J. E. Rechcigl

Phosphogypsum in agriculture: a review.

Publisher Summary Phosphogypsum is the term used for the gypsum by-product of wet-acid production of phosphoric acid from rock phosphate. It is essentially hydrated CaSO 4 , with small proportions of P, F, Si, Fe, Al, several minor elements, heavy metals, and radionuclides as impurities. Phosphogypsum appears to be good source of S and Ca for crops. Most of the studies showed that surface-applied gypsum or phosphogypsum ameliorated subsoil Al toxicity, acidity, and infertility in shorter time periods than did surface-applied lime materials. Phosphogypsum may prove to be superior to mined gypsum as an ameliorant for subsoil A1 toxicity, acidity, and infertility and as a conditioner for sodic soils, hardsetting clay soils, and subsoil hardpans because of its much higher rate of dissolution compared to that of mined gypsum. Gypsum and phosphogypsum, where they are readily accessible, are potential bulk carriers for micronutrients and low-analysis fertilizers. Increasing environmental demands to prevent contamination of ground water with nitrates and to minimize applied N and P losses in runoff, losses that promote rapid eutrophication of surface waters, may require the use of low-analysis fertilizers in commercial agriculture, at more frequent application, as they are now commonly used in recreational and residential lawns and gardens. Radionuclides, heavy metal impurities, and other pollutants at concentrations found in phosphogypsum do not appear to constitute environmental hazards to surficial ground water, soil, crop tissue, and the ambient atmosphere at rates normally used in agriculture.

Comparison of a microwave digestion system to other digestion methods for plant tissue analysis

Abstract Most digestion procedures for the preparation for plant tissue for elemental analysis are often very laborious. Elemental contents of plant tissue prepared by microwave digestion were compared to those obtained by conventional dry ashing and sulfuric acid‐hydrogen peroxide wet digestion. All three digestion methods produced comparable quantitative values for the elements P, K, Ca, Mg, Fe, Mn, Zn, and Cu for all plant materials used. Thus, the microwave digestion technique was shown to be a viable rapid method for digesting relatively small numbers of samples prior to elemental analysis.

Effect of acid rain on the soil environment: a review

Abstract This paper reviews the literature on acid rain, with emphasis on soils and leaching of soil elements. Several questions still exist concerning the effects of atmospheric acid deposition on soils: 1) does acid rain enhance mobilization of harmful heavy metals in soils which could leach into the groundwater; 2) does acid rain accelerate the kinetics of weathering of primary minerals and of secondary clay minerals in soils which would release large quantities of Al, Fe, and Si into the groundwater making it unfit for human consumption; and 3) do the beneficial effects of acid deposition outweigh the negative effects or vice versa? Literature pertaining to these questions is addressed in this review.

Initial calibration and correlation of inorganic-phosphorus soil test methods with a bahiagrass field trial

Abstract In recent field studies, bahiagrass (Paspalum notatum L.), a major forage crop in Florida, did not respond to added P fertilizer even though preplant Mehlich‐1 (M‐1) soil test indicated very low extractable P (<10 mg/kg). Selected extractants for soil P were statistically compared to improve the predicted need for P fertilization. A separate field study was used to provide yield and nutrient uptake data. The field experiment was arranged in a randomized complete block design with four replications on a Myakka fine sand (hyperthermic aeric Haplaquod). Plots were fertilized in March of 1989 and 1990 with 0,17, 34, 51, and 68 kgP/ha. Soil samples were taken from the Ap horizon (0 to 15 cm) in January, 1990. Extractants included iron hydroxide impregnated filter paper (Pi), anion exchange resin (trimethyl benzyl ammonium active group), M‐1, Mehlich‐3 (M‐3), and water. There was a high correlation between Pi and the resin procedures (r2 = 0.96). These methods gave higher extractable P values compared ...

Comparison of various soil drying techniques on extractable nutrients

Abstract Changes that take place in soil samples as they are dried and stored may pose serious problems in predicting plant responses compared to moist soils under field conditions. The effects of drying and storage techniques (air, microwave, oven‐drying, and frozen) on the levels of Mehlich‐I‐extractable nutrients were evaluated in six diverse soils. The use of microwave‐drying as a rapid soil drying method prior to chemical analysis was also evaluated. Drying and freezing caused large changes in the levels of extractable nutrients in all soils. The effects of drying were dependent on drying intensity and the initial physical and chemical properties of the soil. Many of the changes in the levels of extractable nutrients resulting from drying the soil appear to be associated with the oxidation of organic matter (OM) and changes in hydration state and redox status of different soil components. Results from this study also indicate that microwave drying of soils has potential for rapid drying of soil sampl...

Inorganic phosphorus and manure effects on bahiagrass production on a Spodosol

Bahiagrass (Paspalum notatum Flugge) pasture fertilization recommendations have traditionally been based upon clipping studies. Inclusion of P from manure, not originally considered when P recommendations were developed for pastures, may minimize the need for P fertilization without reducing bahiagrass production or P uptake. The objective of this research was to determine if manure contributes greatly to the P crop nutrient requirement. A 2-year field study utilized a factorial arrangement of 0 and 6.9 Mg air-dried manure ha-1 with 0, 17, 34, 51, and 68 kg inorganic P ha-1 from triple superphosphate to evaluate bahiagrass yield, root distribution, and P uptake response on a Myakka fine sand (sandy, siliceous, hyperthermic Aeric Alaquod). Because air-dried manure was used in the field study, a greenhouse study was employed to confirm that there were no differences in bahiagrass yield or P uptake from either air-dried or fresh cattle (Bos spp.) manure sources. There were no manure or manure by P interaction effects on yield or P uptake of bahiagrass indicating that manure source did not effect grass production in the greenhouse. In the field study, bahiagrass roots were distributed into the Bh horizon, and the Bh horizon had at least four times more Mehlich-1 extractable P than that of the Ap horizon. This horizon was most likely acting as a main source for P-uptake by the grass. This observation was further confirmed by no yield response to levels of inorganic P application in 1989. A linear-response-and-plateau (R2=0.196) relationship with a critical point of 15.4 kg P ha-1 was found in 1990. Bahiagrass yield and P uptake were not dependent on P fertilization, either from manure or inorganic P, due to the availability of P from the Bh horizon.

Fate of phosphorus on bahiagrass (Paspalum notatum) pastures

Abstract Phosphorus is considered to be the major factor causing eutrophication of Lake Okeechobee and other waterways in Florida. An important source of P for Lake Okeechobee is runoff of soluble P fertilizer applied to bahiagrass (Paspalum notatum Flugge) pastures. The present study was conducted to ascertain whether P application levels could be reduced below current agronomic recommendations without affecting pasture yields or quality and to determine the effects of P application on surface water quality. A field study was conducted on a bahiagrass pasture to assess the yield response of bahiagrass to five annual rates of P (0, 6, 12, 24 and 48 kg ha−1) and two application times (dry season and wet season). Fertilizer treatments were arranged in a randomized complete block design with four replications on an Immokalee fine sand (sandy, siliceous, hyperthermic Arenic Haplaquods). Results indicate that P fertilization rates could be reduced from 48 to 24 kg P ha−1 without affecting yields or quality of bahiagrass. Yields in 1989 averaged 11.4, 14.7 and 10.4 Mg ha−1 for the 48, 24 and 0 kg P ha−1 treatment, repectively. Time of P application had no effect on yields or quality of bahiagrass. There was a linear increase in Mehlich I extractable P in the A and E horizons and a quadratic increase to P in the Bh horizon in 1989. Extractable P ranged from 3.8 to 22.5, 1.3 to 2.5, and 21 to 55 mg P kg−1 for the A, E and Bh horizons, respectively. Phosphorus concentrations in surface water runoff was reduced from 33 to 60% as P application rates were decreased from 48 to 12 kg P ha−1 while total P loss was reduced from 17 to 78%, respectively. Recommended reductions in P application should result in substantial cost savings to producers and also reduce P inputs into surface water.

Effects of dolomite and gypsum on weeds

Abstract Liming is recognized by most growers in the United States as an essential part of crop production on acid soils. Greenhouse and field studies were conducted on a sandy, siliceous, hyperthermic Ultic Hapliquod (Pomona fine sand) soil to determine the effects of dolomitic limestone and gypsum on weed populations. Under greenhouse conditions, addition of dolomite increased weed populations in pots of soil. Optimum conditions for weed growth occurred at pH 5.3 to 5.5. At pH levels greater than 5.5, weed populations were stable or showed a general decrease in number. Under field conditions, dolomite and gypsum were applied prior to plantings of three different grass species (stargrass, bahiagrass, and annual ryegrass). Addition of dolomite reduced weed populations because of a more favorable soil pH for rapid grass growth. Competition from the grasses was greater at a pH level near 5.8 to 6.0, whereas greatest weed numbers occurred at a pH of 4.8 to 4.9. Results of these studies indicate that liming i...

Methods of measuring ambient atmospheric radon and radon surface flux associated with phosphogypsum treatment of a Florida spodosol soil

Abstract Phosphogypsum (PG) is a by‐product gypsum (CaSO4.2H2O) of the manufacture of phosphoric acid and is a major potential source of S and Ca for crops. The PG used in this study contained 25.6% Ca, 62.1% SO4‐S, and 18 pCi 226Ra g‐1 . Radon (222Rn) emanations from a bahiagrass (Paspalum notatum Flugge) pasture on a typical Florida Spodosol fertilized with PG up to 4.0 Mg ha−1 as a source of S were measured as atmospheric ambient radon (pCi L−1) using electret ion chambers (EIC) and as radon surface flux (pCi m2 s−1) using large‐area activated charcoal canisters (LAACC). Atmospheric ambient radon values before PG application measured twice, each over a 30‐d period from June 11 to August 24, 1990, and after PG application measured seven times, each over a 30‐ or 60‐d period from August 25, 1990 to July 16, 1991, averaged 0.17±0.07 and 0.19±0.09 pCi L−1, respectively. Post‐application measurements over treated and untreated plots (including external controls) were 0.20±0.08 and 0.18±0.09 pCi L−1, respect...

Evaluation of various nitrogen sources and rates on nitrogen movement, pensacola bahiagrass production, and water quality

Abstract Movement of N through the soil profile under various N sources and rates was investigated in order to provide information that can be used to protect groundwater quality in Florida. The objective of this greenhouse experiment was to determine the distribution and leaching potential of various rates (0, 84 and 168 kg N ha−1) and sources ((NH4)2SO4 and NH4NO3) of N applied to Pensacola bahiagrass (Paspalum notatum Flugge). Bahiagrass sod was planted in PVC soil columns which were packed using each horizon (Ap, A22, Bh) of a virgin Myakka fine sand soil (sandy, siliceous, hyperthermic Aeric Haplaquods). Water was added to the soil columns once every 4 d and the effluent was collected from each soil column twice a week for a period of 3 months. Water and soil samples from each horizon (collected at the end of the experiment) were analyzed for NO3‐N, NH4‐N, pH, and electrical conductivity. Yield and tissue N were determined on grass samples harvested every 30 d. There was no significant differences in...