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G.H. Neilsen, D. Neilsen, L.C. Herbert and E.J. Hogue

A split-plot experimental design was imposed in the year of planting and maintained for the first five growing seasons in a high density apple orchard on M.9 rootstock planted at 1.5 m (within row) × 4 m (between row) in a loamy sand soil susceptible to K deficiency when drip-irrigated. Four N-K fertigation treatments involving low (N1) and high (N2) rates of N combined with 0 (K0) or 15 g K/tree per year (K1) were applied in five replicated and randomized main plot units. Subplots consisted of three-tree plots of each of the apple cultivars Gala, Fuji, Fiesta and Spartan. Soil solution monitoring indicated the maintenance of distinctly different soil solution N and K concentrations in the respective N-K treatments during the study. The most important plant response was prevention of the development of K deficiency by the K1-fertigation treatment. Fertigation of 15 g K/tree generally increased leaf K, fruit K and Mg concentrations, fruit size and yield and fruit titratable acidity and red coloration at harvest for all cultivars. K fertigation also decreased leaf Mg and B concentrations, fruit N, P and Ca concentration and fruit firmness. In addition to leaf K concentrations <1%, K deficiency was associated with fruit K concentrations <100 mg/100 g fresh weight and soil solution K concentration <5 mg·L-1. Increasing the rate of fertigated N when growth was constrained by K deficiency increased leaf N and Mn and decreased leaf P and B, but had no effect on tree vigor or fruit production and quality.

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E.E. Albregts, C.M. Howard and C.K. Chandler

Strawberry (Fragaria × ananassa Duch.) was grown for two seasons on a fine sand soil to study the plant and fruiting response of three cultivars to K rates of O, 56, 112, 168, and 224 kg·ha-1. `Dover' total fruit yields increased linearly with rate both seasons while the maximum March yield the first season was with 170 kg K/ha. April yields increased linearly with K rate the first season. `Tufts' and `Chandler' responses to K rates were not consistent for monthly or total fruit yield. The average fruit weight of `Dover' and `Tufts' decreased linearly with increasing K rate for March and for the season in 1984, while `Dover' gave a positive linear average fruit weight response to K rate during Apr. 1986. `Dover' leaf K decreased from December to February, and K deficiency symptoms were expressed by February in treatments receiving lower rates of K. Leaf K concentrations of `Dover' correlated well with K rate.

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Earl E. Albregts, George J. Hochmuth and C. K. Chandler

During the 1992-93 fruiting season, straw berry plants were fertigated weekly with either 0.28, 0.56, 0.84, 1.12, or 1.40 kg/ha/day of K derived from KCl. Other nutrients were applied in the plant bed before fumigation except for N which was applied at 0.84 kg/ha/day by fertigation. Soil moisture in the plant beds was maintained between 10 and 15 cbs. Initial soil K tested medium with the Mehlich I soil test. Seasonal average fruit weight and percent marketable fruit decreased with increasing K rate. Seasonal fruit yields did not increase with K rates above 0.56 kg/ha/day. Leaf K concentrations increased with increasing K rates throughout the harvest season. The leaf K concentrations in the 0.28 K treatment were below 1% during the last month of harvest. K rates did not affect fruit firmness.

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Ivan dos Santos Pereira, Luciano Picolotto, Michél Aldrighi Gonçalves, Gerson Kleinick Vignolo and Luis Eduardo Corrêa Antunes

36 and 84 kg·ha −1 of K ( Harkins et al., 2014 ). As the need is greatest during fruiting, K deficiency is common in years of high production, with symptoms including reduced growth, followed by chlorosis and necrosis in the leaves, and shortening of

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Alan W. Meerow and Timothy K. Broschat

Anatomical differences in leaves of queen palm [Syagrus romanzoffiana (Chamisso) Glassman] showing visible K, Mn, and Fe deficiency symptoms are described. Potassium-deficient leaves showed less organization in the mesophyll than healthy leaves. Adaxial fibers increased in diameter. Chloroplast frequency was reduced overall, but most severely in areas of the leaf showing gross symptoms of the deficiency. Manganese-deficient leaves had reduced chloroplast frequency, especially in tissue near necrotic areas, and thicker and more fibers per unit length. Iron-deficient leaves had few chloroplasts throughout the mesophyll, and also thicker and more fibers per unit length.

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Dr. Robert K. Soost, 88, Professor Emeritus in the Department of Botany and Plant Sciences, University of California (UC)–Riverside, died on 8 Mar. 2009. Dr. Soost was internationally known for his work in citrus breeding. His research included a

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Gerry H. Neilsen, Denise Neilsen, Sung-hee Guak and Tom Forge

stimulates tree K uptake, resulting in a depression of leaf K relative to fruit K concentration ( Jadczuk and Lenz, 1998 ). Changes in fruit nutrient concentrations can alter fruit quality as demonstrated by Volz et al. (1993) , who found that lightly

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Eugene J. Hogue, John A. Cline, Gerry Neilsen and Denise Neilsen

The development and consequences of K deficiency in intensively managed apple orchards grown on coarse-textured soils under drip irrigation have been identified previously ( Cummings, 1985 ; Neilsen et al., 1998 ). Correction of K deficiency

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Qiupeng Zeng, Patrick H. Brown and Brent A. Holtz

A field experiment was conducted from 1996 to 1998 to examine the effects of K fertilization on leaf K, nut yield, and quality in pistachio (Pistacia vera L.). There were six treatments, including four annual rates of K application (0, 110, 220, and 330 kg·ha-1) and three K sources (K2SO4, KCl, and KNO3). Pistachio trees exhibited highly fluctuating seasonal leaf K levels. Leaf K concentration was low (<10 g·kg-1) during spring flush, increased dramatically during fruit development, and declined rapidly after harvest. Leaf K concentration increased following K fertilization. Potassium fertilization at the rate of 110 to 220 kg·ha-1 K significantly increased nut yield and quality, but nut yield tended to decrease when the annual rate exceeded 220 kg·ha-1 K. There were no significant differences among the K sources in their effects on leaf K concentration, nut yield, and quality. The use of KCl as a K source for 3 years did not increase leaf Cl concentration. There was a significant, positive correlation between nut yield and leaf K concentration during nut fill. The critical leaf K value for optimal pistachio production determined from 3 years' cumulative data was 16.9 g·kg-1. For sustained production in highly productive pistachio orchards, we recommend annual application rates of 110 to 220 kg·ha-1 K, using K2SO4, KCl, or KNO3.

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Stephen M. Olson, Sal J. Locascio, George J. Hochmuth and Robert C. Hochmuth

Experiments were conducted in the spring of 1990 at Quincy and Live Oak, Florida and 1991 in Quincy to study the effect of 3 K sources (KCl, K2SO4 and KNO3) and 5 K rates (0, 75, 150, 225 and 300 kg ha-1) of yield of `Sunny' tomatoes. Preplant soil test K values were 37 and 54 ppm in 1990, respectively, and 44 ppm in 1991. These K concentrations are considered medium (36-60) for Florida mineral soils. K source had no effect on yield, fruit weight or percent marketable fruit in all studies. In 1990, total yields, yield of extra large (> 7.0 cm) fruit and percent marketable fruit were increased with application of 75 kg ha-1 of K but there was no further response to applied K at both locations. In 1991, total yield increased with applied K up to 150 kg ha-1 then decreased. Fruit size and percent marketable fruit increase with 75 kg ha-1 of K but no further response occurred. There was no interaction of K source and K rate.