Scott Subler - Academia.edu (original) (raw)
Papers by Scott Subler
Biocycle, 1998
Trials in soil and container media reveal some differences that may exist between vermicomposts a... more Trials in soil and container media reveal some differences that may exist between vermicomposts and composts and point to a growing awareness of the potential importance of microbial activity in plant growth.
Compost Science & Utilization, Jun 1, 2000
Tomato, pepper, lettuce, and marigold seedlings were grown in a standard commercial soilless plan... more Tomato, pepper, lettuce, and marigold seedlings were grown in a standard commercial soilless plant growth medium (Metro-Mix 360), and in coir/perlite and peat/perlite-based container media substituted with 10% or 20%, by volume, of vermicompost derived from pig manure or ...
Pedobiologia, 2003
Earthworms affect agroecosystem processes and few studies have addressed population dynamics when... more Earthworms affect agroecosystem processes and few studies have addressed population dynamics when earthworms are intentionally introduced. Handsorting and formalin extraction were used semi-annually from fall 1994 to fall 1997 to measure populations in plots with and without added earthworms under chisel till in a corn-soybean rotation (CT) and a ridge-till system in a corn-soybean-wheat rotation (RT) in Ohio, USA. Earthworm communities were altered by adding 76 Lumbricus terrestris (L.) m-2 each spring and fall into plots with no, or very few of these anecic earthworms. Increases in L. terrestris were small (~7 m-2) compared to the number added and their establishment was at the expense of the epigeic earthworm L. rubellus (Hoff.), which declined four and twofold in CT and RT, respectively. Populations of the endogeic earthworm Octolasion tytaeum (Sav.) were unaffected by the addition of L. terrestris. Sampling 5 years after the additions indicated that L. terrestris persisted only in the RT plots. The decline in L. rubellus populations in plots with added anecic worms was no longer evident. We understand that the increased number and amounts of residues and the minimal level of disturbance found in RT probably increased the extent and quality of earthworm habitat over CT plots, which had fewer crops, less cover, and periodic disturbance. Apparently, population dynamics and competitive relationships among different earthworm functional groups were regulated by agroecosystem type, and their correspondent disturbance regimes and resource distributions.
Communications in Soil Science and Plant Analysis, Sep 1, 1995
We compared estimates of soil nitrogen (N) mineralization rates using the buried bag and PVC core... more We compared estimates of soil nitrogen (N) mineralization rates using the buried bag and PVC core methods in an ongoing investigation of the effects of earthworms and N fertilizer sources on agroecosystem N dynamics. Over a seven‐month period, we paired monthly buried bag and PVC core soil incubations within research plots receiving one of three N treatments (inorganic, legume, or
Soil Biology & Biochemistry, Nov 1, 2001
The use of fungicides in agriculture, to protect plants from soil-borne pathogens, is a common pr... more The use of fungicides in agriculture, to protect plants from soil-borne pathogens, is a common practice. However, there is a dearth of information on the side-effects of fungicides on key soil ecological processes. We investigated the effects of three fungicides, benomyl, captan and chlorothalonil, on soil microbial activity (substrate-induced respiration and dehydrogenase activity), and nitrogen dynamics (NH 4 ±N and NO 3 ±N) in two laboratory experiments, one with captan and chlorothalonil and another with captan. In each laboratory batch incubation, soil was treated with a fungicide at approximately recommended ®eld application rates (benomyl, 51 mg a.i. kg 21 , captan,125 mg a.i. kg 21 and chlorothalonil, 37 mg a.i. kg 21) and incubated at 308C for 8 weeks. Some soils were amended with either ground alfalfa leaves or ground wheat straw to provide additional substrates for soil microorganisms and to alter rates of nitrogen mineralization/immobilization. All three fungicides suppressed the peak soil respiration in unamended soil by 30±50%, but the three fungicides had different effects in the amended soils. Soil dehydrogenase activity was stimulated by benomyl (18±21%) and chlorothalonil (8±15%) except in the alfalfa amended soil, but was decreased by captan (40±58%) in both the straw-amended and unamended soils. The fungicide-treated soils in general had less microbial biomass N concentrations than the untreated soils. Captan-treated soils had much higher NH 4 N concentrations than the control soils, with or without the organic amendments. Benomyl and chlorothalonil had little in¯uence on soil NH 4 N concentrations. Net N mineralization and nitri®cation rates were in¯uenced by all fungicide treatments as well as by the addition of organic materials. N mineralization rates were signi®cantly higher in captan-treated soils than in untreated soils. N dynamics were in¯uenced by chlorothalonil in a similar pattern to captan but reached peak nitri®cation rates earlier (day 7), in the alfalfa-amended soil. The effects of the three fungicides on soil microbial activity and nitrogen dynamics depended on the quality of the organic materials added to the soil. The patterns of effects of the fungicides on soil nutrient cycling processes were not large and were speci®c to each fungicide. Captan appeared to have more pronounced overall effects on soil microbial activity and nitrogen dynamics than either benomyl or chlorothalonil.
Soil Science Society of America Journal, Nov 1, 1999
Concern about NO−3 contamination of surface waters has prompted the development of agricultural w... more Concern about NO−3 contamination of surface waters has prompted the development of agricultural water table management systems to reduce NO−3 loss in subsurface drainage outflow by subirrigating through the existing subsurface drainage lines during the growing season and controlling off‐season outflows. We hypothesized that soil N pools, crop yields, and N uptake in a corn (Zea mays L.)–soybean (Glycine max.) rotation differ between subirrigation (water table at 40 cm) with controlled drainage (SI/CD) vs. subsurface drainage (SD) alone on Omulga silt loam (Aeric Fragiaqualfs). Mean microbial biomass N, potentially mineralizable N, dissolved organic N, and ammonia N were not affected by the water table management system. Mean NO−3–N was not affected by the water table management system at 0‐ to 15‐cm and 15‐ to 30‐cm depths, but the 2‐yr mean soil NO−3 concentration at the 30‐ to 75‐cm depth was 46% lower in SI/CD compared with SD. The average corn yield was 19% greater, and the average soybean yield was 64% greater, in SI/CD plots, compared with SD. Corn N uptake was 13% greater and soybean N uptake was 62% greater with SI/CD, compared with SD. The SI/CD water table management system increased plant N uptake and reduced deep‐profile NO−3 concentrations, thereby reducing the amount of NO−3 potentially available to move via drains to surface waters.
Journal of Environmental Quality, Jul 1, 2008
Oecologia, Mar 23, 1999
There are few studies in natural ecosystems on how spatial maps of soil attributes change within ... more There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part, this is due to methodological diculties associated with sampling the same spatial locations repeatedly over time. We describe the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in space¯uctuate over time. We used this method to examine spatial patterns of soil ammonium (NH 4) and nitrate (NO À 3) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in time, we also measured soil NH 4 and NO À 3 concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH 4 and NO À 3 concentrations increased with the age of the dune, whereas coecients of variation for NH 4 and NO À 3 concentrations decreased with the age of the dune. Soil NO À 3 concentration showed strong spatial structure, but soil NH 4 concentration was not spatially structured. Plant-available NH 4 and NO À 3 showed relatively little spatial structure: only NO À 3 availability in the second sampling period had signi®cant patch structure. Spatial maps of NH 4 and NO À 3 availability changed greatly over time, and there were few signi®cant correlations among soil nitrogen availability at dierent points in time. NO À 3 availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO À 3 concentrations, providing some evidence that patches of plant-available NO À 3 may reappear at the same spatial locations at irregular points in time. Key words Coastal dune ecosystems á Ion exchange membrane spikes á Soil nitrogen availability á Soil resource heterogeneity á Spatial statistics Oecologia (1999) 118:397±404
Pedobiologia, 2000
Vermicomposts, which are produced by the fragmentation of organic wastes by earthworms, have a fi... more Vermicomposts, which are produced by the fragmentation of organic wastes by earthworms, have a fine particulate structure and contain nutrients in forms that are readily available for plant uptake. In greenhouse trials, the growth of marigold and tomato seedlings, in a commercial horticultural potting medium (Metro-Mix 360), was enhanced significantly upon substitution of Metro-Mix 360 with 10 % or 20 % vermicomposted pig solids or vermicomposted food wastes, when all required nutrients were supplied. Same enhancement in marigold and tomato seedlings' growth occurred also upon substitution of Metro-Mix 360 with composted biosolids, but not with leaf compost. The shoot dry weights of raspberry plants, grown in a mineral soil mixed with vermicomposted pig wastes weighed more than those grown in unfertilized control soil, and were as great as those in soil receiving a complete fertilizer treatment. By comparison, raspberry shoot growth in soils amended with yard, leaf or bark composts, was poorer than that in the unfertilized control soil. Amending the soil with 4 % chicken manure compost killed most of the raspberry plants. However, plant mortality was reduced and growth restored when the chicken manure compost was mixed with vermicomposted pig solids, but not with bark or yard composts. Plant growth in soils containing a mixture of chicken manure compost with 20% vermicomposted pig wastes was similar to that of plants grown in the unfertilized control. Our results showed that vermicomposts have the potential for improving plant growth when added to greenhouse container media or soil. However, there seem to be distinct differences
Applied Soil Ecology, Mar 1, 2002
We investigated the effects of two commercially available soil biostimulants, designated Z93 and ... more We investigated the effects of two commercially available soil biostimulants, designated Z93 and W91, on key microbial and nutrient cycling processes in the soil, by conducting short-term (1 week) and longer-term (8 weeks) soil incubations in the laboratory. In the short-term soil incubations, the two compounds differed in their effects on microbial activity: Z93 was effective over a wide range, stimulating substrate-induced respiration (SIR) and dehydrogenase activity (DHA) at remarkably low concentrations (0.5-500 nl/g soil); W91 stimulated SIR at these concentrations, but also inhibited DHA. In longer-term soil incubations, we amended batches of soil with either finely-ground alfalfa leaves, wheat straw, or added no amendments, to alter patterns of soil nitrogen mineralization and immobilization. We treated these soils with Z93 and W91 at two concentrations (0.005 and 0.5 l/g soil), and incubated them for up to 8 weeks. These extremely low doses of both Z93 and W91 influenced soil SIR, DHA, and cellulase activity significantly (P < 0.05). Both compounds also influenced soil nitrogen dynamics significantly; the extent depending upon the quality of the organic amendments. In the alfalfa-amended soil there was a steep increase in NO 3-N concentration during the incubation due to the rapid mineralization of nitrogen-rich alfalfa material. However, in this soil, both Z93 and W91 reduced NO 3-N concentrations greatly after 56 days. In the straw-amended soil, mineral nitrogen concentrations were very low, probably due to rapid immobilization of nitrogen by microbial biomass. In this soil, treatment with both compounds decreased microbial biomass nitrogen and increased dissolved organic nitrogen (DON), relative to that in the controls. Our results suggest that the two biostimulants can stimulate both the breakdown and mineralization of soil organic materials, perhaps by selectively inhibiting or stimulating particular components of the microbial community, leading to lasting (8 weeks or longer) increases in soil nitrogen availability.
Applied Soil Ecology, Sep 1, 2001
The effects of benomyl and captan on soil ecological processes were tested in integrated terrestr... more The effects of benomyl and captan on soil ecological processes were tested in integrated terrestrial microcosms containing agricultural soil, organic amendments and wheat seedlings. The effects of the two fungicides on important soil ecological processes were evaluated by measuring soil microbial activity and biomass, including soil substrate-induced respiration (SIR), soil enzyme activity (dehydrogenase, urease and acid phosphatase) and microbial biomass nitrogen concentrations; nitrogen dynamics, including extractable inorganic nitrogen, dissolved organic nitrogen concentrations, net N mineralization and nitrification rates; rates of organic matter decomposition, using chopped wheat straw; in situ inorganic nitrogen concentrations using ion-exchange resin bags, and plant growth. The quality of the organic amendments (ground alfalfa leaves or chopped wheat straw) influenced the effects of the two fungicides on soil microbial processes and nitrogen availability strongly. Rates of SIR, soil enzyme activities (except urease activity), microbial biomass N and dissolved organic N concentrations were all decreased significantly by the fungicide treatments. Rates of wheat straw decomposition were also inhibited by the fungicide applications. Soil urease activity, NH4+–N and NO3−–N concentrations, and initial net N mineralization and nitrification rates were increased by the fungicide treatments. In situ concentrations of NH4+–N and NO3−–N in ion-exchange resin bags differed between the two fungicide treatments. Captan increased amounts of NH4+–N and NO3−–N in the resin bags significantly, compared to those in the untreated controls, or in benomyl-treated soils. The germination success of wheat seeds after 7 days, plant biomass (shoot+roots) as well as the total nitrogen uptake, were all increased by the captan treatment. The two fungicides differed in their effects on some soil processes and plant growth, as well as on rates of nitrogen uptake by plants; captan having a greater and long-lasting overall influence than benomyl. We concluded that these integrated microcosm techniques and resultant data can provide a better understanding of the interactions between fungicide applications and soil ecological processes than single investigations of the individual processes.
Applied Soil Ecology, Sep 1, 1998
To investigate the in¯uence of earthworms on net rates of N mineralization in agricultural soils,... more To investigate the in¯uence of earthworms on net rates of N mineralization in agricultural soils, we manipulated earthworm populations for three years in three corn agroecosystems that differed in nutrient inputs (inorganic N, legume, or manure). Each spring and fall, earthworms were added to, removed from, or left unmodi®ed in ®eld enclosures within each agroecosystem. In the second and third year, we measured soil concentrations of mineral N (0±15 cm depth) in these enclosures, as well as net rates of N mineralization using an in situ soil core incubation method. In the inorganic N-fertilized agroecosystem, mineral N concentrations were often greatest in the enclosures with earthworm additions or least in enclosures with earthworm reductions. The largest differences were seen following inorganic fertilizer application, suggesting either greater net N immobilization or increased N loss from the surface soil in the enclosures with earthworm reductions. Subsequent net rates of N mineralization were greater in the enclosures with reduced earthworm populations, possibly due to the turnover of N in microbial biomass. In the legume-fertilized agroecosystem, overall rates of net N mineralization were greater in enclosures with earthworm additions than in enclosures with earthworm reductions. In this agroecosystem, cumulative net N mineralization during the two-year study was signi®cantly higher in enclosures with earthworm additions than in enclosures with unmodi®ed or reduced populations. Earthworms can signi®cantly in¯uence the net rates of N mineralization in agricultural soils, but the timing, direction, and the magnitude of this in¯uence appears to be dependent on the nature of the nutrient inputs.
Pedobiologia, 2001
W Wa at te er r s st ta ab bi il li it ty y o of f e ea ar rt th hw wo or rm m c ca as st ts s i ... more W Wa at te er r s st ta ab bi il li it ty y o of f e ea ar rt th hw wo or rm m c ca as st ts s i in n m ma an nu ur re e-a an nd d i in no or rg ga an ni ic c-f fe er rt ti il li iz ze er r a am me en nd de ed d a ag gr ro oe ec co os sy ys st te em ms s i in nf fl lu u-e en nc ce ed d b by y a ag ge e a an nd d d de ep pt th h
Communications in Soil Science and Plant Analysis, Apr 1, 1998
Go to AGRIS search. Communications in soil science and plant analysis (Apr 1998). Assessing biolo... more Go to AGRIS search. Communications in soil science and plant analysis (Apr 1998). Assessing biological activity of agricultural biostimulants: bioassays for plant growth regulators in three soil additives. ...
Soil Biology & Biochemistry, Mar 1, 1997
Available evidence suggests that earthworms enhance the mineralization of carbon in soil, but the... more Available evidence suggests that earthworms enhance the mineralization of carbon in soil, but there are few data from field experiments that demonstrate that earthworms increase soil respiration under natural environmental conditions. We measured soil respiration (CO2 flux) during 1993–1994 in 20-m2 field enclosures in which earthworm populations had been decreased, increased, or left unmodified (the latter serving as a control). The enclosures were in corn agroecosystems receiving one of three different nutrients: legume cover crop, cow manure or inorganic fertilizer (NH4NO3). Soil respiration was measured in the enclosures by the static diffusion method. Earthworms had significant effects on soil respiration, but their effects varied seasonally and were influenced by environmental conditions. There were significant differences in respiration rates among earthworm treatments on seven of the 24 sampling dates, and where significant differences did occur, respiration rates were greates in plots with increased populations and lowest in plots with decreased populations. Most of the significant effects of earthworms on soil respiration were observed during the growing season (June–August) of 1994. A severe drought in the summer of 1993 decreased overall respiration rates relative to 1994, and also inhibited earthworm activity. Soil respiration was significantly greater, during the growing season, in the organically-amended plots than in plots treated with inorganic fertilizer; there were no differences in soil respiration among nutrient treatments in the autumn or in the spring before amendments were added. Our results show that earthworms had a significant influence on soil respiration in the field, but that their influence was seasonal, depended on environmental conditions, and was affected by temporal patterns in C supply.
Bioresource Technology, Mar 1, 2005
Recirculating aquaculture systems are highly intensive culture systems that actively filter and r... more Recirculating aquaculture systems are highly intensive culture systems that actively filter and reuse water, thus minimizing water requirements and creating relatively small volumes of concentrated waste (compared to flow-through aquaculture systems). Vermicomposting, which uses earthworms to stabilize and transform organic wastes into valuable end-products, has been proposed as an alternative treatment technology for high-moisture-content organic wastes from agricultural, industrial and municipal sources. This study was conducted to determine if the effluent solids from a large recirculating aquaculture facility (Blue Ridge Aquaculture, Martinsville, Virginia) were suitable for vermicomposting using the earthworm Eisenia fetida. In two separate experiments, worms were fed mixtures of solids removed from aquaculture effluent (sludge) and shredded. Mixtures containing 0%, 5%, 10%, 15%, 20%, 25%, and 50% aquaculture sludge (dry weight basis) were fed to the worms over a 12-week period and their growth (biomass) was measured. Worm mortality, which occurred only in the first experiment, was not influenced by feedstock sludge concentration. In both experiments worm growth rates tended to increase with increasing sludge concentration, with the highest growth rate occurring with feedstocks containing 50% aquaculture sludge. Effluent solids from recirculating aquaculture systems mixed with shredded cardboard appear to be suitable feedstocks for vermicomposting.
Soil Biology & Biochemistry, 2003
... soil amendment, and chemical treatment (P=0.10); subsequent analyses detected a significant i... more ... soil amendment, and chemical treatment (P=0.10); subsequent analyses detected a significant increase ... Table 2. 15 N enrichment of extractable mineral nitrogen in microcosm soils treated with ... microcosms continued to increase until Day 56, probably because new shoots were ...
Pedobiologia, 2000
The biochemical changes in fresh cow manure caused by the earthworm Eisenia andrei (Bouché) were ... more The biochemical changes in fresh cow manure caused by the earthworm Eisenia andrei (Bouché) were measured over a period of four months, under controlled laboratory conditions. Earthworms were introduced into each of four plastic containers (0.4 × 0.27 × 0.15 m) containing fresh cow manure (2500 g), and four containers containing manure but without earthworms served as controls. Earthworms reduced the pH and decreased the moisture content in the manure. The C:N ratio of the manure with or without earthworms decreased progressively from 36 to 21. The ash and total nitrogen contents increased greatly for a few weeks after the introduction of earthworms, reflecting a rapid breakdown of carbon compounds and mineralization of nitrogen by the earthworms. CO 2 evolution decreased rapidly (44 %) one week after the introduction of earthworms, and continued at a lower rate throughout the 17 weeks (51 % reduction as compared to 22 % without earthworms), indicating increasing stability of the organic matter. Earthworms reduced microbial biomass early in the process, but enhanced nitrogen mineralization and increased the rates of conversion of ammonium-nitrogen into nitrate. The major general effect of earthworms on the organic wastes was to accelerate the maturation of the organic wastes as demonstrated by enhanced growth of lettuce and tomato seedlings.
Applied Soil Ecology, Sep 1, 1996
An ecosystem approach to soil toxicity testing allows for integration of the effects of chemical ... more An ecosystem approach to soil toxicity testing allows for integration of the effects of chemical contaminants on different components of the soil food web (system structure) and ecosystem-level processes (system function). We used this approach to study copper contamination in small laboratory soil microcosms. Microcosm soils were treated with CuSO 4 at the following concentrations: 0, 50, 100, 200, 400, and 800 mg Cu kg-~ soil. Five, 10, 20 and 40 days after soil treatment, we made the following organism-level measurements: microbial biomass N, substrate-induced respiration (SIR) and soil urease activity; total nematode numbers; earthworm mortality, growth and body accumulation of Cu. Our process-level measurements were net N mineralization and litter decomposition. SIR was the most sensitive of the parameters measured with significant effects observed at Cu concentrations as low as 50 mg kg ~. Microbial biomass N and earthworm growth showed intermediate sensitivity with effects at 200 mg kg-J Cu. The least sensitive organism-level parameters were soil urease activity and nematode abundance, both showing significant effects only at 800 mg kg-~ Cu. At the process-level, there was an inhibition of litter decomposition starting at 100 mg kg-] Cu, and a sharp increase in net N mineralization at 800 mg kg-1 Cu. By examining both the structure and function of the soil system, we were able to link the direct effects of copper on organisms to indirect effects on ecosystem-level processes and were able to suggest mechanisms to account for our results. The release of nitrogen from microbial cells killed by direct toxicity of Cu at 800 mg kg-t resulted in a transient increase in dissolved organic N, followed by a flush of N mineralization, resulting in large increase in NH4-N compared with the untreated control. Microbial mortality also apparently led to the inhibition of litter decomposition. Measuring the effects of contamination at different trophic levels simultaneously, and linking them to ecosystem processes, provided insights into the ecological mechanisms of the observed effects. This makes the ecosystem approach particularly valuable for analyzing the highly complex soil system. We suggest that the information obtained in a laboratory test based on the ecosystem approach is the most appropriate method for extrapolation to field situations.
Biocycle, 1998
Trials in soil and container media reveal some differences that may exist between vermicomposts a... more Trials in soil and container media reveal some differences that may exist between vermicomposts and composts and point to a growing awareness of the potential importance of microbial activity in plant growth.
Compost Science & Utilization, Jun 1, 2000
Tomato, pepper, lettuce, and marigold seedlings were grown in a standard commercial soilless plan... more Tomato, pepper, lettuce, and marigold seedlings were grown in a standard commercial soilless plant growth medium (Metro-Mix 360), and in coir/perlite and peat/perlite-based container media substituted with 10% or 20%, by volume, of vermicompost derived from pig manure or ...
Pedobiologia, 2003
Earthworms affect agroecosystem processes and few studies have addressed population dynamics when... more Earthworms affect agroecosystem processes and few studies have addressed population dynamics when earthworms are intentionally introduced. Handsorting and formalin extraction were used semi-annually from fall 1994 to fall 1997 to measure populations in plots with and without added earthworms under chisel till in a corn-soybean rotation (CT) and a ridge-till system in a corn-soybean-wheat rotation (RT) in Ohio, USA. Earthworm communities were altered by adding 76 Lumbricus terrestris (L.) m-2 each spring and fall into plots with no, or very few of these anecic earthworms. Increases in L. terrestris were small (~7 m-2) compared to the number added and their establishment was at the expense of the epigeic earthworm L. rubellus (Hoff.), which declined four and twofold in CT and RT, respectively. Populations of the endogeic earthworm Octolasion tytaeum (Sav.) were unaffected by the addition of L. terrestris. Sampling 5 years after the additions indicated that L. terrestris persisted only in the RT plots. The decline in L. rubellus populations in plots with added anecic worms was no longer evident. We understand that the increased number and amounts of residues and the minimal level of disturbance found in RT probably increased the extent and quality of earthworm habitat over CT plots, which had fewer crops, less cover, and periodic disturbance. Apparently, population dynamics and competitive relationships among different earthworm functional groups were regulated by agroecosystem type, and their correspondent disturbance regimes and resource distributions.
Communications in Soil Science and Plant Analysis, Sep 1, 1995
We compared estimates of soil nitrogen (N) mineralization rates using the buried bag and PVC core... more We compared estimates of soil nitrogen (N) mineralization rates using the buried bag and PVC core methods in an ongoing investigation of the effects of earthworms and N fertilizer sources on agroecosystem N dynamics. Over a seven‐month period, we paired monthly buried bag and PVC core soil incubations within research plots receiving one of three N treatments (inorganic, legume, or
Soil Biology & Biochemistry, Nov 1, 2001
The use of fungicides in agriculture, to protect plants from soil-borne pathogens, is a common pr... more The use of fungicides in agriculture, to protect plants from soil-borne pathogens, is a common practice. However, there is a dearth of information on the side-effects of fungicides on key soil ecological processes. We investigated the effects of three fungicides, benomyl, captan and chlorothalonil, on soil microbial activity (substrate-induced respiration and dehydrogenase activity), and nitrogen dynamics (NH 4 ±N and NO 3 ±N) in two laboratory experiments, one with captan and chlorothalonil and another with captan. In each laboratory batch incubation, soil was treated with a fungicide at approximately recommended ®eld application rates (benomyl, 51 mg a.i. kg 21 , captan,125 mg a.i. kg 21 and chlorothalonil, 37 mg a.i. kg 21) and incubated at 308C for 8 weeks. Some soils were amended with either ground alfalfa leaves or ground wheat straw to provide additional substrates for soil microorganisms and to alter rates of nitrogen mineralization/immobilization. All three fungicides suppressed the peak soil respiration in unamended soil by 30±50%, but the three fungicides had different effects in the amended soils. Soil dehydrogenase activity was stimulated by benomyl (18±21%) and chlorothalonil (8±15%) except in the alfalfa amended soil, but was decreased by captan (40±58%) in both the straw-amended and unamended soils. The fungicide-treated soils in general had less microbial biomass N concentrations than the untreated soils. Captan-treated soils had much higher NH 4 N concentrations than the control soils, with or without the organic amendments. Benomyl and chlorothalonil had little in¯uence on soil NH 4 N concentrations. Net N mineralization and nitri®cation rates were in¯uenced by all fungicide treatments as well as by the addition of organic materials. N mineralization rates were signi®cantly higher in captan-treated soils than in untreated soils. N dynamics were in¯uenced by chlorothalonil in a similar pattern to captan but reached peak nitri®cation rates earlier (day 7), in the alfalfa-amended soil. The effects of the three fungicides on soil microbial activity and nitrogen dynamics depended on the quality of the organic materials added to the soil. The patterns of effects of the fungicides on soil nutrient cycling processes were not large and were speci®c to each fungicide. Captan appeared to have more pronounced overall effects on soil microbial activity and nitrogen dynamics than either benomyl or chlorothalonil.
Soil Science Society of America Journal, Nov 1, 1999
Concern about NO−3 contamination of surface waters has prompted the development of agricultural w... more Concern about NO−3 contamination of surface waters has prompted the development of agricultural water table management systems to reduce NO−3 loss in subsurface drainage outflow by subirrigating through the existing subsurface drainage lines during the growing season and controlling off‐season outflows. We hypothesized that soil N pools, crop yields, and N uptake in a corn (Zea mays L.)–soybean (Glycine max.) rotation differ between subirrigation (water table at 40 cm) with controlled drainage (SI/CD) vs. subsurface drainage (SD) alone on Omulga silt loam (Aeric Fragiaqualfs). Mean microbial biomass N, potentially mineralizable N, dissolved organic N, and ammonia N were not affected by the water table management system. Mean NO−3–N was not affected by the water table management system at 0‐ to 15‐cm and 15‐ to 30‐cm depths, but the 2‐yr mean soil NO−3 concentration at the 30‐ to 75‐cm depth was 46% lower in SI/CD compared with SD. The average corn yield was 19% greater, and the average soybean yield was 64% greater, in SI/CD plots, compared with SD. Corn N uptake was 13% greater and soybean N uptake was 62% greater with SI/CD, compared with SD. The SI/CD water table management system increased plant N uptake and reduced deep‐profile NO−3 concentrations, thereby reducing the amount of NO−3 potentially available to move via drains to surface waters.
Journal of Environmental Quality, Jul 1, 2008
Oecologia, Mar 23, 1999
There are few studies in natural ecosystems on how spatial maps of soil attributes change within ... more There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part, this is due to methodological diculties associated with sampling the same spatial locations repeatedly over time. We describe the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in space¯uctuate over time. We used this method to examine spatial patterns of soil ammonium (NH 4) and nitrate (NO À 3) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in time, we also measured soil NH 4 and NO À 3 concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH 4 and NO À 3 concentrations increased with the age of the dune, whereas coecients of variation for NH 4 and NO À 3 concentrations decreased with the age of the dune. Soil NO À 3 concentration showed strong spatial structure, but soil NH 4 concentration was not spatially structured. Plant-available NH 4 and NO À 3 showed relatively little spatial structure: only NO À 3 availability in the second sampling period had signi®cant patch structure. Spatial maps of NH 4 and NO À 3 availability changed greatly over time, and there were few signi®cant correlations among soil nitrogen availability at dierent points in time. NO À 3 availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO À 3 concentrations, providing some evidence that patches of plant-available NO À 3 may reappear at the same spatial locations at irregular points in time. Key words Coastal dune ecosystems á Ion exchange membrane spikes á Soil nitrogen availability á Soil resource heterogeneity á Spatial statistics Oecologia (1999) 118:397±404
Pedobiologia, 2000
Vermicomposts, which are produced by the fragmentation of organic wastes by earthworms, have a fi... more Vermicomposts, which are produced by the fragmentation of organic wastes by earthworms, have a fine particulate structure and contain nutrients in forms that are readily available for plant uptake. In greenhouse trials, the growth of marigold and tomato seedlings, in a commercial horticultural potting medium (Metro-Mix 360), was enhanced significantly upon substitution of Metro-Mix 360 with 10 % or 20 % vermicomposted pig solids or vermicomposted food wastes, when all required nutrients were supplied. Same enhancement in marigold and tomato seedlings' growth occurred also upon substitution of Metro-Mix 360 with composted biosolids, but not with leaf compost. The shoot dry weights of raspberry plants, grown in a mineral soil mixed with vermicomposted pig wastes weighed more than those grown in unfertilized control soil, and were as great as those in soil receiving a complete fertilizer treatment. By comparison, raspberry shoot growth in soils amended with yard, leaf or bark composts, was poorer than that in the unfertilized control soil. Amending the soil with 4 % chicken manure compost killed most of the raspberry plants. However, plant mortality was reduced and growth restored when the chicken manure compost was mixed with vermicomposted pig solids, but not with bark or yard composts. Plant growth in soils containing a mixture of chicken manure compost with 20% vermicomposted pig wastes was similar to that of plants grown in the unfertilized control. Our results showed that vermicomposts have the potential for improving plant growth when added to greenhouse container media or soil. However, there seem to be distinct differences
Applied Soil Ecology, Mar 1, 2002
We investigated the effects of two commercially available soil biostimulants, designated Z93 and ... more We investigated the effects of two commercially available soil biostimulants, designated Z93 and W91, on key microbial and nutrient cycling processes in the soil, by conducting short-term (1 week) and longer-term (8 weeks) soil incubations in the laboratory. In the short-term soil incubations, the two compounds differed in their effects on microbial activity: Z93 was effective over a wide range, stimulating substrate-induced respiration (SIR) and dehydrogenase activity (DHA) at remarkably low concentrations (0.5-500 nl/g soil); W91 stimulated SIR at these concentrations, but also inhibited DHA. In longer-term soil incubations, we amended batches of soil with either finely-ground alfalfa leaves, wheat straw, or added no amendments, to alter patterns of soil nitrogen mineralization and immobilization. We treated these soils with Z93 and W91 at two concentrations (0.005 and 0.5 l/g soil), and incubated them for up to 8 weeks. These extremely low doses of both Z93 and W91 influenced soil SIR, DHA, and cellulase activity significantly (P < 0.05). Both compounds also influenced soil nitrogen dynamics significantly; the extent depending upon the quality of the organic amendments. In the alfalfa-amended soil there was a steep increase in NO 3-N concentration during the incubation due to the rapid mineralization of nitrogen-rich alfalfa material. However, in this soil, both Z93 and W91 reduced NO 3-N concentrations greatly after 56 days. In the straw-amended soil, mineral nitrogen concentrations were very low, probably due to rapid immobilization of nitrogen by microbial biomass. In this soil, treatment with both compounds decreased microbial biomass nitrogen and increased dissolved organic nitrogen (DON), relative to that in the controls. Our results suggest that the two biostimulants can stimulate both the breakdown and mineralization of soil organic materials, perhaps by selectively inhibiting or stimulating particular components of the microbial community, leading to lasting (8 weeks or longer) increases in soil nitrogen availability.
Applied Soil Ecology, Sep 1, 2001
The effects of benomyl and captan on soil ecological processes were tested in integrated terrestr... more The effects of benomyl and captan on soil ecological processes were tested in integrated terrestrial microcosms containing agricultural soil, organic amendments and wheat seedlings. The effects of the two fungicides on important soil ecological processes were evaluated by measuring soil microbial activity and biomass, including soil substrate-induced respiration (SIR), soil enzyme activity (dehydrogenase, urease and acid phosphatase) and microbial biomass nitrogen concentrations; nitrogen dynamics, including extractable inorganic nitrogen, dissolved organic nitrogen concentrations, net N mineralization and nitrification rates; rates of organic matter decomposition, using chopped wheat straw; in situ inorganic nitrogen concentrations using ion-exchange resin bags, and plant growth. The quality of the organic amendments (ground alfalfa leaves or chopped wheat straw) influenced the effects of the two fungicides on soil microbial processes and nitrogen availability strongly. Rates of SIR, soil enzyme activities (except urease activity), microbial biomass N and dissolved organic N concentrations were all decreased significantly by the fungicide treatments. Rates of wheat straw decomposition were also inhibited by the fungicide applications. Soil urease activity, NH4+–N and NO3−–N concentrations, and initial net N mineralization and nitrification rates were increased by the fungicide treatments. In situ concentrations of NH4+–N and NO3−–N in ion-exchange resin bags differed between the two fungicide treatments. Captan increased amounts of NH4+–N and NO3−–N in the resin bags significantly, compared to those in the untreated controls, or in benomyl-treated soils. The germination success of wheat seeds after 7 days, plant biomass (shoot+roots) as well as the total nitrogen uptake, were all increased by the captan treatment. The two fungicides differed in their effects on some soil processes and plant growth, as well as on rates of nitrogen uptake by plants; captan having a greater and long-lasting overall influence than benomyl. We concluded that these integrated microcosm techniques and resultant data can provide a better understanding of the interactions between fungicide applications and soil ecological processes than single investigations of the individual processes.
Applied Soil Ecology, Sep 1, 1998
To investigate the in¯uence of earthworms on net rates of N mineralization in agricultural soils,... more To investigate the in¯uence of earthworms on net rates of N mineralization in agricultural soils, we manipulated earthworm populations for three years in three corn agroecosystems that differed in nutrient inputs (inorganic N, legume, or manure). Each spring and fall, earthworms were added to, removed from, or left unmodi®ed in ®eld enclosures within each agroecosystem. In the second and third year, we measured soil concentrations of mineral N (0±15 cm depth) in these enclosures, as well as net rates of N mineralization using an in situ soil core incubation method. In the inorganic N-fertilized agroecosystem, mineral N concentrations were often greatest in the enclosures with earthworm additions or least in enclosures with earthworm reductions. The largest differences were seen following inorganic fertilizer application, suggesting either greater net N immobilization or increased N loss from the surface soil in the enclosures with earthworm reductions. Subsequent net rates of N mineralization were greater in the enclosures with reduced earthworm populations, possibly due to the turnover of N in microbial biomass. In the legume-fertilized agroecosystem, overall rates of net N mineralization were greater in enclosures with earthworm additions than in enclosures with earthworm reductions. In this agroecosystem, cumulative net N mineralization during the two-year study was signi®cantly higher in enclosures with earthworm additions than in enclosures with unmodi®ed or reduced populations. Earthworms can signi®cantly in¯uence the net rates of N mineralization in agricultural soils, but the timing, direction, and the magnitude of this in¯uence appears to be dependent on the nature of the nutrient inputs.
Pedobiologia, 2001
W Wa at te er r s st ta ab bi il li it ty y o of f e ea ar rt th hw wo or rm m c ca as st ts s i ... more W Wa at te er r s st ta ab bi il li it ty y o of f e ea ar rt th hw wo or rm m c ca as st ts s i in n m ma an nu ur re e-a an nd d i in no or rg ga an ni ic c-f fe er rt ti il li iz ze er r a am me en nd de ed d a ag gr ro oe ec co os sy ys st te em ms s i in nf fl lu u-e en nc ce ed d b by y a ag ge e a an nd d d de ep pt th h
Communications in Soil Science and Plant Analysis, Apr 1, 1998
Go to AGRIS search. Communications in soil science and plant analysis (Apr 1998). Assessing biolo... more Go to AGRIS search. Communications in soil science and plant analysis (Apr 1998). Assessing biological activity of agricultural biostimulants: bioassays for plant growth regulators in three soil additives. ...
Soil Biology & Biochemistry, Mar 1, 1997
Available evidence suggests that earthworms enhance the mineralization of carbon in soil, but the... more Available evidence suggests that earthworms enhance the mineralization of carbon in soil, but there are few data from field experiments that demonstrate that earthworms increase soil respiration under natural environmental conditions. We measured soil respiration (CO2 flux) during 1993–1994 in 20-m2 field enclosures in which earthworm populations had been decreased, increased, or left unmodified (the latter serving as a control). The enclosures were in corn agroecosystems receiving one of three different nutrients: legume cover crop, cow manure or inorganic fertilizer (NH4NO3). Soil respiration was measured in the enclosures by the static diffusion method. Earthworms had significant effects on soil respiration, but their effects varied seasonally and were influenced by environmental conditions. There were significant differences in respiration rates among earthworm treatments on seven of the 24 sampling dates, and where significant differences did occur, respiration rates were greates in plots with increased populations and lowest in plots with decreased populations. Most of the significant effects of earthworms on soil respiration were observed during the growing season (June–August) of 1994. A severe drought in the summer of 1993 decreased overall respiration rates relative to 1994, and also inhibited earthworm activity. Soil respiration was significantly greater, during the growing season, in the organically-amended plots than in plots treated with inorganic fertilizer; there were no differences in soil respiration among nutrient treatments in the autumn or in the spring before amendments were added. Our results show that earthworms had a significant influence on soil respiration in the field, but that their influence was seasonal, depended on environmental conditions, and was affected by temporal patterns in C supply.
Bioresource Technology, Mar 1, 2005
Recirculating aquaculture systems are highly intensive culture systems that actively filter and r... more Recirculating aquaculture systems are highly intensive culture systems that actively filter and reuse water, thus minimizing water requirements and creating relatively small volumes of concentrated waste (compared to flow-through aquaculture systems). Vermicomposting, which uses earthworms to stabilize and transform organic wastes into valuable end-products, has been proposed as an alternative treatment technology for high-moisture-content organic wastes from agricultural, industrial and municipal sources. This study was conducted to determine if the effluent solids from a large recirculating aquaculture facility (Blue Ridge Aquaculture, Martinsville, Virginia) were suitable for vermicomposting using the earthworm Eisenia fetida. In two separate experiments, worms were fed mixtures of solids removed from aquaculture effluent (sludge) and shredded. Mixtures containing 0%, 5%, 10%, 15%, 20%, 25%, and 50% aquaculture sludge (dry weight basis) were fed to the worms over a 12-week period and their growth (biomass) was measured. Worm mortality, which occurred only in the first experiment, was not influenced by feedstock sludge concentration. In both experiments worm growth rates tended to increase with increasing sludge concentration, with the highest growth rate occurring with feedstocks containing 50% aquaculture sludge. Effluent solids from recirculating aquaculture systems mixed with shredded cardboard appear to be suitable feedstocks for vermicomposting.
Soil Biology & Biochemistry, 2003
... soil amendment, and chemical treatment (P=0.10); subsequent analyses detected a significant i... more ... soil amendment, and chemical treatment (P=0.10); subsequent analyses detected a significant increase ... Table 2. 15 N enrichment of extractable mineral nitrogen in microcosm soils treated with ... microcosms continued to increase until Day 56, probably because new shoots were ...
Pedobiologia, 2000
The biochemical changes in fresh cow manure caused by the earthworm Eisenia andrei (Bouché) were ... more The biochemical changes in fresh cow manure caused by the earthworm Eisenia andrei (Bouché) were measured over a period of four months, under controlled laboratory conditions. Earthworms were introduced into each of four plastic containers (0.4 × 0.27 × 0.15 m) containing fresh cow manure (2500 g), and four containers containing manure but without earthworms served as controls. Earthworms reduced the pH and decreased the moisture content in the manure. The C:N ratio of the manure with or without earthworms decreased progressively from 36 to 21. The ash and total nitrogen contents increased greatly for a few weeks after the introduction of earthworms, reflecting a rapid breakdown of carbon compounds and mineralization of nitrogen by the earthworms. CO 2 evolution decreased rapidly (44 %) one week after the introduction of earthworms, and continued at a lower rate throughout the 17 weeks (51 % reduction as compared to 22 % without earthworms), indicating increasing stability of the organic matter. Earthworms reduced microbial biomass early in the process, but enhanced nitrogen mineralization and increased the rates of conversion of ammonium-nitrogen into nitrate. The major general effect of earthworms on the organic wastes was to accelerate the maturation of the organic wastes as demonstrated by enhanced growth of lettuce and tomato seedlings.
Applied Soil Ecology, Sep 1, 1996
An ecosystem approach to soil toxicity testing allows for integration of the effects of chemical ... more An ecosystem approach to soil toxicity testing allows for integration of the effects of chemical contaminants on different components of the soil food web (system structure) and ecosystem-level processes (system function). We used this approach to study copper contamination in small laboratory soil microcosms. Microcosm soils were treated with CuSO 4 at the following concentrations: 0, 50, 100, 200, 400, and 800 mg Cu kg-~ soil. Five, 10, 20 and 40 days after soil treatment, we made the following organism-level measurements: microbial biomass N, substrate-induced respiration (SIR) and soil urease activity; total nematode numbers; earthworm mortality, growth and body accumulation of Cu. Our process-level measurements were net N mineralization and litter decomposition. SIR was the most sensitive of the parameters measured with significant effects observed at Cu concentrations as low as 50 mg kg ~. Microbial biomass N and earthworm growth showed intermediate sensitivity with effects at 200 mg kg-J Cu. The least sensitive organism-level parameters were soil urease activity and nematode abundance, both showing significant effects only at 800 mg kg-~ Cu. At the process-level, there was an inhibition of litter decomposition starting at 100 mg kg-] Cu, and a sharp increase in net N mineralization at 800 mg kg-1 Cu. By examining both the structure and function of the soil system, we were able to link the direct effects of copper on organisms to indirect effects on ecosystem-level processes and were able to suggest mechanisms to account for our results. The release of nitrogen from microbial cells killed by direct toxicity of Cu at 800 mg kg-t resulted in a transient increase in dissolved organic N, followed by a flush of N mineralization, resulting in large increase in NH4-N compared with the untreated control. Microbial mortality also apparently led to the inhibition of litter decomposition. Measuring the effects of contamination at different trophic levels simultaneously, and linking them to ecosystem processes, provided insights into the ecological mechanisms of the observed effects. This makes the ecosystem approach particularly valuable for analyzing the highly complex soil system. We suggest that the information obtained in a laboratory test based on the ecosystem approach is the most appropriate method for extrapolation to field situations.