Thomas A. Obreza

Efficacy of drinking-water treatment residual in controlling off-site phosphorus losses: a field study in Florida.

Land application of drinking-water treatment residuals (WTR) has been shown to control excess soil soluble P and can reduce off-site P losses to surface and ground water. To our knowledge, no field study has directly evaluated the impacts of land application of WTRs on ground water quality. We monitored the effects of three organic sources of P (poultry manure, Boca Raton biosolids, Pompano biosolids) or triple superphosphate co-applied with an aluminum-based WTR (Al-WTR) on soil and ground water P and Al concentrations under natural field conditions for 20 mo in a soil with limited P sorption capacity. The P sources were applied at two rates (based on P or nitrogen [N] requirement of bahiagrass) with or without Al-WTR amendment and replicated three times. Without WTR application, applied P sources increased surface soil soluble P concentrations regardless of the P source or application rate. Co-applying the P sources with Al-WTR prevented increases in surface soil soluble P concentrations and reduced P losses to shallow ground water. Total dissolved P and orthophosphate concentrations of shallow well ground water of the N-based treatments were greater (>0.9 and 0.3 mg L(-1), respectively) in the absence than in the presence ( approximately 0.6 and 0.2 mg L(-1), respectively) of Al-WTR. The P-based application rate did not increase ground water P concentrations relative to background concentrations. Notwithstanding, Al-WTR amendment decreased ground water P concentrations from soil receiving treatments with P-based application rates. Ground water total dissolved Al concentrations were unaffected by soil Al-WTR application. We conclude that, at least for the study period, Al-WTR can be safely used to reduce P leaching into ground water without increasing the Al concentration of ground water.

Effect of Age of Cocomposted MSW And Biosolids on Weed Seed Germination

The influence of municipal solid waste (MSW) and biosolids compost maturity on germination of several weed species seeds was evaluated. Ivyleaf morning glory (Ipomoea hederacea L.), barnyard grass (Echinochloa crus-galli L.), common purslane (Portulaca oleracea L.), and corn (Zea mays L.) were selected as plant indicators to determine the compost maturity stage with maximum germination inhibition. Extracts were prepared from immature (three day-old, four week-old, eight week-old), and mature (one year-old) composts. Extract from eight week-old compost decreased percentage germination, root growth, and germination index (a combination of germination percentage and root growth), and increased mean days to germination of each indicator specie. Extract from eight week-old compost was evaluated for effect on germination percentage of 14 economically important weed species. Extract from eight week-old compost inhibited germination of most weed species, except yellow nutsedge (Cyperus esculentus L.) for which tu...

Yard Trimming-Biosolids Compost: Possible Alternative to Sphagnum Peat Moss in Tomato Transplant Production

Large volumes of yard trimmings (YT) and biosolids (BS) co-compost have recently become available to the Florida vegetable industry. Compost used as vegetable transplant medium may be less expensive than traditional Sphagnum peat moss, since it can be locally produced. ‘Agriset 761’ tomato (Lycopersicon esculentum Mill.) seed were sown in five combinations of compost, peat, and vermiculite amended media: 0:70:30 (control), 18:52:30, 35:35:30, 52:18:30, and 70:0:30 % by weight, respectively. The experiment was repeated 3 times over a one-year period to accommodate the Florida transplant production season. YT-BS compost were sieved to a particle size less than 2.4 mm (33 % by weight) to be utilized as a transplant media.The YT-BS compost had a high initial EC that restricted plant growth in one of the three batches used. By mixing YT-BS compost with peat and vermiculite the EC was reduced to an optimal 0 to 2 dS·m−1 in the Fall 1997 and Spring 1998a experiments, but not for Spring 1998b.Transplant media wit...

Impact of Organic Amendments on Groundwater Nitrogen Concentrations for Sandy and Calcareous Soils

Experiments were conducted on calcareous and sandy soils to investigate the effects of organic amendments for vegetable production on groundwater nitrogen (N) concentration in south Florida. The treatments consisted of applying yard and food residuals compost, biosolids compost, a cocompost of the municipal solid waste and biosolids, and inorganic fertilizer. Nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N), and total N concentrations were collected for a period of two years for both soils. Statistical analysis results revealed that for the three species tested, there were no significant differences among treatments. NO3-N concentrations for all treatments remained less than the maximum contamination level (10 mg/L). NO3-N transport to groundwater was higher in calcareous soil (mean=5.3 mg/L) than in sandy soil (mean=0.6 mg/L). NH4-N concentrations ranged from 0 to 13.6 mg/L throughout the experiment. Calcareous soil had lower NH4-N concentrations (mean=0.1 mg/L) than sandy soils (mean=0.7 mg/L). Total N ranged from 0.4 to 21.7 mg/L for all treatments for both soils reflecting high adsorption of dissolved organic N in both soils. Overall, results indicated that all the compost treatments were comparable to inorganic fertilizer with regard to N leaching and N concentrations in the groundwater while producing similar or higher yields.

Relative Efficacy of a Drinking‐Water Treatment Residual and Alum in Reducing Phosphorus Release from Poultry Litter

Abstract Amending poultry litter with alum (aluminum sulfate) effectively reduces soluble phosphorus (P) concentrations, but the practice can be expensive. Aluminum (Al)‐based drinking‐water treatment residuals (WTRs) can be obtained free of charge and are enriched in Al hydr(oxides) that make them efficient P sorbents. Substituting Al‐WTRs for alum would be a cost‐effective practice to reduce soluble P in manures when compared with alum‐only use. The research studied the reductions in soluble P, Al, and total organic carbon (TOC) concentrations in suspensions prepared by mixing variable Al‐WTR and alum rates (0 to 25% by weight) with poultry litter. Suspensions were maintained at pH of 6.5 during the sorption step, and allowed to react up to 50 d, without shaking. On a per‐mole of oxalate‐extractable Al basis, the Al‐WTR was nearly as effective as alum in reducing P release. Increasing mixed alum/WTR mass loads resulted in greater soluble P reduction, simply due to increased molar Al/P ratios. Contact time did not significantly influence soluble P reduction. Two significant advantages of Al‐WTRs compared to alum indicated by this study are cost effectiveness and significantly less release of dissolved Al. Soluble Al and TOC concentrations were least for suspensions with the lowest soluble P levels, suggesting that P was removed from solution as an organo‐Al‐P amorphous phase. The amount of P desorbed from the mixtures decreased to <1% with increasing molar Al/P ratios ≥1. Results suggest that Al‐WTR application with or without alum can reduce soluble P in poultry litter; however, field validation of the amendment effectiveness is needed. This research was supported by the Florida Agricultural Experiment Station and a grant from a USEPA grant CP‐82963801, and approved for publication as Journal Series No. R‐10112.

Immature Compost Suppresses Weed Growth Under Greenhouse Conditions

The influence of immature municipal solid waste-biosolids composts on emergence and mean days to emergence (MDE) of several weed species was evaluated in a pot trial under greenhouse conditions. The experiment consisted of placing a 7.5 cm deep layer of three-day-old immature compost, a mature and stable compost, an artificial medium or control sand as a mulch on ivyleaf morning glory seeds. Immature three-day-old compost decreased percentage emergence, shoot and root dry weight, and increased MDE of ivyleaf morning glory. In an experiment with eight-week-old immature compost utilizing mulching depths of 2.5, 5, 7.5, 10 cm and the untreated control on seeds of three weed species, common purslane did not emerge under any of the immature compost treatments. The MDE of ivyleaf morning glory and barnyard grass increased linearly as immature compost depths increased. Next, eight economically important weed species were sown in pots with either mature or immature (eight-week-old) compost utilizing mulching depths of 2.5 and 10 cm, in addition to an untreated control. Control pots yielded higher percentages of emergence than compost treatments for all species evaluated. Common purslane, large crabgrass, pig-weed, Florida beggarweed, and dichondra did not emerge through a 10-cm deep layer of mature compost mulch, or 2.5 or 10 cm deep layer of immature mulch. Significant compost maturity/depth interactions were observed for percent emergence on common purslane, ground cherry, large crabgrass, Florida beggarweed, and ivyleaf morning glory. A thinner layer was required to suppress germination using immature eight-week-old compost as compared to mature and stable compost. Immature (three-day or eight-week-old) compost containing acetic acid concentrations of 2474 and 1776 mg.kg−1 respectively reduced percentage emergence of several economically important weed species. These studies suggest that immature composts can be used to control weeds under conditions where spatial separation is maintained between the crop and the compost and phytotoxic fermentation products do not affect the health of the mulched plants and where odors associated with such partially stabilized products do not pose problems.

Drinking‐Water Treatment Residual Effects on the Phosphorus Status of Field Soils Amended with Biosolids, Manure, and Fertilizer

Abstract Concerns about surface water pollution with phosphorus (P) from biosolids and manures are prompting land application guidelines that limit residual application rates to those based on crop‐P removals (typically, no more than 2 Mg ha−1). Such rates are so low that the beneficial recycling of residuals is seriously threatened. Greater application rates [i.e., nitrogen (N) based] require judicious selection of residuals (low soluble P contents) and/or soil amendments, such as drinking‐water treatment residuals (WTRs) to control soluble P concentration. Although in the short term, WTR is effective in reducing soluble P levels, field studies to evaluate the stability of WTR‐immobilized P are scarce. The initial objective of this study was to determine the effects of WTR on P losses to surface and groundwater from Florida sand amended with different P sources (biosolids, manure, and inorganic fertilizer) applied at P‐ and N‐based rates. However, this objective could not be pursued to its logical conclusion because of severe flooding of the field 17 months after amendment application. The flooding appears to have compromised the treatments (moved soil and associated amendments across plots), which forced early termination of the experiment. Measurements taken after the flooding, however, provided a unique opportunity to assess the usefulness of WTR in controlling P solubility following severe flooding of WTR‐amended plots. Soluble P values measured from WTR‐amended A horizon plots were significantly lower than the plots without WTR amendment throughout the study. Phosphorus‐specific measurements in the Bh horizon suggest that excessive P leaching apparently occurred in the plots without WTR amendment and the control plots, whereas very little or no P leaching occurred in the WTR‐amended plots. Thus, despite extensive hurricane‐induced flooding of the fields, the WTR was able immobilize P and prevent excessive P leaching. We conclude that WTR could reduce offsite P transport, which will lower P loads into nutrient‐sensitive surface water systems, and that WTR‐immobilized P is stable even under severe flooding conditions.

Heavy Metal Accumulation in a Sandy Soil and in Pepper Fruit Following Long-term Application Of Organic Amendments

Heavy metals are toxic and persistent pollutants that may be present in organic waste materials used as soil amendments. Following accumulation in amended soil, crop plants could assimilate these pollutants in sufficient concentrations to pose a threat to humans consumers. The Federal Clean Water Act and additional state regulations set minimum standards for heavy metals in organic amendments. Cumulative amounts of heavy metal pollutants that may be added to soils through amendments are regulated through national and state environmental protection agencies and the Federal Food and Drug Administration regulate maximum tolerances of heavy metal contaminants in food. The objective of the research was to study the effects of long-term organic amendment application on the accumulation of heavy metal pollutants in soil and subsequent contamination in pepper fruits. Organic amendments were applied yearly to replicate large plots during 1996 to 2000. Controls received no amendments. Different organic amendments were applied every year to simulate grower organic amendment availability throughout long-term application. Although higher levels of extractable Cd, Cu, Ni, Pb, and Zn were observed from amended soils during 1996 to 2000, all were within acceptable levels. Furthermore, no accumulation of Cd, Cu, Pb, and Ni was observed in pepper fruit. Therefore, long-term application of organic amendments made from waste materials with pollutant content below maximum acceptable levels under state and federal regulations should be suitable for vegetable production.

Mulching with composted MSW for biological control of weeds in vegetable crops

Compost maturity is one of several issues that the composting industry must face as it attempts to provide a high quality product to the agricultural community. In this paper, we examine the potential for using immature compost prepared from a mixture of municipal solid waste (MSW) and biosolids as a mulch for control of weeds in vegetable crop row-alleys. Two field experiments were conducted with 4 and 8-week-old composts in the fall of 1995 and the spring of 1996. The 4-week-old compost was applied to mulching depths of 3.8 (68 t dry weight .ha−1), 7.5 (135 t dry weight .ha−1), 11.3 (203 t dry weight .ha−1), and 15 cm (270 t dry weight .ha−1) in the fall, and at 2.0 (35 t dry weight .ha−1), 3.8, 7.5, and 11.3 cm depths in the spring. Other treatments were paraquat applied at 0.6 kg.ha−1 and an untreated control. All treatments were applied in row-alleys between raised, polyethylene-covered soil beds. The 8-week-old compost was applied to depths of 3.8, 7.5, 11.3, and 15 cm in fall and to depths of 2.0, 3.8, 7.5 and 11.3 cm in the spring. Untreated alleys served as controls. In the fall 1995 experiment under low weed pressures, the 4-week-old compost applied to 7.5 cm or greater depths completely inhibited weed germination and growth for 240 days after treatment. In the spring 1996 experiment, 4-week-old compost completely inhibited weed germination and growth for only 65 days if applied to a depth of 7.5 cm or deeper due to higher prevailing weed pressures, particularly due to yellow nutsedge (Cyperus esculentus L.). In the same spring experiment, a 50 % reduction in percentage weed cover was obtained for 240 days with a 11.25 cm deep layer of mulch compared to the control. In the fall 1995 experiment, 8-week-old compost applied at 7.5 cm or depths completely inhibited weed germination and growth for 240 days. In the spring 1996 experiment, 8-week-old compost applied as a 11.25 cm mulch reduced percent weed cover as compared to the control up to 240 days. In general, weed cover and weed dry weight decreased linearly as the depth of the mulch increased.Under these immature composts, inhibition of germination or subsequent weed growth may have been due to both the physical effects of the mulch and the concentrations of phytotoxic fatty acids during the first few days after mulches were applied. At the time of mulching with the 4-week old compost, acetic acid was present at a concentration of 1221 mg.kg−1 in the fall mulch, and at 4128 mg.kg−1 in the spring mulch. The same concentrations in the 8-week-old compost for the fall and spring mulches were 1118 mg.kg−1 and 3113 mg.kg−1, respectively. In conclusion, immature compost may provide an effective alternative weed control method for row-alleys in vegetable crop production systems. During these experiments, it was observed that man-made contaminants such as glass, hard and soft plastics in the composts were esthetically unacceptable and potentially posed hazards to field workers.

Production of Chinese cabbage in relation to nitrogen source, rate, and leaf nutrient concentration

Abstract Chinese cabbage (Brassica rapa L. Chinensis group) production is expanding in the U. S., and guidelines regarding its production under Western cultural practices are needed. The objectives of this study were to investigate the effects of N source and rate on Chinese cabbage yield, marketability, and wrapper leaf nutrient concentrations, and to estimate the critical wrapper leaf‐N concentration associated with maximum yield and marketability. Chinese cabbage was grown in five sequential plantings using raised‐bed, polyethylene mulch culture with subsurface irrigation on a sandy soil. Nitrogen fertilizer was applied at rates of 0, 67,112, and 157 kg/ha using the following sources: 1) ammonium nitrate. 2) calcium nitrate, 3) urea‐ammonium nitrate solution (Uram, 32% N), 4) urea, and 5) a urea‐calcium solution (18% N). Mature Chinese cabbage wrapper leaf concentrations of P, Ca, and Mg increased with increasing N rate, while leaf‐K concentration decreased. Leaf‐N concentration increased in response t...