Location: Fruit and Nut ResearchTitle: Influence of elevating tree potassium on fruit-drop and yield of pecan Author
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2010
Publication Date: 7/1/2010
Citation: Wood, B.W., Wells, L., Funderburke, F. 2010. Influence of elevating tree potassium on fruit-drop and yield of pecan. HortScience. 45:911-917. Interpretive Summary: Excessive fruit-drop and poor tree potassium (K) nutritional status are often yield limiting problems in pecan orchards. The causes of these drops are not fully understood and there is a near death of methods to rapidly increase tree K nutritional health. It was found that concentrated banding of K can rapidly improve tree health and that at least a certain portion of June-drop can potentially be attributed to a K deficiency of young fruit. This work provides a method that farmers can use to rapidly increase tree K nutrition and also to reduce excessive fruit drop. It also indicates that orchard K management thresholds need further study.
Technical Abstract: Excessive Stage-II fruit-drop often limits profitability of certain pecan [Carya illinoinensis (Wangenh.) C. Koch] cultivars. Anecdotal evidence indicates that one cause of drop is linked to a nutrient element deficiency. This study examines the consequences of improving tree K nutrition on fruit-drop, nutmeat yield and kernel quality (i.e., % kernel) in ‘Desirable’ orchards in which generally accepted foliar analysis standards indicate satisfactory tree K nutritional status (i.e., = 0.75-2.5% K dw). Multiyear field studies of two such orchards found that elevating leaf and fruit K concentration, via soil banding of potash over drip irrigation emitters, a) increased fruit retention by reducing Stage-II fruit-drop, b) increased in-shell nut yield, and c) increased nut quality by increasing percentage kernel. Potash applied via soil banding elevated foliar and fruit K concentration by ˜ 0.1- 0.4% units within a few months post-application, depending on amount applied; however, the beneficial effects of a single potash soil band application diminished after the first year. A comparison of the K concentration of retained fruit vs. abscised fruit during the Stage-II fruit-drop window found that retained fruit possessed endogenous K concentrations of 1.2 – 1.7% (dry weight basis) in one orchard and 1.45-1.9% in a second orchard; whereas aborted fruit possessed K at 0.65 to 1.2% in one orchard and 0.75 – 1.2% in a second orchard, respectively, thus establishing ˜ 1.25 % K as a “drop threshold” under conditions of this study. The total K concentration of retained fruit is typically 0.25-0.50 % K dw greater than dropped fruit. Considerable K-associated late-spring fruit-drop can occur in ‘Desirable’ even though early- to mid-summer leaf analysis indicates trees were K-sufficient; hence, implying that young fruit likely possesses a higher K requirement than does foliage. These K associated benefits to trees meeting accepted K sufficiency criteria is evidence that K nutrition management of ‘Desirable’ pecan merits reevaluation, and possibly pecan K nutrition in general.