Influence of elevating tree potassium on fruit drop and yield of pecan.

摘要

Excessive Stage II fruit drop (i.e., June drop) often limits profitability of certain pecan cultivars. Anecdotal evidence indicates that 1 cause of drop is linked to a nutrient element deficiency. In this study, the consequences of improving tree K nutrition on fruit drop, nutmeat yield and kernel quality (% kernel) in Desirable orchards, in which generally accepted foliar analysis standards indicate satisfactory tree K nutritional status (>=0.75% to 2.5% K/dry wt.), were examined. Multiyear field studies of 2 such orchards found that elevating leaf and fruit K concn. through soil banding of potash over drip irrigation emitters: increased fruit retention by reducing Stage II fruit drop; increased in-shell nut yield; and increased nut quality by increasing percentage kernel. Potash applied through soil banding elevated foliar and fruit K concn. by approx. 0.1-0.4% units within a few months post-application depending on the amount applied; however, the beneficial effects of a single potash soil band application diminished after the first yr. A comparison of the K concn. of retained fruit vs. abscised fruit during the Stage II fruit drop window found that retained fruit possessed endogenous K concn. of 1.2-1.7% (dry wt. basis) in 1 orchard and 1.45-1.9% in a second orchard, whereas aborted fruit possessed K at 0.65-1.2% in 1 orchard and 0.75-1.2% in a second orchard, respectively, thus establishing approx. 1.25% K as a 'drop threshold' under conditions of this study. Total K concn. of retained fruit is typically 0.25% to 0.50 K/dry wt. greater than dropped fruit. Considerable K-associated late-spring fruit drop can occur in Desirable, although early- to midsummer 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 r-evaluation and possibly pecan K nutrition in general