter soils ^[K21]. In areas where soils are known to fix K, such as the east side of the San Joaquin Valley, analyzing the soil for its K fixation capacity before the orchard is planted helps adjust the K fertilization program. A discussion about K fixation in the San Joaquin Valley can be found here. For more information about soil K fertilization in your area,contact your local farm advisor specializing in prune or plum production.

Mode of Application

Fertilizer Type

Time of Application

Foliar K

Foliar Potassium

A large proportion of the K contained in a mature prune tree is concentrated in the fruits. If there is a heavy crop and large prunes are needed, foliar sprays through July are recommended, especially on soils with marginal K availability ^[K17]. Research suggests that prunes may receive their entire K requirement foliarly. In a 3-year study in a chronically K-deficient orchard in the north Sacramento Valley, Southwick and coworkers ^[K27] found no yield, fruit quality or July leaf K differences between trees receiving an annual fall soil application of 600 lbs per acre KCl and trees receiving four annual foliar applications of 25 lbs potassium nitrate (KNO₃) per acre over the course of the growing season. A study on Japanese plums in Tunisia found that the trees receiving 100% of their K requirement foliarly maintained similar yields and K status to fertigated trees, and that plums from trees which received at least some foliar K matured earlier, weighed more and had higher total soluble solids, particularly in the earlier harvests ^[K13].

Application Rate and Time

Fertilizer Type

Fall Applied K

Soil Applied K - Fall

Granular fertilizers are usually applied in fall. A disadvantage of this approach is that it does not allow rate adjustment based on spring weather and expected crop load.

Application Rate

Prunes remove an estimated 23 lbs K₂O per dry ton harvested per acre. Assuming that 50% of the fertilizer applied is plant available, about 100 lbs of potassium sulfate fertilizer (0-0-50) per acre would be needed to replace K removed by each ton of yield ^{[K2,K24,K28,K32]}. A common recommendation for mature, heavily cropped prune trees is 240-250 lbs K₂O/acre banded as K₂SO₄ or KCl. Since more of the K applied through drip systems is plant available, this application rate is higher than when in-season fertigation is used (150 lbs K₂O/acre) ^[K7].

July leaf K analyses and the previous year's crop are used to determine the rate of fall fertilization ^[K6]. Fruit is the driver of K uptake, so in years where crop load is light less in-season K is necessary, and as long as tissue K levels are acceptable fall K application may be reduced ^[K7,K24,K32]. In plums or prunes grown for the fresh market, the K requirement will be lower because of the lighter crop load ^[K5]. If trees are K deficient, higher application rates may be used.

Soil properties can affect K availability. Prunes are not commonly planted on sandy soils, but where they are, lower rates of fall applied K are suggested as the soil has less K holding capacity. Experience with almonds suggests that when soil CEC is less than 15 meq/ 100 g soil, K applications should be reduced ^[K10]. Conversely on heavier soils higher rates may be required, as more K is held on soil surfaces ^[K20]. In areas where soils are known to fix K, such as the east side of the San Joaquin Valley, analyzing the soil for its K fixation capacity before the orchard is planted helps adjust the K fertilization program. A discussion about K fixation in the San Joaquin Valley can be found here. For more information about soil K fertilization in your area, contact your local farm advisor specializing in plum or prune production.

Mode of Application

Fertilizer Type

Time of Application

Zinc (Zn)

Soil Test

Leaf Analysis

In orchards, leaf analyses are more reliable for the diagnosis of nutrient deficiencies than soil analyses. Leaf analyses allow growers to evaluate their fertilization program.

Sampling Procedure

Leaf nutrient concentrations drop sharply from spring through spring and into summer, and stabilize around July. For this reason, University of California critical nutrient values have been established for July sampling, at which point nutrient concentrations are relatively stable. Samples taken earlier do not currently have any reliable interpretation ^[Zn10].

Leaf sampling should be done as follows ^{[Zn2,Zn6,Zn8,Zn13]}:

The orchard should be divided into uniform blocks with respect to soil type, tree age, variety, location and management.
Unhealthy, stunted or injured trees are avoided and non-representative areas are sampled separately.
Fully expanded leaves from non-bearing spurs 5-7 feet above the ground are chosen.
Leaves which may have received or been contaminated with Zn from a foliar fertilizer or Zn- containing pesticide spray should not be used.
One or two normal, healthy leaves are collected from each tree for a total of 50-75 leaves per sample.
Visual evaluation of orchard health and vigor should be made and recorded. This will aid interpretation of test results. This is particularly important for Zn, for which leaf concentrations may be reduced in a vigorously growing tree.
Samples are submitted to a lab as soon as possible. If a delay is anticipated, they should be refrigerated until they can be sent.

Interpretation of Results

Zn to Young Trees

Foliar Zn

Foliar Zinc

Zinc is most often applied foliarly to plums and prunes. Foliar Zn application may make symptoms disappear without necessarily increasing leaf Zn concentrations. The application rate must be chosen with care. If too little is applied the leaf may not absorb the fertilizer, and if too much is applied it may become toxic ^[Zn8].

Zinc application may be done every year or every other year, depending on the site. Application strategies depend on whether Zn is applied in spring, fall, or during dormancy ^[Zn3,Zn8].

References:

Nitrogen

Beutel, J., Uriu, K., Lilleland, O., 1976. Leaf analysis for California deciduous fruits. In: Reisenauer, H.M. (Ed.) Soil and Plant-Tissue Testing in California. University of California Cooperative Extension Bulletin 1879. pp. 15-17.
Bondada, B.R., Syvertsen, J.P., Albrigo, L.G., 2001. Urea nitrogen uptake by citrus leaves. HortScience 36, 1061-1065.
Brown, P.H., Muhammad, S., Saa Silva, S., 2012a. Update 2012: Fertigation trials in almond.
Brown, P.H., Saa Silva, S., Muhammad, S., 2012b.Development of leaf sampling interpretation methods for almond and development of a nutrient budget approach to fertilizer management in almond. Almond Board of California Final Research Report.
Brown, P.H. Niederholzer, F., Sepulveda R., 2014. Development of nutrient management tools for prunes. Report submitted to the California Dried Plum Board.
Buchner, R.P., 2013. Nitrogen management for French prune. Sacramento Valley Regional Prune Notes, February 2013.
Day, K.R., Johnson, R.S., Crisosto, C., DeJong, T., Klassen, K., Banuelos, G., 2002. Plum nutrition studies. California Tree Fruit Agreement Research Report.
Day, K.R., Buchner, R.P., 2012. Growing prunes for the fresh market. In: Buchner, R.P. (Ed.). Prune Production Manual. University of California, Division of Agriculture and Natural Resources, Publication 3507. pp. 279-282.
Doll, D., 2011. Fertilizing young almond trees – a few tips.
Fulton, A.E., Sanden, B.L., 2012. Managing salinity in soils and water. In: Buchner, R.P. (Ed.). Prune Production Manual. University of California, Division of Agriculture and Natural Resources, Publication 3507. pp. 43-62.
Holtz, B., 2010. Fertilizing one-year old trees – Be careful!
Johnson, R.S., Uriu, K., 1989. Mineral nutrition. In: LaRue, J.H., Johnson, R.S. (Eds.). Peaches, Plums and Nectarines: Growing and Handling for the Fresh Market. University of California, Division of Agriculture and Natural Resources, Publication 3331. pp. 68-81.
Krueger, W., 2006. Summer nutrition and leaf sampling. Yolo-Solano Counties Fruit and Nut Notes, May 2006.
Kreuger, W., 2008. Considerations for in-season nutrition of prunes. Sacramento Valley Prune News, March 2008.
LaRue,J.H., 1989. Establishing the orchard. In: LaRue, J.H., Johnson, R.S. (Eds.). Peaches, Plums and Nectarines: Growing and Handling for the Fresh Market. University of California, Division of Agriculture and Natural Resources, Publication 3331. pp. 21-30.
LaRue, J.H., Gerdts, M., 1973. Growing plums in California. California Experiment Station Extension Service, Circular 563.
Leece, D.R., Dirou, J.F., 1977. Organosilicone and alginate adjuvants evaluated in urea sprays foliar-applied to prune trees. Communications in Soil Science and Plant Analysis 8, 169-176.

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Leece, D.R., Dirou, J.F., 1979. Comparison of urea foliar sprays containing hydrocarbon or silicone surfactants with soil-appled nitrogen in maintaining the leaf nitrogen concentration of prune trees. Journal of the American Society for Horticultural Science 105, 644-648.
Liu, G., Williamson, J., 2013. What is urea-triazone nitrogen? University of Florida IFAS Extension Publication HS1233
Niederholzer, F.J.A., 2007. Improving the nutrient efficiency of tree crops. California Plant and Soil Conference 2007, February 6&7, 2007, Sacramento.
Niederholzer, F.J.A., 2011. Using urea efficiently. Glenn County Orchard Facts, April, 2011.
Niederholzer, F., 2012. Nitrogen use efficiency in almonds. Sacramento Valley Almond News, April 2012.
Niederholzer, F.J.A., 2013. Efficient nitrogen management in prune production. Sacramento Valley Regional Prune Newsletter, April, 2013.
Niederholzer, F.J.A., 2014. Prune orchard fertility review. Glenn County Orchard Facts, January 2014.
Niederholzer, F.J.A., Buchner, R.P., Southwick, S.M., 2012. Nutrition and fertilization. In: Buchner, R.P. (Ed.). Prune Production Manual. University of California, Division of Agriculture and Natural Resources, Publication 3507. pp. 151- 168.
Olson, W., Andris, H., Buchner, R., Holtz, B., Klonsky, K., Krueger, W., Walton, J., 2004. Integrated prune farming practices (I.P.F.P.)- 2004. A six year summary. Report submitted to the California Dried Plum Board.
Olson, W., Ramos, D., Yeager, J., Uriu, K., Pearson, J., 1982. Efficient nitrogen application timing in prune production. Report submitted to the California Dried Plum Board.
Olson, W., Uriu, K., Sibbett, S., Krueger, W., Weakley, C., 1986. Verification of field nitrogen timing trial results- 1986 prune nitrogen survey. Report submitted to the California Dried Plum Board.
Sibbett, G.S., Southwick, S., 1993. Comparison of foliar vs soil applied nitrogen for maintaining its sufficiency in French prune. Report submitted to the California Dried Plum Board.
Sibbett, G.S., Southwick, S., Yeager, J., 1991. Effect of foliar applied urea on percent leaf N and fruit size of French prune. Report submitted to the California Dried Plum Board.
Southwick, S.M., Rupert, M.E., Yeager, J.T., Weis, K.G., DeJong, T., Shackel, K., Bonin, A., 1996. Nitrogen fertigation of young prune trees and effects on horticultural performance: 1996 Final report. Report submitted to the California Dried Plum Board.
Southwick, S.M., Rupert, M.E., Yeager, J.T., Lampinen, B.D., DeJong, T.M., Weis, K.G., 1999. Effects of nitrogen fertigation on fruit yield and quality of young 'French' prune trees. Journal of Horticultural Science & Biotechnology 74, 187-195.
Uriu, K., 1981. Soil and plant analysis and symptomology for diagnosis of mineral deficiencies and toxicities. In: Ramos, D.E., (Ed.). Prune Orchard Management. University of California Division of Agricultural Sciences Special Publication 3269. pp. 89-97.
Weinbaum, S.A., 1978. Feasibility of satisfying total nitrogen requirement of non-bearing prune trees with foliar nitrate. Hortscience 13, 52-53.
Weinbaum, S.A., Merwin, M.L., Muraoka, T.T., 1978. Seasonal variation in nitrate uptake efficiency and distribution of absorbed nitrogen in non-bearing prune trees. Journal of the American Society for Horticultural Science 103, 516-519.
Weinbaum, S.A., Brown, P.H., Johnson, R.S., 2002. Application of selected macronutrients (N,K) in deciduous orchards: physiological and agrotechnical perspectives. Acta Horticulturae 594, 59-64.
Weinbaum, S.A., Niederholzer, F.J.A., Ponchner, S., Rosecrance, R.C., Carlson, R.M., Whittlesey, A.C., Muraoka, T.T., 1994. Nutrient uptake by cropping and defruited field-grown 'French' prune trees. Journal of the American Society of Horticultural Science 119, 925-930.
Zasoski, R.J., 1994. Nitrogen efficiency in drip irrigated almonds.FREP Final Report.

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Phosphorus

Beutel, J., Uriu, K., Lilleland, O., 1976. Leaf analysis for California deciduous fruits. In: Reisenauer, H.M. (Ed.) Soil and Plant-Tissue Testing in California. University of California Cooperative Extension Bulletin 1879. pp. 15-17.
Brown, P.H. Niederholzer, F., Sepulveda R., 2014. Development of nutrient management tools for prunes. Report submitted to the California Dried Plum Board.
California Plant Health Association, 2002. Western Fertilizer Handbook 9^th edition. Interstate Publishers, Inc.
Doll, D., 2011. Fertilizing young almond trees – a few tips.
Johnson, R.S., Uriu, K., 1989. Mineral nutrition. In: LaRue, J.H., Johnson, R.S.(Eds.). Peaches, Plums and Nectarines: Growing and Handling for the Fresh Market. University of California, Division of Agriculture and Natural Resources, Publication 3331. pp. 68-81.
Krueger, W., 2006. Summer nutrition and leaf sampling. Yolo-Solano Counties Fruit and Nut Notes, May 2006.
Fulton, A., 2010. Understanding and applying information from a soil test: Part 2 – NPK.
Fulton, A.E., Sanden, B.L., 2012. Managing salinity in soils and water. In: Buchner, R.P. (Ed.). Prune Production Manual. University of California, Division of Agriculture and Natural Resources, Publication 3507. pp. 43-62.
Niederholzer, F.J.A., Buchner, R.P., Southwick, S.M., 2012. Nutrition and fertilization. In: Buchner, R.P. (Ed.). Prune Production Manual. University of California, Division of Agriculture and Natural Resources, Publication 3507. pp. 151-168.
Olson, W., Andris, H., Buchner, R., Holtz, B., Klonsky, K., Krueger, W., Walton, J., 2004. Integrated prune farming practices (I.P.F.P.)- 2004. A six year summary. Report submitted to the California Dried Plum Board.
Shear, C.B., Faust, M., 1980. Nutritional ranges in deciduous tree fruits and nuts. In: Janick, J. (Ed.). Horticultural Reviews. The AVI Publishing Company, Inc.
Southwick, S.M., Rupert, M.E., Yeager, J.T., Weis, K.G., DeJong, T., Shackel, K., Bonin, A., 1996. Nitrogen fertigation of young prune trees and effects on horticultural performance: 1996 Final report. Report submitted to the California Dried Plum Board.
Strand, L.L., 1999. Integrated Pest Management for Stone Fruits. University of California, Division of Agriculture and Natural Resources, Publication 3389.
Uriu, K., 1981. Soil and plant analysis and symptomology for diagnosis of mineral deficiencies and toxicities. In: Ramos, D.E., (Ed.). Prune Orchard Management. University of California Division of Agricultural Sciences Special Publication 3269. pp. 89-97.
Vercambre, G., Pagès, L., Doussan, C., Habib, R., 2003. Architectural analysis and synthesis of plum tree root system in an orchard using a quantitative modelling approach. Plant and Soil 251, 1-11.

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Potassium

Beutel, J., Uriu, K., Lilleland, O., 1976. Leaf analysis for California deciduous fruits. In: Reisenauer, H.M. (Ed.) Soil and Plant-Tissue Testing in California. University of California Cooperative Extension Bulletin 1879. pp. 15-17.
Brown, P.H. Niederholzer, F., Sepulveda R., 2014. Development of nutrient management tools for prunes. Report submitted to the California Dried Plum Board.
Buchner, R.P., Olson, W.H., Niederholzer, F.J.A., Reil, W.O., Krueger, W.H., Fulton, A.E., 2012. Prune production calendar of operations in the Sacramento Valley. In: Buchner, R.P. (Ed.). Prune Production Manual. University of California, Division of Agriculture and Natural Resources, Publication 3507. pp. 297.
Carlson, R.M., Buchanan, J.R., Kapustka, T.E., Uriu, K., 1974. Displacement of fertilizer potassium in soil columns with gypsum. Journal of the American Society for Horticultural Science 99, 221-222.
Day, K.R., Buchner, R.P., 2012. Growing prunes for the fresh market. In: Buchner, R.P. (Ed.). Prune Production Manual. University of California, Division of Agriculture and Natural Resources, Publication 3507. pp. 279-282.
DeBuse, C., 2012. Prune orchard nutrition. Sutter-Yuba Counties Pomology Notes, November 2012.
DeBuse, C., Niederholzer, F.J.A., 2011. In-season potassium fertilization options for prunes. Glenn County Orchard Facts, April, 2011.
DeVay, J.E., Gerdts, M., English, H., Lukezic., F.L., 1974. Controlling cytospora canker in President plum orchards of California. California Agriculture 28, 12-14.
Doll, D., 2011. Fertilizing young almond trees – a few tips.
Doll, D., 2014. Almond orchard nitrogen and potassium fertilization. Presented at the South San Joaquin Valley Almond Symposium, 5/29/2014.
Fulton, A., 2010. Understanding and applying information from a soil test: Part 2 – NPK.
Fulton, A.E., Sanden, B.L., 2012. Managing salinity in soils and water. In: Buchner, R.P. (Ed.). Prune Production Manual. University of California, Division of Agriculture and Natural Resources, Publication 3507. pp. 43-62.
Ghanem, M., Ben Mimoun, M., 2010. Effect of potassium foliar spray on two plum trees cultivars: 'Strival' and 'Black Star'. Acta Horticulturae 874, 83-90.
Hoagland, D.R., Chandler, W.H., 1932. Some effects of deficiencies of phosphate and potassium on the growth and composition of fruit trees, under controlled conditions. Proceedings of the American Horticultural Society 29, 267-271.
Johnson, R.S., Uriu, K., 1989. Mineral nutrition. In: LaRue, J.H., Johnson, R.S. (Eds.). Peaches, Plums and Nectarines: Growing and Handling for the Fresh Market. University of California, Division of Agriculture and Natural Resources, Publication 3331. pp. 68-81.
Krueger, W., 2006. Summer nutrition and leaf sampling. Yolo-Solano Counties Fruit and Nut Notes, May 2006.
Krueger, W. 2009. Steps for producing large prunes. Western Farm Press, May 2009.

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LaRue, J.H., Gerdts, M., 1973. Growing plums in California. California Experiment Station Extension Service, Circular 563.
Lilleland, O., 1932. Experiments in K and P deficiencies with fruit trees in the field. Proceedings of the American Society for Horticultural Science 29, 272-276.
Niederholzer, F.J.A., 2014. Prune orchard fertility review. Glenn County Orchard Facts, January 2014.
Niederholzer, F.J.A., Buchner, R.P., Southwick, S.M., 2012. Nutrition and fertilization. In: Buchner, R.P. (Ed.). Prune Production Manual. University of California, Division of Agriculture and Natural Resources, Publication 3507. pp. 151-168.
Olson, W.H, Uriu., K., Carlson, R.M., Krueger, W.H., Pearson,J., 1987. Correcting potassium deficiency in prune trees is profitable. California Agriculture 41, 20-21.
Olson, W., Andris, H., Buchner, R., Holtz, B., Klonsky, K., Krueger, W., Walton, J., 2004. Integrated prune farming practices (I.P.F.P.)- 2004. A six year summary. Report submitted to the California Dried Plum Board.
Pope, K., 2014. Potassium nutrition- maintaining optimum levels by replacing what you've lost. Glenn County Orchard Facts, October 2014.
Shear, C.B., Faust, M., 1980. Nutritional ranges in deciduous tree fruits and nuts. In: Janick, J. (Ed.). Horticultural Reviews. The AVI Publishing Company, Inc.
Strand, L.L., 1999. Integrated Pest Management for Stone Fruits. University of California, Division of Agriculture and Natural Resources, Publication 3389.
Southwick, S.M., Olson, W., Yeager J., Weis, K.G., 1996a. Optimum timing of potassium nitrate spray applications to 'French' prune trees. Journal of the American Society for Horticultural Science 121, 326-333.
Southwick, S.M., Rupert, M.E., Yeager, J.T., Weis, K.G., DeJong, T., Shackel, K., Bonin, A., 1996b. Nitrogen fertigation of young prune trees and effects on horticultural performance: 1996 Final report. Report submitted to the California Dried Plum Board.
Uriu, K., Carlson, R.M., Henderson, D.W., Shulbach, H., Aldrich, T.M., 1980. Potassium fertilization of prune trees under drip irrigation. Journal of the American Society for Horticultural Science105, 508-510.
Uriu, K., 1981. Soil and plant analysis and symptomology for diagnosis of mineral deficiencies and toxicities. In: Ramos, D.E., (Ed.). Prune Orchard Management. University of California Division of Agricultural Sciences Special Publication 3269. pp. 89-97.
Vercambre, G., Pagès, L., Doussan, C., Habib, R., 2003. Architectural analysis and synthesis of plum tree root system in an orchard using a quantitative modelling approach. Plant and Soil 251, 1-11.
Weinbaum, S.A., Niederholzer, F.J.A., Ponchner, S., Rosecrance, R.C., Carlson, R.M., Whittlesey, A.C., Muraoka, T.T., 1994. Nutrient uptake by cropping and defruited field-grown 'French' prune trees. Journal of the American Society for Horticultural Science 119, 925-930.

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Zinc

California Plant Health Association, 2002. Western Fertilizer Handbook 9^th Ed. Interstate Publishers, Inc.
Connell, J., 2013. Prune tissue sampling for leaf analysis. Sacramento Valley Regional Prune Newsletter, April, 2013.
DeBuse, C., 2012. Prune orchard nutrition. Sutter-Yuba Counties Pomology Notes, November 2012.
Johnson, R.S., Crisosto, C., Andris, H., Day, K., Holtz, B., Beede, B., Klassen, K., 2003. The effect of nutrient deficiencies on stone fruit production and quality. FREP Final Report.
Johnson, R.S., Day, K.R., 2013. Zinc Deficiency and Correction in California Plum Orchards. Acta Horticulturae 985, 189-192.
Krueger, W., 2006. Summer nutrition and leaf sampling. Yolo-Solano Counties Fruit and Nut Notes, May 2006.
LaRue, J.H., Gerdts, M., 1973. Growing plums in California. California Experiment Station Extension Service, Circular 563.
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Prune and Plum

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Nitrogen (N)

Prune and Plum N Nutrition

Deficiency Symptoms

Excessive Nitrogen

Soil Test

Soil Analysis

Spring Sampling

Fall Sampling

Leaf Analysis

Leaf Analysis N

Sampling Procedure

Interpretation of Results

N to Young Trees

N Fertilization of Young Trees

Application Rate

Mode of Application

Fertilizer Type

Time of Application

Soil Applied N

Soil Applied Nitrogen

Application Rate

Nitrate in the Irrigation Water

Mode of Application

Fertilizer Type

Time of Application

Foliar N

Foliar Nitrogen

Application Rate and Time

Fertilizer Type

Phosphorus (P2O5)

Prune and Plum P Nutrition

Deficiency Symptoms

Soil Test

Soil Analysis

Soil Sampling and Analysis

Interpretation of Test Results

Leaf Analysis

Leaf Analysis

Sampling Procedure

Interpretation of Results

P to Young Trees

P Fertilization of Young Trees

Soil Applied P

Soil Applied Phosphorus

Application Rate

Mode of Application

Fertilizer Type

Time of Application

Potassium (K2O)

Prune and Plum K Nutrition

Deficiency Symptoms

Soil Test

Soil Analysis

Soil Sampling and Analysis

Interpretation of Test Results

Leaf Analysis

Leaf Analysis

Sampling Procedure

Interpretation of Results

May Leaf Interpretation

K to Young Trees

K Fertilization of Young Trees

Soil Applied K

Soil Applied K - In-Season

Application Rate

Mode of Application

Fertilizer Type

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Phosphorus (P₂O₅)

Potassium (K₂O)