Optimum timing of potassium nitrate spray applications to 'French' prune trees

• Published in: Journal of the American Society for Horticultural Science Vol. 121; no. 2; pp. 326 - 333
• Main Authors: Southwick, S.M, Olson, W, Yeager, J, Weis, K.G
• Format: Journal Article
• Language: English
• Published: 01.03.1996
• Subjects: amendement du sol; aplicacion foliar; application foliaire; california; californie; canopy; carence en substance nutritive; chemical composition; chlorure de potassium; cloruro potasico; composicion quimica; composition chimique; contenido de materia seca; contenido de nitrogeno; couvert; crop yield; cubierta de copas; deficiencias nutritivas; developmental stages; dimension; dimensions; dry matter content; drying; enmiendas del suelo; etapas de desarrollo; foliar application; fruits; frutas; nitrate de potassium; nitrato de potasio; nitrogen content; nutrient deficiencies; nutritive value; portainjertos; porte greffe; potasio; potassium; potassium chloride; potassium nitrate; prunus cerasifera; prunus domestica; rendement des cultures; rendimiento de cultivos; rootstocks; secado; sechage; soil amendments; stade de developpement; teneur en azote; teneur en matiere seche; urea; uree; valeur nutritive; valor nutritivo
• ISSN: 0003-1062; 2327-9788
• DOI: 10.21273/jashs.121.2.326

During the fruit growing season, April through August 1990, 1991, and 1992, four sprays of 20-22 liters/tree of KNO3 were applied to 'French' prune trees (Prunus domestica L. syn. 'Petite d'Agen). Spray applications of KNO3 were compared to single annual soil applications of KCl (1.4-2.3 kg/tree) and sprays of urea + KNO3 with respect to leaf K and N, fruit size, drying ratio, and dry yield. Potassium nitrate sprays were as effective, or better, than soil-applied K in maintaining adequate levels of leaf K throughout the season. Treatment effects were not carried over into the next year. Lowest leaf K was found in trees where no K had been applied. Those values were below the adequate level of 1.3% K and the untreated group developed K deficiency symptoms. Consistent effects on leaf K were not obtained when urea was applied and no negative effect on leaf K was demonstrated. Equivalent dry yields per tree were obtained by foliar and soil K applications. There was no best time for KNO3 sprays. Yield per tree was not enhanced when foliar K-N sprays were applied to trees that had levels of 1.3% K or more as of 15 Apr. 1992. Trees that were below optimum K in April tended toward improved dry yields after four K-N sprays. Trees that had no applied K were lowest yielding. Drying ratios and fruit size (number of fruit per kilogram) were not different among K treatments. Dry yields per tree were increased without a decrease in fruit size or an increase in drying ratio with either soil or foliar K application. These results suggest that foliar KNO3 sprays applied four times throughout the growing season can be used to correct incipient K deficiency in 'French' prune and to obtain dry yields equivalent to those obtained with soil applications of KCl.