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Luis A. Valdez-Aguilar, David William Reed, and John A. Cornell

., 2002 ). Rubidium can also substitute K + , which in nature occurs mainly in acidic soils as a result of excessive K + leaching ( Nyholm and Tyler, 2000 ). Because the counter-cations may prevent the delineation of the actual alkalinity effect, a series

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Regina L. Reickenberg and Marvin P. Pritts

The dynamics of nutrient uptake from foliar applied 15N-urea and Rb (a K analog) were quantified in red raspberries. Both N and Rb in an aqueous solution were absorbed rapidly into the leaf and transported throughout the plant. In the greenhouse, about half of the urea and a third of the Rb were absorbed within 32 hours of application. The addition of a surfactant to the foliar solution reduced uptake, while solution pH, time of application and leaf age had little effect. The lower leaf surface exhibited a faster rate of absorption than the upper surface, but the difference was not large. In the field, some foliar N appeared to have been washed off leaves and taken up by the root system; however, none of the foliar applications affected plant growth. We conclude that significant uptake of foliar applied N and K occurs in raspberry, but the absolute amount delivered through a single foliar application is small. The percentage of total plant nutrient supplied through a foliar application is reduced to < 5% over time as the plant grows, so multiple applications would be required to maintain levels significantly higher than would exist through root uptake alone.

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J. R. Davenport

Foliar feeding of crop plants is an increasingly popular practice. The use of foliar nutrients relies on the ability of the plant to sorb nutrients through the leaves. Cranberries (Vaccinium macrocarpon Ait.) are known to have a waxy cuticle on the leaf surface which may impede nutrient uptake, leaving only the lower leaf surface for effective uptake. This study was undertaken to determine the extent of foliar nutrient uptake by cranberries using rubidium as a tracer. Rubidium was chosen for its similarity to potassium in plant uptake. In replicated plots, cranberries were sprayed with rubidium at the rate recommended for foliar potassium at three different growth stages and three different times of day. Washed and unwashed leaves were analyzed one day, one week, and one month after rubidium applications. Stem, soil, and root material was analyzed for rubidium at the one week and one month sample times. Results will be discussed with reference to uptake and movement of foliar applied nutrients in cranberries.

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C. Navarro, R. Fernández-Escobar, and M. Benlloch

A low-pressure injection method for introducing chemical formulations into trees is presented. The apparatus consists of a plastic injector and a tube providing a pressure of 60 to 80 kPa, which is below the injurious level for the xylem. The efficiency of the method was determined by injecting PTS, a marker of apoplastic flux dye solutions, and rubidium chloride into young trees, main scaffolds, or tree trunks. The depth of the hole drilled) and the number of injections necessary to distribute the solutions was also determined. The injected solutions moved mainly upward through the older rings of the xylem, suggesting that uptake is directly controlled by the transpiration rate. A single injection was enough to distribute solutions in scaffolds with a diameter of 8 cm, but two injections were necessary for 17-cm-diameter trunks. According to the results, the injection method was effective in introducing chemicals into olive (Olea europaea L.) trees. The method is easy to use, safe and economical and does not involve special equipment. Chemical name used: trisodium, 3-hydroxi-5,8,10-pyrenetrisulfonate (PTS).

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Timothy K. Broschat

.A. 1995 The effect of wood mulch type and depth on weed and tree growth and certain soil parameters J. Arboriculture 21 225 232 Helmke, P.A. Sparks, D.L. 1996 Lithium, sodium, potassium, rubidium, and cesium 551 574 Sparks D.L. Methods of soil analysis

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Genhua Niu, Pedro Osuna, Youping Sun, and Denise S. Rodriguez

157 Helmke, P.A. Sparks, D.L. 1996 Lithium, sodium, potassium, rubidium, and cesium. In: Sparks, D.L. (ed.). Methods of soil analysis, Part 3, chemical methods. 5 th series. Soil Science Society of America and American Society of Agronomy, Madison, WI

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Eleanor W. Hoffman, Dirk U. Bellstedt, and Gerard Jacobs

. Hort. Sci. 126 182 187 Hanekom, A.N. Deist, J. Blommaert, K.L.J. 1973 Seasonal uptake of 32 phosphorus and 86 rubidium by Protea cynaroides Agroplantae 5 107 110 Hettasch, H