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Dissolved organic matter (DOM) from biosolids can alter the sorption of orthophosphate (inorganic phosphorus (IP)) to soils and, therefore, affect the bioavailability of IP. It is not clear how clay mineralogy and solution composition interfere with DOM effects on IP sorption by soils. Hence, we studied the effect of DOM on IP sorption to five semi-arid soils dominated by either illite/smectite (I/S) or kaolinite clays. IP sorption isotherms were constructed in either NaCl or CaCl 2 background solution, with and without the addition of DOM. The IP sorption capacity maxima ( S MAX , Langmuir model) of the I/S soils were 33–102% higher in the presence of CaCl 2 , as compared to NaCl. Although DOM had no effect on the IP- S MAX in the presence of CaCl 2 , it increased the IP- S MAX by 35–59% in the presence of the NaCl solution. Surprisingly, DOM sorption to the I/S soils was 30–90% greater in the presence of a Na + -dominated solution, as compared to a Ca 2+ -dominated solution. In contrast to the I/S soils, the S MAX of the kaolinitic soil was not affected by the background electrolyte (Na + , Ca 2+ ) or the addition of DOM. Furthermore, the addition of IP reduced the sorption of DOM to the kaolinitic soil (by up to 50%) in both background electrolyte solutions. These results highlight the contrasting roles of divalent and monovalent cations in conjunction with DOM in IP sorption to semi-arid I/S soils. We propose a new approach based on two conceptual mechanisms to explain the DOM’s enhancement of IP sorption to I/S soils. (1) Under dispersion conditions in the Na + -dominated solutions, Ca 2+ -mediated DOM-IP complexes bind to the clay’s negative planar surfaces. (2) Under flocculation conditions in the Ca + -dominated solutions, the distance between adjacent platelets decreases, reducing both the electronegative charge spillover and Ca 2+ bridge-mediated DOM sorption. In contrast, the addition of DOM to kaolinite, a multi-platelet clay with a low isomorphic negative charge, reduces IP sorption due to competitive sorption on the clay’s broken edges.

Core Ideas Additional N can enhance cereal cover crop biomass production and maximize benefits. Cover crop N fertilizer recovery efficiency averaged 37% across all treatments. Commercial N fertilizer increased biomass for less money compared to poultry litter. Winter cereal cover crops are necessary to achieve maximum benefits of conservation tillage in the southeastern United States. These benefits generally increase as cover crop biomass increases; therefore, we conducted a study to evaluate N application times, sources, and optimal rates to maximize cover crop biomass production at Headland, AL, on a Fuquay sand (loamy, kaolinitic, thermic Arenic Plinthic Kandiudults) during the 2006–2008 growing seasons. Treatments were arranged in a split‐split plot treatment restriction in a randomized complete block design with four replications. Main plots were time of fertilizer application (fall and spring), subplots were N source (commercial fertilizer and poultry [Gallus gallus domesticus] litter), and sub‐subplots were N rate (0, 34, 67, and 101 kg N ha−1 as commercial fertilizer and 0, 2.2, 4.5, and 6.7 Mg ha−1 as poultry litter [as‐sampled basis]) for a cereal rye (Secale cereale L.) cover crop. Commercial fertilizer produced 13% greater biomass compared to poultry litter across all rates and application times. Lower biomass production and higher costs for poultry litter reduced the feasibility of poultry litter as an N source compared with commercial N. Higher C/N ratios were measured for fall‐applied N compared to spring‐applied N, while N fertilizer recovery efficiency (REN) averaged 37% across the experiment. Results indicated fall application of commercial fertilizer N produced superior results across cover crop responses examined in this study, while providing general information about N fertilizer requirements to increase surface residue associated with cover crops across the southeastern United States.

Adding anionic polyacrylamide (PAM) to soils stabilizes existing aggregates and improves bonding between and aggregation of soil particles. However, the dependence of PAM efficacy as an aggregate stabilizing agent with soils having different clay mineralogy has not been studied. Sixteen soil samples (loam or clay) with predominantly smectitic, illitic, or kaolinitic clay mineralogy were studied. We measured aggregate sensitivity to slaking in soils that were untreated or treated with an anionic high-molecular-weight PAM using the high energy moisture characteristic (HEMC) method and deionized water. The index for aggregate susceptibility to slaking, termed stability ratio (SR), was obtained from quantifying differences in the water retention curves at a matric potential range of 0 to -5.0 J kg-1 for the treatments studied. For the untreated soils, the SR ranged widely from 0.24 to 0.80 and generally SR of kaolinitic > illitic > smectitic soils. The SR of PAM-treated aggregates exhibited a narrow range from 0.70 to 0.94. The efficiency of PAM in improving aggregate and structural stability relative to untreated soils ranged from 1.01 to 3.90 and the relative SR of kaolinitic < illitic < smectitic samples. These results suggest that the less stable the aggregates the greater the effectiveness of PAM in increasing aggregates stability (i.e., smectitic vs. kaolinitic samples). The effectiveness of PAM in improving structure and aggregate stability was directly related to clay activity and to soil conditions affecting PAM adsorption (e.g., electrolyte resources, pH, and exchangeable cations) to the soil particles and inversely to the inherent aggregate stability.

Environmental pressure to reduce nutrient losses from agricultural fields has increased in recent years. To abate this nutrient loss to the environment, better management practices and new technologies need to be developed. Thus, research was conducted to evaluate if subsurface banding poultry litter (PL) would reduce nitrogen (N) and phosphorus (P) loss in surface water runoff using a four-row prototype implement. Rainfall simulations were conducted to create a 40-min runoff event in an established bermudagrass (Cynodon dactylon L.) pasture on soil types common to the Coastal Plain and Piedmont regions. The Coastal Plain soil type was a Marvyn loamy sand (fine-loamy, kaolinitic, thermic Typic Kanhapludults) and the Piedmont soil type was a Hard Labor loamy sand (fine, kaolinitic, thermic Oxyaquic Kanhapludults). Treatments consisted of surface- and subsurface-applied PL at a rate of 9 Mg ha−1, surface broadcast–applied commercial fertilizer (CF; urea and triple superphosphate blend) at the equivalent N (330 kg N ha−1) and P (315 kg N ha−1) content of PL, and a nonfertilized control. The greatest loss for inorganic N, total N, dissolved reactive P (DRP), and total P occurred with the surface broadcast treatments, with CF contributing to the greatest loss. Nutrient losses from the subsurface banded treatment reduced N and P in surface water runoff to levels of the control. Subsurface banding of PL reduced concentrations of inorganic N 91%, total N 90%, DRP 86%, and total P 86% in runoff water compared with surface broadcasted PL. These results show that subsurface band–applied PL can greatly reduce the impact of N and P loss to the environment compared with conventional surface-applied PL and CF practices.

In this research, field emission scanning electron microscopy coupled with an energy-dispersive X-ray analyser was employed to study the micro-textural features and elemental composition of lime-stabilized soil. This technique was used to visualize the time-dependent morphological changes in different clay mineral structure and, moreover, to observe the formation of new cementing products that could not be detected by X-ray diffraction method. Due to the “surface associated” nature of soil–lime reactions, the N₂-BET surface area of treated soils was also monitored with curing time. Unconfined compressive strength test as an index of soil’s improvement was performed on cured samples. Based on the results it was found that the type of cementing compounds that were formed after 8 months of curing was dependent on the type of clay minerals present. Also the progression of pozzolanic reaction was highly sensitive to the impurities present on the surface of soil particles. From an engineering point of view, the lime stabilization technique was effective in increasing the strength properties of natural soils with sodium bentonite (comprised mainly of montmorillonite mineral) showing the highest degree of improvement.

Soil mineralogy and texture have substantial effects on aggregate stability and, therefore, may influence infiltration rate (IR) and soil loss under rainfall. The objective was to study the effects of soil mineralogy and texture on crust micromorphology, infiltration, and erosion. Five soils with differing properties were subjected to 80 mm of simulated rainfall. The aggregate stability of these soils was determined by the fast wetting method. The mean‐weight diameters of the particles after the fast wetting were 2.8 mm in the clayey kaolinitic soil, 0.25 and 0.31 mm in the clayey and sandy loam montmorillonitic soils, respectively, and 0.84 and 0.87 mm in the clayey nonphyllosilicate soils. The final IR was 20.5 mm h−1 in the clayey kaolinitic soil and ≤9.3 mm h−1 in the remaining soils. Scanning electron microscope (SEM) observations indicated that the kaolinitic soil had a thin crust (∼0.1 mm) containing large particles (∼0.1 mm), whereas the montmorillonitic soils had thicker crusts (>0.2 mm) comprising either small (∼0.02 mm) particles with a very developed washed‐in zone underneath or large (∼0.2 mm) ones with fine material between them. The crust layer in the nonphyllosilicate soils was ∼0.2 mm thick and composed of fine particles ∼0.01 mm. The high aggregate stability and the low dispersivity of the kaolinitic soil, which minimized soil detachment, and its low runoff, which minimized its transport capacity, limited the soil loss to 0.33 kg m−2, whereas the low aggregate stability and high runoff of the montmorillonitic soils contributed to their soil losses of 1.24 and 1.14 kg m−2 The intermediate aggregate stability and the high runoff of the nonphyllosilicate soils accounted for their intermediate soil losses of 0.75 and 0.8 kg m−2

Sodicity adversely affects soil physical conditions reflected by weak structural stability. Soil clay mineralogy influences the degree of aggregate disruption induced by sodicity. The main objective of this research was to evaluate the interactive effects of clay mineralogy, prewetting rate (PWR), and sodicity on soil aggregation. Three soils with predominantly clay minerals of smectite, vermiculite-smectite, and kaolinite were equilibrated with NaCl-CaCl₂ solutions having sodium adsorption ratio (SAR) values of 0, 20, and 50 and electrical conductivity (EC) = 3.0 dS m⁻¹. After air-drying, the treated samples were packed and prewetted at rates of 2 and 30 mm h⁻¹ with the NaCl-CaCl₂ solutions. Aggregate-size distribution, macroscopic swelling, and surface soil dispersion were determined after the packed samples were equilibrated to a matric potential of -0.1 MPa. The kaolinitic soil showed the lowest inherent aggregate stability when subjected to slow PWR and the lowest SAR. Furthermore, aggregate stability of the kaolinitic loam soil was not significantly affected by increasing SAR. The Millox (smectitic) soil, on the other hand, was most susceptible to aggregate slaking, whereas the Malibu (vermiculitic) soil was most susceptible to differential swelling (at slow PWR). When SAR was low, aggregate slaking by fast PWR was the main cause of the aggregate breakdown. At SAR >or= 20, swelling and dispersion became more important to the structural stability.

The nutrient content of sludge produced by municipal water treatment works often far exceeds the requirements of nearby crops. Transporting sludge further afield is not always economically viable. This study reports on the potential to export large volumes of anaerobically digested municipal sewage sludge through turfgrass sod production. Hypotheses examined are that sludge loading rates far above recommendations based on crop nutrient removal (i) are possible without reducing turf growth and quality, (ii) do not cause an accumulation of N and P below the active root zone, (iii) can minimize soil loss through sod harvesting, and (iv) do not cause unacceptably high nitrate and salt leaching. An 8 Mg ha−1 sludge control (the recommended limit) was compared with sludge rates of 0, 33, 67, and 100 Mg ha−1 on a loamy, kaolinitic, mesic, Typic Eutrustox soil near Johannesburg, South Africa. Sludge application rates up to 67 Mg ha−1 signifi cantly improved turfgrass establishment rate and color. The ability of sods to remain intact during handling and transport improved as the sludge application rate increased to 33 Mg ha−1 but deteriorated at higher rates. A sludge application rate of 100 Mg ha−1 was needed to eliminate soil loss, but this rate was associated with unacceptably high N leaching losses. All our hypotheses were accepted for application rates not exceeding 33 Mg ha−1 on the proviso that some soil loss was acceptable and that the leaching fraction was carefully managed during the first 2 mo after sludge application.

The effectiveness of persulfate oxidation for the destruction of tetrachlorobiphenyl a representative polychlorobiphenyl (PCB), in spiked subsurface soils was evaluated in this study. Kaolin and glacial till soils were selected as representative low permeability soils; both soils were spiked with 50 mg PCB per dry kilogram of soil. Activation of persulfate oxidation was necessary to achieve effective destruction of PCBs in soils. As persulfate oxidation activators, temperature and high pH were used in order to maximize PCB destruction. In addition, the effect of oxidant dose and reaction time was investigated. The optimal dose for persulfate was found to be 30% for maximum oxidation. The persulfate activation with temperature of 45°C was superior to persulfate activation with high pH (pH 12), where higher PCB destructions were observed for kaolin and glacial till soils. PCB destruction increased with reaction time, where maximum degradation was achieved after 7 days. The highest PCB destruction was achieved with temperature activation at 45°C using a dosage of 30% persulfate at pH 12 for kaolin and glacial till soils after 7 days.

Depositional seals, formed when turbid waters infiltrate into soils, lead to a reduction in the hydraulic conductivity (HC) of soils and increased runoff. In this study, the effect of anionic polyacrylamide (PAM) on the HC and flocculation of depositional seals made of three clay minerals (montmorillonite, illite, and kaolinite), saturated with either Na or Ca, was investigated. A silt loam soil was packed in columns and leached with 5 g L-1 suspensions of the reference clays. Deposition of the clay particles on the soil surface formed seals. In the PAM treatment, dry granules of linear PAM were spread on the soil surface before the suspension application. Calcium seals were more permeable than Na seals in all the clay types, up to 26 times greater for montmorillonite. The HC of the seals for the clay minerals was in the order kaolinite (2.8-3.5 mm h-1) > illite (0.6-3.0 mm h-1) > montmorillonite (0.09-1.0 mm h-1). The addition of PAM generally enhanced clay flocculation, with the magnitude of the enhancement depending on the type of the exchangeable cation. The Na-saturated seals in the three clay types had significantly higher initial HC with the PAM treatment. This increase, however, was transient except in Na-illite. The impact of PAM on the degree of clay flocculation and floc density partially explained the effects of PAM on the HC of the depositional seals. An increase in clay flocculation or a decrease in floc density caused by PAM resulted in an increase in depositional seal HC.