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Excess manure phosphorus (P) in areas of intensive animal production can lead to applying more P to fields than crops require, and local water quality can consequently be affected. Dietary strategies, reducing P overfeeding, using feed additives to enhance dietary P utilization, and developing high available phosphorus (HAP) grains have all been shown to decrease fecal P excretion without impairing animal performance. Total P in manures can be reduced by all dietary strategies, but the impact of different approaches on the solubility of P in manures and amended soils has been more variable. Soluble P continues to be of particular concern because of links between solubility of P in manure and P losses from manure-amended soils. Maguire et al. (2093–2103) outline the major strategies for reducing dietary P in different species, review the literature on how these approaches affect P forms in manures and amended soils, and discuss the potential benefits to animal agriculture and the environment.
Long-Term Effects of Alum
Aluminum sulfate (alum) additions to poultry litter decrease phosphorus runoff, reduce ammonia emissions, and improve poultry production and crop yields. However, the long-term effects of this practice on aluminum availability in soil were not known. In a long-term study, Moore and Edwards (2104–2111) showed that fertilizing soil with alum-treated litter did not increase soil aluminum availability, aluminum uptake by plants, and/or aluminum runoff. In contrast, using ammonium nitrate fertilizer was found to acidify the soil, increasing exchangeable aluminum in soils. Tall fescue yields were higher after treatment with alum-treated litter than with untreated poultry litter or ammonium nitrate. This study indicates that using alum-treated poultry litter is a sustainable practice.
Water Treatment Residual Best Management Practice Reduces Phosphorus Risk
The P risk index system has been developed to identify agricultural fields vulnerable to P loss, with the goal of protecting surface water. Because of their high P adsorption maxima (Pmax), use of drinking water treatment residuals (WTR) should be considered as a best management practice (BMP) to reduce P risk index scores. Dayton and Basta (2112–2117) found that applying WTR as an enhanced buffer strip reduced runoff P up to 86%; incorporating WTR into a high soil test phosphorus (STP) soil reduced 0.01 M CaCl2–extractable P up to 96% and reduced Mehlich 3–extractable P from up to 87%; co-blending WTR with manure and biosolids reduced 0.01 M CaCl2–extractable P up to 98%. Using WTR as a modifying factor for P risk index will promote effective use of WTR as a BMP to reduce P loss from agricultural land.
Phosphorus Pathways
Concentrations of phosphorus in runoff from agricultural catchments in southern Australia are high and well above national and international limits. Cox et al. (2118–2128) found that phosphorus exited two subcatchments with texture-contrast soils in South Australia via both overland flow and interflow. Interflow at the boundary of the B and C soil horizons accounted for as much as half the total water flow that was measured (overland flow, A–B interflow, and B–C interflow) and had high concentrations of mainly dissolved phosphorus. In some years, interflow was the major pathway for phosphorus loss off these catchments. The B–C interflow cannot be discounted when searching for management options to reduce phosphorus loss from texture-contrast soils to waterways. High concentrations of gypsum applied to one of the subcatchments substantially modified the soil chemistry and, thereby, soil structure but not phosphorus concentrations.
Agricultural Phosphorus Losses
High phosphorus concentrations in many of the world's rivers, lakes, reservoirs, and estuaries damage the ecological quality to such an extent that river basin managers must mitigate phosphorus discharge from point sources and phosphorus losses from agricultural areas. Kronvang et al. (2129–2144) report that phosphorus losses from agricultural areas in European river basins vary at least one order of magnitude depending on the strength of phosphorus pathways linking source areas to surface waters. Kronvang et al. also report experimental results on ways to combat agricultural phosphorus losses in mapped risk areas, mitigation measures that include soil tillage changes, iron treatment of soils, establishing buffer zones, and restoring river and floodplain systems to enhance phosphorus storage.
Wetlands Can Protect Some Waters
Phosphorus from agricultural areas may contribute to eutrophication of water even with best management practices on the fields. Constructing wetlands in small agricultural streams is often the last chance to mitigate the phosphorus losses to our waterways. Braskerud et al. (2145–2155) show that some wetlands can effectively reduce phosphorus transport, while others have little effect (1–88% retention). The phosphorus retention, in percentage of load, usually increases as the wetland size increases. However, even more important is the form of phosphorus entering the wetland, soluble or particulate. Thus, catchment-specific factors must be identified to correctly predict retention performance of individual wetlands.
Age of Cluster Roots Determines Functions of Rhizosphere Microorganisms
The increase of atmospheric CO2 concentration may influence plant growth, root exudates, and thereby plant–microbial interactions. White lupine plants show an extraordinary high expression of root-induced chemical changes under conditions of limited phosphorus (P). Wasaki et al. (2157–2166) report that the functional and structural diversity of the rhizosphere of white lupin grown under ambient or elevated atmospheric CO2 changed depending on the phosphorus status of plants. Intense accumulation of citrate and increased activity of acid- and alkaline-phosphatases as well as chitinase in the rhizosphere were mainly confined to later stages of cluster root development in P treatments. Changes in enzyme activities involved in C, N, and P cycling in the rhizosphere are most probably dominated by secretion from root clusters. Rhizosphere bacterial community structures were mainly affected by the developmental stage of cluster roots and the related alterations in root exudation and rhizosphere chemistry, with marginal effects of CO2 treatments.
Mica Weathering in Potassium-Depleted Rhizosphere Increases Radiocesium Uptake
The availability of radiocesium in bulk soils is usually controlled by weathered mica bearing frayed edge sites (FES) with a high selectivity for trace Cs adsorption. Gommers et al. (2167–2173) show that root uptake of radiocesium was not reduced by the formation of FES through phlogopite weathering in K-depleted rhizosphere soil. The more acute the K depletion, the larger the release of K and Cs from phlogopite and the larger the root uptake of trace Cs. The importance of root-induced mica weathering in increasing the soil-to-plant transfer of radiocesium needs further investigation.
The Alterability of Cesium-Fixing Clay Mineral in Plant Rhizosphere Directly Governs Radiocesium Uptake
In K-depleted rhizosphere soil, two processes can lead to increased root uptake of radiocesium: the very low uptake of potassium and the weathering of Cs-fixing clay minerals. Their respective importance is, however, unclear. Thiry et al. (2174–2180) demonstrated that mica weathering can have a major and direct influence on radiocesium bioavailability. The degree of root-induced mica weathering, the K release and uptake, and the 134Cs mica-to-plant transfer were all related to the mica alterability, increasing in the order muscovite < biotite < phlogopite. Potassium depletion was most acute in the presence of muscovite and thus did not seem to be the sole driving force in root uptake of trace Cs.
Mycorrhizae Increase Arsenic Uptake
Arsenic (As) in soil and water is toxic, yet Chinese brake fern (Pteris vittata L.) is known to actively hyperaccumulate this element. Mechanisms of tolerance and As uptake in this plant are not fully known. Mycorrhizal symbiosis may be involved because arbuscular mycorrhizal (AM) fungi have a well-documented role in increasing plant phosphorus (P) uptake. Phosphorus and As have similar chemical properties, and ferns are known to be colonized by AM fungi. Al-Agely et al. (2181–2186) report that AM fungi not only tolerated high As concentration, but their presence increased plant dry mass. Furthermore, AM fungi increased As uptake across a range of P concentrations, while P uptake was only increased when soil received no additional As amendments. These data indicate that AM fungi have an important role in As accumulation. Therefore, to effectively phytoremediate As-contaminated soils, the mycorrhizal status of ferns needs to be taken into account.
Corn Root Exudates Degrade Atrazine
Atrazine poses a risk to surface and ground waters world wide. Significant amounts of these compounds slowly leach from soils into the subsurface zone beneath or are transported by runoff or erosion to rivers and other surface waters. Corn and other grasses biosynthesize benzoxazinones in their secondary metabolism. Wenger et al. (2187–2196) report that benzoxazinones degrade atrazine and its toxic breakdown products outside of the plants in the soil, showing that higher plants have potential to reduce toxicity and mobility of certain pesticides in soils. Plants that can exude high amounts of these chemicals into the rhizosphere show promise in environmental protection and sustainable management of agricultural land.
Novel Tool to Manage Fumigant Exposure
SOFEA (SOil Fumigant Exposure Assessment system) is a new stochastic numerical modeling tool for evaluating and managing human inhalation exposure to soil fumigants. Cryer (2197–2207) reports that SOFEA calculates fumigant concentrations in air arising from volatility losses from treated fields for large agricultural regions using multiple transient source terms (treated fields), GIS information, agronomic-specific variables, user-specified buffer zones, and field reentry intervals. Both current and anticipated or forecast fumigant scenarios can be simulated using SOFEA to provide risk managers and product stewards the necessary information to make sound regulatory decisions about the use of soil fumigants in agriculture.
Laboratory to Field Extrapolation of Pesticide Degradation May Be Possible
There is evidence that degradation of pesticides in simple laboratory systems may differ from that in the field, but it is not clear which of the simplifications inherent in laboratory studies present serious shortcomings. Beulke et al. (1933–1943) evaluated the hypotheses that (i) degradation in structured soil with fluctuating moisture and temperature in the field can be characterized by the results from laboratory studies with disturbed soil and constant temperature and moisture regimes, (ii) degradation is independent of sorption, and (iii) degradation under flow conditions is identical to that in static systems. The evaluated assumptions were not serious shortcomings for the test system comprising a clay loam soil and contrasting pesticides, which suggests that degradation in the field can potentially be characterized using standard laboratory studies. Additional work is required before general conclusions can be drawn.
Biotic and Abiotic Degradation of CL-20 and RDX in Soils
Differences in the relative importance of biotic and abiotic degradation mechanisms to the environmental fates of the new explosive CL-20 and the well-known explosive RDX are poorly understood. Crocker et al. (2208–2216) report that both abiotic and biotic degradation mechanisms were important factors governing the fate of CL-20 in aerobic soils. By contrast, biodegradation was the major factor determining the fate of RDX in these soils. Biological mineralization of 14C-CL-20 to 14C-CO2 (41–57%) proved that the heterocyclic cage structure of CL-20 is broken, which is important to determining the biodegradative pathway. The data suggest that CL-20 should be less recalcitrant than RDX in aerobic soils and that CL-20 may have a lower potential than RDX to migrate through soil to ground water.
Environmental Index for Phosphorus
The degree of phosphorus saturation (DPS) has been used in evaluating the risk of P loss from soil to runoff. While techniques are available for calculating DPS for acid soils, no widely used technique exists for neutral to calcareous soils. Ige et al. (1944–1951) reported a new technique for estimating the DPS in neutral to calcareous soils that are typical of the Northern Great Plains (Canada). The DPS of these soils was estimated as the ratio of Olsen or Mehlich 3–extractable P to either the sum of Mehlich 3–extractable Ca and Mg or Mehlich 3–extractable Ca using a saturation factor (
) of 0.2. This technique is more appropriate for neutral and calcareous soils than the ratio of oxalate-extractable P to the sum of oxalate-extractable Al and Fe commonly adopted for acid soils. With this new approach, the degree of P saturation for neutral and calcareous soils can be estimated without the need to generate a P adsorption maximum.
Antibacterial Activity of Soil-Bound Antibiotics
There is some concern that antibiotic residues in land-applied manure may promote the emergence of antibiotic resistant bacteria (ARB) in the environment. Not much information is available about the antimicrobial properties of soil-bound antibiotics. In a laboratory study, Chander et al. (1952–1957) determined that antibiotics retain their antimicrobial activity after binding with soil. Soil adsorbed antimicrobial activity was higher for Hubbard loamy sand than Webster clay loam, possibly because of higher affinity (higher clay content) of the Webster soil for antibiotics. Soil-bound tetracycline was found to be more active in inhibiting the growth of three bacterial species (introduced into soil) than tylosin, possibly because more tetracycline was soil adsorbed and also because most bacteria have lower minimum inhibitory concentration for tetracycline than tylosin. Decline in microbial population was more pronounced under dynamic growth conditions than static conditions because agitation under dynamic growth conditions helped increase tetracycline desorption and/or increase contact between soil-adsorbed tetracycline and bacteria. These results suggest that although antibiotics are tightly held by the clay particles, they are still biologically active and select for the ARB by providing selective environment.
Autoclaving Soil Releases Phosphorus
It is common practice to autoclave soil and sediment samples before determining the amount of phosphorus they release during incubation with algae. Anderson and Magdoff (1958–1963) found that autoclaving causes P release and, therefore, overestimation of the detrimental effects of soil or sediment. However, they also found that autoclaving samples before incubation with algae is acceptable if the purpose is to rank soils according to their potential effects on algal growth.
Coalbed Natural Gas Water Irrigation Impact on Soils
Land application of coalbed natural gas (CBNG) co-produced water is a popular management option in the northwestern Powder River Basin of Wyoming. Quality of CBNG water, however, varies in the region and is often not suitable for direct irrigation. Ganjegunte et al. (2217–2227) discovered, compared to control soils, a significant buildup of salts and sodium in the upper 30 cm of soils that were irrigated with saline-sodic CBNG water, as measured by electrical conductivity of soil saturated paste extracts (ECe) and sodium adsorption ratio of soil saturated paste extracts (SARe). Results indicate that irrigation with CBNG water significantly affects certain soil properties, particularly if proper amendments are not used. This study helps us better understand changes in soil properties because of land application of CBNG water.
Soluble Organic Phosphorus Reacts Less Strongly with Soil than Soluble Inorganic Phosphorus
There is concern about excess P moving from agricultural soils to surface waters. Although most research on P movement has focused on soluble inorganic P, it has recently become possible to easily track soluble organic P compounds. Anderson and Magdoff (2228–2233) have found that soluble organic P compounds tend to react less strongly with soil and to move more easily through soils. The implication is that soluble P from such sources as animal manures may travel to ground and surface waters more easily than the inorganic P contained in commercial fertilizers.
Revegetation of Pyritic Waste Rock
Harsh chemical and physical conditions inhibit voluntary recolonization of sulfide-bearing waste rock dumps by native vegetation. Borden and Black (2234–2242) examined the controls on voluntary revegetation of pyritic waste rock surfaces at the Bingham Canyon porphyry copper deposit in Utah. Vegetation cover and species richness are most dependent on soil pH and salinity, and to a lesser extent on surface age, compaction, and distance from seed source. Cover and richness both decline below a pH of about 6 and above a paste conductivity (on a 1:1 soil to water mixture) of about 0.7 dS/m. As reactive pyrite is depleted in older acidic waste rock surfaces, soil salinity eventually declines. By adding adequate limestone and preparing the surface to reduce compaction, direct planting of older, acidic but low salinity waste rock surfaces can greatly accelerate natural revegetation.
Management Influences on Nitrate Leaching
Applying N fertilizer and irrigating to meet but not exceed crop requirements is important to reducing the NO3 leaching from irrigated sandy soils. Gehl et al. (2243–2254) report that irrigation and N fertilizer inputs exceeding crop requirements increase NO3 leaching in coarse-textured soils. Irrigation in excess (25%) of that required to replenish crop water use did not enhance corn yield but did result in substantial increases in growing-season NO3 leaching losses. Total NO3 leaching losses were highest when excess irrigation was applied to plots receiving single preplant fertilizer applications rather than split applications. Differences in growing season soil water flux and NO3 leaching among N and water treatments emphasize the importance of irrigation scheduling and N management to minimize the potential for NO3 leaching.
Long-Term Availability of Biosolids-Applied Trace Metals
The possible increase in phytoavailability of biosolids-applied trace metals causes concern because of the loss of metal-binding organic matter with time. Sukkariyah et al. (2255–2262) assessed the effect of time on chemical extractability and concentration of Cd, Cu, Ni, and Zn in plants grown on plots given a single application of biosolids with trace metal content vastly exceeding levels found in present-day biosolids. An initial increase in soil organic matter content of 18 to 65 g kg–1 with the application of 210 Mg ha–1 decreased to 42 g kg–1 by 1992 and remained unchanged thereafter. DTPA-extractable Cu had decreased by 58% and Zn by 42% 17 yr after application. Metal concentrations in plant tissue plateaued in most cases and fell within the normal range of the evaluated crops. Uptake coefficients calculated for corn, lettuce, and radish agreed with the values set by the Part 503 Rule. The authors concluded that availability of trace metals as assessed by soil extractants and plant uptake did not increase 17 to 19 yr after application despite reduced soil organic matter content. Therefore, risk to the environment of metal toxicity and increased phytoavailability from biosolids application at this site and for soil with similar conditions appears to be negligible.
Sampling Soil for Assessing Risk to Water Quality?
Soils reputedly contribute to problems of water quality. To assess their contribution and predict potential risk, scientists need to be able to sample and analyze soils. However, this is not as easy as it sounds, because soils are highly variable, as Page et al. (2263–2277) have demonstrated for phosphorus (P). Soil P measurements showed large spatial variability, not only between fields and land uses, but also within individual fields. Observed soil P distribution is variable and is also difficult to relate to nationally available soil P data, so any assessment of soil P status for determining risk of P loss is uncertain and problematic.
Ground Water Transport of Nitrate and Pesticides
There is continuing concern over the impact of nutrients and pesticides on water quality. Puckett and Hughes (2278–2292) report that selected pesticides were mainly detected beneath the field where they were applied, whereas nitrate was transported to an adjacent creek in ground water. Both nitrate and pesticides were transported to the creek by subsurface drainage. Hydrology and geology were found to be strong influences in their transport and fate.
Oxytetracycline Sorbs to Metal–Humate Complexes
In the environment, the primary sources of the antibiotic oxytetracycline are manure disposal and wastewater treatment sludges. MacKay and Canterbury (1964–1971) identified metal cation bridging as an important sorption interaction between oxytetracycline and organic matter. At pH 5.5, more oxytetracycline was sorbed to humic acid with increasing concentrations of complexed iron(III) and aluminum. A small portion of oxytetracycline also interacted by cation exchange. No detectable oxytetracycline sorption was measured for cellulose and lignin, sorbents with low capacity to complex cations. The results suggest that organic matter may be an important sorbent phase in soils and sediments for pharmaceutical compounds that have complex metals.
The Transfer Factor Concept Is Inadequate under Field Conditions
The radiological impact of radionuclides released to the terrestrial environment is usually predicted with mathematical models in which the transfer of radionuclides from soil to plant is described with the transfer factor (TF). This paper questions the validity of the protocols proposed by the International Atomic Energy Agency (IAEA) to measure TF in the field and under greenhouse conditions. Centofanti et al. (1972–1979) observed that surface-applied radionuclides (54Mn, 57Co, 65Zn, and 134Cs) in the preferential flow paths had a higher concentration than in the soil matrix, indicating that they infiltrated heterogeneously in the soil profile because of the structure-induced non-uniform water flow. A significantly higher recovery of 57Co and 134Cs occurred in maize grown in the field soil, whereas no differences in the recovery of 54Mn and 65Zn were observed between plants grown in the field soil and plants grown in the greenhouse in the same soil previously sieved and homogeneously labeled with the same radionuclides before being repacked in pots. These results suggest that under field conditions: (i) the soil-to-plant transfer of radionuclides that coexist as stable elements present at low concentrations in the soil and in the plant is higher than that measured under greenhouse conditions, and (ii) the implicit assumption made when calculating the TF (that radionuclides are homogeneously distributed in the soil profile) is not valid, thereby preventing the calculation of an average concentration to obtain the TF parameter.
Pollution Sources Found Using Simple Water Quality Measures
Many lakes and rivers are affected by pollution. Finding the cause of pollution is problematic when multiple sources, both point and nonpoint, may be present. Zeng and Rasmussen (1980–1991) show that, for rivers flowing into a southeastern U.S. reservoir, total dissolved solids (TDS) is a good indicator of point sources of pollution, while total suspended solids (TSS) is a good indicator of nonpoint sources. In lakes, dissolved oxygen concentration is a good indicator of stratification, while nutrients and biomass concentration are useful indicators of lake water quality variation.
Soluble Soil Carbon Contains Most Trihalomethane Precursors
Influxes of soil organic carbon to the Sacramento–San Joaquin Delta (Delta) waterways affect the quality of drinking water for two-thirds of the population in California, because certain soil organic carbon moieties can react with chlorine, a common disinfectant, to form harmful trihalomethanes (THM). Isolating chlorine reactive carbon and quantifying their THM formation potential is necessary before developing effective strategies to reduce organic carbon loads to Delta waters and for removing them during drinking water treatment. Chow et al. (1992–1997) extracted organic carbon from two representative Delta soils using electrolytes representing natural runoff conditions. Extracts were nondestructively separated into particulate, colloidal, fine colloidal, and soluble organic carbon for trihalomethane formation potential (THMFP) quantification. Results suggested that most THMFP was associated with soluble soil organic carbon isolates with particle sizes less than 0.025 µm in diameter. Further molecular characterization of the fractions with high THMFP may help explain the nature of chlorine-reactive organic carbon from Delta soils.
Polyacrylamide in Runoff Water
Agricultural runoff water is often contaminated with suspended sediments and fertilizer nutrients, which lead to eutrophication in receiving waters. Mason et al. (1998–2004) report that a combination of alum (aluminum sulfate) and nonionic polyacrylamide (PAM) was effective in reducing both sediment and dissolved phosphorus (P) in saline, agricultural wastewater. Anionic PAM effectively flocculated and settled suspended solids but was ineffective when used in combination with alum. Alum treatment was needed to remove the soluble P, which dominated the nutrient load.
Water Troughs Decrease Stream Contamination by Cattle
Contamination of unfenced streams with phosphorus, sediments, and pathogenic bacteria from cattle activity may be affected by the availability of shade and water troughs in pastures. Byers et al. (2293–2300) report that stream contamination was highest in a pasture with the least nonriparian shade. Also, the availability of water troughs decreased stream contamination by sediments and pathogenic bacteria. Thus, providing shade and water troughs away from the stream may reduce overall stream contamination by cattle activity.
Freeze–Thaw Events Affect Phosphorus Losses
Mitigation strategies that reduce losses of nitrogen may not have the same effect on phosphorus. Establishing a green plant cover reduces nitrogen loss, but it may have the opposite effect on phosphorus loss. Bechmann et al. (2301–2309) show that grasses release phosphorus from the plant material during freezing. Repeated freezing–thawing of the plant material increased phosphorus release; most of the plant phosphorus was released after eight freeze–thaw cycles. Runoff from grass exposed to eight freeze–thaw cycles showed phosphorus concentrations approximately 100 times the concentration in runoff from nonfrozen grass. These results are based on simulated rainfall on soil runoff boxes. For soil runoff boxes that were not frozen, the grass reduced concentrations of suspended sediments by 3% and phosphorus by 25% in runoff compared to concentrations in runoff from soil boxes with no plant cover. The risk of phosphorus losses from green plants needs to be included in the total risk assessment of phosphorus losses in cold climates.
Ponds: Conduits to Ground Water
Preemergence herbicide residues were detected in domestic wells sampled near Tracy, California. Because developing mitigation measures depends on knowing the exact pathway of offsite movement, soil distribution of diuron and hexazinone within an alfalfa field with a cracking clay soil was compared to infiltration of residues in water captured by an adjacent holding pond. Prichard et al. (2005–2017) found very little downward movement within the field. In contrast, runoff water containing diuron and hexazinone residues collected in the pond and infiltrated rapidly to shallow ground water. Adding a surfactant did not reduce runoff concentrations, so mitigation will focus on minimizing pond water infiltration.
Pig Diet and Air Bubbling Control Hydrogen Sulfide
The sudden agitation of manure slurry can cause the release of dangerous amounts of hydrogen sulfide. Clark et al. (2018–2023) have shown that both reducing the sulfur concentration in pig diets and very low-level bubbling of air through slurry can reduce peak hydrogen sulfide emissions. Slurry samples stored in bench-scale digesters released much less hydrogen sulfide when suddenly agitated if they had been continuously bubbled with air at an extremely low rate. Moreover, the manure slurry from pigs fed diets with reduced sulfur concentration emitted less hydrogen sulfide than did slurry from pigs fed high-sulfur diets. Both of these approaches appear to control hydrogen sulfide emissions from slurry, but these results must be validated at larger scales.
Phosphorus Leaching from Swine Waste
Land application of waste increases soil P concentrations and therefore increases the risk of P loss to surface water. Because P is strongly adsorbed to soil, P leaching is a potential loss pathway that can often be overlooked. Nelson et al. (2024–2035) documented P leaching losses past 45 cm that equaled or exceeded P applications from swine waste. Phosphorus concentrations in soil solution were more than 100 times higher than the P concentration associated with P-induced eutrophication of surface waters. Phosphorus leaching increased dramatically when the soil P concentration increased above 45% of the P sorption capacity. These results show that P leaching should be considered when assessing the long-term risk of P loss from waste-amended soils.
Manure Distribution on Wisconsin Dairy Farms
Livestock operations in the United States need to know the amount of manure produced on their farms, and the amount of manure collected and available for land-spreading. Much information is available to calculate manure production, but little is known about the types and amounts of manure actually collected on typical dairy farms. Powell et al. (2036–2044) discovered that less manure is collected in the hilly southwest (56% of total annual herd production) than in the undulating south central (72%) or the flat northeast (68%) regions of Wisconsin. Collection of lactating cow manure is lower in stanchion (66% of total annual production) than free-stall (89%) housing and lower on farms with small to medium herds than on farms with large herds. Farms having small to medium herds might require help in managing manure in outside confinement areas to reduce the risk of impairing surface and ground water quality.
Nitrogen Fertilizer Recommendations for Corn
Soil and plant indices of soil fertility status have traditionally been developed using conventional soil and crop management practices. Data on managing N fertilizer for corn produced on soils amended with C-rich organic materials, such as oily food waste, is scarce. Rashid and Voroney (2045–2051) report that presidedress soil NO3–N contents had a higher inverse relationship with maximum economic rate of nitrogen (r = –0.88) compared to soil NO3–N at preplant (r = –0.74) time of sampling. A linear regression model (Y = 180.1 – 8.22 NO3–N at presidedress time of sampling) was proposed for making N fertilizer recommendations to corn grown on soil amended with oily food waste in southern Ontario.
Waste Wool and Hair Can Provide Nutrients to Crops
A number of waste materials, such as biosolids, industrial composts, and animal manures, have been traditionally used as nutrient sources for agricultural crops or to improve soil quality. Sheep production and barbershops generate significant amounts of by-products such as sheep wool waste and human hair waste that are either landfilled or composted. Zheljazkov (2310–2317) evaluated uncomposted sheep wool and human hair as nutrient sources and soil conditioners for high-value crops. Adding wool or hair waste to soil increased yields and protein content of the medicinal crops basil, thorn apple, peppermint, and garden sage; stimulated soil microbial biomass; and decreased mycorrhizae colonization of plant roots of thorn apple but not basil. Wool and hair-waste additions to soil slightly altered the content and composition of essential oils and alkaloids; however, overall, the constituents remained within the typical range for the respective crops. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis showed that wool and hair wastes decompose slowly under field or greenhouse conditions and that they act as a slow release S, N, P, and K fertilizer. A single addition of wool or hair waste of only 3.3 g kg–1 of soil may support two to five harvests or crops under greenhouse conditions and two to four field seasons for field grown crops and improved soil biological and chemical characteristics.
Phosphogypsum-Amended Manure Compost Properties
Nitrogen loss during beef cattle (Bos taurus) feedlot manure composting may contribute to greenhouse gas emissions and increase ammonia in the atmosphere while decreasing the fertilizer value of the final compost. Zvomuya et al. (2318–2327) report that co-composting of feedlot manure with phosphogypsum reduces total nitrogen loss and increases both available nitrogen and the percentage of total nitrogen in the available form. Thus, adding phosphogypsum before composting manure may be an inexpensive strategy for improving the value of the final compost as a fertilizer supplement. The practice also presents an opportunity to combine two perceived waste products (manure and phosphogypsum) to create a desirable end-product that supplies nitrogen, phosphorus, and sulfur for crop production.
The Products of Remediating Sulfonate Wastes
Colored wastes coming from dye industries have undergone a remediation treatment to remove their color. Does the loss of color guarantee the absence of toxicity? The answer is no, because many dyes are aromatic sulfonates; the remediation treatment often destroys only the chromophoric group while possibly giving rise to species more toxic than the original. Using HPLC–MS, Gosetti et al. (2328–2333) studied the destruction pathway of a very diffused aromatic sulfonate, 1,5-naphthalenedisulfonate, when thermally activated in the presence of persulfate. Some intermediates were identified, and the kinetics were studied. The results indicate that after 20 h of oxidative treatment, the naphthalene structure is broken and that, when the molar ratio of persulfate to aromatic sulfonate is approximately 100, mineralization takes place about 90% of the time.
Nitrate Concentrations Limit Peatland Denitrification Rates
Atmospheric deposition of nitrogenous compounds to ombrotrophic peatlands (i.e., those that have peat layers higher than their surroundings and receive nutrients and minerals exclusively by precipitation) has the potential to significantly alter ecosystem functioning. Hayden and Ross (2052–2061) discovered that nitrate was a limiting factor for denitrification in a Vermont peatland. Denitrification rates were measured using the acetylene inhibition technique in both field and laboratory studies. While ombrotrophic peatlands do not lose nitrogen through drainage into ground water, they do appear to provide conditions conducive to significant nitrogen loss through denitrification. As a result, the processes of denitrification and nitrogen assimilation by plants may serve to protect these threatened ecosystems from significant alterations that come from increased atmospheric nitrogen deposition.
Wetlands Rapidly Remove Nitrate and Sulfate
Wetlands improve water quality by removing nitrate as water passes through them; most of the removal is via a microbial process known as denitrification. Whitmire and Hamilton (2062–2071) used an innovative in situ tracer approach to document the rapid rates of nitrate removal in wetland sediments in Michigan, which were capable of stripping out added nitrate in a matter of hours. Removing sulfate, another ubiquitous pollutant, began once nitrate was depleted. However, at some sites, sulfate was produced during nitrate removal, suggesting that sulfur bacteria could be responsible for much of the nitrate uptake. All wetland sediments examined were consistently capable of removing nitrate and sulfate at concentrations found in ground water and precipitation inputs, quickly and in small areas. These results show how a remarkably small area of wetland sediment can strongly influence water quality, such as in the cases of narrow riparian zones or small isolated wetlands, which may be excluded from legal protection.
Soil Development in Created Wetlands
The amount of time it takes for created wetlands to develop soils comparable to natural wetlands is relatively unknown and may depend on several factors. Anderson et al. (2072–2081) reported that surface soil conditions at two created wetlands changed considerably through sedimentation and organic accretion over 10 yr. Soils were surveyed in three separate years over 10 yr to examine changes in soil physiochemical parameters. After flooding the wetlands in 1993, short-term (18 mo) changes in soils were influenced by sediment deposits and senescent macroalgae, the mobilization of soluble nutrients, and CaCO3 precipitation. Longer-term (10 yr) changes were influenced more by the deposition of organic matter from colonized macrophyte communities. Spatial variability of soil organic matter concentrations (an indicator of wetland soil development) was high in 2004 (compared to 1993 and 1995) throughout both wetlands suggesting that soil conditions are progressing toward natural conditions.
Antibiotic Uptake by Plants from Manure
Antibiotics used in feed to promote growth of food animals are not completely absorbed in the animal gut. As a result, substantial amounts of antibiotics are excreted in urine and feces and end up in manure. Manure is used worldwide not only as a source of plant nutrients but also as a source of organic matter to improve soil quality, especially in organic and sustainable agriculture. Greenhouse studies by Kumar et al. (2082–2085) showed that plants take up small quantities of antibiotics when grown in soil amended with antibiotic-laden manure. This finding calls attention to the risks of consuming fresh vegetables grown in soils amended with antibiotic-laden manures, especially for people who are allergic to antibiotics. Consuming these vegetables routinely may also lead to enhanced antimicrobial resistance in humans.
Manure Decreases Bacteria Attachment to Soil
Attachment of bacteria to soil is an important component of bacterial fate and transport. Despite the fact that E. coli are derived exclusively from feces and manure, how manure colloids affect bacteria attachment to agricultural soils has never been directly studied. Guber et al. (2086–2090) studied E. coli attachment to soil in batch experiments with samples of loam and sandy clay loam topsoil. The maximum E. coli attachment occurred in the absence of manure. Increasing manure content generally resulted in decreased E. coli attachment to all studied soils.
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