Associated release of magnesium and phosphorus from active and abandoned dairy soils

Dairy manure application to soils can result in phosphorus (P)-related degradation of water quality. The P in these manure-impacted soils can be labile even years after abandonment and under conditions normally associated with high P stability. Failure of P to stabilize with time compounds the environmental consequences of dairy manure disposal, especially on sandy soils. The objectives of this study were to compare chemical characteristics of active and abandoned dairy manure-impacted soils and minimally impacted soils and to assess the continuous release of P in relation to sparingly soluble salts using repeated water extractions, X-ray diffraction, and speciation modeling of column leachates. Soil samples from Ap horizons were collected from nine highly manure-impacted (total P > 1000 mg P kg(-1) soil) areas on four active and five abandoned dairies and four minimally impacted soils (total P < 200 mg P kg(-1) soil). Soil extracts were analyzed for electrical conductivity (EC), soluble reactive phosphorus (SRP), Ca, Mg, Na, and K. The EC of the soil solutions decreased as active dairy > abandoned dairy > minimally impacted soils. Release of Mg and SRP were significantly correlated (r2 = 0.68) and did not decline after abandonment; Ca release was not correlated with SRP (r2 = 0.01), and declined significantly (p < 0.05) after abandonment. Speciation data from column leachates suggested that Mg-P phases and/or the most soluble Ca-P phases could control P solution activities. An implication of this study is that P stabilization via crystallization of calcium phosphates (even at near-neutral pH) may be preempted by Mg-P association. Thus, mechanisms to minimize P release may require P-retaining soil amendments or management of animal rations to eliminate Mg-P formation.     

Lightning Fires in a Brazilian Savanna National Park: Rethinking Management Strategies

Fire occurrences and their sources were monitored in Emas National Park, Brazil (17°49′–18°28′S; 52°39′–53°10′W) from June 1995 to May 1999. The extent of burned area and weather conditions were registered. Forty-five fires were recorded and mapped on a GIS during this study. Four fires occurred in the dry winter season (June–August; 7,942 ha burned), all caused by humans; 10 fires occurred in the seasonally transitional months (May and September) (33,386 ha burned); 31 fires occurred in the wet season, of which 30 were caused by lightning inside the park (29,326 ha burned), and one started outside the park (866 ha burned). Wet season lightning fires started in the open vegetation (wet field or grassy savanna) at a flat plateau, an area that showed significantly higher fire incidence. On average, winter fires burned larger areas and spread more quickly, compared to lightning fires, and fire suppression was necessary to extinguish them. Most lightning fires were patchy and extinguished primarily by rain. Lightning fires in the wet season, previously considered unimportant episodes, were shown to be very frequent and probably represent the natural fire pattern in the region. Lightning fires should be regarded as ecologically beneficial, as they create natural barriers to the spread of winter fires. The present fire management in the park is based on the burning of preventive firebreaks in the dry season and exclusion of any other fire. This policy does not take advantage of the beneficial effects of the natural fire regime and may in fact reduce biodiversity. The results presented here stress the need for reevaluating present policies and management procedures concerning fire in cerrado conservation areas.     

Mercury sequestration in forests and peatlands: a review

Nearly all Hg in vegetation is derived directly from the atmosphere. Mass of Hg in forest vegetation (roughly 0.1 mg m(-2)) is about an order of magnitude smaller than that in the forest floor (1 mg m(-2)) and two orders of magnitude smaller than that in the mineral soil (10 mg m(-2)). Mass of Hg in peat (20 mg m(-2)) is greater than the sum of that in mineral soil and the forest floor; wetlands usually sequester more Hg than associated uplands. The strong relationship of Hg to organic matter, associated with binding by reduced S groups, is fundamental to understanding Hg distribution and behavior in terrestrial systems. The stoichiometry of the Hg-C relationship varies; Hg-S relationships, though less variable, are not constant. Because of the Hg-organic matter link, landscape conditions that lead to differential soil organic matter accumulation are likely to lead to differential Hg accumulation. The ratio of methylmercury (MeHg) to total Hg is generally low in both vegetation (near 1.5%) and soil (<1%), but areas of poorly drained soils and wetlands are sites of MeHg production. The annual emission of anthropic Hg from the 48 contiguous states of the USA (144 Mg) is two orders of magnitude less than the pool of Hg in forests of those states (30,300 Mg). Peatlands, less than 2% of total land area, sequester more than 20 times annual emissions (2930 Mg). If global climate change affects C storage it will indirectly affect Hg storage, having a major effect on the balance between emissions and sequestration and on the global Hg cycle.     

SOIL CHANGES CAUSED BY MUNICIPAL WASTEWATER APPLICATIONS IN EASTERN SOUTH DAKOTA1

ABSTRACT: Wastewater from a municipal treatment plant was applied in rapid infiltration basins for four years to determine a poorly drained soils effectiveness in removing influent N and P and the soil changes that might limit their removal. About half the total PO₄-P lost from the influent was sorbed in the upper 91 cm of the soil and the other half was sorbed by the soil below the perforated pipe, which was used to drain the basins and collect the effluent for analysis. Drying of the basin soils converted more sorbed PO₄-P to Ca phosphates but the total sorbed was about the same. The in. fluent N decreased, probably by volatilization, because the two basins with surface soil lost soil N rather than gained soil N. The soil total Ca, Mg, and K contents did not change significantly but Na increased slightly. Changes in the physical characteristics of the soils were slight and would have little effect on the longevity of a rapid infiltration basin.     

The availability of copper in soils historically amended with sewage sludge, manure, and compost

Metals in soils amended with sewage sludge are typically less available compared with those in soils spiked with soluble metal salts. However, it is unclear if this difference remains in the long term. A survey of copper (Cu) availability was made in soils amended with sewage sludge, manure, and compost, collectively named organic amendments. Paired sets of amended and control soils were collected from 22 field trials where the organic amendments had aged up to 112 yr. Amended soils had higher total Cu concentrations (range, 2-220 mg Cu kg; median, 15 mg Cu kg) and organic C (range, 1-16 g kg; median, 4 g kg) than control soils. All samples were freshly spiked with CuCl, and the toxicity of added Cu to barley was compared between amended and control soils. The toxicity of added Cu was significantly lower in amended soils than in control soil in 15 sets by, on average, a factor of 1.4, suggesting that aged amendments do not largely increase Cu binding sites. The fraction of added Cu that is isotopic exchangeable Cu (labile Cu) was compared between control soils freshly spiked with CuCl and amended soils with both soils at identical total Cu concentrations. Copper derived from amendments was significantly less labile (on average 5.9-fold) than freshly added Cu in 18 sets of soils. This study shows that Cu availability after long-term applications of organic amendments is lower than that of freshly added Cu salts, mainly because of its lower availability in the original matrix and ageing reactions than because of increased metal binding sites in soil.     

Impact of land drainage on peatland hydrology

There is a long history of drainage of blanket peat but few studies of the long-term hydrological impact of drainage. This paper aims to test differences in runoff production processes between intact and drained blanket peat catchments and determine whether there have been any long-term changes in stream flow since drainage occurred. Hillslope runoff processes and stream discharge were measured in four blanket peat catchments. Two catchments were drained with open-cut ditches in the 1950s. Ditching originally resulted in shorter lag times and flashier storm hydrographs but no change in the annual catchment runoff efficiency. In the period between 2002 and 2004, the hydrographs in the drained catchments, while still flashy, were less sensitive to rainfall than in the 1950s and the runoff efficiency had significantly increased. Drains resulted in a distinctive spatial pattern of runoff production across the slopes. Overland flow was significantly lower in the drained catchments where throughflow was more dominant. In the intact peatlands, matrix throughflow produced by peat layers below 10 cm was rare and produced <1% of the runoff. However, in drained peatlands, matrix throughflow in deeper peat layers was common and provided around 23% of the runoff from gauged plots. Macropore flow, the density of soil piping, and pipeflow were significantly greater in drained peatlands than in intact basins. Gradual changes to peat structure could explain the long-term changes in river flow, which are in addition to those occurring in the immediate aftermath of peatland drainage.     

SOIL MOISTURE VARIATION PATTERNS OBSERVED IN HAND COUNTY,SOUTH DAKOTA1

ABSTRACT: Sail moisture data were taken during nine sampling events (1976-1978) at a test site in South Dakota as part of the ground truth used in NASA's aircraft experiments studying the microwave sensing of soil moisture. This portion of the study dealt only with the spatial variability observed with regard to the ground data. Samples were taken over three surface depths at each point, and the data reported as the mean field moisture content within each of three surface horizons. The results shed additional light on the relationship between ground sampling and remote sensing of soil moisture. First, it was found that it is best to partition data of well drained sites from poorly drained areas when attempting to characterize the surface moisture content throughout an area of varying soil and cover conditions. It was also found that the moisture coefficient of variation within a field decreased as the mean field soil moisture increased, and that the standard deviation was at a maximum in the mid-range of observed moisture conditions (15-25 percent). Within field sample variation also decreases as the sample is integrated over a greater surface depth. It was determined that a sampling intensity of 10 samples per kilometer was adequate to characterize the mean field soil moisture at all three depths along a transect in the areas of moderate to good drainage-.     

A PRELIMINARY STUDY OF THE EFFECTS OF DRAINAGE AND HARVESTING ON WATER QUALITY IN OMBROTROPHIC BOGS NEAR SEPT-ILES,QUEBEC1

ABSTRACT: Runoff and ground-water samples were collected from four ombrotrophic bogs, representing undisturbed and drained/harvested conditions, at two-week intervals during the summer of 1984. Analyses of samples for water quality parameters revealed significant (P < 0.05 level) increases in specific conductance, NH4⁺-N, total dissolved P, Mg, K, and Na and a decrease in the E₄:E₆ ratio (suggesting increased proportions of humic acid) associated with drainage. There were no significant changes in dissolved organic carbon, Ca concentrations, or pH. Comparison of samples collected before, during, and after ditching showed increases in the dissolved organic carbon, NH₄⁺-N, total dissolved P, K, and Na and a decrease in the E₄:E₆ ratio, but these changes were short lived; water quality returned to preditching values after about a week. The observed changes in water quality are small, probably because the peat is very acid (pH 3.0 to 4.5).     

Trihalomethane formation potential of filter isolates of electrolyte-extractable soil organic carbon

Certain organic C moieties of soil origin in drinking source waters of Sacramento-San Joaquin Delta (Delta) can react with chlorine to form trihalomethanes (THMs) during the disinfection process. Isolation and characterization of them and quantitation of their THM formation potential (THMFP) is necessary for developing effective strategies to reduce their influxes in Delta waters and for removing them during drinking water treatment. In this study, organic C from two Delta soils was extracted using deionized H(2)O and four Na- or Ca-based electrolytes of varying electrical conductivity values. Extracts were filtered into particulate, colloidal, fine colloidal, and soluble organic C for quantitation and THMFP determination. Results suggested that <1.5% of soil organic C was electrolyte-extractable. The soluble organic C fraction from both soils dominated in quantity and THMFP. Electrolyte effects were cation dependent. Sodium-based electrolytes at either conductivity level did not significantly decrease extractable organic C (EOC) or THMFP compared with deionized H(2)O. In contrast, Ca-based electrolytes reduced EOC and THMFP by >50% even at 1 dS m(-1). Further increase in Ca concentration did not significantly decrease EOC or THMFP. Most reduction in EOC and THMFP by Ca-based electrolytes occurred with the fractions other than the soluble organic C. Results suggested that under natural soil leaching and runoff conditions, the majority of THMFP is associated with organic C of <0.025 mum in diameter. Further molecular characterization of the fractions with high THMFP may help understand the nature of chlorine-reactive organic C from Delta soils.     

Runoff losses of sediment and phosphorus from no-till and cultivated soils receiving dairy manure

Managing manure in no-till systems is a water quality concern because surface application of manure can enrich runoff with dissolved phosphorus (P), and incorporation by tillage increases particulate P loss. This study compared runoff from well-drained and somewhat poorly drained soils under corn (Zea mays, L.) production that had been in no-till for more than 10 yr. Dairy cattle (Bos taurus L.) manure was broadcast into a fall planted cover crop before no-till corn planting or incorporated by chisel/disk tillage in the absence of a cover crop. Rainfall simulations (60 mm h(-1)) were performed after planting, mid-season, and post-harvest in 2007 and 2008. In both years and on both soils, no-till yielded significantly less sediment than did chisel/disking. Relative effects of tillage on runoff and P loss differed with soil. On the well-drained soil, runoff depths from no-till were much lower than with chisel/disking, producing significantly lower total P loads (22-50% less). On the somewhat poorly drained soil, there was little to no reduction in runoff depth with no-till, and total P loads were significantly greater than with chisel/disking (40-47% greater). Particulate P losses outweighed dissolved P losses as the major concern on the well-drained soil, whereas dissolved P from surface applied manure was more important on the somewhat poorly drained soil. This study confirms the benefit of no-till to erosion and total P runoff control on well-drained soils but highlights trade-offs in no-till management on somewhat poorly drained soils where the absence of manure incorporation can exacerbate total P losses.     

Alum amendment effects on phosphorus release and distribution in poultry litter-amended sandy soils

Increased poultry production has contributed to excess nutrient problems in Atlantic Coastal Plain soils due to land application of poultry litter (PL). Aluminum sulfate [alum, Al(2)(SO(4))(3).14H(2)O] amendment of PL effectively reduces soluble phosphorus (P) in the PL; however, the effects of these litters when added to acidic, sandy soils are not well understood. The objective of this study was to investigate the efficacy of alum-amended poultry litter in reducing P release from three Delaware Coastal Plain soils: Evesboro loamy sand (Ev; excessively drained, mesic, coated Typic Quartzipsamments), Rumford loamy sand (Ru; well drained, coarse-loamy, siliceous, subactive, thermic Typic Hapludults), and Pocomoke sandy loam (Pm; very poorly drained, coarse-loamy, siliceous, active, thermic Typic Umbraquults). Long-term (25 d) and short-term (24 h) desorption studies were conducted, in addition to chemical extractions and kinetic modeling, to observe the changes that alum-amended versus unamended PL caused in the soils. The Ev, Ru, and Pm soils were incubated with 9 Mg ha(-1) of alum-amended or unamended PL. Long-term desorption (25 d) of the incubated material resulted in approximately 13.5% (Ev), 12.7% (Ru), and 13.3% (Pm) reductions in cumulative P desorbed when comparing soil treated with unamended and alum-amended PL. In addition, the P release from the soil treated with alum-amended litter was not significantly different from the control (soil alone). Short-term desorption (24 h) showed 7.3% (Ev), 15.4% (Ru), and 20% (Pm) reductions. The overall implication from this study is that the use of alum as a PL amendment is useful in coarse-textured soils of the Coastal Plain. With increased application of alum-amended PL, more significant decreases may be possible with little or no effect on soil quality.     

Salt Marsh Diking and Restoration: Biogeochemical Implications of Altered Wetland Hydrology

Experimental short-term desalination and drainage of salt marsh cores in greenhouse microcosms caused Spartina production to increase after one growing season, reflecting decreased salt stress and sulfide toxicity. However, production thereafter declined, likely due to pyrite oxidation and acidification in drained treatments and sulfide accumulation in waterlogged treatments. A survey of longer-term (decadal) effects of diking on peat composition of Cape Cod, Massachusetts, USA, marshes revealed acidification, Fe(II) mobilization, and decreased organic content in drained sites. Despite the aerobic decomposition of organic matter, abundant nutrients remained as sorbed NH₄ and mineral-bound PO₄. In diked, seasonally waterlogged sites, porewater alkalinity, sulfide, ammonium and orthophosphate were much lower, and organic solids higher, than in adjacent natural marsh. Seawater was added to cores from diked marshes to study the effects of tidal restoration. Salination of the drained peat increased porewater pH, alkalinity, ammonium, orthophosphate, Fe, and Al; copious ammonium N, and Fe(II) for sulfide precipitation favored Spartina growth. Salination of diked–waterlogged peat increased sulfate reduction and caused 6–8 cm of sediment subsidence. The resulting increase in porewater sulfides and waterlogging decreased vigor of transplanted Spartina alterniflora. Results indicate that seawater restoration should proceed cautiously to avoid nutrient loading of surface waters in drained sites or sulfide toxicity in diked–waterlogged marshes.     

Soil carbon and nitrogen storage in response to fire in a temperate mixed-grass savanna

Vegetation fires may alter the quantity and quality of organic matter inputs to soil, rates of organic matter decay, and environmental factors that influence those processes. However, few studies have evaluated the impacts of this land management technique on soil organic carbon (SOC) and total N in grasslands and savannas. We evaluated the impact of repeated fires and their season of occurrence on SOC and total N storage in a temperate mixed-grass-mesquite savanna where fire is used to control woody plant encroachment. Four fire treatments varying in season of occurrence were examined: summer only (SF), winter only (WF), alternate summer and winter fires (SWF), and unburned controls. In each treatment, soils were sampled to 1 m under three vegetation types: C3 grasses, C4 grasses, and mesquite trees. The SOC storage at 0 to 20 cm was significantly greater in SF (2693 g C m(-2)) and SWF (2708 g C m(-2)) compared to WF (2446 g C m(-2)) and controls (2445 g C m(-2)). The SWF treatment also increased soil total N (271 g N m(-2)) relative to all other treatments (228-244 g N m(-2)) at 0 to 20 cm. Fire had no effect on SOC or total N at depths of > 20 cm. Vegetation type had no significant influence on SOC or total N stocks. The delta13C value of SOC was not affected by fire, but increased from -21 per thousand at 0 to 10 cm to -15 per thousand at depths of > 20 cm indicating that all treatments were once dominated by C4 grasses before woody plant encroachment during the past century. These results have implications for scientists, land managers, and policymakers who are now evaluating the potential for land uses to alter ecosystem C storage and influence atmospheric CO2 concentrations and global climate.     

Wildfire effects on soil nutrients and leaching in a tahoe basin watershed

A wildfire burned through a previously sampled research site, allowing pre- and post-burn measurements of the forest floor, soils, and soil leaching near Lake Tahoe, Nevada. Fire and post-fire erosion caused large and statistically significant (P < or = 0.05) losses of C, N, P, S, Ca, and Mg from the forest floor. There were no statistically significant effects on mineral soils aside from a decrease in total N in the surface (A11) horizon, an increase in pH in the A11 horizon, and increases in water-extractable SO4(2-) in the A11 and A12 horizons. Burning caused consistent but nonsignificant increases in exchangeable Ca2+ in most horizons, but no consistent or statistically significant effects on exchangeable K+ or Mg2+, or on Bray-, bicarbonate-, or water-extractable P concentrations. Before the burn, there were no significant differences in leaching, but during the first winter after the fire, soil solution concentrations of NH4+, NO3-, ortho-P, and (especially) SO4(2-) were elevated in the burned area, and resin lysimeters showed significant increases in the leaching of NH4+ and mineral N. The leaching losses of mineral N were much smaller than the losses from the forest floor and A11 horizons, however. We conclude that the major short-term effects of wildfire were on leaching whereas the major long-term effect was the loss of N from the forest floor and soil during the fire.     

Denitrification potential in relation to lithology in five headwater riparian zones

The influence of riparian zone lithology on nitrate dynamics is poorly understood. We investigated vertical variations in potential denitrification activity in relation to the lithology and stratigraphy of five headwater riparian zones on glacial till and outwash landscapes in southern Ontario, Canada. Conductive coarse sand and gravel layers occurred in four of the five riparian areas. These layers were thin and did not extend to the field-riparian perimeter in some riparian zones, which limited their role as conduits for ground water flow. We found widespread organic-rich layers at depths ranging from 40 to 300 cm that resulted from natural floodplain processes and the burial of surface soils by rapid valley-bottom sedimentation after European settlement. The organic matter content of these layers varied considerably from 2 to 5% (relic channel deposit) to 5 to 21% (buried soils) and 30 to 62% (buried peat). Denitrification potential (DNP) was measured by the acetylene block method in sediment slurries amended with nitrate. The highest DNP rates were usually found in the top 0- to 15-cm surface soil layer in all riparian zones. However, a steep decline in DNP with depth was often absent and high DNP activity occurred in the deep organic-rich layers. Water table variations in 2000-2002 indicated that ground water only interacted frequently with riparian surface soils between late March and May, whereas subsurface organic layers that sustain considerable DNP were below the water table for most of the year. These results suggest that riparian zones with organic deposits at depth may effectively remove nitrate from ground water even when the water table does not interact with organic-rich surface soil horizons.     

Bedding and seasonal effects on chemical and bacterial properties of feedlot cattle manure

Nutrients, soluble salts, and pathogenic bacteria in feedlot-pen manure have the potential to cause pollution of the environment. A three-year study (1998-2000) was conducted at a beef cattle (Bos taurus) feedlot in southern Alberta, Canada to determine the effect of bedding material [barley (Hordeum vulgare L.) straw versus wood chips] and season on the chemical and bacterial properties of pen-floor manure. Manure was sampled for chemical content (N, P, soluble salts, electrical conductivity, and pH) and populations of four groups of bacteria (Escherichia coli, total coliforms, and total aerobic heterotrophs at 27 and 39 degrees C). More chemical parameters of manure were significantly (P < or = 0.05) affected by season (SO4, Na, Mg, K, Ca, sodium adsorption ratio [SAR], total C, NO3-N, NH4-N, total P, and available P) than by bedding (K, pH, total C, C to N ratio, NH4-N, and available P). Bedding had no significant (P > 0.05) effect on the four bacterial groups whereas season affected all four groups. Numbers of E. coli and total coliforms (TC) were significantly higher by 1.72 to 2.02 log10 units in the summer than the other three seasons, which was consistent with a strong positive correlation of E. coli and TC with air temperature. The low ratio of bedding to manure in the pens was probably the major cause of the lack of significant bedding effects. Bedding material and seasonal timing of cleaning feedlot pens and land application of manure may be a potential tool to manage nutrients, soluble salts, and pathogens in manure.     

Aerating grasslands: effects on runoff and phosphorus losses from applied broiler litter

Aeration has been promoted as improving infiltration of rainfall and extending grass or forage productivity, but research on the impact of this practice on P losses from grasslands has had mixed results. We designed a study to determine at the field scale, using a paired watershed approach, the impact of slit aeration on runoff volume and P losses in runoff from fescue (Festuca arundinacea Schreb.)/bermudagrass (Cynodon dactylon L.) hay fields fertilized with broiler litter. Three pairs of 0.8-ha fields, each with similar soils (Typic Kanhapludults, Aquic Hapludults, and Aquultic Hapludalfs), were fertilized with broiler litter and monitored under similar management from 1995 through 1998, then one field in each pair received aeration treatment from 2001 through 2003. In the field with mostly well-drained soils, grassland aeration reduced surface runoff volume and mass losses of dissolved reactive P (DRP) in runoff by approximately 35%. In contrast, when poorly drained soils dominated, grassland aeration increased runoff volume (4.8 mm/runoff event) and mass losses of DRP and total P (0.25 kg TP ha-1 per runoff event). This implies that aeration of well-drained soils in the top poultry-producing counties of Georgia (0.2 million ha) could decrease dissolved phosphorus losses by more than 500 Mg P each year. This is not the case if soils are poorly drained.     

Adsorption of cadmium on biosolids-amended soils

Debate exists over the biosolid phase (organic or inorganic) responsible for the reduction in phytoavailable Cd in soils amended with biosolids as compared with soils amended with inorganic salts. To test the importance of these two phases, adsorption isotherms were developed for soil samples (nine biosolids-amended soils and their five companion controls) and two biosolids samples from five experimental sites with documented histories of biosolids application. Subsamples were treated with 0.7 M NaClO to remove organic carbon. Cadmium nitrate was added to both moist soil samples and their soil inorganic fractions (SIF) in a 0.01 M Ca(NO3)2 solution at three pH levels (6.5, 5.5, and 4.5), and equilibrated at 22 +/- 1 degrees C for at least 48 h. Isotherms of Cd adsorption for biosolids-amended soil were intermediate to the control soil and biosolids. Decreasing pH did not remove the difference between these isotherms, although adsorption of Cd decreased with decreasing pH level. Organic matter removal reduced Cd adsorption on all soils but had little influence on the observed difference between biosolids-amended and control soils. Thus, increased adsorption associated with biosolids application was not limited to the organic matter addition from biosolids; rather, the biosolids application also altered the adsorptive properties of the SIF. The greater affinity of the inorganic fraction of biosolids-amended soils to adsorb Cd suggests that the increased retention of Cd on biosolids-amended soils is independent of the added organic matter and of a persistent nature.     

Salinity management using an anionic polymer in a pecan field with calcareous-sodic soil

Soil salinity and sodicity have long been recognized as the major concerns for irrigated agriculture in the Trans-Pecos Basin, where fields are being flood irrigated with Rio Grande River water that has elevated salinity. Reclamation of these salt-affected lands is difficult due to fine-texture, high shrink-swell soils with low permeability. Conventional practice of subsoiling to improve soil permeability is expensive and has had limited success on the irrigated soils that have appreciable amounts of readily weatherable Ca minerals. If these native Ca sources can be effectively used to counter sodicity, it can improve soil permeability and reduce amelioration costs. This study evaluated the effects of 3 yr of polyacrylamide (PAM) application at 10 mg L concentration during the first irrigation of the season to evaluate soil permeability, in situ Ca mineral dissolution, and leaching of salts from the effective root zone in a pecan field of El Paso County, TX. Results indicated that PAM application improved water movement throughout the effective root zone that resulted in Na leaching. Polymer application significantly decreased CaCO (estimated based on inorganic C analysis) concentrations in the top 45 cm compared with baseline levels, indicating solubilization and redistribution of calcite. The PAM application also reduced soil electrical conductivity (EC) in the top 60 cm (4.64-2.76 dS m) and sodium adsorption ratio (SAR) from 13.1 to 5.7 mmol L in the top 75-cm depths. As evidence of improved soil conditions, pecan nut yields increased by 34% in PAM-treated fields over the control. Results suggested that PAM application helped in effective use of native Ca sources present in soils of the study site and reduced Na by improving soil permeability.     

Soil and tree-ring chemistry response to liming in a sugar maple stand

An evaluation of the impact of dolomitic lime [CaMg(CO3)2] on soils (five years after treatment) and sapwood chemistry (after four growing seasons) was realized for a Ca-deficient sugar maple stand at the lake Clair watershed. The effect on humus chemistry was significant: exchangeable Mg and Ca, effective acidity (EA), base saturation (BSe), pH, and effective cation exchange capacity (CECe) significantly increased, while exchangeable Fe significantly decreased. In the B horizon, liming increased exchangeable Ca, Mg, and Mn concentrations while decreasing other acid cations. No significant temporal trends in element concentrations in tree rings could be detected, although the lime treatment significantly changed the average xylem Mg and Mn concentrations as well as the average Mg/Mn and Ca/Mn ratios of the sapwood. The absence of temporal trends in rings from the last 20 yr implied a significant re-equilibration of elements through the sapwood. Significant relationships were found between averaged xylem Ca/Mn and Mg/Mn ratios and exchangeable humus Ca, Mg, Mn, Al, Fe, and H+ concentration, EA, CECe, and BSe, suggesting that the average xylem Ca/Mn and Mg/Mn ratios are strong indicators of the soil acid-base status.