Environmental and production consequences of using alum-amended poultry litter as a nutrient source for corn

Field trials were established to compare alum-treated poultry litter (ATPL), normal poultry litter (NPL), and triple superphosphate (TSP) as fertilizer sources for corn (Zea mays L.) when applied at rates based on current litter management strategies in Virginia. Trials were established in the Costal Plain and Piedmont physiographic regions near Painter and Orange, VA, respectively. Nitrogen-based applications of ATPL or NPL applied at rates estimated to supply 173 kg of plant-available nitrogen (PAN) ha(-1) resulted in significantly lower grain yields than treatments receiving commercial fertilizer at the same rate in 2000 and 2001 at Painter. These decreases in grain yield at the N-based application rates were attributed to inadequate N availability, resulting from overestimates of PAN as demonstrated by tissue N concentrations. However, at Orange no treatment effects on grain yield were observed. Applications of ATPL did not affect Al concentrations in corn ear-leaves at either location. Exchangeable soil Al concentrations were most elevated in treatments receiving only NH4NO3 as an N source. At N-based application rates, the ATPL resulted in lower Mehlich 1-extractable P (M1-P) and water-extractable soil phosphorus (H2O-P) concentrations compared to the application of NPL. A portion of this reduction could be attributed to lower rates of P applied in the N-based ATPL treatments. Runoff collected from treatments which received ATPL 2 d before conducting rainfall simulations contained 61 to 71% less dissolved reactive phosphorus (DRP) than treatments receiving NPL. These results show that ATPL may be used as a nutrient source for corn production without significant management alterations. Alum-treated poultry litter can also reduce the environmental impact of litter applications, primarily through minimizing the P status of soils receiving long-term applications of litter and reductions in runoff DRP losses shortly after application.     

What is soil organic matter worth?

The conservation and restoration of soil organic matter are often advocated because of the generally beneficial effects on soil attributes for plant growth and crop production. More recently, organic matter has become important as a terrestrial sink and store for C and N. We have attempted to derive a monetary value of soil organic matter for crop production and storage functions in three contrasting New Zealand soil orders (Gley, Melanic, and Granular Soils). Soil chemical and physical characteristics of real-life examples of three pairs of matched soils with low organic matter contents (after long-term continuous cropping for vegetables or maize) or high organic matter content (continuous pasture) were used as input data for a pasture (grass-clover) production model. The differences in pasture dry matter yields (non-irrigated) were calculated for three climate scenarios (wet, dry, and average years) and the yields converted to an equivalent weight and financial value of milk solids. We also estimated the hypothetical value of the C and N sequestered during the recovery phase of the low organic matter content soils assuming trading with C and N credits. For all three soil orders, and for the three climate scenarios, pasture dry matter yields were decreased in the soils with lower organic matter contents. The extra organic matter in the high C soils was estimated to be worth NZ$27 to NZ$150 ha(-1) yr(-1) in terms of increased milk solids production. The decreased yields from the previously cropped soils were predicted to persist for 36 to 125 yr, but with declining effect as organic matter gradually recovered, giving an accumulated loss in pastoral production worth around NZ$518 to NZ$1239 ha(-1). This was 42 to 73 times lower than the hypothetical value of the organic matter as a sequestering agent for C and N, which varied between NZ$22,963 to NZ$90,849 depending on the soil, region, discount rates, and values used for carbon and nitrogen credits.     

Increased wind erosion from forest wildfire: implications for contaminant-related risks

Assessments of contaminant-related human and ecological risk require estimation of transport rates, but few data exist on wind-driven transport rates in nonagricultural systems, particularly in response to ecosystem disturbances such as forest wildfire and also relative to water-driven transport. The Cerro Grande wildfire in May of 2000 burned across ponderosa pine (Pinus ponderosa Douglas ex P.&C. Lawson var. scopulorum Englem.) forest within Los Alamos National Laboratory in northern New Mexico, where contaminant transport and associated post-fire inhalation risks are of concern. In response, the objectives of this study were to measure and compare wind-driven horizontal and vertical dust fluxes, metrics of transport related to wind erosion, for 3 yr for sites differentially affected by the Cerro Grande wildfire: unburned, moderately burned (fire mostly confined to ground vegetation), and severely burned (crown fire). Wind-driven dust flux was significantly greater in both types of burned areas relative to unburned areas, by more than one order of magnitude initially and by two to three times 1 yr after the fire. Unexpectedly, the elevated dust fluxes did not decrease during the second and third years in burned areas, apparently because ongoing drought delayed post-fire recovery. Our estimates enable assessment of amplification in contaminant-related risks following a major type of disturbance-wildfire, which is expected to increase in intensity and frequency due to climate change. More generally, our results highlight the importance of considering wind- as well as water-driven transport and erosion, particularly following disturbance, for ecosystem biogeochemistry in general and human and ecological risk assessment in particular.     

Upflow reactors for riparian zone denitrification

We used permeable reactive subsurface barriers consisting of a C source (wood particles), with very high hydraulic conductivities ( approximately 0.1-1 cm s(-1)), to provide high rates of riparian zone NO3-N removal at two field sites in an agricultural area of southwestern Ontario. At one site, a 0.73-m3 reactor containing fine wood particles was monitored for a 20-mo period and achieved a 33% reduction in mean influent NO3-N concentration of 11.5 mg L(-1) and a mean removal rate of 4.5 mg L(-1) d(-1) (0.7 g m(-2) d(-1)). At the second site, four smaller reactors (0.21 m3 each), two containing fine wood particles and two containing coarse wood particles, were monitored for a 4-mo period and were successful in attenuating mean influent NO3-N concentrations of 23.7 to 35.1 mg L(-1) by 41 to 63%. Mean reaction rates for the two coarse-particle reactors (3.2 and 7.8 mg L(-1) d(-1), or 1.5 and 3.4 g m(-2) d(-1)) were not significantly different (p > 0.2) than the rates observed in the two fine-particle reactors (5.0 and 9.9 mg L(-1) d(-1), or 1.8-3.5 g m(-2) d(-1)). A two-dimensional ground water flow model is used to illustrate how permeable reactive barriers such as these can be used to redirect ground water flow within riparian zones, potentially augmenting NO3- removal in this environment.     

Phosphorus fractions in manure from growing pigs receiving diets containing micronized peas and supplemental enzymes

Different livestock feeds manipulations have been reported to reduce the total P concentration in manure. Information on the influence of these dietary manipulation strategies on the forms of P in manure is, however, limited. This study was, therefore, conducted to investigate the effect of diet manipulation through feed micronization and enzyme supplementation on the forms of P in swine manure. Eight growing pigs were fed four diets: barley-raw pea (BRP), barley-micronized pea (BMP), barley-raw pea with enzyme (BRPE), and barley-micronized pea with enzyme (BMPE) in a 4 x 4 Latin square design. Because we are interested in the effect of enzyme cocktail and pea micronization on manure P, we did not reduce the non-phytate P with enzyme addition in this study. The fecal material and urine were collected and analyzed for total P. Fecal material was fractionated to determine the total P in H2O-, NaHCO3-, NaOH-, and HCl-extractable fractions. The total P in the residual fractions was also determined. About 98% of the total P excreted by the pigs was found in the fecal material. Inclusion of micronized pea in pig diet did not have any significant effect (p > 0.1) on either the total P or the different P fractions in the manure. The labile P (the sum of H2O-P and NaHCO3-P) was significantly reduced (p < 0.05) by the addition of enzyme to swine diets. Pigs fed the BRPE and BMPE had 14 and 18% lower labile P, respectively, compared with pigs fed the BRP. Enzyme addition to pig diets reduced not only the total P in manure, but also the labile P fraction, which is of great environmental concern. Thus, the potential of P loss to runoff and the subsequent eutrophication can be reduced by enzyme addition to pig diets.     

Soil organic carbon sequestration in cotton production systems of the southeastern United States: a review

Past agricultural management practices have contributed to the loss of soil organic carbon (SOC) and emission of greenhouse gases (e.g., carbon dioxide and nitrous oxide). Fortunately, however, conservation-oriented agricultural management systems can be, and have been, developed to sequester SOC, improve soil quality, and increase crop productivity. Our objectives were to (i) review literature related to SOC sequestration in cotton (Gossypium hirsutum L.) production systems, (ii) recommend best management practices to sequester SOC, and (iii) outline the current political scenario and future probabilities for cotton producers to benefit from SOC sequestration. From a review of 20 studies in the region, SOC increased with no tillage compared with conventional tillage by 0.48 +/- 0.56 Mg C ha(-1) yr(-1) (H(0): no change, p < 0.001). More diverse rotations of cotton with high-residue-producing crops such as corn (Zea mays L.) and small grains would sequester greater quantities of SOC than continuous cotton. No-tillage cropping with a cover crop sequestered 0.67 +/- 0.63 Mg C ha(-1) yr(-1), while that of no-tillage cropping without a cover crop sequestered 0.34 +/- 47 Mg C ha(-1) yr(-1) (mean comparison, p = 0.04). Current government incentive programs recommend agricultural practices that would contribute to SOC sequestration. Participation in the Conservation Security Program could lead to government payments of up to Dollars 20 ha(-1). Current open-market trading of C credits would appear to yield less than Dollars 3 ha(-1), although prices would greatly increase should a government policy to limit greenhouse gas emissions be mandated.     

Iron and arsenic release from aquifer solids in response to biostimulation

Biostimulation has been used at various contaminated sites to promote the reductive dechlorination of trichloroethylene (TCE), but the addition of carbon and energy donor also stimulates bacteria that use Fe(III) as the terminal electron acceptor (TEA) in potential competition with dechlorination processes. Microcosm studies were conducted to determine the influence of various carbon donors on the extent of reductive dissolution of aquifer solids containing Fe(III) and arsenic. Glucose, a fermentable and respirable carbon donor, led to the production of 1500 mg Fe(II) kg(-1), or 24% of the total Fe in the aquifer sediment being reduced to Fe(II), whereas the same concentration of carbon as acetate resulted in only 300 mg Fe(II) kg(-1) being produced. The biogenic Fe(II) produced with acetate was exclusively associated with the solid phase whereas with fermentable carbon donors as whey and glucose, 22 and 54% of the Fe(II) was in solution. With fermentation, some of the metabolites appear to be electron shuttling chemicals and chelating agents that facilitate the reductive dissolution of even crystalline Fe(III) oxides. Without the presence of electron shuttling chemicals, only surficial Fe in direct contact with the bacteria was bioavailable, as illustrated when acetate was used. Regardless of carbon donor type and concentration, As concentrations in the water exceeded drinking water standards. The As dissolution appears to have been the result of the direct use of As as an electron acceptor by dissimilatory arsenic reducing bacteria. Our findings indicate that selection of the carbon and energy donor for biostimulation for remediation of chlorinated solvent impacted aquifers may greatly influence the extent of the reductive dissolution of iron minerals in direct competition with dechlorination processes. Biostimulation may also result in a significant release of As to the solution phase, contributing to further contamination of the aquifer.     

Sorption dynamics of organic and inorganic phosphorus compounds in soil

Phosphorus retention in soils is influenced by the form of P added. The potential impact of one P compound on the sorption of other P compounds in soils has not been widely reported. Sorption isotherms were utilized to quantify P retention by benchmark soils from Indiana, Missouri, and North Carolina when P was added as inorganic P (Pi) or organic P (beta-D-glucose-6-phosphate, G6P; adenosine 5'-triphosphate, ATP; and myoinositol hexaphosphate, IP6) and to determine whether soil P sorption by these organic P compounds and Pi was competitive. Isotherm supernatants were analyzed for pH and total P using standard protocols, while Pi and organic P compounds were assayed using ion chromatography. Under the controlled conditions of this study, the affinity of all soils for P sources followed the order IP6 > G6P > ATP > Pi. Each organic P source had a different potential to desorb Pi from soils, and the order of greatest to least Pi desorption was G6P > ATP > IP6. Glucose-6-phosphate and ATP competed more directly with Pi for sorption sites than IP6 at greater rates of P addition, but at the lesser rates of P addition, IP6 actually desorbed more Pi. Inositol hexaphosphate was strongly sorbed by all three soils and was relatively unaffected by the presence of other P sources. Decreased total P sorption due to desorption of Pi can be caused by relatively small additions of organic P, which may help explain vertical P movement in manured soils. Sorption isotherms performed using Pi alone did not accurately predict total P sorption in soils.     

Use of beryllium-7 to document soil redistribution following forest harvest operations

Rapid and reliable methods for documenting soil erosion associated with forest harvest operations are needed to support the development of best management practices for soil and water conservation. To address this need, the potential for using 7Be measurements to estimate patterns and amounts of soil redistribution associated with individual post-harvest events was explored. The 7Be technique, which was originally developed for use on agricultural land, was employed to estimate soil redistribution associated with a period of heavy rainfall within a harvested forest area located in the Lake Region of Chile (39 degrees 44'7' S, 73 degrees 10'39' W; 22% slope; and mean annual rainfall 2300 mm yr(-1)). The results provided by the 7Be technique were validated against direct measurements of soil gain or loss during the same period obtained using erosion pins. The information produced by the two approaches was similar. The results of this study demonstrate the potential for using 7Be measurements to document event-based erosion in recently harvested forest areas.     

Effects of elevated atmospheric carbon dioxide on biomass and carbon accumulation in a model regenerating longleaf pine community

Plant species vary in response to atmospheric CO2 concentration due to differences in physiology, morphology, phenology, and symbiotic relationships. These differences make it very difficult to predict how plant communities will respond to elevated CO2. Such information is critical to furthering our understanding of community and ecosystem responses to global climate change. To determine how a simple plant community might respond to elevated CO2, a model regenerating longleaf pine community composed of five species was exposed to two CO2 regimes (ambient, 365 micromol mol(-1) and elevated, 720 micromol mol(-1)) for 3 yr. Total above- and belowground biomass was 70 and 49% greater, respectively, in CO2-enriched plots. Carbon (C) content followed a response pattern similar to biomass, resulting in a significant increase of 13.8 Mg C ha(-1) under elevated CO2. Responses of individual species, however, varied. Longleaf pine (Pinus palustris Mill.) was primarily responsible for the positive response to CO2 enrichment. Wiregrass (Aristida stricta Michx.), rattlebox (Crotalaria rotundifolia Walt. Ex Gmel.), and butterfly weed (Asclepias tuberosa L.) exhibited negative above- and belowground biomass responses to elevated CO2, while sand post oak (Quercus margaretta Ashe) did not differ significantly between CO2 treatments. As with pine, C content followed patterns similar to biomass. Elevated CO2 resulted in alterations in community structure. Longleaf pine comprised 88% of total biomass in CO2-enriched plots, but only 76% in ambient plots. In contrast, wiregrass, rattlebox, and butterfly weed comprised 19% in ambient CO2 plots, but only 8% under high CO2. Therefore, while longleaf pine may perform well in a high CO2 world, other members of this community may not compete as well, which could alter community function. Effects of elevated CO2 on plant communities are complex, dynamic, and difficult to predict, clearly demonstrating the need for more research in this important area of global change science.