Earthworms affect soil structure and the movement of agrochemicals. Yet, there have been few field-scale studies that quantify the effect of earthworms on dissolved nitrogen fluxes in agroecosystems. We investigated the influence of semi-annual earthworm additions on leachate production and quality in different row crop agroecosystems. Chisel-till corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation (CT) and ridge-till corn-soybean-wheat (Triticum aestivum L.) rotation (RT) plots were arranged in a complete randomized block design (n = 3) with earthworm treatments (addition and ambient) as subplots where zero-tension lysimeters were placed 45 cm below ground. We assessed earthworm populations semi-annually and collected leachate biweekly over a three-year period and determined leachate volume and concentrations of total inorganic nitrogen (TIN) and dissolved organic nitrogen (DON). Abundance of deep-burrowing earthworms was increased in addition treatments over ambient and for both agroecosystems. Leachate loss was similar among agroecosystems, but earthworm additions increased leachate production in the range of 4.5 to 45.2% above ambient in CT cropping. Although leachate TIN and DON concentrations were generally similar between agroecosystems or earthworm treatments, transport of TIN was significantly increased in addition treatments over ambient in CT cropping due to increased leachate volume. Losses of total nitrogen in leachate loadings were up to approximately 10% of agroecosystem N inputs. The coincidence of (i) soluble N production and availability and (ii) preferential leaching pathways formed by deep-burrowing earthworms thereby increased N losses from the CT agroecosystem at the 45-cm depth. Processing of N compounds and transport in soil water from RT cropping were more affected by management phase and largely independent of earthworm activity.

The influence of two experimental soil treatments, Z93 and W91, on nitrogen transformations, microbial activity and plant growth was investigated in soil microcosms. These compounds are commercially marketed fermentation products (Agspectrum) that are sold to be added to field soils in small amounts to promote nitrogen and other nutrient uptake by crops in USA. In laboratory microcosm experiments, soils were amended with finely ground alfalfa-leaves or wheat straw, or left unamended, in an attempt to alter patterns of soil nitrogen mineralization and immobilization. Soils were treated in the microcosms with Z93 and W91 at rates equivalent to the recommended field application rates, that range from 0.2 to 1.1lha−1, (0.005–0.03μlg−1 soil). We measured their effects on soil microbial activity (substrate-induced respiration (SIR), dehydrogenase activity (DHA) and acid phosphatase activity (PHOS)), soil nitrogen pools (microbial biomass N, mineral N, dissolved organic N), and transformations (net N mineralization and nitrification, 15N dilution of the mineral N pool, and accumulation of mineral N on ion-exchange resins), and on wheat plant germination and growth (shoot and root biomass, shoot length, N uptake and 15N enrichment of shoot tissues), for up to 56 days after treatment. To follow the movement of nitrogen from inorganic fertilizer into plant biomass we used a 15N isotopic tracer. Most of the soil and plant responses to treatment with Z93 or W91 differed according to the type of organic amendment that was used. Soil treatment with either Z93 or W91 influenced phosphatase activity strongly but did not have much effect on SIR or DHA. Both chemicals altered the rates of decomposition and mineralization of organic materials in the soil, which was evidenced by significant increases in the rates of the decomposition of buried wheat straw, and by the acceleration of net, rates of N mineralization, relative to those of the controls. Soil nitrate availability increased at the end of the experiment in response to both chemical treatments. In alfalfa-amended soils, the final plant biomass was decreased significantly by treatment with W91. Increased plant growth and N-use efficiency in straw-amended soil, resulting from treatments with Z93 or W91, was linked to increased rates of N mineralization from indigenous soil organic materials. This supports the marketing of these compounds as promoters of N uptake at these low dosage inputs.

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 similar to76 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 (similar to7 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 two-fold 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.

Although it is known that deep-burrowing earthworms can increase the depth of penetration of solutes in soil, their comparative effect on solute transport when they are added to communities composed solely of epigeic and endogeic species is not clear. Ionic tracers were applied as artificial rainfall to the surface of plots with or without added deep-burrowing earthworms (n=3). We determined the soil water content, total nitrogen, soil organic carbon (SOC), strontium, and bromide concentrations in soil samples taken from a 320mm×380mm, 56-position grid with 40mm sample spacing. Earthworm inoculations increased populations of deep-burrowing Lumbricus terrestris L., and decreased those of the surface-dwelling L. rubellus Hoffmeister, and had no impact on geophagous species; compared to the earthworm communities in control plots. The average soil concentrations of SOC, bromide and strontium were higher where earthworms were inoculated compared to controls. Solute concentrations, SOC, and soil water content all decreased with depth. Synthetic data derived from multivariate analyses were used as an index of solute transport intensity. Solute transport intensity was greater at any given depth in response to earthworm inoculations, compared to that in controls. Although we observed a characteristic breakthrough of solutes to greater depths where deep-burrowing earthworms were inoculated, there were no differences in the spatial distribution of solutes between the two earthworm communities studied. We concluded that although the activity of deep-burrowing species allowed solute breakthrough to greater depth, the more diffuse distribution of solutes was the result of the dominant random burrowing activity of epigeic and endogeic earthworm species, which comprised the larger proportion of earthworms in these communities.

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 μl/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 NO3-N concentration during the incubation due to the rapid mineralization of nitrogen-rich alfalfa material. However, in this soil, both Z93 and W91 reduced NO3-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.

Earthworm casts can contribute significantly to surface soil structure in agroecosystems. We suggest that the water stability of such earthworm casts depends on the earthworm food source, and the depth at which casts are made. We studied the effects of fertilizer inputs to cropping systems as earthworm feedstocks, and depth of cast placement on cast water stability and texture. We collected air-dried earthworm casts from manure and inorganic fertilizer-amended agroecosystems. Cast water-stability index and the cast texture were measured at 1, 2, 4, 8, and 16 weeks. We found that fertilizer treatments did not account for all of the variation in the measured water stability of earthworm casts. The placement of casts at 10 cm depth resulted in small changes in the water-stability index with time, while casts placed near the soil surface were degraded rapidly in terms of both water stability, and textural attributes. This was less marked in the inorganic treatment than in organic treatments. The differences in casts from different earthworm species, especially in terms of ecological groupings, may have affected the stability of the casts collected. Our results suggest that the form of fertilizer inputs can influence cast stability to some extent. However, cast placement in terms of depth, which is largely a function of earthworm ecological group, may be more important overall.

We investigated the influence of earthworms on the three-dimensional distribution of soil organic carbon (SOC) in a chisel-tilled soil. By burrowing, foraging, and casting at the surface and throughout the soil, anecic earthworms such as Lumbricus terrestris L. may play a major role in regulating the spatial distribution of organic matter resources both at the surface and within the soil. In the fall of 1994, we manipulated ambient earthworm communities, which were without deep burrowing species, by adding 100 earthworm individuals m−2 in spring and fall for 3 years. Overall, the biomass of L. terrestris was increased with earthworm additions and total earthworm biomass declined compared with ambient control treatments. To investigate the spatial variability in soil organic carbon due to this shift in earthworm community structure, we sampled soil on a 28×24cm grid from the surface to 40cm in four layers, 10 cm deep. Samples were analyzed for total carbon. We found that additions of anecic earthworms significantly increased average soil organic carbon content from 16.1 to 17.9gCkg−1 for the 0–10cm soil, and from 12.4 to 14.7gkg−1 at 10–20-cm depth, and also changed the spatial distribution of soil organic carbon from uniform to patchy, compared with the ambient treatment.

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.

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.

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 between specific vermicomposts and composts in terms of their nutrient contents, the nature of their microbial communities, and their effects on plant growth.

The presence of deep-burrowing earthworms can affect soil structure and infiltration, therefore influencing agricultural productivity. We investigated the effects of deep-burrowing earthworm species on soil structure at the surface of chisel-plowed or ridge-tilled cropping systems in Pike County, OH, planted to corn (Zea mays L.). Earthworm populations were experimentally manipulated in field enclosures by adding predominantly deep-burrowing Lumbricus terrestris L., or leaving enclosures unmodified in each tillage system. In 1995, after 2 years of bi-annual additions, we measured surface residue cover, dry sieved aggregates (DSA)- and water-stable aggregates (WSA), and carbon and nitrogen concentration of aggregates by size class, in each treatment combination. Also, in 1998, we used tension infiltrometry to examine crusting effects at the soil surface among earthworm treatments in the chisel-plow treatment. Earthworm additions yielded increased density and biomass of L. terrestris than ambient controls, and to a greater extent in the ridged corn–soybean (Glycine max L. Mess.)–wheat (Triticum aestivum L.) (CSW) than corn–soybean (CS) rotation. Percentage residue cover in CS cropping decreased with earthworm additions. Earthworm additions decreased the geometric mean weight diameter (GMWD) of DSA and WSA in chisel-plow treatment compared to no additions. Earthworm additions influenced carbon-to-nitrogen (C/N) ratios for smaller DSA and WSA. Water-stable aggregate C/N decreased with size class. The overall effect of earthworm additions was an increase in deep-burrowing earthworms, a decrease in surface residue cover, and more pronounced crusting, which decreased mesopore conductivity.

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.