Florida Sandy Research Articles

Surface runoff phosphorus (P) loss in relation to phosphatase activity and soil P fractions in Florida sandy soils under citrus production

Phosphorus losses by surface runoff from agricultural lands have been of public concern due to increasing P contamination to surface waters. Five representative commercial citrus groves (C1–C5) located in South Florida were studied to evaluate the relationships between P fractions in soils, surface runoff P, and soil phosphatase activity. A modified Hedley P sequential fractionation procedure was employed to fractionate soil P. Soil P consisted of mainly organically- and Ca/Mg-bound P fractions. The organically-bound P (biological P, sum of organic P in the water, NaHCO 3 and NaOH extracts) was dominant in the acidic sandy soils from the C2 and C3 sites (18% and 24% of total soil P), whereas the Ca/Mg-bound P (HCl-extractable P) accounted for 45–60% of soil total P in the neutral and alkaline soils (C1, C4 and C5 soils). Plant-available P (sum of water and NaHCO 3 extractable P fractions) ranged from 27 to 61 mg P kg −1 and decreased in the order of C3>C4>C1>C2>C5. The mean total P concentrations (TP) in surface runoff water samples ranged from 0.51 to 2.64 mg L −1. Total P, total dissolved P (TDP), and PO 4 3−-P in surface runoff were significantly correlated with soil biological P and plant-available P forms ( p<0.01), suggesting that surface runoff P was directly derived from soil available P pools, including H 2O– and NaHCO 3– extractable inorganic P, water-soluble organic P, and NaHCO 3- and NaOH-extractable organic P fractions, which are readily mineralized by soil microorganisms and/or enzyme mediated processes. Soil neutral (55–190 mg phenol kg −1 3 h −1) and natural (measured at soil pH) phosphatase activities (77–295 mg phenol kg −1 3 h −1) were related to TP, TDP, and PO 4 3−-P in surface runoff, and plant-available P and biological P forms in soils. These results indicate that there is a potential relationship between soil P availability and phosphatase activities, relating to P loss by surface runoff. Therefore, the neutral and natural phosphatase activities, especially the natural phosphatase activity, may serve as an index of surface runoff P loss potential and soil P availability.

An Environmental Threshold for Degree of Phosphorus Saturation in Sandy Soils

There is critical need for a practical indicator to assess the potential for phosphorus (P) movement from a given site to surface waters, either via surface runoff or subsurface drainage. The degree of phosphorus saturation (DPS), which relates a measure of P already adsorbed by a soil to its P adsorption capacity, could be a good indicator of that soil's P release capability. Our primary objective was to find a suitable analytical protocol for determining DPS and to examine the possibility of defining a threshold DPS value for Florida's sandy soils. Four farmer-owned dairy sprayfields were selected within the Suwannee River basin and soil profiles were randomly obtained from each site, as well as from adjacent unimpacted sites. The soil samples were divided either by horizon or depth, and DPS was determined for each soil sample using ammonium-oxalate (DPSOx), Mehlich-1 (DPSM1), and Mehlich-3 (DPSM3) extracts. All methods of DPS calculations were linearly related to one another (r2 > 0.94). Relationships between water-soluble P and DPS indicate that the respective change points are: DPSOx = 20%, DPSM1 = 20%, and DPSM3 = 16%. These relationships include samples from Ap, E, and Bt horizons, and various combinations thereof, suggesting that DPS values can be used as predictors of P loss from a soil irrespective of the depth of the soil within a profile. Taking into consideration the change points, confidence intervals, agronomic soil test values, and DPS values from other studies, we suggest replacing Mehlich-1 P values in the Florida P Index with the three DPS categories (DPSM1 = <30, 30–60, and >60%) to assign different P loss ratings in the P Index.

An environmental threshold for degree of phosphorus saturation in sandy soils.

There is critical need for a practical indicator to assess the potential for phosphorus (P) movement from a given site to surface waters, either via surface runoff or subsurface drainage. The degree of phosphorus saturation (DPS), which relates a measure of P already adsorbed by a soil to its P adsorption capacity, could be a good indicator of that soil's P release capability. Our primary objective was to find a suitable analytical protocol for determining DPS and to examine the possibility of defining a threshold DPS value for Florida's sandy soils. Four farmer-owned dairy sprayfields were selected within the Suwannee River basin and soil profiles were randomly obtained from each site, as well as from adjacent unimpacted sites. The soil samples were divided either by horizon or depth, and DPS was determined for each soil sample using ammonium-oxalate (DPS(Ox)), Mehlich-1 (DPS(M1)), and Mehlich-3 (DPS(M3)) extracts. All methods of DPS calculations were linearly related to one another (r2 > 0.94). Relationships between water-soluble P and DPS indicate that the respective change points are: DPS(Ox) = 20%, DPS(M1) = 20%, and DPS(M3) = 16%. These relationships include samples from Ap, E, and Bt horizons, and various combinations thereof, suggesting that DPS values can be used as predictors of P loss from a soil irrespective of the depth of the soil within a profile. Taking into consideration the change points, confidence intervals, agronomic soil test values, and DPS values from other studies, we suggest replacing Mehlich-1 P values in the Florida P Index with the three DPS categories (DPS(M1) = <30, 30-60, and >60%) to assign different P loss ratings in the P Index.

Persistence, Distribution, and Emission of Telone C35 Injected into a Florida Sandy Soil as Affected by Moisture, Organic Matter, and Plastic Film Cover

Abstract With the phase-out of methyl bromide scheduled for 2005, alternative fumigants are being sought. This study of Telone C35, a mixture of (Z)- and (E)-1,3-dichloropropene (1,3-D) with chloropicirin (CP), focuses on its emissions, distribution, and persistence in Florida sandy soil in microplots with different soil–water and organic matter carbon (C) content with and without two different plastic film mulches. The addition of CP did not affect the physical behavior of the isomers of 1,3-D. Slower subsurface dispersion and longer residence time of the mixed fumigant occurred at higher water content. An increase in the percent organic carbon in the soil led to a more rapid decrease for chloropicirin than for 1,3-dichloropene isomers. The use of a virtually impermeable film (VIF) for soil cover provided a more even distribution and longer persistence under all the conditions studied in comparison to polyethylene (PE) film cover or no cover. The conditions of near field capacity water content, low organic matter, and a virtually impermeable film cover yielded optimum conditions for the distribution, emission control, and persistence of Telone C35 in a Florida sandy soil.

Persistence, Distribution, and Emission of Telone C35 Injected into a Florida Sandy Soil as Affected by Moisture, Organic Matter, and Plastic Film Cover

With the phase-out of methyl bromide scheduled for 2005, alternative fumigants are being sought. This study of Telone C35, a mixture of (Z)- and (E)-1,3-dichloropropene (1,3-D) with chloropicirin (CP), focuses on its emissions, distribution, and persistence in Florida sandy soil in microplots with different soil–water and organic matter carbon (C) content with and without two different plastic film mulches. The addition of CP did not affect the physical behavior of the isomers of 1,3-D. Slower subsurface dispersion and longer residence time of the mixed fumigant occurred at higher water content. An increase in the percent organic carbon in the soil led to a more rapid decrease for chloropicirin than for 1,3-dichloropene isomers. The use of a virtually impermeable film (VIF) for soil cover provided a more even distribution and longer persistence under all the conditions studied in comparison to polyethylene (PE) film cover or no cover. The conditions of near field capacity water content, low organic matter, and a virtually impermeable film cover yielded optimum conditions for the distribution, emission control, and persistence of Telone C35 in a Florida sandy soil.

Atmospheric Volatilization and Distribution of (Z)- and (E)-1,3-Dichloropropene in Field Beds with and without Plastic Covers

The fumigant 1,3-dichloropropene (1,3-D) is considered to be a potential replacement for methyl bromide when methyl bromide is phased out in 2005. This study on surface emissions and subsurface diffusion of 1,3-D in a Florida sandy soil was conducted in field beds with or without plastic covers. After injection of the commercial fumigant Telone II by conventional chisels to field beds at 30 cm depth which were covered with polyethylene film (PE), virtually impermeable film, or no cover (bare), (Z)- and (E)-1,3-D rapidly diffused upward. Twenty hours after injection, majority of (Z)- and (E)-1,3-D had moved upward from 30 cm depth to the layer of 5–20 cm depth. Downward movement of the two isomers in the beds with or without a plastic cover was not significant. (Z)-1,3-D diffused more rapidly than (E)-1,3-D. Virtually impermeable films (VIF) had a good capacity to retain (Z)- and (E)-1,3-D in soil pore air space. Vapor concentrations of the two isomers in the shallow subsurface of the field bed covered with VIF were greater than that in the two beds covered with polyethylene film (PE) or no cover (bare). In addition, VIF cover provided more uniform distribution of (Z)- and (E)-1,3-D in shallow subsurface than PE cover or no cover. Virtually impermeable film also had a better capability to retard surface emissions of the two isomers from soil in field beds than PE cover or no cover.

Diffusion and emissions of 1,3-dichloro propene in Florida sandy soil in microplots affected by soil moisture, organic matter, and plastic film.

The main objective of this study was to determine the influence of soil moisture, organic matter amendment and plastic cover (a virtually impermeable film, VIF) on diffusion and emissions of (Z)- and (E)-1,3-dichloropropene (1,3-D) in microplots of Florida sandy soil (Arredondo fine sand). Upward diffusion of the two isomers in the Arredondo soil without a plastic cover was greatly influenced by soil-water content and (Z)-1,3-D diffused faster than (E)-1,3-D. In less than 5 h after 1,3-D injection to 30 cm depth, (Z)- and (E)-1,3-D in air dry soil had diffused to a 10 cm depth, whereas diffusion for the two isomers was negligible in near-water-saturated soil, even 101 h after injection. The diffusion rate of (Z)- and (E)-1,3-D in near-field-capacity soil was between the rates in the two water regimes. Yard waste compost (YWC) amendment greatly reduced diffusion of (Z)- and (E)-1,3-D, even in air-dry soil. Although upward diffusion of (Z)- and (E)-1,3-D in soil with VIF cover was slightly less than in the corresponding bare soil; the cover promoted retention of vapors of the two isomers in soil pore air in the shallow subsurface. More (Z)-1,3-D vapor was found initially in soil pore air than (E)-1,3-D although the difference declined thereafter. As a result of rapid upward movement in air-dry bare soil, (Z)- and (E)-1,3-D were rapidly volatilized into the atmosphere, but emissions from the near-water-saturated soil were minimal. Virtually impermeable film and YWC amendment retarded emissions. This study indicated that adequate soil water in this sandy soil is needed to prevent rapid emissions, but excess soil water slows diffusion of (Z)- and (E)-1,3-D. Thus, management for optimum water in soil is critical for pesticidal efficacy and the environment.

Phosphorus and Heavy Metal Attachment and Release in Sandy Soil Aggregate Fractions

The presence of P and heavy metals in different forms or in association with different size fractions influences availability and discharge of these elements from watersheds. Understanding the association of P and heavy metals with size fractions can improve evaluation of leaching potential of P and heavy metals from soils. In this study, five aggregate-size fractions, ranged from 1.00 to 0.50 to <0.053 mm, were separated from seven Florida sandy soils by dry sieving. Each aggregate fraction was characterized by phosphate sorption, sequential fractionation of P, total, water- and Mehlich III-extractable concentrations of P and heavy metals. Size differences in sand, silt, and clay aggregates influence the amount and strength of element binding. Elemental attachment (particularly heavy metals) increased with decreasing aggregate sizes. Phosphorus and heavy metals in the sandy soils are readily transported to surface waters with suspended fine particles. Higher percentages of water-extractable, Mehlich III-extractable P, and heavy metals were found in both the 0.50- to 0.25- and 0.25- to 0.125-mm aggregate fractions, suggesting that P and heavy metals in these two fractions had higher release potential. The sequential fractionation of P suggested that the 1.00- to 0.50-mm fraction contained a larger percentage of Ca-bound P, whereas the 0.50- to 0.25-, 0.25- to 0.125-, and 0.125- to 0.053-mm fractions had higher ratios of labile P (H2O-P and NaHCO3–P). Phosphorus release from smaller aggregate fractions is faster with a higher P1/P168 ratio than from larger aggregate fractions because of larger amounts of water soluble P attached in the smaller aggregate fractions.

Surface runoff losses of copper and zinc in sandy soils.

Increased anthropogenic inputs of Cu and Zn in soils have caused considerable concern relative to their effect on water contamination. Copper and Zn contents in surface soil directly influence the movement of Cu and Zn. However, minimal information is available on runoff losses of Cu and Zn in agricultural soils, and soil-extractable Cu and Zn in relation to runoff water quality. Field experiments were conducted in 2001 to study dissolved Cu and Zn losses in runoff in Florida sandy soils under commercial citrus and vegetable production and the relationship between soil-extractable Cu and Zn forms and dissolved Cu and Zn concentrations in runoff water. Five extraction methods were compared for extracting soil available Cu and Zn. Concentrations of dissolved Cu and Zn in runoff were measured and runoff discharge was monitored. Mean dissolved Cu in field runoff water was significantly correlated with the extractable Cu obtained only by 0.01 mol L(-1) CaCl2, Mehlich 1, or DTPA-TEA methods. Dissolved Zn in runoff water was only significantly correlated with extractable Zn by 0.01 mol L(-1) CaCl2. The highest correlations to dissolved Cu in runoff were obtained when soil-available Cu was extracted by 0.01 mol L(-1) CaCl2. The results indicate that 0.01 mol L(-1) CaCl2-extractable Cu and Zn are the best soil indexes for predicting readily released Cu and Zn in the sandy soils. Both runoff discharge and 0.01 mol L(-1) CaCl2-extractable Cu and Zn levels had significant influences on Cu and Zn loads in surface runoff.

Surface Runoff Losses of Copper and Zinc in Sandy Soils

Increased anthropogenic inputs of Cu and Zn in soils have caused considerable concern relative to their effect on water contamination. Copper and Zn contents in surface soil directly influence the movement of Cu and Zn. However, minimal information is available on runoff losses of Cu and Zn in agricultural soils, and soil-extractable Cu and Zn in relation to runoff water quality. Field experiments were conducted in 2001 to study dissolved Cu and Zn losses in runoff in Florida sandy soils under commercial citrus and vegetable production and the relationship between soil-extractable Cu and Zn forms and dissolved Cu and Zn concentrations in runoff water. Five extraction methods were compared for extracting soil available Cu and Zn. Concentrations of dissolved Cu and Zn in runoff were measured and runoff discharge was monitored. Mean dissolved Cu in field runoff water was significantly correlated with the extractable Cu obtained only by 0.01 mol L−1 CaCl2, Mehlich 1, or DTPA–TEA methods. Dissolved Zn in runoff water was only significantly correlated with extractable Zn by 0.01 mol L−1 CaCl2 The highest correlations to dissolved Cu in runoff were obtained when soil-available Cu was extracted by 0.01 mol L−1 CaCl2 The results indicate that 0.01 mol L−1 CaCl2–extractable Cu and Zn are the best soil indexes for predicting readily released Cu and Zn in the sandy soils. Both runoff discharge and 0.01 mol L−1 CaCl2–extractable Cu and Zn levels had significant influences on Cu and Zn loads in surface runoff.

USE OF MUCK SEDIMENTS TO IMMOBILIZE PHOSPHORUS IN FLORIDA SANDY SOILS 1

Phosphorus that accumulates in the surface of sandy soils is susceptible to leaching and surface runoff. Converting dissolved P to less soluble forms using materials containing Fe, Al, and Ca can reduce the amount of soil P released to runoff. The dredged muck of the St. Lucie Estuary has been proposed as a manufactured soil for application on local sandy soil. It is assumed that the application of the muck will enhance soil P retention. In this study, the effects of muck sediments on water-soluble P, Olsen-P, and P fractions of some Florida sandy soils were investigated. In the muck type and rate experiment, two soils (a high P soil and a low P soil) were incubated for 30 days with the mucks at 0, 5, 15, and 30%. Application of muck reduced water-soluble P and Olsen-P significantly in the high P soil, and also reduced water-soluble P and Olsen-P slightly but consistently in the low P soil. When a high rate of muck (30%) was applied, the high Fe and Al muck reduced water-soluble P by 69 to 89% and Olsen-P by 27 to 62%, whereas the low Fe and Al muck reduced water-soluble P by 23 to 61% and Olsen-P by 22 to 34%. At low rates (15%), water-soluble P was reduced by 35 to 79% for the high Fe and Al muck and 2 to 43% for the low Fe and Al muck, whereas Olsen-P was reduced by 24 to 44% for the high Fe and Al muck and 12 to 31% for the low Fe and Al muck. The decreased P solubility resulted from the conversion of readily soluble P (H2O-P and NaHCO3-P) to less soluble pools (HCl-P and residual P). Amending the high P soils with mucks has the potential to reduce P enrichment of runoff by decreasing the solubility of soil P. These data indicate that application of muck can result in significant reductions in nonpoint-source P runoff from high P soils.

RELEASE POTENTIAL OF PHOSPHORUS IN FLORIDA SANDY SOILS IN RELATION TO PHOSPHORUS FRACTIONS AND ADSORPTION CAPACITY

ABSTRACT Information on P release potential in relation to labile P and P fractions in sandy soils is limited. In this study, P release potential was determined by leaching, and labile P, soil P fractionation, and P adsorption capacity were measured in the laboratory using 96 Florida sandy soil samples to evaluate the relationship between P release in water and soil P status. The sandy soils had a very low P adsorption capacity. The adsorption maximum, as calculated from the Langmuir equation, averaged 40.4 mg P kg−1. More than 10% of the soil P was water soluble, indicating a high risk of P leaching from soil to water. Successive leaching using deionized water released, on average, 7.7% of total P (144.5 mg kg−1) in different soils, whereas labile P recovered by successive water extraction accounted for 39.2% of the total P. Variation in P release potential among the different soils could be explained more by the difference in amounts of extractable P than the adsorption capacity. Total amounts of P released by successive leaching were significantly correlated with all labile P indices measured by different methods and all soil P fractions except for residual P. The correlation coefficients (r) were 0.97** for water-soluble P, 0.96** for 0.01 M CaCl2-P, 0.94** for Olsen P, 0.86** for Mehlich 1-P, 0.77*** for Mehlich 3-P, and 0.64*** for Bray 1-P. There were no obvious turning points in the relationships between Olsen-P, water-soluble P, or CaCl2-P and the amounts of P released from the sandy soils. The release of P from the sandy soils appeared to be controlled by a precipitation–dissolution reaction rather than a P sorption–desorption process. Furthermore, the sequential extraction of soils using deionized water indicated that P released was not limited to the labile P (H2O-P, NaHCO3-IP) and potentially labile P (NaOH-P) pools, but also from the HCl-P, indicating that all of P fractions except for residual P in the sandy soils can contribute to P release.

Determination of Field Capacity in a Florida Sandy Soil and Drainage Time at Different Depths

The development of improved equipment for measuring soil water content has created the need for a better understanding of soil water drainage and movement. Without this understanding, it is impossible to know if an observed decrease in soil water content at a particular depth is due to evapotranspiration and/or continual drainage. This study was designed to determine the length of time for different soil depths of a Florida Candler fine sand to reach field capacity. A field site with no vegetation on it was saturated with water and covered with a plastic tarp to prevent evaporation. At 6- to 24-hour intervals, soil water content was measured gravimetrically in the top 15 cm (6 inches) and with the neutron probe from 30 to 150 cm (12 to 59 inches). The 15-cm depth reached field capacity after one day, but it took 4 days for the 30- to 150-cm depths to reach field capacity because of rewetting by water draining form higher horizons. The time required for drainage to stop must be considered when evaluating changes in soil water status at a particular depth. This is important for distinguishing between plant water uptake and drainage for different soil layers.Soil water characteristic curves of undisturbed soil samples, bulkdensity, porosity, and field capacity in situ were also determined for this soil. Field capacity values found in situ were compared to those found using the pressure plate technique. Laboratory values were higher than field values because the laboratory data were closer to hydrostatic conditions than the field data and the degree of saturation provided during wetting of the cores was higher in the laboratory. Water was not readily retained in Candler fine sand because the soil was very porous, infiltration rates were high, drainage was rapid, and water storage capacity was limited. Using field measurements, field capacity values of soil at different depths ranged from 4.8% to 6.2% volume for Candler fine sand. These are considered to be low values when compared to other types of soil.

Using Composted Wastes on Florida Vegetable Crops

Large volumes of compost produced from waste materials like yard trimmings, household trash (municipal solid waste), or biosolids (wastewater sludge) will likely become available for use by the Florida vegetable industry in the future. Using compost to produce vegetables has the potential to increase water and fertilizer conservation and reduce leaching from inorganic fertilizers in Florida's sandy soils. Compost quality for vegetable production systems should be based on soluble salts, phytotoxic compounds, C:N ratio, plant nutrients, trace metals, weed seeds, odor, moisture, pH, water-holding capacity, bulk density, cation exchange capacity, and particle size. In Florida, immature compost contained phytotoxic compounds that were harmful to crop germination and growth. Amending soil with mature composted waste materials has been reported to increase the growth and yields of vegetable crops grown in Florida. However, a beneficial response does not always occur, and the magnitude of the response is often not predictable.

The Zooplankton Community in an Acidic Central Florida Lake

ABSTRACT Since Florida's sandy soils have low buffering capacities, many of Florida's lakes are susceptible to acid rain effects. The objective of this study was to provide a portrait of the zooplankton community within Lake Ruby, an acidic, central Florida lake. Water chemistry and zooplankton were monitored during January—December, 1989. Mean pH ranged from 3.72 to 5.08 (annual mean—4.35). Low nutrient concentrations (phosphorous, nitrogen, carbon) and high water clarity were characteristically oligotrophic. The zooplankton community contained an average of three species of rotifers, three species of cladocerans and four species of copepods. Annual mean zooplankton abundance was 60 individuals/L. Species diversity of the zooplankton community was low; its annual mean was 1.81; monthly mean values ranged from 1.08 (February, 1989) to 2.24 (November, 1989).

Arthropod Footprints in the Sands of Time

Arthropod distribution in Florida's sandy uplands shows some obvious patterns. Arthropods endemic to Florida scrub are concentrated on the Lake Wales Ridge, apparently a long-term refuge. Scrub areas to the north apparently lost diversity, as some species that must have migrated through there from southwestern North America are now only in southern scrubs. The more recently formed Coastal Ridge was apparently colonized by the remnant fauna of north Florida, not by Lake Wales Ridge species. North Florida scrubs have few known endemics, but there are probably many endemics in sandhill habitats. Expansion and contraction of sandhill areas may explain some faunal patterns. Rapid destruction of Florida's upland habitats demands prompt research.

Fibrous Root Distribution of ‘Pineapple’ Orange Trees on Rough Lemon Rootstock at Three Tree Spacings1

Abstract Fibrous root densities were determined for 16-year-old ‘Pineapple’ orange [Citrus sinensis (L.) Osb.] trees on rough lemon (C. jambhiri Lush.) rootstock spaced 3.0 × 4.6 m, 4.6 × 6.1 m, and 6.1 × 7.6 m and growing in a deep, central Florida sandy soil. Samples were taken from 1.9 m deep borings at 2 dripline locations and midway between trees in the row and between adjacent rows. The fibrous root systems penetrated to 1.9 m and were well-distributed. Samples from the widest spaced trees generally had lower root densities while the densities of samples from the other spacings were greater and suggested the overlapping of adjacent root systems. Root density was greatest in the surface sample for all spacings and generally decreased with depth. The extensive development and density of the fibrous root systems suggested that root competition was not likely to be a primary limiting factor in higher density plantings grown under comparable conditions.

Plant and Row Spacing, Mulch, and Fertilizer Rate Effects on Watermelon Production1

Abstract The effects of plant and row spacing, mulch, and fertilizer rate on ‘Charleston Gray’ watermelons [Citrullus lanatus (Thunb.) Matsum. &amp; Nakai] were evaluated in field studies on 2 Florida sandy soils. Marketable fruit yields decreased while yield/plant and mean fruit weight increased with an increase in plant spacing from 0.6 to 2.4 m and row spacing from 1.5 to 4.5 m. On a Kanapaha sandy soil with adequate water, yields and mean fruit weights were higher with mulch than without and with 1680 than 840 kg/ha of 12-7-13 (N-P-K) fertilizer.