The points of zero charge (PZC) of manganese oxide (MnO ₂), titanium dioxide (TiO ₂), aluminum (Al) laterite, ferruginous (Fe) laterite, aluminum oxide (Al ₂O ₃), and a commercial activated carbon ...sample (AC001) were determined using acid-base potentiometric (PT) and mass titration (MT). The MT technique has been used extensively for carbonaceous materials but less for soils. In addition, little work has been done on the PZC of these metal oxides and carbon materials under similar experimental conditions concurrently. Our aim is to buttress the ease of MT usage over PT in routine laboratory analysis. The experimental PZC measured by acid-base potentiometric and mass titrations respectively were 4.97 and 4.11 for MnO ₂; 5.38 and 5.74 for TiO ₂; 4.19 and 4.08 for Al laterite; and 4.45 and 4.10 for Fe laterite. For Al ₂O ₃ and activated carbon, mass titration gave 7.53 and 8.41 respectively. Calculated standard deviations between the means of PT and MT were less than 1, and Student’s t-test at 95% confidence interval (CI) gave a P value of 0.135, suggesting that there is no significant difference between PT and MT and buttressing the reliability of the experimental procedures. In routine laboratory work, mass titration should be preferred for PZC measurement of (hydr)oxides and soil materials because it saves time.
The cow-calf (Bos taurus) industry in subtropical United States and other parts of the world depends almost totally on grazed pastures. Establishment of complete, uniform stand of bahiagrass (BG) in ...a short time period is important economically. Failure to obtain a good BG stand early means increased encroachment of weeds and the loss of not only the initial investment costs, but production and its cash value. Forage production often requires significant inputs of lime, N fertilizer, and less frequently of P and K fertilizers. Domestic sewage sludge or biosolids, composted urban plant debris, waste lime, phosphogypsum, and dredged materials are examples of materials that can be used for fertilizing and liming pastures. Perennial grass can be a good choice for repeated applications of sewage sludge. Although sewage sludge supply some essential plant nutrients and provide soil property-enhancing organic matter, land-application programs still generate some concerns because of possible health and environmental risks involved. The objectives of this study were to evaluate the cumulative and residual effects of repeated applications of sewage sludge on (i) bahiagrass (BG, Paspalum notaturn Flügge) production over years with (1997-2000) and without (2001-2002) sewage sludge applications during a 5-yr period, and (ii) on nutrients status of soil that received annual application of sewage sludge from 1997 to 2000 compared with test values of soils in 2002 (with no sewage sludge application) in South Florida.
The field experiment was conducted at the University of Florida Agricultural Research and Education Center, Ona, FL (27 degrees 26'N, 82 degrees 55'W) on a Pomona fine sandy soil. With the exception of the control, BG plots received annual sewage sludge and chemical fertilizers applications to supply 90 or 180 kg total N ha(-1) yr(-1) from 1997 to 2000. Land application of sewage sludge and fertilizer ceased in 2001 season. In early April 1998, 1999, and 2000, plots were mowed to 5-cm stubble and treated with the respective N source amendments. The experimental design was three randomized complete blocks with nine N-source treatments: ammonium nitrate (AMN), slurry biosolids of pH 7 (SBS7), slurry biosolids of pH 11 (SBS11), lime-stabilized cake biosolids (CBS), each applied to supply 90 or 180 kg N ha(-1), and a nonfertilized control (Control). Application rates of sewage sludge were calculated based on the concentration of total solids in materials as determined by the American Public Health Association SM 2540G method and N in solids. The actual amount of sewage sludge applications was based on the amount required to supply 90 and 180 kg N ha(-1). Sewage sludge materials were weighed in buckets and uniformly applied to respective BG plots. Soil samples were collected in June 1997, June 1999, and in June 2002 from 27 treatment plots. In 1997 and 1999, soil samples were collected using a steel bucket type auger from the 0- to 20-, 20- to 40-, 40- to 60-, and 60- to 100-cm soil depths. Forage was harvested on 139, 203, 257, and 307 day of year (DOY) in 1998; 125, 202, 257, and 286 DOY in 1999; 179, 209, 270, and 301 DOY in 2000; and on 156 and 230 DOY in 2002 (no sewage sludge applications) to determine the residual effect of applied sewage sludge following repeated application. Forage yield and soils data were analyzed using analysis of variance (PROC ANOVA) procedures with year and treatment as the main plot and sub-plot, respectively. As a result of significant year effects on forage yield, data were reanalyzed annually (i.e., 1998, 1999, 2000, and 2002).
All sewage sludges used in this study were of class B in terms of USEPA's pathogens and pollutant concentration limit. Pathogen and chemical composition of the class B sewage sludge that were used in the study were all in compliance with the USEPA guidelines. The liquid sludge (SBS11) had the lowest fecal coliform counts (0.2 x 10(6) CFU kg(-1)) while the cake sewage sludge (CBS) had the greatest coliform counts of 178 x 10(6) CFU kg(-1). The fecal coliform counts for SBS7 was about 33 x 10(6) CFU kg(-1). Average soil test values in June 2002 exhibited: i) decrease in TIN (NO3-N + NH4-N), TP, K, Ca, Mg, Mn, and Fe; and ii) slight increase in Zn and Cu when compared with the June 1997 soil test results. The overall decrease in soil test values in 2002 might be associated with nutrient cycling and plant consumption. Although the average BG forage yield in 2002 (2.3 +/- 0.7 Mg ha(-1)) was slightly lower than in 2000 (3.5 +/- 1.2 Mg ha(-1)), yield differences in 2002 between the control (1.2 +/- 0.2 Mg ha(-1)) and treated plots (2.3 +/- 0.5 Mg ha(-1) to 3.3 +/- 0.6 Mg ha(-1)) were indicative of a positive residual effect of applied sewage sludge. This study has shown that excessive build up of plant nutrients may not occur in beef cattle pastures that repeatedly received sewage sludge while favoring long-term increased forage yield of BG. All sources of N (sewage sludge and AMN) gave better forage production than the unfertilized control during years with sewage sludge application (1997-2000) and also during years with no sewage sludge application (2001-2002). The favorable residual effects of applied sewage sludge in 2002 may have had received additional boost from the amount of rainfall in the area.
Repeated applications of sewage sludge indicate no harmful effects on soil quality and forage quality. Our results support our hypothesis that repeated land application of sewage sludge to supply 90 and 180 kg N ha(-1) would not increase soil sorption for nutrients and trace metals. Results have indicated that the concentrations of soil TIN and TP declined by almost 50% in plots with different nitrogen sources from June 1997 to June 2002 suggesting that enrichment of nitrogen and phosphorus is insignificant. The concentrations of soil nitrogen and phosphorus in 2002 following repeated application of sewage sludge were far below the contamination risk in the environment. The residual effect of these sewage sludge over the long term can be especially significant in many areas of Florida where only 50% of the 1 million ha of BG pastures are given inorganic nitrogen yearly.
Successive land application of sewage sludge for at least three years followed by no sewage sludge application for at least two years may well be a good practice economically because it will boost and/or maintain sustainable forage productivity and at the same time minimize probable accumulation of nutrients, especially trace metals. Consecutive applications of sewage sludge may result in build up of some trace metals in some other states with initial high metallic content, but in this study, no detrimental effects on soil chemical properties were detected. The possibilities for economically sound application strategies are encouraging, but more and additional research is required to find optimal timing and rates that minimizes negative impacts on soil quality in particular or the environment in general. For proper utilization of sewage sludge, knowledge of the sewage sludges' composition, the crop receiving it, are absolutely crucial, so that satisfactory types and rates are applied in an environmentally safe manner. There is still much to be learned from this study and this investigation needs to continue to determine whether the agricultural and ecological objectives are satisfied over the longer term.
A new speciation model developed and implemented in Polymath was found to be successful in predicting struvite precipitation in soils. Struvite (NH
4
MgPO
4
) has been identified as a mineral for the ...recovery of nitrogen (N) and phosphorus (P). Predicting struvite precipitation potential in soil is important for optimal quantification of nutrient species. Polymath and Visual Minteq models were used for prediction of several solid phases in the soil. One approach to immobilize P for solid-phase formation is by co-blending. Immobilization was achieved through the blending of an Al-based water treatment residual (Al-WTR) and with Ca–Mg-based materials slag and magnesium oxide (MgO). The results suggest that Polymath model revealed solid Phases of dicalcium phosphate pentahydrate (DCPP), magnesium hydroxide (MHO), magnesium orthophosphate (v) docosahydrate (MP22), magnesium orthophosphate (v) octahydrate (MP8), and struvite, which were lacking in the modeling from Visual Minteq. Residual leachate from the co-blended amendments; Soil+WTR+Slag, Soil+WTR+MgO, Soil+MgO, Soil+Slag, Soil+WTR, and the control (without amendment) had struvite of 353, 199, 119, 90, 37, and 12 mg l
-1
, respectively. This implies that struvite, a phosphate mineral can be precipitated in the soil and could be released as nutrients for plant uptake. Struvite precipitation in soil and for reuse may reduce cost and may be a safe practice for sustainable environmental nutrient management.
Approximately 70% of Florida's biosolids is land‐applied with little supporting agronomic information. This experiment was conducted on bahiagrass (Paspalum notatum Flugge), on Pomona fine sand soil ...(sandy, siliceous, hyperthermic Ultic Alaquods), to compare the agronomic value of aerobically digested slurry biosolid, lime‐stabilized slurry biosolid, lime‐stabilized cake biosolid, and ammonium nitrate all applied to supply 90 or 180 kg N ha−1 vs. an unfertilized control. Forage production (3–5 Mg ha−1 yr−1) was similar for the ammonium nitrate and the slurries in 1998 and 1999, highest for the lime‐stabilized slurry in 2000, but always 30% lower for the cake biosolid due to the cake's lower N availability. The slurries and ammonium nitrate gave 50% or more forage and higher spring crude protein (CP) concentration (100–170 g kg−1) than the control (75–110 g kg−1). The CP was improved with ammonium nitrate in early spring, after which, there were no consistent differences in CP or in vitro organic matter digestion (460–600 g kg−1) among N sources. Tissue P (2.0–3.5 g kg−1), Ca (3.0–8.0 g kg−1), and Fe (40–250 mg kg−1) were increased by both biosolid slurries in the spring, whereas tissue Cu (6–15 mg kg−1) and Mn (10–100 mg kg−1) were elevated periodically only by the aerobically digested slurry. Forage was deficient in K and Mn in summer across treatments. Lime‐stabilized biosolid could boost bahiagrass production in Florida because it is lower in pathogens, inexpensive, and provides lime and organic matter.
A remediation strategy called “co-blending” was developed for rapid phosphorus (P) immobilization. Immobilization was achieved through the combination of an Al-based water treatment residual (Al-WTR) ...with Ca-Mg-based materials (Slag and magnesium oxide) for use in incubation and leaching experiments. Al-WTR was co-blended with Slag and MgO as “Al-WTR+Slag” and “Al-WTR+MgO,” respectively. Sequential extraction was used to delineate P species into operationally defined fractions: soluble or exchangeable, Al-Fe, and Ca-Mg-bound pools. Results from soils used in the incubation experiment showed that Al-amended material tended to sequester P bound (∼26%) to the Al-Fe pool. On the other hand, Ca-Mg-based materials tended to sorb (∼70%) of P greatly associated to the Ca-Mg pool. Amendments were applied at 2% or 20 g kg⁻¹ as Al-WTR, MgO, and Slag and at 1%+1% or 10 g kg⁻¹+10 g kg⁻¹ as co-blended Al-WTR+MgO and Al-WTR+Slag, respectively, on mass basis. Results from leaching data suggest that treatment effects on pH are significant at (p < 0.0001) and also significant (p < 0.01) with weeks of leaching. A similar significant (p < 0.0001) trend was observed for effects of treatment on redox potential (Eh). However, treatment effects on weeks of leaching were not significant. Cumulative soluble P (mg) of leachate showed linear reduction (96%) from the control (without amendments) using a regression model. Potential co-blended material selected was Al-WTR+Slag (1%+1%) due to less P in leachates, moderate effect on pH, and fewer amounts of Al-WTR and Slag used compared with 2% Al-WTR and Slag, respectively. In addition, the RMSE of Al-WTR+Slag data fitted to a regression model was the least. Results suggested that the metal cations Al, Ca, and Mg tended to bind different forms of total P at any given pH. Through co-blending, less soluble P may be lost to the environment than using sorption materials independently.
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