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Abstract

Vesicular-arbuscular mycorrhizal (VAM) development of Glomus intraradices Schenck & Smith and growth response of Carrizo citrange [Poncirus trifoliata (L.) Raf. × Citrus sinensis (L.) Osbeck] and sour orange (C. aurantium L.) seedlings were examined in peat-perlite medium fertilized with 4 levels of superphosphate (SP) and rock phosphate (RP). Loss of P from SP-amended medium was exponential, whereas release of P was linear from RP-amended medium. With SP, root colonization by G. intraradices and growth response of both citrus rootstocks were reduced compared to RP-amended medium. VAM colonization and growth response were less with SP-amended medium than RP, probably because of the initially high available P from SP which inhibited VAM development, and because P later declined to levels insufficient to support maximum growth. When RP was used as a controlled-release source of P, VAM colonization was comparable to that observed in mineral soils. Growth of VAM plants exceeded that of uninoculated plants fertilized with increased levels of soluble P because of P-induced Cu deficiency in absence of VAM. An additional advantage of RP was long-term availability of P, compared to SP which leached within weeks after application to peat-perlite. No further P fertilization may be necessary if RP and VAM inoculum are incorporated into soilless media before planting, whereas repeated application of soluble P would be required for slow-growing woody plants like citrus.

Open Access

Phosphorus is one of the primary nutrients essential for plant growth and crop production ( Mengel and Kirkby, 2004 ). At present, most commercial phosphorus (P) fertilizers on the market such as single superphosphate are derived from phosphate rock

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-based nutrient sources (e.g., crop residue, compost, manure) and nonprocessed mineral sources (e.g., rock phosphate, lime, gypsum). As such, nutrient management in organic production systems is fundamentally different from that in conventional systems. Phosphorus

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Air contamination by fluorides is one of our major air pollution problems. These compounds are released by industries processing clays, ores, phosphate rock, coal, or any other fluorine-containing materials. Aluminum reduction, ceramic, phosphate, chemical, steel, and thermal power generation works all release fluorides in their normal manufacturing processes. Both gaseous and particulate fluorides may be emitted.

Open Access

Commercial cranberry (Vaccinium macrocarpon Ait.) soils are high in iron and calcium and have low pH. This soil chemistry causes conditions where phosphorus is tightly bound and is, to a large extent, unavailable to the cranberry plants. In theory, P forms that directly enter the plant (foliar), or that do not quickly dissolve to become rapidly immobilized (organic, slow-release, other insoluble forms) could be more efficient for cranberry production. To test this hypothesis, two separate sets of field plots, one comparing 19 kg P/ha from sole P sources (all received 22 kg·ha–1 each N and K2O as ammonium sulfate and potassium sulfate) and the other comparing “complete” N–P–K fertilizers containing P, were established at six locations on three cranberry cultivars. Experiment #1 showed that, over all locations, there were no differences in mean yield for plots fertilized with triple super phosphate (current practice), foliar, or rock phosphate. However, fruit rot levels differed by treatment. In Experiment #2, organic forms (except bone meal) gave the lowest yields, while rock phosphate plots had the greatest yields. These field studies indicated that, while some organic P sources may not be suitable for cranberry production, low-leaching P forms such as bone meal and rock phosphate were as effective for cranberry production as the more-soluble triple super phosphate.

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Tremendous changes have occurred during the past century in the sources and methods for supplying nutrients for horticultural crops. Reliance on animal manure, cover crops, and animal tankage was insufficient to meet the crop nutrient demand for a rapidly expanding population. The Haber-Bosch process for ammonia synthesis (1910s) revolutionized the availability and affordability of nitrogen (N) fertilizer. Discovery of large-scale deposits of rock phosphate in South Carolina (1860s) and Florida (1880s) alleviated widespread nutrient deficiencies. Acidification of rock phosphate and bone material significantly improved phosphorus (P) availability for plants. Discovery of potassium (K)-bearing minerals in New Mexico (1920s) and later in Canada (1960s) now provide a long-term nutrient source. Modern fertilizer technology allows nutrients to be applied in the correct ratio and amount to meet crop needs. Advances in understanding plant nutrition, coupled with slow-release fertilizers, foliar fertilization, soluble nutrients, and the development of soil and tissue testing have all improved the yield and quality of horticultural crops. Future developments will likely focus on fertilization in an increasingly competitive global economy, while requiring sophisticated management to minimize environmental impacts.

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Until the development of modern chemical fertilizers began in about 1840, natural and organic materials supplied virtually all the plant nutrients to the soil. The use of chemical fertilizers increased gradually until about 1940. Since then the total consumption of chemical fertilizers in the United States has increased nearly fivefold to about 40,000,000 tons annually (28). The development and use of modern chemical fertilizers has decreased the relative importance of organic fertilizers. Today, organic materials account for less than 1% of the N fertilizers sold in this country (27). Phosphate rock materials account for about 20% of the present P fertilizer consumption in the United States, and over 85% of these materials are consumed in Illinois and Missouri (4). Natural potassic fertilizers, such as seaweed, greensand, and granite dust, apparently account for an insignificant fraction of the K fertilizer materials sold in this country, since muriate of potash alone accounts for nearly 90% of the commercial K fertilizers consumed here (4).

Open Access
Authors: and

Abstract

Vesicular–arbuscular mycorrhizal (VAM) development of Glomus intraradices Schenck & Smith and growth response of container-grown rough lemon (Citrus jambhiri Lush.) were compared in a phosphorus-deficient (2 μg P/g) sand-soil and peat-perlite, soilless mix, both fertilized with 3 levels of superphosphate (SP) and rock phosphate (RP). Mycorrhizal development and growth response were affected primarily by initial P availability in the media. In both soil and peat-perlite, VAM formation was greatest at 8 μg available P/g medium and maximum growth responses occurred over a range of 4 to 8 μg P/g medium. Available P from SP greater than 20 μg P/g medium inhibited mycorrhizal colonization and eliminated growth response. Less VAM development in peat-based media compared to soil suggested an effect of organic matter. In peat-perlite, moderate levels of colonization and a growth response equal to that of nonmycorrhizal plants grown in soilless media with high levels of available P were attained if RP was used to provide a low but sustained level of available P. In soilless media, mycorrhizae prevented P-induced, copper-deficiency symptoms in rough lemon.

Open Access

Abstract

The establishment and performance of vesicular–arbuscular mycorrhizae (VAM) formed by Glomus fasciculatum (Thaxter) Gerd. & Trappe were studied on geranium (Pelargonium × hortorum L.H. Bailey) and subterranean clover (Trifolium subterraneum L.) in various growth media at 2 P fertility levels. Colonization by G. fasciculatum was not extensive and shoot dry weight and P uptake consequently were not increased by VAM in soilless media such as peat, bark, perlite, and vermiculite. In media containing soil and fertilized at the low P level, roots were colonized extensively by G. fasciculatum, and host shoot growth and P concentrations were increased by VAM. Host growth enhancement by VAM was not observed at the higher P fertility level. Differences in colonization and mycorrhizal response in different fertilized growth media were correlated negatively with the logarithm of the equilibrium solution P concentration. Colonization, growth response, and P uptake by geranium inoculated with G. mosseae (Nic. & Gerd.) Gerd. & Trappe or Acaulospora spinosa Walker & Trappe were affected by growth medium and P fertilizer in the same way as plants inoculated with G. fasciculatum. Peat mosses from different sources varied considerably in their effects on mycorrhiza formation by G. fasciculatum, and on growth response of geranium when the peat was diluted with different amounts of soil. These differences appeared to be related to the equilibrium solution P concentration of the fertilized peats, and not to extractable P of the unfertilized peats. Use of rock phosphate or bonemeal instead of NaH2PO4 as a source of P did not improve the establishment of VAM and host growth response in soil, peat, or vermiculite. Addition of 5–10% Turface, bentonite, silt loam soil, or clay subsoil to peat or vermiculite resulted in increased colonization of host roots and significant mycorrhizal growth response, whereas amendment with liquid sludge inhibited formation of mycorrhizae.

Open Access
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Cadmium (Cd) concentrations in some phosphorus (P) fertilizers may be high enough to cause significant Cd accumulation in plants. A 2-year field experiment was conducted on a Sultan silt loam (Aquandic Xerochrept) to determine how the availability to cucumber (Cucumis sativus L.) of Cd from a triple superphosphate (TSP) and a western phosphate rock (PR) was affected by rate of Cd input and liming. A water-soluble Cd salt, CdCl2, was included for comparison. Cucumber vine growth increased with increasing TSP application rates but was unaffected by the application of PR or CdCl2. Cucumber fruit yield, however, was unaffected by the application of either P fertilizer or CdCl2. Concentrations of Cd in cucumber vine or fruit responded to increased Cd inputs from PR, TSP, or CdCl2, and the vine was the primary sink for Cd that accumulated in the plant. Both vine and fruit Cd correlated better with soil total Cd than with labile Cd extractable by 0.05 m CaCl2 or DTPA (diethylenetriaminepentaacetic acid). A unique characteristic of cucumber vine- or fruit-Cd is that it was unaffected (P > 0.05) by lime rate and Cd source and not closely related to labile or exchangeable Cd as measured by 0.05 m CaCl2, in contrast to previous findings for other vegetable or grain crops. Root exudates could have controlled the solubility of Cd in the soil. The low availability of Cd from these sources to the plant was evidenced by the low uptake coefficient of Cd (0.461 to 1.059) from the soil to the cucumber fruit and low Cd recovery (0.43%) in both vine and fruit of Cd added.

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