Lee E. Sommers

Availability of phosphorus to algae from eroded soil fractions

Abstract A study was conducted to determine the concentrations of algal-available P (P aa ) in unfractionated samples and size-classified separates of soil eroded from wheat stubble plots during a simulated rainfall experiment conducted in Warren County, Indiana, U.S.A. Run-off samples were collected, concentrated, dispersed by sonification, separated according to size and incubated with algal cells ( Selanastrum capricornutum ) in P-free nutrient medium for 2 weeks. Algal-available P in soil separates was determined by decreases in sediment inorganic P (P i ) over the incubation period. The initial concentrations of dissolved molybdate-reactive P i (DMRP), P i extractable with NaOH (NaOH-P i ), P i extractable with HCl (HCl-P i ), organic P (P o , and total P increased with decreasing particle size. A higher proportion of P i was HCl-extractable in fractions > 2 μ m than in clay-size separates. The level of P aa in samples increased with decreasing particle size. Available P concentrations in separates 50 μ m and unfractionated samples averaged 447, 282, 113, 26 and 261 μg g −1 , respectively. From 42 to 69% of the P i and 20–37% of the total P in unfractioned samples was P aa . A lower proportion of P i in the > 50 μ m fraction was P aa than in the other size fractions (34 vs. 50%). There was no relationship between particle size and the proportion of total P that was available. The majority (> 84%) of P aa originated in the P i fraction extractable with NaOH, whereas HCl-P i only contributed small amounts of P aa . The proportion of initial NaOH-P i assimilated by algae in 2 weeks ranged between 43 and 77%, whereas an average of 16% of HCl-P i in separates was P aa . On average, a greater proportion of NaOH-P i was assimilated by algae in samples from no-till plots as compared to those from chisel-plowed plots.

The decomposition of phthalate esters in soil

Abstract Factors affecting the decomposition of carboxyl‐labelled (14C) phthalic acid (PA), monobutyl phthalate (MBP), and dibutyl phthalate (DBP) were studied in soil incubation experiments conducted under labortory conditions. A lag phase of 10 to 20 days occurred before soil microbes initiated metabolism of MBP and DBP while PA was rapidly decomposed. Approximately 90% of DBP added to soils at rates of 0.1 to 0.4% was decomposed within 80 days under both aerobic and anaerobic conditions. Decomposition of DBP was enhanced in soils by increasing soil pH from 5.2 to 7.0, by adding organic matter, and by elevating the temperature from 23°C to 30°C. Varying soil characteristics and the simultaneous addition of ammonium, CaCO3 or sewage sludge had little effect on the rate or extent of DBP degradation. The addition of DBP in sewage sludge or other waste materials to soils should not pose a long‐term persistence problem.

Preparation and characterization of model humic polymers containing organic phosphorus

The nature of organic P in soil organic matter was studied by evaluating the incorporation of serine, phosphoserine, ethanolamine, phosphoethanolamine and glycerophosphate into model humic polymers prepared by chemical oxidation of polyphenols. Elemental and functional group analysis indicated that the composition of model humic polymers ranged as follows: organic C, 50.6–56.8%; total acidity, 7.86–11.87m-equiv g−1; carboxyl, 1.42–2.00 m-equiv g−1; total hydroxyl, 6.79-10.0 m-equiv g−1; ash, 6.4–13.9%; E4/E6 ratio, 5.34–6.19; organic N, 0.70–1.65% and organic P, 0.254–0.942%. These values are within the ranges reported for soil humic substances. The only non-phenolic compounds incorporated into model humic polymers were those containing free amino groups. The P content of model polymers was not increased by the presence of KH2PO4, glycerophosphate, serine or ethanolamine whereas phosphoserine and phosphoethanolamine resulted in model polymers containing 0.254 and 0.942% P, respectively. Further characterization studies of the model polymer containing phosphoethanolamine (HA-PE) showed that most of the C (83.2%), N (79.8%) and P (75.3%) was in the humic acid fraction. Gel filtration of HA-PE showed that 0.5% of the polymer was present in high molecular weight (mol. wt) components (mol. wt > 100,000) and 74.8% of the polymer was in two components of mol. wt 10,000–50,000. The majority of the organic P in HA-PE was associated with the medium molecular weight fractions (79.2%) while 16.8% of the P was associated with materials possessing mol. wt < 10,000. Attempts to demonstrate the presence of organic P functional groups contained in HA-PE by infrared spectroscopy was limited by the relatively small amounts of organic P incorporated into the model humic polymers. The results obtained show that a portion of the unidentified organic P in soil humic substances may arise from the incorporation of organic compounds containing both amino and phosphate ester functional groups during oxidative polymerization of polyphenols.

Chemical models of inorganic pollutants in soils

The principal inorganic pollutants of soils are particular chemical species of elements normally found at trace concentrations in soil solutions. Chemical models of the behavior of these elements have been developed to describe both the rates with which their reactions in soils occur and their resulting speciation among liquid and solid phases. The focus of most models has been the quantitative estimation of soil solution concentrations as controlled by precipitation or adsorption reactions. Models of precipitation reactions involve the construction of predominance and activity ratio diagrams valid for a chosen set of chemical conditions (e.g., proton and electron activity, ionic strength). Models of adsorption reactions employ typically the concept of surface complexation. The strengths and limitations of these models are reviewed, as are the successes and failures of computer programs based on them.

Stability and mineralization of organic phosphorus incorporated into model humic polymers

Abstract The stability of the phosphate ester linkage in phosphoserine (PS) and phosphoethanolamine (PE) was evaluated after incorporation of these compounds into model humic polymers. Humic polymers prepared by oxidation of a mixture of substituted phenols in the presence of either PS or PE resulted in model humic materials containing from 0.25 to 0.94% P, values within the range found for organic P in natural soil humic materials. The organic P contained in model humic polymers was resistant to hydrolysis with 1 n HC1 and 1 n NaOH and resistance of the P ester to hydrolysis with 6 n HCl was increased through incorporation into model humic polymers. Organic P in model humic polymers was also stabilized towards hydrolysis with acid and alkaline phosphomonoesterases. Less than 11% of the organic P in polymers containing PS and PE was hydrolyzed by acid or alkaline phosphatase. The incorporation of PE into a model humic polymer markedly reduced the amount of P mineralized during incubation in soil when compared to P mineralized in soils treated with PE. For all environmental conditions imposed during soil incubations (i.e. pH, aeration, temperature), only 20% of the P in model humic polymer containing PE was released during a 16-week period. In contrast, > 60% of the P in either PS and PE added individually to soils or PS and PE intimately mixed with preformed model humic polymer and then added to soils was released during the initial 7 days of soil incubation. The results suggest that a portion of the unidentified organic P in soils may arise from the incorporation of organic compounds containing both amine and phosphate ester functional groups into humic materials and that the organic P thus formed is resistant to both chemical and enzymatic hydrolysis.

Use of urease inhibitors and urea fertilizers on winter wheat

Phosphoroamide urease inhibitors were evaluated for their ability to increase grain protein and yield of winter wheat (Triticum aestivum L.) when added to surfaceapplied urea-based fertilizers. Six urease inhibitors [trichloroethyl phosphorodiamidate, diethyl phosphoric triamide, dimethyl phosphoric triamide, N-(diaminophosphinyl)-cyclohexylamine, N-benzyl-N-methyl phosphoric triamide, and phenylphosphorodiamide] were evaluated. Nitrogen treatments were urea prills, urea solution, and ureaammonium nitrate (UAN) solution broadcast and UAN solution band applied. Ammonium sulfate and no N treatments were included as controls. Fertilizer treatments were applied in the fall and spring. Soils were Ryker silt loam (Typic Paleudalf), Rensselaer loam (Typic Argiaquoll), and Avonburg silt loam (Aeric Fragiaqualf).Grain yield was a more responsive indicator of N addition than was grain N content. Urea prills and ammonium sulfate were more effective fertilizers than was UAN solution. UAN was not more effective applied in a band than broadcast. Urease inhibitors did not improve the efficiency of urea fertilizers since NH3 volatilization did not appear to be a problem following addition of urea fertilizers in spring or fall.

EFFECTIVENESS OF PHOSPHOROAMIDES IN RETARDING HYDROLYSIS OF UREA SURFACE-APPLIED TO SOILS WITH VARIOUS pH AND RESIDUE COVER1

A field experiment compared the ability of several phosphoroamide compounds to retard urea hydrolysis on a fallowed notill (NT) and conventionally tilled (CT) silt loam soil (pH 5.70). Treatments consisted of urea prills (200 kg N ha-1) with and without inhibitors (4.0 kg ha-1) and a no-fertilizer check. Fertilizers were surface-applied to 10-cm-diameter polyvinyl chloride (PVC) cylinder microplots partially embedded in the soil. Duplicate microplots were removed at intervals after fertilization and analyzed for the quantity of urea remaining. Results indicate that, of the compounds tested, phenyl phosphorodiamidate (PPD) most effectively inhibited urea hydrolysis. Addition of PPD reduced the initial (first 4 to 10 d after fertilization) rate of hydrolysis by 60 to 70% in three of four trials conducted. A laboratory study conducted on a soil at two contrasting initial pH values (5.6 and 7.4) showed that PPD was more effective in the acidic than in the alkaline soil. Two other inhibitors (UI4 and UI5) retarded hydrolysis to a greater degree than did PPD in the alkaline soil. In the same laboratory study phosphoroamide (UI6), not tested in the field, was found to be least effected by soil pH and showed promise as a urease inhibitor in both acidic and alkaline soils. Field and laboratory studies indicate that urea was hydrolyzed 2.3 to 3 times faster when added to corn-residue-covered surfaces than to bare soil. This finding suggests that the residue contained high levels of urease activity.

Transformations and losses of fertilizer nitrogen on no-till and conventional till soils

A field study was conducted in 1982 to measure the effect of no-till (NT) and conventional till (CT) systems on N transformation after surface and subsurface applications of N fertilizers. Urea, urea-ammonium nitrate (UAN) solution, (NH4)2SO4 (AS), and CA(NO3)2 were applied to NT and CT plots (5.95 m2) at a rate of 448 kg N ha−1. A comparison of fertilizer N recovered in soils receiving incorporated or surface applied N was used to estimate NH3 volatilization while denitrification was estimated from fertilizer N recovered in the presence and absence of nitrapyrin with incorporated N. Immobilization was assessed in microplots (0.37 m2) after surface application of (15NH4)2SO4 to NT and CT systems at a rate of 220 kg N ha−1.The results indicate little difference between NT and CT systems on urea hydrolysis rates and immobilization of surface applied fertilizer N. Approximately 50% and 10% of the surface applied N was recovered in the inorganic and organic fractions, respectively, on both tillage systems. The N not recovered was likely lost from plot areas through soil runoff. Incorporation of UAN, urea and AS resulted in 20 to 40% greater inorganic N recovery than from surface application. Nitrification rates were greater under the NT than the CT system. The similarities in concentration in the various N pools observed between the two tillage systems may be partially due to the short length of time that NT was imposed in this field study (<1 year) since other researchers using established tillage systems (>5 y) indicate that NT tends to promote decreased efficiency of fertilizer N.

Evaluation of crystalline components in sewage sludge 1

Abstract Crystalline minerals in anaerobically digested sewage sludges were determined by x‐ray diffraction analysis. Sludge samples were prepared for x‐ray analysis by either washing with H2O to remove soluble salts or oxidizing organic matter with H2O. A limited number of minerals are present as crystalline materials in sludge. Even though the sludges contained appreciable concentrations of Cu, Zn, Cd, Pb and Ni, no crystalline metal sulfides, phosphates, hydroxides, oxides or carbonates were found with the exception of a possible Cu, Zn carbonate hydroxide. All other crystalline components detected are common minerals such as quartz, feldspar, montmorillonite, chlorite, mica, dolomite and calcite.