An ASAE Meeting Presentation Paper Number: 052063
Preferential Flow of Liquid Manure in Macropores and Cracks Martin J. Shipitalo, USDA-ARS, North Appalachian Experimental Watershed, P.O. Box 488 Coshocton, OH 43812-0488,
[email protected] Frank Gibbs, USDA-NRCS, 7868 County Road 140, Suite F, Findlay, OH 45840-1898,
[email protected]
Written for presentation at the 2005 ASAE Annual International Meeting Sponsored by ASAE Tampa Convention Center Tampa, Florida 17 - 20 July 2005 Abstract. Substitution of conservation tillage for conventional tillage practices can greatly decrease runoff and losses of soil and agrochemicals in overland flow, but enhanced infiltration increases the potential for ground water contamination. Earthworm populations also frequently increase with a reduction in tillage intensity, which suggests that their effects on soil structure and porosity may contribute to the decrease in runoff. In particular, the size and number of Lumbricus terrestris (L.) burrows suggest that they may have a major impact on hydrology. Field research indicates that the amount of rainfall transmitted by L. terrestris burrows increases with storm intensity and is as much as 10% of total rainfall. Laboratory studies indicate that if a heavy, intense storm occurs shortly after surface application of agrochemicals, the water transmitted to the subsoil by earthworm burrows may contain significant amounts of applied chemical, up to a few per cent, regardless of the affinity of the chemical for the soil. Transport can be reduced by an order of magnitude or more with the passage of time or if light rainstorms precede the first major leaching event. Because of movement into the soil matrix and sorption, solutes normally strongly adsorbed should only be subject to significant transport in earthworm burrows and other macropores in the first few storms after application. In the case of fields with subsurface drainage, however, close association of earthworm burrows to the drains may substantially increase the risk of surface water contamination by surface-applied agrochemicals and injected animal wastes. Likewise, earthworm burrows may connect to subsoil fractures and contribute to rapid water and chemical movement to drains and ground water. Keywords. Agricultural wastes, best management practices, conservation tillage, drainage systems, earthworms, infiltration, liquid manures, no till, subsurface drainage 2
Introduction The effects of soil management practices on runoff, erosion, and water quality have been measured using small (0.5 to 1 ha), gauged watersheds at the USDA-ARS North Appalachian Experimental Watershed near Coshocton, Ohio USA since the mid 1930's. In general, the results of these studies indicate that conservation tillage practices, and no-till in particular, can be very effective in reducing runoff and erosion compared to conventional tillage practices (Shipitalo and Edwards, 1998). The reduction in runoff, however, increases the amount of water available to leach agrochemicals and can potentially increase ground water contamination. Since no-till soils usually have higher bulk density, hence lower total porosity than conventionally tilled soils, particularly shortly after tillage, this suggests that the pores in no-till soil must be more effective in transmitting water than those in plowed soil. One factor that helps explain this observation is that raindrops hitting the unprotected surface of conventionally tilled soil can cause a crust to form that blocks water movement into pores. The residue cover on notill soil significantly reduces the effects of raindrop impact and the propensity for the soil to crust. The residue also produces a more favorable environment for earthworms by keeping the soil cool and moist and providing a continuous supply of food for surface-feeding earthworms (Edwards and Bohlen, 1996). Since they can ingest and process a large amount of soil and residue on a yearly basis, earthworms have the potential to greatly affect how water moves through the soil (Shipitalo and Le Bayon, 2004)
Conservation Tillage and Earthworms Earthworm populations can be measured using a variety of techniques, such as digging and hand-sorting, chemical and electrical extraction, all of which have drawbacks and strengths. Perhaps the most commonly used technique, however, is chemical extraction using a weak solution of formalin. Although earthworm populations can vary considerably from year-to-year due to variation in soil water content and other conditions affecting earthworm survival and reproduction (Bohlen et al., 1995; Butt et al., 1999), earthworm numbers are usually much greater in no-till than in tilled fields (Edwards and Bohlen, 1996; Curry, 2004). Populations of two million worms per hectare in no-till fields are not uncommon. Also, earthworm burrows in no-till fields can last longer than the worms that formed them because the burrows are not destroyed by tillage. The total number of earthworm species in the world is unknown, but estimates are normally upwards of 3000 species (Lee, 1985), few of which have been investigated in detail. These species are normally divided into three ecological groups based on the classification proposed by Bouché (Edwards and Bohlen, 1996; Lee, 1985). Epigeic earthworms are generally found beneath or within accumulations of organic matter and rarely burrow into or ingest much soil. Typical habitats include forest litter or manure piles, thus they have little direct effect on the structure of mineral soils. Endogeic earthworms burrow extensively below ground and obtain their nutrition by ingesting a mixture of mineral soil and organic matter. They form extensively branched, sub-horizontal networks of burrows in search of food, but most of their activity is in the upper 10-15 cm where organic matter levels are generally highest. Portions of their burrows are often occluded with their excrement (casts) and they occasionally cast on the soil surface. Anecic earthworms normally live in permanent or semi-permanent burrows that can extend deep into the soil. They feed primarily on decaying surficial organic litter that they frequently pull into their burrows or mix with excrement to form a midden. The midden blocks the burrow entrance and promotes further decay of the incorporated organic residues.
3
The most common anecic earthworm found in North America is Lumbricus terrestris (L.), often referred to as a nightcrawler. Like most of the earthworm species found in agricultural soils in North America, it is believed to be a native of Europe and was accidentally introduced by the early settlers and has since become widespread (James and Hendrix, 2004). L. terrestris feeds on litter at the soil surface and constructs nearly vertical, permanent, burrows about 5-10 mm in diameter and up to one meter or more in length. The openings of inhabited burrows are covered by middens. Under suitable conditions, nearly all a crop residue small enough to be moved by the worms is piled up in middens. At a long-term, continuous corn, no-till field at Coshocton, there are an estimated 1.6 million L. terrestris burrows per hectare (Edwards et al., 1989).
Earthworms and Water and Chemical Movement A number of techniques have been used to investigate whether L. terrestris burrows affect water and chemical movement. Edwards et al. (1989) and Shipitalo et al. (1994) buried small bottles underneath L. terrestris burrows in no-till watersheds and in farmers’ fields and noted that the amount of water flowing in the burrows depended on storm intensity and soil properties. Up to 10% of the rain from intense, short-duration, thunderstorms was captured by these samplers. While this may not seem like a large proportion of the rainfall, if this water had runoff it could have caused significant soil and chemical loss. Annually, an estimated 1 to 4% of the rainfall infiltrated in the earthworm burrows. Water and chemical movement in earthworm burrows has also been investigated in the laboratory by applying simulated rainfall to undisturbed blocks of soil collected from no-till fields (Edwards et al., 1992; Shipitalo et al., 1990). These experiments have shown that heavy, intense, storms shortly after surface application of an agrochemical are the conditions most likely to cause significant amounts of water and chemical to enter and move within earthworm burrows. Subsequent storms can have relatively little impact on chemical movement and the water transmitted in earthworm burrows may be of better quality than that moving through the soil matrix. Light intervening rainfalls or any delays between the time chemicals are applied and the occurrence of a heavy rainfall can reduce chemical transport in earthworm burrows. The overall effect of earthworm burrows on chemical movement is greater for chemicals that are strongly retained by soil (such as most pesticides) than for chemicals (such as nitrate) that are not strongly held by soil. Even under worst-case conditions, the chemical transport attributable to earthworm burrows amounts to only a few percent of the total application. By changing the way agricultural chemicals are formulated or applied to no-till fields, it may be possible to further reduce the potential for transport in earthworm burrows (Shipitalo et al., 2000).
Earthworm Burrows and Liquid Manure Although research suggests that earthworm burrows should normally have minor effect on chemical movement; they may have a major influence on the fate of land-applied liquid animal wastes, particularly when it is applied via subsurface injection. Subsurface injection of liquid animal wastes is a Best Management Practice (BMP) that reduces odors and promotes efficient nutrient usage (Johnson and Eckert, 1995). In fields with subsurface drainage, however, injected wastes have been observed emerging from drainage outlets shortly after application. This appears to be a particular concern in no-till fields where L. terrestris are often numerous (Shipitalo and Gibbs, 2000). The issue of liquid manure entering subsurface drainage systems is being increasingly recognized as an important environmental issue throughout drained areas in the US Midwest. In the 4-year period, 2000 to 2003, ninety-eight incidents where agricultural wastes in drainage waters contaminated streams were reported to authorities in Ohio. Violations occurred most
4
frequently with liquid swine or dairy wastes and with all methods of application – irrigation, surface spreading, and subsurface injection (Hoorman and Shipitalo, In Review). These incidents have resulted in substantial fines being imposed by the Ohio Environmental Protection Agency (OEPA) for contaminating waters of the state. For example, in July 2004 a dairy farm received a $15,000 civil penalty for mishandling liquid wastes (Ohio EPA, 2004). In order to investigate how liquid animal wastes can be rapidly transmitted to subsurface drains we have used a turbine blower to force smoke into drainage systems at various locations and soil types throughout Ohio. Frequently smoke was observed coming out of L. terrestris middens in the vicinity of the buried drains (Fig.1), but in some instances smoke was also observed
Figure 1. Smoke emerging from a L. terrestris burrow (Photo by Jennifer Smeltzer, Williams County, OH SWCD) coming out of cracks, root holes, and structural porosity. In one study the burrows that emitted smoke were marked and a Mariotte-type infiltrometer filled with dyed water was used to measure the infiltration in individual burrows (Shipitalo and Gibbs, 2000). The infiltration rates in burrows that did not emit smoke were also measured using water dyed a different color. The dyed water quickly entered the drain and was observed in the outlet more than 12 m downstream from the nearest burrow only 14 minutes after infiltration measurements were begun and after only a total of only 9.3 L of water had been added to the burrows, even though the drain was not flowing at the time the experiment was begun. The dyed water added to the burrows that did not emit smoke was never observed in the drain. Moreover, the measured infiltration rates dropped dramatically with distance from the buried drain (Fig. 2). Plastic replicas of the earthworm burrows made in situ revealed that the burrows passed within a few cm of the drain, but never entered it. These results suggest that the rapid movement of liquid animal wastes could be avoided, in this instance, if they were not applied within ~0.5 m of the drain or if the burrows in this region were disrupted by tillage before waste application. At other locations, however, smoke has been observed coming out of the soil several meters either side of the drain. It is unlikely that L. terrestris burrows could be solely responsible for this phenomenon as they are normally single, more or less vertical channels that extend only about 1 meter deep (Shipitalo and Butt, 1999).
5
Figure 2. Average infiltration rate in individual L. terrestris burrows as a function of distance from the buried drain (From Shipitalo and Gibbs, 2000)
Earthworm Burrows and Cracks One explanation for this observation is that there may be interaction between several types of macropores that allowed the smoke to move relatively large distances from where it was introduced into the soil. When infiltration rates of individual L. terrestris burrows were measured in a clayey soil with prominent cracks open to the soil surface the infiltration rates were uniformly high (~ 1 L/min) regardless of the proximity of the burrows to the drain (Shipitalo et al., 2004). Observations suggested that the high infiltration rates were attributable to water moving from the burrows to cracks below the soil surface. When dye was poured directly into the cracks, however, it revealed that the cracks did not extend much beyond the plow layer. In addition, the base of the plow layer acted as a hydraulic barrier that caused the water to move laterally along this interface until open earthworm burrows were encountered that conducted the dyed water deeper into the soil profile and to the envelope of sand surrounding the drain (Fig. 3). These observations suggest that entry of water into this soil is dominated by cracks when conditions promote their formation, but rapid movement of solutes and suspended particles to the subsurface drains depends on connection of the cracks to L. terrestris burrows. This would have the effect of increasing the potential supply of water to the burrows and greatly expanding the area contributing to rapid flow to the drain. Similarly, Kladivko et al. (2001) and Stamm et al. (2002) noted that preferential flow can cause pesticides and tracers applied several meters from drains to be rapidly transported to the subsurface drainage systems. Thus, under these circumstances the area above the drains that would need to be avoided during liquid manure application would be too large to make this a practical remedy for reducing contamination of the drainage water. Furthermore, the observations of Shipitalo et al. (2004) were on a soil that had been moldboard plowed the previous fall prior to the planting of spring barley. Thus, preferential flow to drain lines is not restricted to soils that have been in conservation tillage. In fact, in Ohio
6
Figure 3. Movement of methylene blue dye along the base of plow layer then down an earthworm burrow. L. terrestris burrowing to the sand layer surrounding a buried drain. 17% of the 98 incidents of liquid animal wastes contaminating subsurface drains occurred when these materials were applied to tilled soil or incorporated during application (Hoorman and Shipitalo, In Review). This indicated that disruption of macropores by these measures was insufficient to preclude movement of liquid wastes to subsurface drains in all instances.
Impact of Liquid Manure Spills Although rapid movement of liquid animal wastes to subsurface drains has been frequently documented, in most cases it is uncertain how much of this applied material reaches the drains. In 10 of the 98 incidents that were reported in Ohio from 2000 to 2003 an attempt was made to measure the volume. These estimates ranged from 2 to 117% (average 16%) of the amount applied. Since these values include water in the ditches and streams that diluted the liquid wastes, they undoubtedly overestimate the actual amount lost (Hoorman and Shipitalo, In Review). Nevertheless, the volumes are often large enough to severely impact water quality and in 33 of the 98 incidents resulted in documented fish kills in the receiving waters. In some instances, however, the amounts of liquid wastes exiting the drainage system may be small or movement may only happen after sufficient rain has fallen to initiate drain flow. When this occurs, the impact on nutrient levels, organic matter content, and dissolved oxygen levels in the receiving waters may be minimal due to dilution, but microbial contamination still might be of concern. In fact, liquid manure application to sub-drained land has been identified as a significant source of bacterial contamination contributing to beach closure (Dean and Foran, 1992). When 11 mm of liquid dairy manure (2% solids) spiked with Campylobactor jujuni, and non-pathogenic Escherichia.coli O157:H7 was added to the surface of undisturbed soil blocks in a laboratory experiment 30% of the applied wastes exited the 30-cm-deep, no-till columns
7
almost immediately, but none moved through blocks that had been tilled to a depth of 10 cm (Wang et al., 2003). When simulated rainfall was subsequently applied to the no-till blocks, percolation began sooner and pathogen concentrations in the leachate were up to several orders of magnitude higher than observed with the tilled soil. Thus, in this instance, tillage prevented the acute problem of immediate movement through the soil and lessened, but did not eliminate pathogen movement initiated by rainfall. Similarly, Artz et al. (2005) noted that the activity of L. terrestris increased transport of E.coli O157:H7 through soil columns and Jamieson et al. (2002) noted that tillage reduced bacterial transport. Furthermore, Joy et al. (1998) noted that bacterial concentrations in subsurface drainage water decreased as the time interval between application and rainfall increased.
Control Measures Given the potential for liquid animal wastes to adversely affect water quality when applied to land that has subsurface drainage, both immediately after application and when mobilized by subsequent rainfalls, there are several control measures that might reduce these concerns. In fields where these problems occur, it maybe possible to reduce movement to the subsurface drains by using precision farming technology to till the soil above the drains or to avoid waste application in the immediate vicinity of drains. In many instances, however, this will be impractical because of uncertainty in locating the drains, the random nature of the drainage network, and the size of the area that needs to be avoided or tilled. Alternatively, inflatable plugs or shut-off valves might be used to block the drains when liquid animal wastes are being applied, thereby allowing any wastes that enter the drain time to reenter the soil. Inflatable plugs, however, have a high failure rate because the drainage outlets are often not designed to withstand the pressure heads that can develop (Hoorman and Shipitalo, In press). Moreover, these devices would not be useful in controlling contamination that is the result of subsequent rainfall. The use of catch basins in conjunction with permanently installed shut-off valves can reduce the failure rate encounter with plugs and valves alone, but still does not address the issue of rainfall-mobilized wastes. The use of application equipment that disrupts the continuity of macropores to the drains can promote diffusion of liquid animal wastes into the soil matrix and thereby reduce both immediate movement to the drains and rainfall-mobilized movement, but probably will not eliminate these losses. Likewise, tillage will probably reduce losses by disrupting macropores and promoting diffusion, but has undesirable consequences of negating the beneficial soil and water quality aspects of conservation tillage.
Conclusion Earthworm burrowing activity has only a limited potential to increase ground water contamination and this might be further reduced by adopting alternative management practices. Earthworm burrows can have a much larger effect on reducing runoff, which is oftentimes a greater concern and a more significant source of water contamination. Moreover, there are other benefits associated with maintaining thriving earthworm populations in agricultural fields. These include improved soil aggregation, burying and mixing of residue, and more efficient cycling of nutrients. Deep burrowing earthworms and cracks, however, can contribute to the movement of liquid animal wastes to subsurface drainage systems. This movement can occur immediately upon waste application or can be the result of subsequent rainfall. Although there are management practices that can be used to reduce these concerns, our knowledge of the extent of the problem and the soil and waste properties that affect movement is limited. In particular, research is needed on how the solids content of liquid animal wastes affects retention in the soil.
8
References Artz, R.R.E., J. Townend, K. Brown, W. Towers, and K, Killham. 2005. Soil macropores and compaction control the leaching potential of Escherichia coli O157:H7. Environ. Microbiology 7(2):241-248. Bohlen, P.J., W.M. Edwards, and C.A. Edwards. 1995. Earthworm community structure and diversity in experimental watersheds in Northeastern Ohio. Plant Soil 170(1):233-239. Butt, K.R., M.J. Shipitalo, P.J. Bohlen, W.M. Edwards, and R.W. Parmelee. 1999. Long-term trends in earthworm populations of cropped experimental watersheds in Ohio, USA. Pedobiologia 43(6):713-719. Curry, J.P. 2004. Factors affecting the abundance of earthworms in soil. p. 91-113. In Earthworm Ecology. 2nd ed. C.A. Edwards, ed. CRC Press, Boca Raton, FL. Dean, D.M., and M.E. Foran. 1992. The effect of liquid waste application on tile drainage. J. Soil Water Conserv. 47(5):368-369. Edwards, C.A., and P.J. Bohlen. 1996. Biology and Ecology of Earthworms. 3rd edition. Chapman & Hall, London, 426 pp. Edwards, W.M., M.J. Shipitalo, W.A. Dick, and L.B. Owens. 1992. Rainfall intensity affects transport of water and chemicals through macropores in no-till soil. Soil Sci. Soc. Am. J. 56(1):52-58. Edwards, W.M., M.J. Shipitalo, L.B. Owens, and L.D. Norton. 1989. Water and nitrate movement in earthworm burrows within long-term no-till cornfields. J. Soil Water Conserv. 44(3):240-243. Johnson, J., and D. Eckert. 1995. Best management practices: Land application of animal manure. The Ohio State University Extension Publication AGF-208-95. Available at http://ohioline.osu.edu/agf-fact/0208.html. Accessed 2 May 2005. Hoorman, J.J., and M.J. Shipitalo. In Review. Factors contributing to the movement of liquid animal wastes to subsurface drains. J. Soil Water Conserv. James, S.W., and P.F. Hendrix. 2004. Invasion of exotic earthworms into North America and other regions. p. 75-88. In Earthworm Ecology. 2nd ed. C.A. Edwards, ed. CRC Press, Boca Raton, FL. Jamieson, R.C., R.J. Gordon, K.E. Sharples, G.W. Stratton, and A. Madani. 2002. Movement and persistence of fecal bacteria in agricultural soils and subsurface drainage water: A review. Canadian Biosystems Eng. 44:1.1-1.9. Joy, D.M., H. Lee, C.M. Reaume, H.R. Whiteley, and S. Zelin. 1998. Microbial contamination of subsurface tile drainage water from field applications of liquid manure. Canadian Agricultural Eng. 40(3):153-160. Kladivko, E.J., L.C. Brown, and J.L. Baker. 2001. Pesticide transport to subsurface tile drains in humid regions of North America. Critical Rev. Environ. Sci. Technol. 31(1):1-62. Lee, K.E. 1985. Earthworms, Their Ecology and Relationships with Soils and Land Use. Academic Press, New York, 411 pp. Ohio EPA. 2004. Ohio EPA Issues Orders to Address Violations at Dairy Farm. Available at http://www.epa.state.oh.us/pic/nr/2004/july/hendren.html. Accessed 2 May 2005. Shipitalo, M.J., and K.R. Butt. 1999. Occupancy and geometrical properties of Lumbricus terrestris L. burrows affecting infiltration. Pedobiologia 43(6):782-794. Shipitalo, M.J., W.A. Dick, and W.M. Edwards. 2000. Conservation tillage and macropore factors that affect water movement and the fate of chemicals. Soil Tillage Res. 53(34):167-183.
9
Shipitalo, M.J., and W.M. Edwards. 1998. Runoff and erosion control with conservation tillage and reduced-input practices on cropped watersheds. Soil Tillage Res. 46(1-2):1-12. Shipitalo, M.J., W.M. Edwards, W.A. Dick, and L.B. Owens. 1990. Initial storm effects on macropore transport of surface-applied chemicals in no-till soil. Soil Sci. Soc. Am. J. 54(6):1530-1536. Shipitalo, M.J., W.M. Edwards, and C.E. Redmond. 1994. Comparison of water movement and quality in earthworm burrows and pan lysimeters. J. Environ. Qual. 23(6):1345-1351. Shipitalo, M.J., and F. Gibbs. 2000. Potential of earthworm burrows to transmit injected animal wastes to tile drains. Soil Sci. Soc. Am. J. 64(6):2103-2109. Shipitalo, M.J., and R.C. Le Bayon. 2004. Quantifying the effects of earthworms on soil aggregation and porosity. p. 183-200. In Earthworm Ecology 2nd ed. C.A. Edwards, ed. CRC Press, Boca Raton, FL. Shipitalo, M.J., V. Nuutinen, and K.R. Butt. 2004. Interaction of earthworm burrows and cracks in a clayey, subsurface-drained soil. Applied Soil Ecology 26(3):209-217. Stamm C., R. Sermet, J. Leuenberger, H. Wunderli, H. Wydler, H. Flhhler, and M. Gehre. 2002. Multiple tracing of fast solute transport in a drained grassland soil. Geoderma 109 (34):245-268. Wang, P., W. Yu, N.E. Ramirez, L. Ward, J.T. LeJeune, M. Shipitalo, and W.A. Dick. 2003. Effects of soil tillage and rainfall on leaching of two bacterial pathogens through soil blocks. Agronomy Abstracts, S03-wang198667-poster.
10
