Search

There are unique advantages and disadvantages to using the field, greenhouse, growth chamber, and media-less techniques for growing maize (Zea mays L.) for research purposes. Soil-buffered nutrients such as phosphorus (P) do not allow for precise control of solution concentrations in the field, while greenhouses, growth chambers, and hydroponics provide limiting conditions. The objectives of this study were to develop a practical technique for productively cultivating several maize plants from seed to physiological maturity (R6) in a grow room environment, with precise control of nutrient availability and timing, and evaluate its utility for the purpose of measuring plant responses to variations in nutrient concentrations. The construction and testing of a semi-automated grow room for conducting nutrient studies on 96 maize plants utilizing simulated or artificial conditions are described. Plant growth response to a range of solution phosphorus (P) concentrations was tested to evaluate the utility of the technique. Maize yield components were measured and compared to values for field-grown plants. Due to ideal conditions and successful simulation of light intensity, diurnal fluctuations in temperature and RH, and changing photoperiod, grain yield and tissue nutrient concentrations were comparable to field-grown maize, although with greater shoot biomass. Plants responded positively to increased P concentrations in fertigation. The technique can be used for large-scale plant nutrient studies that require precise control of bioavailability and timing as well as manipulation of light intensity and photoperiod duration.

The purpose of this special issue is to explore current challenges and develop a better understanding of the processes that control dissolved phosphorus (P) removal among P removal structures [...]

Phosphorus (P) removal structures are a new best management practice for filtering dissolved P in non‐point drainage from legacy P soils through use of P sorption materials (PSMs). Structures must be designed according to characteristics of the site (hydrology and constraints) and PSMs to be utilized, as well as user‐defined goals (P removal, lifetime, and flow rate), making it a cumbersome process. A freely available P Transport Reduction App (P‐TRAP) allows users to quickly produce a custom design or evaluate a hypothetical or existing structure. The software includes a library of P removal flow‐through curves for many different PSMs conducted under various conditions of inflow P concentration and retention time. Design output includes the necessary PSM mass and orientation, pipe requirement, and a table of annual P removal. The software enables conservationists and engineers to quickly compare cost and efficiency among possible designs. Phosphorus Transport Reduction App (P‐Trap) software is used to evaluate and design site‐specific P removal structures based on (a) user inputs regarding site and P sorption material (PSM) characteristics and (b) P removal performance goals.

Several structural, treatment, and management approaches exist to minimize phosphorus (P) transport from agricultural landscapes (e.g., cover cropping and conservation tillage). However, many of these practices are designed to minimize particulate P transport and are not as effective in controlling dissolved P (DP) losses. Phosphorus removal structures employ a P sorption material (PSM) to trap DP from flowing water. These structures have been successful in treating surface runoff by utilizing aluminum (Al)-treated steel slag, but subsurface tile drainage has never been tested with this material. The goal of this study was to evaluate the performance and economics of a ditch-style P removal structure using Al-treated steel slag for treating agricultural subsurface drainage discharge. The structure treated subsurface drainage water from a 4.5 ha agricultural field with elevated soil test P levels. Overall, the structure removed approximately 27% and 50% of all DP and total P (TP) entering the structure, respectively (i.e., 2.4 and 9.4 kg DP and TP removal). After an initial period of strong DP removal, the discrete DP removal became highly variable. Flow-through analysis of slag samples showed that the slag used to construct the structure was coarser and less sorptive compared to the slag samples collected prior to construction that were used to design and size the structure. Results of this study highlight the importance of correctly designing the P removal structures using representative PSMs.

The reduction of dissolved phosphorus (P) transport to water systems is of critical importance for water quality. Phosphorus sorption materials (PSMs) are media with high affinity for dissolved P, and therefore serve as the core components of P removal structures. These structures can intercept dissolved P in surface and subsurface flows, before discharge into water bodies. While the P removal ability of PSMs has been extensively studied, lesser is known about the capacity to regenerate and recover P from P-saturated PSMs. This article evaluates a methodology to recover the P removal ability of aluminum- and iron-rich P-saturated PSMs. A series of flow-through experiments were conducted, alternating between P sorption (0.5 and 50 mg L &minus, 1 P) and desorption with potassium hydroxide (KOH, 5 or 20 pore volumes [PV]), varying residence times (0.5 min and 10 min), and number of recirculations (0, 6 and 24). Across two cycles of sorption-desorption, Alcan, Biomax and PhosRedeem showed an average P recovery of 81%, 79%, and 7%, with standard deviation of 10%, 21% and 6%, respectively. The most effective regeneration treatment was characterized by the largest KOH volume (20 PV) and no recirculation, with up to 100% reported P recovery. Although KOH at 5 PV was less effective, the use of recirculation did increase P recovery. The lifetime of Al/Fe-dominated PSMs in P removal structures can be extended through feasible regeneration techniques demonstrated in this study, for both high and low P concentration scenarios.

Steel slag, a byproduct of the steel making process, has been adopted as a material to reduce non-point phosphorus (P) losses from agricultural land. Although substantial studies have been conducted on characterizing P removed by steel slag, few data are available on the removal of P under different conditions of P input, slag mass, and retention time (RT). The objective of this study was to investigate P removal efficiency as impacted by slag mass and RT at different physical locations through a horizontal steel slag column. Downstream slag segments were more efficient at removing P than upstream segments because they were exposed to more favorable conditions for calcium phosphate precipitation, specifically higher Ca2+ concentrations and pH. These results showed that P is removed in a moving front as Ca2+ and slag pH buffer capacity are consumed. In agreement with the calcium phosphate precipitation mechanism shown in previous studies, an increase in RT increased P removal, resulting in an estimated removal capacity of 61 mg kg&minus, 1 at a RT of 30 min. Results emphasized the importance of designing field scale structures with sufficient RT to accommodate the formation of calcium phosphate.

Made available in DSpace on 2018-11-26T17:42:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-02-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Growing ruzigrass (Urochloa ruziziensis) in crop rotation systems has been suggested as a strategy to increase soil phosphorus (P) cycling and P availability. However, despite increased P lability shown in routine soil analysis, decreased grain yields of crops grown after ruzigrass have been observed. The objective of this study was to evaluate soil P availability to maize (Zea mays) in low or high-P soil cropped to ruzigrass. Soil P lability was evaluated using Hedley fractionation and pearl resin extractions, and P desorption/adsorption was assessed by isothermal titration calorimetry (ITC). Phosphorus changes in soil-P fractions in the maize rhizosphere were studied in a greenhouse experiment. Growing ruzigrass resulted in higher resin-extractable P and soil organic matter (SOM) contents than fallow. However, in soil cropped with ruzigrass, maize P uptake and P desorption were lower, and P adsorption to soil was higher than soil under fallow. In general, organic P bound to Fe and Al was non-available. Phosphorus sorption as assessed with ITC was a better indicator of P bioavailability to maize than pearl resin and Hedley fractionation, and suggested that P was less bioavailable after ruzigrass due to increased SOM, which resulted in the formation of metal phytate and more effective organo-metal sites for ligand exchange. Greater P solubility and availability in fallowed soil appeared to be partly due to the dissolution of Ca-related P, greater P desorption, and less potential for P adsorption. Isothermal titration calorimetry is a useful semi-quantitative tool for understanding P sorption behavior. Sao Paulo State Univ, Coll Agr Sci, Dept Crop Sci, 1780 Jose Barbosa de Barros St, BR-18610307 Botucatu, SP, Brazil USDA, Natl Soil Eros Res Lab, 275 S Russell St, W Lafayette, IN 47907 USA Sao Paulo State Univ, Coll Agr Sci, Dept Crop Sci, 1780 Jose Barbosa de Barros St, BR-18610307 Botucatu, SP, Brazil FAPESP: 2012/18509-4

Steel slag has been proven to be an effective phosphorus (P) removal media, and a potential aid to mitigate point and nonpoint P pollution in freshwater systems. However, the behavior of steel slag as a P sorption material (PSM) is often oversimplified through the generalization of its chemical and physical properties, preventing proper design of P removal structures. In this work, we tested eighteen steel slag samples from different batches, production processes, and steel-making plants, for the purpose of relating slag origin and chemical and physical properties to P removal ability, under two different flow regimes. Slag samples were also coated with aluminum (Al) and tested for P removal. Characterization included elemental composition, particle density, buffer capacity, and P removal ability. There was great variability in the evaluated properties across slag sources and origin, compelling the individual characterization of steel slag samples, since their intrinsic characteristics were key variables in determining their potential P removal capacity. Specifically, electrical conductivity (EC), bulk density, particle density and magnesium (Mg) content could explain around 70% of the variability of P removal by uncoated steel slags. Increasing residence time (RT) always increased P removal for uncoated slags. Steel slags showed a high variability in their P removal ability, but such variability was considerably decreased by coating the slags with Al. Additionally, the Al-coating process significantly improved P removal performance under more rapid flows (lower RT).

The U.S. Environmental Protection Agency (USEPA) has restricted concentrated animal feeding operation (CAFO) release of waste products into U.S. waters. These waste products must be disposed of using best management practices. Most of the waste is spread on cropland, but some operations have found other creative uses for waste products. Use of a phosphorus (P) reduction system to remove P from wastewater results in magnesium ammonium phosphate (MAP), a slowly soluble fertilizer. Using a P reduction system will not eliminate the need for land application of manure and wastewater, but it reduces the nutrient load in the waste that is applied thereby making compliance with regulations easier. In the first year of this study, MAP was compared to a controlled release fertilizer (CRF) with a similar nutrient element ratio on plant growth, fruit yield, nitrogen (N), P, potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), and zinc (Zn) concentration in tomato (Solanum lycopersicum L. ‘Mountain Fresh Plus’) plant parts. Plant growth and fruit production were similar with the two fertilizers, but the number of tomato culls was greater with either fertilizer than on control plants. Foliar N, P, Ca, and Mg concentration did not differ regardless of fertilizer treatment. Plants fertilized with CRF had a greater leaf K concentration than those fertilized with MAP, but foliar K concentration did not differ between fertilized and nonfertilized plants. Iron and Mn concentration in above-ground vegetative plant parts (stems and leaves) did not differ regardless of fertilizer treatment, but Zn concentration increased linearly as CRF increased. In the second year, MAP, each of the essential elements contained in MAP separately, and a hand mixture of each of these elements was tested for their effect on tomato plant growth, fruit yield, and tissue N, P, K, Ca, Mg, Fe, Mn, and Zn concentration and content. Magnesium ammonium phosphate and the hand mixture of fertilizer resulted in greater above-ground biomass excluding fruit stem weight and fruit yield than any of the individual nutrient treatments. Calcium sulfate resulted in a greater number and weight of tomatoes harvested than MAP. Nitrogen concentration did not differ among the fertilizer treatments for roots, stems, or leaves, but N content was greater in red fruit with the hand mix of fertilizer than with no fertilizer or with ammonium sulfate or Mg oxide. In immature green fruit at termination of the study, N content was greater with no fertilizer or Ca sulfate than with MAP or triple superphosphate (TSP). Phosphorus, K, and Ca concentrations did not differ among fertilizer treatments for any tissue tested. Magnesium concentration in green tomatoes differed among fertilizer treatments such that Mg concentration of green tomatoes from plants fertilized with TSP was greater than Mg concentration of green tomatoes fertilized with ammonium sulfate or Mg oxide. Phosphorus and K content of green fruit differed among fertilizer treatments with P and K concentration highest in green fruit from plants fertilized with Ca sulfate and lowest in green fruit from plants fertilized with MAP or TSP. Iron and Mn concentrations did not differ among fertilizer treatments for any tissue tested. Zinc concentration in leaves was greater when plants were fertilized with MAP, TSP, Ca sulfate, or Mg oxide than with ammonium sulfate. Zinc concentration of green fruit was greater when fertilized with MAP than with the hand mix, Ca sulfate or Mg oxide. Iron content was highest in green fruit from plants fertilized with TSP and lowest in plants fertilized with ammonium sulfate or control plants. Manganese content of leaves from control plants was greater than that of plants receiving ammonium sulfate while red fruit from plants fertilized with the hand mix had a greater Mn content than red fruit from any other treatment. Foliar Zn content was greater in plants fertilized with Ca sulfate than in those fertilized with the hand mix, ammonium sulfate, or TSP. In contrast, Zn content of red fruit fertilized with the hand mix was greater than for red fruit in any other treatment. Green fruit from control plants and those receiving MAP had a greater Zn content than plants fertilized with the hand mix, TSP, or Mg oxide. Fertilizer application increased Fe, Mn, and Zn content of several plant tissues. None of the labels of fertilizers applied stated that they contained micronutrients; however, small amounts of contamination were possible. Differing micronutrient contents of various plant tissues among fertilizer treatments were probably associated with other elements affecting plant growth or nutrient uptake. The nutrient elements present in the various fertilizers were not always the nutrient elements affected in the plants likely due to another element that may have limited plant growth or nutrient uptake.

Occasionally, the classic understanding of the effect of pH on P uptake from soils is questioned through the claim that maximum P uptake occurs at a pH much lower than 6.5–7. The purpose of this paper was to thoroughly examine that claim and provide a critical review on soil processes that control how soil pH affects P solubility and availability. We discuss how individual P retention mechanisms are affected by pH in isolation and when combined in soils, and how both real and apparent exceptions to the classic view can occasionally occur due to dynamics between mechanisms, experimental techniques (equilibration time, method of soluble P extraction, and pH adjustment), and plant species that thrive under acidic conditions. While real exceptions to the rule of thumb of maximum P availability at near neutral pH can occur, we conclude that the classic textbook recommendation is generally sound.

Horizontal directional drilling (HDD) is a trenchless technology mainly used for the installation of gas, sewer lines, and fiber optic cables. Spent HDD fluid is a by-product of the boring process. However, little is known of its constituency, although the land application of spent HDD residuals would be an economical and less time-consuming method of disposal. Physicochemical analysis of spent HDD residuals from broad geographic regions was conducted to determine if the land application would be an environmentally safe option for disposal. Fifty-eight HDD samples were collected from 26 states throughout the United States. After separation of the liquid and solid portion, the materials were assessed for carbon (C), nitrogen (N), plant nutrients, soluble and total trace metals, total dissolved solids, sodium adsorption ratio (SAR), and potential &ldquo, leachable metals&rdquo, All trace metal concentrations in the digested solid portion were well below the limits for biosolids set by the EPA 40 Part 503 rule for land application. Metal concentrations did not exceed the limits of drinking water standards. Besides the total amount of solids, there was nothing chemically limiting HDD residuals from land application. However, if boring through soil with suspected contamination, testing the residual before the application is recommended.

Blind inlets are implemented to promote obstruction-free surface drainage of field depressions as an alternative to tile risers for the removal of sediment and particulate phosphorus (P) through an aggregate bed. However, conventional limestone used in blind inlets does not remove dissolved P, which is a stronger eutrophication agent than particulate P. Steel slag has been suggested as an alternative to limestone in blind inlets for removing dissolved P. The objectives of this study were to construct a blind inlet with steel slag and evaluate its ability to remove dissolved P, nitrogen (N), and herbicides. A blind inlet was constructed with steel slag in late 2015, data from only 2018 are reported due to inflow sampling issues. The blind inlet removed at least 45% of the dissolved P load and was still effective after three years. The dissolved P removal efficiency was greater with higher inflow P concentrations. More than 70% of glyphosate and its metabolite, and dicamba were removed. Total N was removed in the form of organic N and ammonium, although N cycling processes within the blind inlet appeared to produce nitrate. Higher dissolved atrazine and organic carbon loads were measured in outflow than inflow, likely due to the deposition of sediment-bound particulate forms not measured in inflow, which then solubilized with time. At a cost similar to local aggregate, steel slag in blind inlets represents a simple update for improving dissolved P removal.

Reducing dissolved phosphorus (P) losses from legacy P soils to surface waters is necessary for preventing algal blooms. Phosphorus removal structures containing steel slag have shown success in treating surface runoff for dissolved P, but little is known about treating subsurface (tile) drainage. A ditch-style and subsurface P removal structure were constructed using steel slag in a bottom-up flow design for treating tile drainage. Nearly 97% of P was delivered during precipitation-induced flow events (as opposed to baseflow) with inflow P concentrations increasing with flow rate. Structures handled flow rates approximately 12 L s&minus, 1, and the subsurface and ditch structures removed 19.2 (55%) and 0.9 kg (37%) of the cumulative dissolved P load, respectively. Both structures underperformed relative to laboratory flow-through experiments and exhibited signs of flow inhibition with time. Dissolved P removal decreased dramatically when treated water pH decreased &lt, 8.5. Although slag has proven successful for treating surface runoff, we hypothesize that underperformance in this case was due to tile drainage bicarbonate consumption of slag calcium through the precipitation of calcium carbonate, thereby filling pore space, decreasing flow and pH, and preventing calcium phosphate precipitation. We do not recommend non-treated steel slag for removing dissolved P from tile drainage unless slag is replaced every 4&ndash, 6 months.

Stormwater filters are a structural best management practice designed to reduce dissolved P losses from runoff. Various industrial byproducts are suitable for use as P sorbing materials (PSMs) for the treatment of drainage water; P sorption by PSMs varies with material physical and chemical properties. Previously, P removal capacity by PSMs was estimated using chemical extractions. We determined the speciation of P when reacted with various PSMs using X-ray absorption near edge structure (XANES) spectroscopy. Twelve PSMs were reacted with P solution in the laboratory under batch or flow-through conditions. In addition, three slag materials were collected from working stormwater filtration structures. Phosphorus K-edge XANES spectra were collected on each reacted PSM and compared with spectra of 22 known P standards using linear combination fitting in Athena. We found evidence of formation of a variety of Ca-, Al-, and/or Fe-phosphate minerals and sorbed phases on the reacted PSMs, with the exact speciation influenced by the chemical properties of the original unreacted PSMs. We grouped PSMs into three general categories based on the dominant P removal mechanism: (i) Fe- and Al-mediated removal [i.e., adsorption of P to Fe- or Al-(hydro-)oxide minerals and/or precipitation of Fe- or Al-phosphate minerals]; (ii) Ca-mediated removal (i.e., precipitation of Ca-phosphate mineral); and (iii) both mechanisms. We recommend the use of Fe/Al sorbing PSMs for use in stormwater filtration structures where stormwater retention time is limited because reaction of P with Fe or Al generally occurs more quickly than Ca-P precipitation.

Mehlich-3 (M3) is one of the most common agronomic and environmental phosphorus (P) extractants for determining P fertilizer requirements and the potential for non-point source pollution. Understanding how soil properties impact M3 extractability can improve our ability to properly use this soil test. The objectives of this study were to investigate the impact of soil pH on P extractability by M3 and water in different soils containing equal total P, and to ascertain information about mechanisms of M3-P extraction. Soil pH at four field sites was previously adjusted to a range of approximately 4.5&ndash, 7.5. Soils (Grant, Dale, Teller, Easpur) were characterized, and P was extracted with M3 and water. Extraction of Mehlich-3 P decreased 40% to 55% with increasing pH, which was potentially due to changing P forms, partial neutralization of extractant pH, and consumption of extractant fluoride (F&minus, ) by non P-containing calcium (Ca) minerals. Water-soluble P (WSP) increased with increasing pH up to pH 6&ndash, 7. Mehlich-3 P and WSP were not positively correlated except for one soil type. Mehlich-3 P is best utilized with WSP as indicators of quantity and intensity, respectively. Use of M3-P alone at pH &lt, 5.5 may overestimate solubility. Further research should examine the suitability of M3-P at pH &gt, 7.

Three different dairy manure wastewater effluent samples were amended with mine drainage residuals (MDR) to evaluate the suitability of MDR for sequestration of phosphorus (P). Geochemical modeling of the manure wastewater compositions indicated that partially soluble P-bearing minerals including hydroxyapatite, octacalcium phosphate, and vivianite were all oversaturated in each of the manure wastewater samples. Initial MDR amendment test results indicated that these partially soluble P minerals suspended in the wastewater replenished P in the water phase as it was sorbed by the MDR samples. Further investigations revealed that the MDR samples were effective in decreasing soluble P when the amended manure was tested using the water-extractable P procedure. Under these conditions, up to 90 percent of the soluble P in the manure was converted to a sorbed, water-insoluble state. Water contamination and large-scale validation tests of the process were also conducted.

The objective was to differentiate and estimate phosphorus (P)-uptake and P-utilization efficiency among several winter wheat accessions. Twenty-two accessions were characterized for their ability to uptake and utilize P in two low P soils (acid and calcareous). Plants were grown for 28 days in two different sized pots and analyzed for biomass and total P concentration. Total P uptake and biomass was greater in the large pot and calcareous soil. However, there were no significant correlations between the small and large pot for biomass, P uptake, and P concentration, indicating that rooting conditions were different for the two pots, which allowed differentiation between P-utilization and P-uptake efficiency. Possession of ALTM1 gene for malate excretion did not appear to be related to P-uptake efficiency. Several accessions were found to be either P-uptake or P-utilization efficient in both soils. Phosphorus use efficiency mechanisms may contribute to acid soil tolerance.

Subsurface transport of orthophosphate (Pi) from fertilized agricultural fields to freshwaters may lead to eutrophication, reduced biodiversity and fish kills in inland waters. Reduction of Pi transport by means of filters in drains with Pi sorbing materials (PSMs) may be one way to improve water quality. The aims of this study were to investigate and model the effect of retention time (RT) and inlet Pi concentration on Pi sorption and desorption by two PSMs, CaO-based Filtralite®P and Fe oxide-based CFH-12, in a flow-through setting. Four inlet Pi concentrations (1.6, 3.2, 16 and 32 μM) were all tested with 6 different retention times (0.5–9 min). Both materials’ Pi sorption capacity and affinity is highly dependent on the Pi inlet concentration. CFH had a P sorption capacity and affinity 10 times higher than Filtralite®P. CFH released less than 10% of previously sorbed P. Filtralite®P, on the other hand, released ≥35% during desorption. Furthermore, Pi sorption by Filtralite®P was positively correlated to RT. This was not the case for CFH indicating that CFH will be capable of removing Pi even at high flow rates (i.e. low RT). Therefore, CFH would be the preferred material for a P removal structure with fluctuating inlet Pi concentrations and RT. A PSM specific prediction model was successfully developed using flow-through sorption data. This model may be used to show how much Pi can be removed and how long a specific material will last until Pi saturation, as exemplified.

In-house windrowing of broiler litter between flocks has been adopted by producers to reduce pathogens and improve litter quality before chick placement. In this study, 5 consecutive windrow trials were conducted in commercial broiler houses for their effect on litter bacterial populations, organic matter stabilization, cumulative ammonia emissions, and nutrient transformation and compared with litter conditioning (tilling) in adjacent houses. No significant reduction ofClostridium spp. andEscherichia coli populations was found in windrowed litter from d 0 to 7. No significant difference of 7-d mortality was found between windrow and nonwindrow houses. The windrowed house resulted in better foot quality than the nonwindrowed house from 1 of 3 scored flocks. Water-soluble phosphorus increased in both windrowed and nonwindrowed litter; therefore, appreciable biotic and abiotic activity occurred in litter with both treatments after flocks were removed. Overall, no negative effect of windrow treatments on litter quality for agronomic applications was observed. Both the control and windrow treatments resulted in a decrease in litter moisture content (2 to 5%) likely beneficial to bird health conditions. High ammonia emissions persisted after windrow spreading; therefore, a need may exist for an extended period of ventilation or a litter amendment as crucial before chick placement. Litter amendment at a low dose was effective in lowering ammonia concentrations after windrowing and was more economical comparing to operating fans in winter conditions.

Bioretention cells (BRCs) have shown potential for storm water quantity and quality control. However, the phosphorus (P) removal in BRC has been variable due to differences of soil properties in filter media. The objectives of this research were to identify and evaluate P accumulation in filter media and to quantify effluent P reduction in BRC. Each cell has a sand and fly ash media designed to remove phosphorous. Filter media were collected in 2014 across the cell surface and to a depth of 0.6 m to quantify the P accumulation. The mean total P (T-P) concentration increased over the seven years of operation, but the changes were not statistically significant. The average Mehlich-3 P (M3-P) and water-soluble P (WS-P) concentrations in the media profiles showed higher P accumulation in the top 0.15 m. The average M3-P and WS-P concentrations between 0.15 m to 0.30 m, and 0.30 m to 0.60 m were variable on all four BRCs media. The media with 5% fly ash significantly retained M3-P and WS-P over the top 0.15 m. Stormwater influent and effluent samples from three of the BRCs monitored over one year showed reductions in both P concentration (68% to 75%) and P mass (76% to 93%).

Controlling dissolved phosphorus (P) losses to surface waters is challenging as most conservation practices are only effective at preventing particulate P losses. As a result, P removal structures were developed to filter dissolved P from drainage water before reaching a water body. While many P removal structures with different P sorption materials (PSMs) have been constructed over the past two decades, there remains a need to evaluate their performances and compare on a normalized basis. The purpose of this review was to compile performance data of pilot and field-scale P removal structures and present techniques for normalization and comparison. Over 40 studies were normalized by expressing cumulative P removal as a function of cumulative P loading to the contained PSM. Results were further analyzed as a function of retention time (RT), inflow P concentration, and type of PSM. Structures treating wastewater were generally more efficient than non-point drainage water due to higher RT and inflow P concentrations. For Ca-rich PSMs, including slag, increased RT allowed for greater P removal. Among structures with low RT and inflow P concentrations common to non-point drainage, Fe-based materials had an overall higher cumulative removal efficiency compared to non-slag and slag materials.

With the problem of excess P in surface waters established and various non-point sources identified in Chap. 1, this chapter moves deeper into the mechanisms of P transport from terrestrial sources to surface waters. Specifically, P transport is split up into two main categories of sources (incidental and legacy), and broadly described as two main forms in drainage waters: particulate P and dissolved P. The two P forms are especially critical since they behave differently with regard to aquatic bioavailability and the means in which each form is transported. These inherent differences translate to differences in the types of BMPs that can be utilized for reducing transport of each of the P forms, potency of each P form for causing eutrophication, and the temporal aspect of P losses. This chapter focuses more on legacy P sources rather than incidental P losses because of the greater difficulty in controlling the latter. Phosphorus management in the context of legacy P sources is presented as a system in three main categories: (1) prevention of legacy P formation, (2) containment of legacy P, and (3) remediation of legacy P. While some conventional BMPs are effective at reducing particulate P and few are effective at partially containing dissolved transport from legacy P sources, none will remediate dissolved P losses from legacy P sources in the short-term. Because of the unique temporal aspect of legacy P and dissolved P transport, there is a need to utilize both long-term and short-term remediation for reducing dissolved P transport. The long-term remediation of legacy P sources is achieved through soil P drawdown with plants, and the dissolved P losses that occur in the short-term during that slow process can be remediated with P removal structures.

This chapter is dedicated to the most important component of the P removal structure: PSMs, which are the component that actually removes the dissolved P. Phosphorus sorption materials are presented in great detail and explained. Many of these materials are by-products from various industries such as drinking water treatment, steel production, acid mine reclamation, energy generation, metal casting, wall board production, and bauxite mining. Other PSMs are manufactured for the sole purpose of removing dissolved P. The chemical and physical properties relevant to P removal structures are discussed in the context of choosing a suitable PSM for the situation, with a general characterization of several PSMs presented. This will include a discussion of the main mechanisms of P removal by PSMs and the implications of those mechanisms on design. Specifically, the influence of retention time and inflow P concentration on P removal by different types of PSMs are discussed in detail. The reader will clearly understand how the retention time and the inflow P concentration can have a dramatic impact on the design of a site-specific P removal structure. The common “paradox of PSMs” is presented: usually PSMs with the greatest ability to adsorb P tend to conduct water poorly (i.e. low hydraulic conductivity), and vice versa. While there are some exceptions to this, the implications of this issue are explained with several solutions provided. In addition to a general guide in choosing a suitable PSM, the chapter concludes with a discussion on safety considerations of PSMs that originate as by-products, and the need to screen some materials for safety. Recommendations and thresholds for PSM safety screening are provided.

This chapter discusses the disposal options for the spent PSMs after they have achieved their useful lifetime in a P removal structure. This includes (1) use of the spent PSMs as a soil P fertilizer, (2) use as a plant growth media, (3) assessing P availability in the spent PSMs, (4) potential P stripping from the PSMs and recharge, (5) land application of spent PSMs for purposes other than P fertility, (6) non-plant use of spent PSMs, and (6) safety considerations in beneficial re-use of spent PSMs. The majority of this discussion is on the land application of PSMs to soils, and any potential benefit that that the PSMs may have on soil quality and plant growth. The potential beneficial re-use of spent PSMs strongly depends on how stable the PSM-bound P is, and forms of P contained on it. A discussion on the economics of P-stripping and PSM regeneration is also included. Several tables consisting of safety characterization data from various by-product PSMs are shown.

The general theory of P removal structures for treating dissolved P is presented and explained along with the four necessary components for any P removal structure. While P removal structures can take many different forms, these four components must be present for a P removal structure to be effective. These four components are (1) an effective PSM in a sufficient quantity, (2) containment of the PSM, (3) the ability to replace the PSM when necessary, and (4) passive drainage via gravity at sufficient flow rates suitable for the site. The general site requirements for location of a P removal structure are also presented along with a discussion of the many different applications of this technology. A demonstration is given on how to choose the most efficient locations for reducing dissolved P loads with a P removal structure. These concepts will be illustrated through the presentation and illustration of several different styles of P removal structures. For example, ditch filters, surface confined beds for runoff interception, subsurface tile drain filters, surface and blind inlets, “bio-retention cells”, etc. Last, we provide examples of how the P removal structure can be utilized for point sources such as municipal and domestic wastewater.

Phosphorus is introduced at its most basic level: an element on the periodic table and the various forms and abundance in which it exists, as well as its necessity for all biological function, including agricultural production. This chapter serves to lay the foundation and justification for efforts to reduce P loading to surface waters. It describes eutrophication, the major problem caused by excess P in surface waters and describes the resulting negative impact that it has on recreation, drinking water treatment, and ecosystem diversity. The major sources of P to surface waters is discussed, as separated into point and non-point sources, focusing dominantly on non-point sources and describing how such non-point sources came to exist. Examples of non-point urban and agricultural scenarios are given, with some data presented. Within non-point sources, the focus is mostly on “legacy” P in soils since this P source can sustain P transport for several decades.

Pairing denitrifying woodchip bioreactors and phosphorus-sorbing filters provides a unique, engineered approach for dual nutrient removal from waters impaired with both nitrogen (N) and phosphorus (P). This column study aimed to test placement of two P-filter media (acid mine drainage treatment residuals and steel slag) relative to a denitrifying system to maximize N and P removal and minimize pollution swapping under varying flow conditions (i.e., woodchip column hydraulic retention times (HRTs) of 7.2, 18, and 51 h; P-filter HRTs of 7.6-59 min). Woodchip denitrification columns were placed either upstream or downstream of P-filters filled with either medium. The configuration with woodchip denitrifying systems placed upstream of the P-filters generally provided optimized dissolved P removal efficiencies and removal rates. The P-filters placed upstream of the woodchip columns exhibited better P removal than downstream-placed P-filters only under overly long (i.e., N-limited) retention times when highly reduced effluent exited the woodchip bioreactors. The paired configurations using mine drainage residuals provided significantly greater P removal than the steel slag P-filters (e.g., 25-133 versus 8.8-48 g P removed m-3 filter media d-1, respectively), but there were no significant differences in N removal between treatments (removal rates: 8.0-18 g N removed m-3 woodchips d-1; N removal efficiencies: 18-95% across all HRTs). The range of HRTs tested here resulted in various undesirable pollution swapping by-products from the denitrifying bioreactors: nitrite production when nitrate removal was not complete and sulfate reduction, chemical oxygen demand production and decreased pH during overly long retention times. The downstream P-filter placement provided a polishing step for removal of chemical oxygen demand and nitrite.

Introduction Total coffee production in the world in 2013 was 8.7 million Mg of coffee beans. Coffee must be processed after harvest to separate beans from the husk, and the post-harvest process can generate different types of residues. Knowing that 50 % of the harvested coffee is husk, it is important to consider that these by-products can contribute to environmental problems if not disposed of properly. There is a need to find alternatives to the piling of coffee husk as a means of disposal at coffee farms. The objectives in this experiment were to characterize five types of coffee processing residues and assess their value as potassium (K) fertilizer by examining K release. Results Chemical characteristics of coffee residues varied with processing method, such as wet and dry processes. Application of residues to soil columns followed by 40 weeks of simulated leaching increased total K content in the soil for all treatments based on application rate, except for enriched and three-year composted coffee husk (3ycomp). Coffee processing residues had higher concentrations of K leached compared with the control with no K application, but only 3ycomp was higher than other coffee processing residues. Total K released from coffee residues increased linearly with application rate, but the decomposition of the coffee residues was low, which suggest that K release from coffee processing residues is not related to decomposition. Conclusion Post-harvest coffee processes impacted concentrations of K, nitrogen, carbon, cellulose, hemicellulose, lignin, phenol, pH, and electrical conductivity among the coffee processing residues. The K release was high (over 90 %), but it did not depend on the type of coffee processing residue, and thus, the residues can be a substitute for a mineral source of K applied to soils. The use of coffee processing residues as source of K did not prevent K losses by leaching. Some coffee residues resulted in greater K leaching than mineral KCl applied at the same rate.

Decommissioned animal waste lagoons contain large quantities of nutrients including nitrogen (N) and phosphorus (P) and can cause pollution of nearby water resources. Using short-rotation woody crops (SRWCs) for nutrient uptake and biomass production might be an inexpensive and eco-friendly method for the stabilization of decommissioned lagoons. We evaluated the annual growth performance and nutrient uptake by sycamore (Platanus occidentalis) for five growing seasons and 25 different clones of eastern cottonwood (Populus deltoides) for four growing seasons in a soil backfilled, de-watered swine lagoon in north-central Oklahoma. Growth performance and nutrient uptake of cottonwood was higher than the sycamore in our study. At the end of the study, 5-year old sycamore reached an average height of 5.84 m [standard error (SE) = 0.39] and had an average diameter at breast height (dbh) of 5.91 cm (SE = 0.20), compared to 4-year old cottonwood height of 7.58 m (SE = 0.15) and dbh of 8.22 cm (SE = 0.34), respectively. Sycamore produced almost 30 Mg ha−1of total biomass, whereas cottonwood produced 53 Mg ha−1 by the end of the study. Total N and P uptake by sycamore was 327 (SE = 24) and 51 (SE = 4) kg ha−1 respectively, whereas cottonwood N and P uptake was 699 (SE = 41) and 99 (SE = 6) kg ha−1, respectively, by the end of the study. We conclude that SRWCs can use substantial amounts of nutrients from the decommissioned lagoons while producing wood and fiber products.

Phosphorus eutrophication of lakes and streams, coming from drained farmlands, is a serious problem in areas with intensive agriculture. Installation of phosphate (P) sorbing filters at drain outlets may be a solution. The aim of this study was to improve the understanding of reactions involved in P sorption by three commercial P sorbing materials, i.e. Ca/Mg oxide-based Filtralite-P, Fe oxide-based CFH-12 and Limestone in two particle sizes (2–1 mm and 1–0.5 mm), by means of isothermal titration calorimetry (ITC), sorption isotherms, sequential extractions and SEM-EDS. The results indicate that P retention by CFH is due to surface complexation by rapid formation of strong Fe–P bonds. In contrast, retention of P by Filtralite-P and Limestone strongly depends on pH and time and is interpreted due to formation of calcium phosphate precipitate(s). Consequently, CFH can unambiguously be recommended as P retention filter material in drain outlets, whereas the use of Filtralite-P and Limestone has certain (serious) limitations. Thus, Filtralite-P has high capacity to retain P but only at alkaline pH (pH ≥ 10) and P retention by Limestone requires long-time contact and a high ratio between sorbent and sorbate.

The current increase in oil and gas drilling activity has resulted in increased production of oil-base “mud” (OBM) in need of disposal. Land application of OBM to agricultural land is a common disposal technique that presents agronomic and environmental challenges since the material is rich in petroleum hydrocarbons. The objective of this study was to determine the effect of mixing OBM with bulking materials on hydrocarbon degradation and forage production after land application of the mixtures. An OBM was collected from Oklahoma and characterized for environmentally relevant properties such as total petroleum hydrocarbons (TPH) and trace metals. The OBM was bulked with either limestone, gypsum, or caliche, at a ratio of 3:1 or 1.5:1 bulking material/OBM. All mixtures were surface applied at equal TPH loading rates (8625 kg ha–¹) and soil samples taken at 7, 45, 60, and 170 d after application for evaluation of TPH, electrical conductivity (EC), pH, and sodium absorption ratio (SAR). After 7 d >50% of applied TPH degraded, which resulted in soil concentrations less than thresholds recommended for residential neighborhoods. By Day 170, 99% of applied TPH degraded. There was mostly no difference in TPH degradation as a function of type and amount of bulking agents used with OBM. Application of OBM did not significantly decrease forage yield compared to unamended control. Therefore, use of caliche, limestone, or gypsum bulked with OBM at a 1.5:1 ratio (bulking agent/OBM) would suffice for achieving acceptable TPH degradation when mixtures are surface applied and non-incorporated.

Soil Sci. Soc. Am. J. 78:147–156 doi:10.2136/sssaj2013.06.0239 Received 21 June 2013 *Corresponding author: (Chad.penn@okstate.edu). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Application of Isothermal Calorimetry to Phosphorus Sorption onto Soils in a Flow-Through System Soil Chemistry

Nitrogen (N) release rate from organic materials through mineralization is affected by the organic material and environmental conditions. Determining rates of mineralization for canola (Brassica rapa L.) meal and cottonseed (Gossypium hirsutum L.) meal with or without soapstock (a waste byproduct of seed oil extraction) will establish appropriate application rates for consumers. Canola meal, cottonseed meal, cottonseed meal with soapstock, or no treatment (control) was incorporated at a rate of 4.9 g·m−2 N into three loam soils. Experimental units were incubated for 0, 3, 7, 14, 30, or 60 days while maintaining moisture at 60% water-holding capacity and then analyzed for NH4-N and NO3-N, then plant available N was calculated as NH4-N+NO3-N. Ammonium increased with each seed meal amendment during the first 14 days of incubation and then decreased. Nitrate increased in seed meal treatments during the first 14 days of incubation and then continued to increase as NH4-N ions declined. Canola meal and cottonseed meal with or without soapstock increase plant-available soil N.

Soil washing with acidic chelators followed by liming is under consideration for remediating multi-metal contaminated soils. This technique was tested by pot experiments with a mixture of chelators (MC) as a washing agent. After washing and liming treatments, corn (Zea mays L.) was planted to assess bioavailability of heavy metals. A phytoextraction with Sedum alfredii was additionally performed after corn harvest to further decrease heavy metals in the soil. The results showed that the concentrations of Cd, Pb, and Zn in the corn grain with the washing treatment were still higher than the food standard limits in China, and liming the washed soil did not effectively decrease Cd and Pb concentrations in the corn grain. Liming the washed soil significantly increased heavy metals concentrations in leachate. The concentrations of Cd, Pb, Zn, and Cu in S. alfredii after washing were increased by 42.8, 51.2, 7.3, and 25.8%, respectively, compared to nonwashed soils. Phytoextraction rates of Cd and Zn by one crop of S. alfredii after soil washing were 47.8 and 9.82%, respectively, of the soil total metal. The phytoextraction of soils with S. alfredii, and also the liming treatment alone without phytoextraction or washing, were able to reduce exchangeable heavy metal concentrations in soils. This study suggests that the bioavailability of heavy metals could still be high after washing, liming the washed soil may release the adsorbed metal-chelates, and the phytoextraction by S. alfredii after soil washing is an effective approach to deplete the mobile Cd activated by soil washing.

Reduction of phosphorus (P) inputs to surface waters may decrease eutrophication. Some researchers have proposed filtering dissolved P in runoff with P-sorptive byproducts in structures placed in hydrologically active areas with high soil P concentrations. The objectives of this study were to construct and monitor a P removal structure in a suburban watershed and test the ability of empirically developed flow-through equations to predict structure performance. Steel slag was used as the P sorption material in the P removal structure. Water samples were collected before and after the structure using automatic samples and analyzed for total dissolved P. During the first 5 mo of structure operation, 25% of all dissolved P was removed from rainfall and irrigation events. Phosphorus was removed more efficiently during low flow rate irrigation events with a high retention time than during high flow rate rainfall events with a low retention time. The six largest flow events occurred during storm flow and accounted for 75% of the P entering the structure and 54% of the P removed by the structure. Flow-through equations developed for predicting structure performance produced reasonable estimates of structure "lifetime" (16.8 mo). However, the equations overpredicted cumulative P removal. This was likely due to differences in pH, total Ca and Fe, and alkalinity between the slag used in the structure and the slag used for model development. This suggests the need for an overall model that can predict structure performance based on individual material properties.

Sorption of fecal bacteria in soils treated with swine effluents as a fertilizer involves complex mechanisms that are functions of the effluent constituents, soil colloid properties, and fecal bacteria population. Swine effluents contribute significant solutes and organic compounds during application and potentially increase the soil solution pH and ionic strength when in contact with soils. The objective of this research was to investigate sorption of fecal bacteria on soils treated with swine effluents and to derive a fecal bacteria sorption model based on soil properties. Sorption of Escherichia coli was investigated using a series of artificial and natural soils treated with swine effluent at varying dilution ratios (i.e., manure effluent concentrations). Note that this research conducted sorption tests based on multiple strains of the E. coli population in the manure effluent, as opposed to a specific E. coli strain. Fecal bacteria in swine effluents mainly consisted of attached bacteria as opposed to free cells in suspension (i.e., planktonic form). Sorption of surface-bonded E. coli appeared to be controlled by processes occurring in the substrate (i.e., surfaces to which the bacteria attached) as a function of the soil solution pH and ion exchange. For soils up to 30% clay content and 3.0% total carbon content, nonlinear equations characterized the sorption of E. coli in the artificial and natural soils. For soils with percent clay less than or equal to 11%, total carbon played a primary role in the estimated sorption of fecal bacteria. For soils with clay percentages larger than 11% and lower than 30%, sorption of fecal bacteria was directly correlated to amorphous aluminum and iron concentrations, percent clay, and total carbon. In addition, dispersion resulting from alkalinity buildup due to adding effluent to the soils in the presence of soil organic matter decreased observed sorption of E. coli in some cases, especially at higher effluent ratios. Experimental data indicated that predictions based exclusively on the percent clay content overestimated sorption of E. coli on soils treated with swine effluent in most soils. Manure effluent concentration, the presence of attached bacteria, and soil dispersion under high effluent concentrations should be considered when modeling fecal bacteria transport in soils. Future environmental research should be conducted with actual manure sources and multiple strains of an E. coli population.

Phosphorus (P) removal structures have been shown to decrease dissolved P loss from agricultural and urban areas which may reduce the threat of eutrophication. In order to design or quantify performance of these structures, the relationship between discrete and cumulative removal with cumulative P loading must be determined, either by individual flow-through experiments or model prediction. A model was previously developed for predicting P removal with P sorption materials (PSMs) under flow-through conditions, as a function of inflow P concentration, retention time (RT), and PSM characteristics. The objective of this study was to compare model results to measured P removal data from several PSM under a range of conditions (P concentrations and RT) and scales ranging from laboratory to field. Materials tested included acid mine drainage residuals (AMDRs), treated and non-treated electric arc furnace (EAF) steel slag at different size fractions, and flue gas desulfurization (FGD) gypsum. Equations for P removal curves and cumulative P removed were not significantly different between predicted and actual values for any of the 23 scenarios examined. However, the model did tend to slightly over-predict cumulative P removal for calcium-based PSMs. The ability of the model to predict P removal for various materials, RTs, and P concentrations in both controlled settings and field structures validate its use in design and quantification of these structures. This ability to predict P removal without constant monitoring is vital to widespread adoption of P removal structures, especially for meeting discharge regulations and nutrient trading programs.

Phytoextraction using hyperaccumulating plants is generally time-consuming and requires the cessation of agriculture. We coupled chelators and a co-cropping system to enhance phytoextraction rates, while allowing for agricultural production. An experiment on I m3 lysimeter beds was conducted with a co-cropping system consisting of the hyperaccumulator Sedum alfredii and low-accumulating corn (Zea Mays, cv. Huidan-4), with addition ofa mixture of chelators (MC), to assess the efficiency of chelator enhanced co-crop phytoextraction and the leaching risk caused by the chelator. The results showed that the addition of MC promoted the growth of S. alfredii in the first crop (spring-summer season) and significantly increased the metal phytoextraction. The DTPA-extractable and total metal concentrations in the topsoil were also reduced more significantly with the addition of MC compared with the control treatments. However, mono-cropped S. alfredii without MC was more suitable for maximizing S. alfredii growth and therefore phytoextraction of Zn and Cd during the autumn-winter seasons. No adverse impact to groundwater due to MC application was observed during the experiments with three crops and three MC applications. But elevated total Cd and Pb concentrations among subsoils compared to the initial subsoil concentrations were found for the co-crop + MC treatment after the third crop.

Although N fertilizers are not acidic, their inputs to soil are acid forming. As a result of the long-term use of N fertilizers, soils in the Great Plains are becoming more acidic and this acidity may become a yield-limiting factor. In 1970, long-term plots were initiated to compare sources (anhydrous NH 3 , NH 4 NO 3 , urea, and S-coated urea), application rates (34, 68, 136, and 272 kg N ha ―1 ), and an untreated check (0 N) on wheat (Triticum aestivum L.) grain yield, soil pH, exchangeable base cations, and Al saturation. For the soil properties evaluated, significant differences among the different N sources did not exist after 30 annual applications of N fertilizer. The long-term N fertilization significantly reduced soil pH in the surface soil layer (0-15 cm), especially at the higher application levels. Soil pH decreased with time and was significantly related to the amount of total N applied for each N source. Nitrogen fertilization with each N source significantly increased exchangeable Al and Al saturation (Al sat ) but decreased exchangeable base cations (Ca 2+ and Mg 2+ ). Both exchangeable Al and Al sat increased with increasing N rate and were inversely related to soil pH. Despite decreased soil pH levels to

The potential of six industrial by-products for use as phosphorus-sorbing materials (PSMs) in solutions was evaluated. These included two different acid mine drainage treatment residuals (AMDR1 and AMDR2), water treatment residual (WTR), fly ash, bauxite mining residual, and flue gas desulfurization product (FGD). Characterization of the by-products and their mechanisms for sorption and retention of inorganic phosphorus (P) from solution identified those PSMs that sorbed primarily by an iron and aluminum (Fe/Al) mechanism, those that sorbed primarily by a calcium and magnesium (Ca/Mg) mechanism, and those that sorbed by both mechanisms. Degree of P sorption and associated mechanisms were strongly influenced by the pH, buffer capacity, ionic strength, and common ion effects.

Reducing phosphorus (P) loads from soils to surface waters is necessary for solving the problem of eutrophication. Many industrial by-products have been shown to sorb appreciable amounts of dissolved P from solution and it has been proposed to use P sorption materials (PSMs) such as steel slag in landscape scale “filters” for trapping dissolved P in runoff. The objective of this study was to model the effect of retention time (RT) and P concentration on P sorption by steel slag and a surface modified slag in a flow-through system. Sorption of P onto steel slag and rejuvenated-modified steel slag was measured using a traditional batch isotherm and a flow-through setting at several RTs and P concentrations. Flow-through data were used to produce a model that estimated P sorption based on RT and P concentration. The model was tested on a pilot-scale pond filter consisting of the same slag materials. For both the materials, flow-through tests indicated an increase in RT increased P removal efficiency but decreased the total amount of P removed at saturation. The Langmuir model developed from batch isotherms overestimated and underestimated P sorption in normal and rejuvenated slag respectively, relative to flow-through. Normal and rejuvenated slag removed 38 and 36% of P in the pilot-scale pond filter after 2 weeks of pumping. The Langmuir equation poorly predicted P sorption in the pond filter while the flow-through model produced reasonable estimates. Results suggest that flow-through methodology is necessary for estimating P sorption in the context of landscape P filters.

Zeolite minerals are ideal for removing ammonium nitrogen (NH4(+)-N) from animal wastes, leachates, and industrial effluents. The objectives of this study were to compare NH4+ removal and kinetics among several commercially available zeolites under various conditions and determine if calorimetry could provide information regarding kinetics of NH4+ removal. Ammonium sorption onto potassium (K) saturated zeolites was compared using synthetic vs. natural swine effluent and with either traditional batch-shaken system or a "tea bag" approach in which zeolites were contained in a mesh sack and suspended in a solution of swine effluent. Ammonium sorption was measured at four retention times using a flow-through system, and the resulting heat response was measured using isothermal calorimetry. Ammonium removal was not significantly different in synthetic vs. natural swine effluent. Ammonium removal was lower in batch-stirred compared to batch-shaken systems, suggesting that diffusion between particles was rate-limiting in the former system. Flow-through cells possessing contact times > 100 s displayed greater NH4+ sorption than batch systems, suggesting that maintaining high NH4+ concentration in solution, removal of exchange products, and sufficient reaction time are critical to maximizing NH4+ removal by zeolites. Within 100 s after NH4+ addition, endothermic heat responses indicated that NH4(+)-K+ exchange had peaked; this was followed by significant heat rate reduction for 50 min. This confirmed findings of an initial fast NH4(+)-K+ exchange followed by a slower one and suggests the 100-s period of rapid reaction is an indicator of the minimum flow through retention time required to optimize NH4+ sorption to zeolites used in this study.

Field experiments were conducted to evaluate the effects of repeated annual manure applications on sodium adsorption ratios and electrical conductivity in semi-arid environments. Swine effluent, beef manure, and anhydrous ammonia were annually applied at loading rates of 0, 56, 168, and 504 kg nitrogen (N) ha−1 to an irrigated, conventionally tilled, continuous corn (Zea mays L.) cropping study in the Oklahoma panhandle. Sodium adsorption ratios increased with swine effluent additions at the high N loading rate application; however, sodium adsorption ratio decreased with the high anhydrous ammonia loading applications and remained unchanged with beef manure applications. Linear correlations were found for swine effluent and anhydrous ammonia applications when N levels increased. Electrical conductivity levels increased 2.35 dS m−1 with the high anhydrous ammonia loading rate to a level where relative yields for crop production may be at risk of being reduced 50%.

SUMMARY AND CONCLUSIONS Isothermal titration calorimetry provided some indication of the P retention potential of 28 Oklahoma bench-mark soils. Th ere may have been some interference, however, with carbonate dissolution. While the heat of the fi rst titration indicated the degree of P retention, the characteristics of the heat patterns and thermograms (i.e., the endotherm category) may have provided some insight into P retention mechanisms. Based on the results of this study and others (Penn and Warren, 2009; Rhue et al., 2002; Miltenburg and Golterman, 1998), exother-mic peaks occurring from the addition of inorganic P solutions (NaH 2 PO 4 ) to soils indicated acid–base neutralization reac-tions (carbonate dissolution), ligand exchange of P onto Al (and also Fe) minerals, and Ca phosphate precipitation. Endothermic peaks indicated Al and Fe phosphate precipitation, evidenced by pure solution titrations and acid soils showing more endotherm characteristics than the neutral and alkaline soils. Th is confi rms previous studies (Penn and Warren, 2009; Rhue et al., 2002).Unlike the heat of the fi rst titration, endothermic charac-ter (i.e., endotherm category) provided no information on the amount of P retention. Based on the results of this study, the use of heat patterns, thermograms, and subsequent classifi cation into an endotherm category for P additions to soils should be restricted to qualitative interpretation with regard to discerning P retention mechanisms. Th e major limitation of this technique for assessing P retention in soils is mainly due to the fact that the dissolution of carbonates displays an exothermic signal that may mask endothermic signals and overlap with exotherms pro-duced from ligand exchange and Ca phosphate precipitation. Th erefore the technique would probably be improved if the P solution used in the titrations was adjusted to a pH equal to the soil being tested.Th e carbonate dissolution phenomenon also suggests the potential for the development of an ITC method for estimating soil carbonate content due to the highly exothermic nature of carbonate dissolution. Another possibility might be the develop-ment of an ITC method for estimating the surface area of a soil. Titration with a sorptive such as ethylene glycol monomethyl ether (EGME), which is used in surface area analysis, would probably produce a heat signal on sorption to the soil surface. Such a heat signal could be related back to true measurements of EGME retention. Essentially, any reaction resulting in signifi -cant heat change, with little heat from side reactions, can poten-tially be monitored using ITC or fl ow-through calorimetry. Th is makes calorimetry a real-time indicator of reaction processes, as opposed to traditional methodologies of taking discrete mea-surements before and aft er equilibrium.