Scott Subler

Pig manure vermicompost as a component of a horticultural bedding plant medium: effects on physicochemical properties and plant growth

This experiment was designed to characterize the physical, chemical and microbial properties of a standard commercial horticultural, greenhouse container, bedding plant medium (Metro-Mix 360), that had been substituted with a range of increasing concentrations (0%, 5%, 10%, 25%, 50% and 100% by volume) of pig manure vermicompost and to relate these properties to plant growth responses. The growth trials used tomatoes (Lycopersicon esculentum Mill.), grown in the substituted media for 31 days under glasshouse conditions, with seedling growth recorded in 20 pots for each treatment. Half of the tomato seedlings (10 pots per treatment) were watered daily with liquid inorganic fertilizer while the other half received water only. The percentage total porosity, percentage air space, pH and ammonium concentrations of the container medium all decreased significantly, after substitution of Metro-Mix 360 with equivalent amounts of pig manure vermicompost; whereas bulk density, container capacity, electrical conductivity, overall microbial activity and nitrate concentrations, all increased with increasing substitutions of vermicompost. The growth of tomato seedlings in the potting mixtures containing 100% pig manure vermicompost was reduced, possibly as a result of high soluble salt concentrations in the vermicompost and poorer porosity and aeration. The growth of tomato seedlings was greatest after substitution of Metro-Mix 360 with between 25% and 50% pig manure vermicompost, with more growth occurring in combinations of pig manure vermicompost treated regularly with a liquid fertilizer solution than in those with no fertilizer applied. Some of the growth enhancement in these mixtures seemed to be related to the combined effects of improved porosity, aeration and water retention in the medium and the high nitrate content of the substrate, which produced an increased uptake of nitrogen by the plant tissues, resulting in increased plant growth. When the tomato seedlings were watered daily with liquid inorganic fertilizer, substitution of Metro-Mix 360 with a very small amount (5%) of pig manure vermicompost resulted in a significant increase in the growth of tomato seedlings. Such effects could not be attributed solely to the nutritional or physical properties of the pig manure vermicompost. Therefore, it seems likely that the pig manure vermicompost provided other biological inputs, such as plant growth regulators into the container medium, that still need to be identified fully.

Changes in biochemical properties of cow manure during processing by earthworms (Eisenia andrei, Bouché) and the effects on seedling growth

Summary The biochemical changes in fresh cow manure caused by the earthworm Eisenia andrei (Bouche) 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. CO2 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.

Sampling spatial and temporal variation in soil nitrogen availability

Abstract 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 difficulties 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 fluctuate over time. We used this method to examine spatial patterns of soil ammonium (NH+4) and nitrate (NO−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−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−3 concentrations increased with the age of the dune, whereas coefficients of variation for NH+4 and NO−3 concentrations decreased with the age of the dune. Soil NO−3 concentration showed strong spatial structure, but soil NH+4 concentration was not spatially structured. Plant-available NH+4 and NO−3 showed relatively little spatial structure: only NO−3 availability in the second sampling period had significant patch structure. Spatial maps of NH+4 and NO−3 availability changed greatly over time, and there were few significant correlations among soil nitrogen availability at different points in time. NO−3 availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO−3 concentrations, providing some evidence that patches of plant-available NO−3 may reappear at the same spatial locations at irregular points in time.

Earthworm-processed organic wastes as components of horticultural potting media for growing marigold and vegetable seedlings.

We germinated and grew tomato, pepper, lettuce, and marigold seedlings 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 food wastes. Half of the treatments were watered with liquid inorganic fertilizer while the other half received only water. Germination rates of tomato, pepper, lettuce, and marigold seeds in the coir/perlite mixture did not differ significantly from that in Metro-Mix 360. However, the germination rate of tomato, pepper and lettuce seedlings was very low in the peat/perlite mixture. Substituting some of the peat/perlite mixtures with equal amounts of vermicomposts, particularly pig manure vermicompost, enhanced germination rates greatly, making it comparable to that in the commercial medium (Metro-Mix 360). Pepper, lettuce, and marigold seedlings grown in Metro-Mix 360, which already contains a starter nutrient fertilizer in its formulation, had greater root and shoot dry weights than those grown in the control media (coir/perlite mix and peat/perlite mix). Substituting coir/perlite and peat/perlite mixtures with 10% or 20% of either vermicompost enhanced the growth of seedlings significantly, resulting in an overall plant growth as good as and sometimes better than that in Metro-Mix 360. When the plants were provided daily with a complete fertilizer solution, marigold seedlings in peat-based substrate with 20% pig waste vermicompost, and lettuce seedlings in both coir and peat-based substrates, mixed with 20% food wastes vermicompost, produced greater shoot dry weights than those grown in the commercial potting medium. The growth enhancements tended to be greater in peat/perlite-based mixes than in coir/perlite-based mixes, more so with the addition of pig manure vermicompost than with food waste vermicompost. Earthworm-processed pig manure and food wastes would be suitable materials for inclusion into the formulation of soilless potting media, since substitution of these media with relatively low concentrations of vermicomposts can promote plant growth.

Greenhouse Gas Balance for Composting Operations

The greenhouse gas (GHG) impact of composting a range of potential feedstocks was evaluated through a review of the existing literature with a focus on methane (CH(4)) avoidance by composting and GHG emissions during composting. The primary carbon credits associated with composting are through CH(4) avoidance when feedstocks are composted instead of landfilled (municipal solid waste and biosolids) or lagooned (animal manures). Methane generation potential is given based on total volatile solids, expected volatile solids destruction, and CH(4) generation from lab and field incubations. For example, a facility that composts an equal mixture of manure, newsprint, and food waste could conserve the equivalent of 3.1 Mg CO(2) per 1 dry Mg of feedstocks composted if feedstocks were diverted from anaerobic storage lagoons and landfills with no gas collection mechanisms. The composting process is a source of GHG emissions from the use of electricity and fossil fuels and through GHG emissions during composting. Greenhouse gas emissions during composting are highest for high-nitrogen materials with high moisture contents. These debits are minimal in comparison to avoidance credits and can be further minimized through the use of higher carbon:nitrogen feedstock mixtures and lower-moisture-content mixtures. Compost end use has the potential to generate carbon credits through avoidance and sequestration of carbon; however, these are highly project specific and need to be quantified on an individual project basis.

Earthworm additions increased short-term nitrogen availability and leaching in two grain-crop agroecosystems

Abstract Earthworms were added to enclosures in two agroecosystems to determine their influence on soil nitrogen availability and microbial activity, and to quantify their effect on the leaching of water and nitrogen through the surface soil. The two agroecosystems were a corn-soybean rotation with chisel-plow-disk tillage following corn (CS), and a corn-soybean-wheat-vetch rotation with ridge-tillage (CSW). In both agroecosystems, earthworm additions in the fall (100 m−2) led to more abundant deepdwelling earthworms and less abundant surface-dwelling earthworms than in enclosures with no additions, but had little effect on total earthworm abundance after 5 months. In the CS system, earthworm additions led to greater concentrations of potentially mineralizable nitrogen (PMN) and microbial biomass nitrogen (MBN) in the surface soil than in control enclosures in the following spring. In the CSW system, earthworm additions led to greater overall concentrations of dissolved organic nitrogen (DON), but only to localized changes in PMN and MBN at different positions within crop rows and at different soil depths. Soil mineral nitrogen concentrations were not influenced by earthworm additions. Earthworms significantly influenced soil microbial activity in both agroecosystems; earthworm additions generally increased soil dehydrogenase activity (DHA) in the CS system, and reduced it in the CSW system, compared to controls. Earthworm additions led to 4- to 12-fold increases in the volume of soil leachate collected during 1 week in zero-tension pan lysimeters buried 45 cm deep. For both agroecosystems, nitrogen flux in leachate was increased by nearly 10-fold in response to earthworm additions. Most of this response was due to increased flux of DON. We conclude that the composition of earthworm communities can strongly influence the availability and leaching of nitrogen in the surface soil of some grain-crop agroecosystems, at least in the short-term. More work is needed to predict the longer-term consequences of earthworms on crop productivity, nitrogen use efficiency and groundwater quality.

An ecosystem approach to soil toxicity testing: a study of copper contamination in laboratory soil microcosms

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 CuSO4 at the following concentrations: 0, 50, 100, 200, 400, and 800 mg Cu kg−1 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−1. Microbial biomass N and earthworm growth showed intermediate sensitivity with effects at 200 mg kg−1 Cu. The least sensitive organism-level parameters were soil urease activity and nematode abundance, both showing significant effects only at 800 mg kg−1 Cu. At the process-level, there was an inhibition of litter decomposition starting at 100 mg kg−1 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−1 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.

Using anion-exchange membranes to measure soil nitrate availability and net nitrification

Abstract There are few methods that provide adequate integrative measures of soil N availability to plants. We evaluated a new ion-exchange membrane (IEM) technique for measuring soil NO3 availability and nitrification by burying commercially-available anion-exchange membranes (IEMs) in a silt-loam Luvisol (fine, mixed, mesic Typic Fragiudalf) and in the same soil amended with either wheat straw, legume leaves or both materials. Soil was incubated in the laboratory for periods ranging from 1 to 27 days before removing the IEMs and determining membrane-bound NO3 and soil inorganic N concentrations. The soil amendments led to large differences in soil N dynamics and rates of net N mineralization and nitrification among treatments. In all soil treatments, rates of NO3N uptake by IEMs were rapid initially, but slowed after 7 days. On all dates, significantly less NO3N was recovered from IEMs in the amended soils than from those in the control soil, probably because of greater microbial immobilization of NO3 due to the added organic substrates. The IEMs did not act as infinite sinks for NO3, since under strongly N-immobilizing conditions in the wheat straw-amended soil membrane-bound NO3N declined between 3–14 days. Across all soil treatments and sampling dates, membrane-bound NO3N was significantly correlated with soil NO3N concentrations and net soil nitrification (r2 = 0.53 and 0.86, respectively), even when net nitrification was negative. Correlations improved when data from the initial membrane equilibration period (days 1 and 3) were excluded (r2 = 0.85 and 0.96, respectively). The presence of IEMs significantly reduced soil NO3N concentrations in 3 of the 4 soil treatments, and in all of the soil treatments, net soil nitrification and N mineralization were significantly greater in the presence of the IEMs. Results from our correlative study suggest that the IEM technique can be a useful tool for assessing soil nutrient availability and mineralization processes. However, more work is needed to develop this technique before reliable interpretations can be made under a wide variety of field and laboratory conditions.

A microcosm approach for evaluating the effects of the fungicides benomyl and captan on soil ecological processes and plant growth

Abstract 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, NH 4 + –N and NO 3 − –N concentrations, and initial net N mineralization and nitrification rates were increased by the fungicide treatments. In situ concentrations of NH 4 + –N and NO 3 − –N in ion-exchange resin bags differed between the two fungicide treatments. Captan increased amounts of NH 4 + –N and NO 3 − –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.

Quantification of nitrogen excretion rates for three lumbricid earthworms using 15N

Abstract Nitrogen excretion rates of 15N-labeled earthworms and contributions of 15N excretion products to organic (dissolved organic N) and inorganic (NH4-N, NO3-N) soil N pools were determined at 10  °C and 18  °C under laboratory conditions. Juvenile and adult Lumbricus terrestris L., pre-clitellate and adult Aporrectodea tuberculata (Eisen), and adult Lumbricus rubellus (Hoffmeister) were labeled with 15N by providing earthworms with 15N-labeled organic substrates for 5–6 weeks. The quantity of 15N excreted in unlabeled soil was measured after 48 h, and daily N excretion rates were calculated. N excretion rates ranged from 274.4 to 744 μg N g–1 earthworm fresh weight day–1, with a daily turnover of 0.3–0.9% of earthworm tissue N. The N excretion rates of juvenile L. terrestris were significantly lower than adult L. terrestris, and there was no difference in the N excretion rates of pre-clitellate and adult A. tuberculata. Extractable N pools, particularly NH4-N, were greater in soils incubated with earthworms for 48 h than soils incubated without earthworms. Between 13 and 40% of excreted 15N was found in the 15N-mineral N (NH4-N+NO3-N) pool, and 13–23% was in the 15N-DON pool. Other fates of excreted 15N may have been incorporation in microbial biomass, chemical or physical protection in non-extractable N forms, or gaseous N losses. Earthworm excretion rates were combined with earthworm biomass measurements to estimate N flux from earthworm populations through excretion. Annual earthworm excretion was estimated at 41.5 kg N ha–1 in an inorganically-fertilized corn agroecosystem, and was equivalent to 22% of crop N uptake. Our results suggest that the earthworms could contribute significantly to N cycling in corn agroecosystems through excretion processes.