Ohio State University Extension Fact Sheet

Ohio State University Extension

Food, Agricultural and Biological Engineering

590 Woody Hayes Dr., Columbus, Ohio 43210


Understanding Agricultural Drainage

AEX-320-97

Larry C. Brown
Andrew D. Ward

Agriculture is Ohio's largest industry. Because much of the state is characterized by fertile, flat soils and adequate rainfall, crop production occurs on 45 percent of Ohio's land area. About 55 percent of Ohio's agricultural soils need drainage improvement to minimize soil erosion, excess soil-water conditions in the plant root zone, and unfavorable field conditions for farm equipment in the spring and fall. Ohio's agricultural drainage needs are very similar to those in states such as Arkansas, Florida, Indiana, Illinois and Louisiana. Nationally, drainage improvement is required on more than 20 percent of our cropland (approximately 110 out of 421 million acres). Maintaining existing water management improvements is quite important because proper management of the soil, and soil water, is required to sustain production and profitability on agricultural soils.

In recent years, public concern has increased about the nature of agricultural drainage, and the impact of agricultural drainage improvements on the quality of Ohio's water resources and environment. This publication is designed to help Ohio's citizens understand the purpose and nature of agricultural drainage improvements, particularly those related to the drainage of excess water from cropland in Ohio.

This publication does not address the various legal mechanisms that can be used by Ohioans to make drainage improvements (See Ohio's Drainage Laws - An Overview, Extension Bulletin 822). Much of the water terminology used in this publication is defined in Ground- and Surface-Water Terminology, Extension Fact Sheet AEX-460. These publications are available through your Ohio county office of Ohio State University Extension.

Agricultural Drainage

Agricultural drainage is the removal of excess water from the soil surface and/or soil profile of cropland, by either gravity or artificial means. The two main reasons for improving the drainage on agricultural land are for soil conservation and enhancing crop production.

Research conducted in Ohio and throughout the Midwest has documented many benefits of agricultural drainage improvement.

In Ohio, most agricultural producers improve the drainage on their land to help create a healthier environment for plant growth and to provide drier field conditions so farm equipment can access the farm field throughout the crop production season. Healthy, productive plants have the potential to produce greater yields and more food. Also, research in Ohio has shown that agricultural drainage improvement can help reduce the year-to-year variability in crop yield, which helps reduce the risks associated with the production of abundant, high quality, affordable food. Improved access of farm equipment to the field provides more time for field activities, can help extend the crop production season, and helps reduce crop damage at harvest.

Types of Improvements

In Ohio, the two primary types of agricultural drainage improvement are surface and subsurface (Figure 1). Many times a landowner installs a combination of these two types.


Figure 1. Water table level before and after drainage inprovement: a) surface drainage ditch; b)subsurface drainage pipe. (adapted from USDA-ERS, 1987)

Surface Drainage

Surface drainage improvements are designed for two purposes: to minimize crop damage resulting from water ponding on the soil surface following a rainfall event, and to control runoff without causing erosion. Surface drainage can affect the water table by reducing the volume of water entering the soil profile. This type of improvement includes: land leveling and smoothing; the construction of surface water inlets to subsurface drains; and the construction of shallow ditches and grass waterways, which empty into open ditches and streams.

Land smoothing or leveling is a water management practice designed to remove soil from high spots in a field, and/or fill low spots and depressions where water may pond. Shallow ditches may be constructed to divert excess water to grass waterways and open ditches, which often empty into existing surface water bodies.

Some disadvantages of surface drainage improvements exist. First, these improvements require annual maintenance and must be carefully designed to ensure that erosion is controlled. Second, extensive earthmoving activities are expensive, and land grading might expose less fertile and less productive subsoils. Further, open ditches may interfere with moving farm equipment across a field.

Subsurface Drainage

The objective of subsurface drainage is to drain excess water from the plant root zone of the soil profile by artificially lowering the water table level. Subsurface drainage improvement is designed to control the water table level through a series of drainage pipes (or tubing) that are installed below the soil surface, usually just below the root zone (Figure 2). For Ohio conditions, subsurface drainpipe is typically installed at a depth of 30 to 40 inches, and at a spacing of 20 to 80 feet. The subsurface drainage network generally outlets to an open ditch or stream. Subsurface drainage improvement requires some minor maintenance of the outlets and outlet ditches. For the same amount of treated acreage, subsurface drainage improvements generally are more expensive to construct than surface drainage improvements.

Whether the drainage improvement is surface, subsurface or a combination of both, the main objective is to remove excess water quickly and safely to reduce the potential for crop damage. In a situation where water is ponded on the soil surface immediately following a rainfall event, a general rule of thumb for most agricultural crops grown in Ohio is to lower the water table to 10 to 12 inches below the soil surface within a 24-hour period, and 12 to 18 inches below the soil surface within a 48-hour period. Properly draining excess water from the soil profile where plant roots grow helps aerate the soil and reduces the potential for damage to the roots of growing crops (Figure 2). Further, proper drainage will produce soil conditions more favorable for conducting farming operations. In states that depend heavily on irrigation, subsurface drainage is often used to prevent harmful buildup of salt in the soil.


Figure 2. Effect of drainage improvement on crop root development: a) no drainage improvement; b) subsurface drainage improvement (adapted from Irwin, 1989).

Past and Present

Land drainage activities have impacted Ohio's environment and water resources. Early settlers began draining Ohio's swamps in the 1850s, and today approximately 90 percent of Ohio's wetlands have been converted to other uses. This loss is attributed to public health considerations; rural, urban and industrial development; and agriculture. Today, however, an important distinction needs to be made between improving the drainage of wet soils presently in agricultural production and converting our "true" remaining wetlands for other purposes. True wetlands, like bogs, marshes and swamps, have saturated soil conditions over a long enough period of time during the year to maintain water-loving vegetation and wildlife habitat. These areas, once their benefit is determined, should be protected from development.

Wetlands provide many benefits for the environment, including wildlife habitat and enhanced water quality. An important water quality function of wetlands is the trapping and filtering of sediment, nutrients and other pollutants that enter runoff from agricultural, construction and other rural and urban sources. Interestingly, subsurface drainage improvements, in a more limited capacity, provide some of these same water quality benefits while providing a necessary element for sustained agricultural production on a majority of Ohio's productive agricultural soils.

Present agricultural trends are toward more intensive use of Ohio's existing cropland, with much of the emphasis on management. Maintaining existing agricultural drainage improvements and improving the drainage on wet agricultural soils presently in agricultural production helps minimize the need for landowners to convert additional land to agricultural production. In many cases, restoration of previously converted wetlands would be impossible because of large-scale channel improvements, urbanization and Lake Erie shoreline modification. The focus should be placed on protecting existing true wetlands and establishing new wetland areas, while maintaining our highly productive agricultural areas.

Note: The use of surface and subsurface drainage improvements is not limited to agricultural lands. Many residential homes use subsurface drainage systems, similar to those used in agriculture, to prevent water damage to foundations and basements. Golf courses make extensive use of both surface and subsurface drains. Houses, streets and buildings in urban areas depend heavily on surface and subsurface drainage systems for protection. These generally are a combination of plastic or metal gutters, and concrete pipes or channels.

Summary

Throughout Ohio and the Midwest, the removal of excess water from wet agricultural soils is essential for providing a healthy environment for crop growth, and subsequently, helps provide affordable, high-quality food. Agricultural drainage improvement is necessary to sustain agricultural production. This publication was developed to help the reader better understand the purpose and nature of agricultural water management improvements, particularly those relating to the drainage of excess water from cropland in Ohio. Publications and technical references used to support the material in this publication are included in the "Bibliography" section, along with other publications that may be of interest to the reader.

For more information, contact the lead author of this publication or your Ohio county office of Ohio State University Extension.

Factors Contributing to Excess Water Problems in Soils

In Ohio, factors that contribute to excess soil water problems include: fine soil texture; massive soil structure; low soil permeability; topography; soil compaction; restrictive geologic layer; and excess precipitation.

Soil Texture: The sand, silt and clay composition of the solid mineral particles in a soil is called soil texture. For a loam soil texture, for instance, the mineral content might consist of 40 percent clay, 30 percent silt and 30 percent sand. Soil texture can have a dramatic effect on how well the soil holds water, and how easily water can move through the soil. Fine-textured soils have a large percentage of clay and silt particles. These soils generally hold water well, but drain poorly. Coarse-textured soils have a large percentage of sand or gravel particles. These soils drain well, but have poor water-holding ability.

Soil Structure: The physical arrangement of the solid mineral particles of a soil is the soil structure. A granular structure helps promote the movement of water through a soil, but a structure that is massive (lacking any distinct arrangement of soil particles) usually decreases the movement of water.

Permeability: In general terms, the relative ease with which water can move through a block of soil is soil permeability. A soil's permeability can be affected by its texture, structure, human activities, and other factors.

Topography: The shape and slope of the land surface can cause wet soil conditions, especially around depressions where water tends to accumulate. Without an outlet, the water may drain away very slowly.

Geologic Formation: The geological formation underlying a soil can impact the drainage of water from that soil. For instance, a soil could have texture and structure properties that are beneficial to the movement of water. However, if the geologic formation underlying this soil consisted of dense clay or solid rock, it could restrict the downward movement of water, causing the soil above the formation to remain saturated during certain times of the year.

Compaction: Human activities may help create excess soil water problems. For example, operating equipment on a wet soil can compact the soil and destroy its structure. A soil layer that is compacted will generally have no structure, and most of the voids in this layer will have been eliminated. Voids are open spaces between soil particles that can be filled with air, water, or a combination of both. Soil water will tend to accumulate above the compacted layer because movement of water through the compacted layer is severely restricted. If the compacted layer is located at the soil surface, very little water will enter the soil and much of the water will runoff, potentially creating a flooding and/or erosion hazard.

Precipitation: Ohio's average annual precipitation is 38 inches, based on a 50-year period of precipitation records. Even though the distribution of precipitation across the state varies (see Figure 3), the state receives an abundant supply of precipitation in an average year. In an average month, most areas of the state receive 2 to 4 inches of precipitation. This amount is adequate to sustain high crop yields. However, excessive rainfall, and/or winters with heavy snowfall, often produce excess soil water conditions. Furthermore, thunderstorms will frequently result in runoff because the rainfall rate is greater than the rate at which water can enter (infiltrate) into the soil.

Note: The physical properties of a particular soil can vary throughout the soil profile, and from place to place in the same field. All across Ohio, soils have different physical characteristics, and the geological formations underlying soils vary as well. Therefore, each soil will have particular drainage characteristics. Soil scientists and engineers have classified many of Ohio's soils based on their drainage characteristics. For general information about the nature of soils and their properties, refer to a soil science textbook. For specific information regarding the drainage ability of a particular soil in your area, contact the USDA Natural Resources Conservation Service (NRCS) office in your county.


Figure 3. Generalized map of average annual precipitation in Ohio for the period 1931-1980 (adapted from Harstine, 1991).

Bibliography

Brady, N.C. 1990. The Nature and Properties of Soils. (10th Ed.). MacMillan Publishing Co., Inc. NY.

Brown, L.C., and L.P. Black. 1994. Ground- and Surface-Water Terminology. Fact Sheet AEX 460. Ohio State University Extension.

Brown, L.C. 1994. Ohio's Hydrologic Cycle. Fact Sheet AEX 461. Ohio State University Extension.

Brown, L.C. and J.W. Johnson. 1996. Nitrogen and the Hydrologic Cycle. Fact Sheet AEX 463. Ohio State University Extension.

Brown, L.C., and J.L. Stearns. 1991. Ohio's Drainage Laws - An Overview. Bulletin No. 822. Ohio State University Extension.

Fausey, N.R., L.C. Brown, H.W. Belcher and R.S. Kanwar. 1995. Drainage and water quality in Great Lakes and cornbelt states. ASCE J. Irr. and Drain. Engr. 121 (4): 283-288.

Fausey, N.R., E.J. Doering, and M.L. Palmer. 1987. Purposes and Benefits of Drainage. Pp 48-51 In: Farm Drainage in the United States. History, Status, and Prospects. USDA-Economic Research Service. Misc. Pub. No. 1455.

Fogiel, A., and H.W. Belcher. 1991. Research Literature

Review of Water Table Management Impacts on Water Quality. Agricultural Engineering Department, Michigan State University. East Lansing, MI 48823.

Frost, L.H., and W.A. Nichols. 1985. Ohio Water Firsts. Published by Water Resources Foundation of Ohio, Inc. Volume I.

Harstine, L.J. 1991. Hydrologic Atlas for Ohio: Average Annual Precipitation, Temperature, Streamflow, and Water Loss for the 50-Year Period 1931-1980. Water Inventory Report No. 28. ODNR Division of Water.

Irwin, R.W. 1989. Handbook of Drainage Principles. Publication 73. Ministry of Agriculture and Food, Ontario.

Nolte, B.H., and N.R. Fausey. 1986. Soil Compaction and Drainage. AEX 301. Ohio State University Extension.

Schwab, G.O., N.R. Fausey, E.D. Desmond and J.R. Holman. 1985. Tile and Surface Drainage of Clay Soils. Res. Bull. 1166, OARDC, The Ohio State University, Wooster, OH.

Schwab, G.O., D.D. Fangmeier, W.J. Elliot and R.K. Frevert. 1993. Soil and Water Conservation Engineering. (4th Ed.) Wiley and Sons, NY.

Skaggs, R.W., M.A. Breve and J.W. Gilliam. 1994. Hydrologic and water quality impacts of agricultural drainage. Crit. Rev. in Envir. Sci. and Technol. 24 (1): 1-32.

Sporleder, T.L., L.J. Hushak and D. Pai. 1990. OHFOOD: An Ohio Food Industries Input-Output Model. The Farm Income Enhancement Program. (1985 Data). Department of Agricultural Economics & Rural Sociology, The Ohio State University.

USDA-ERS. 1987. Farm Drainage in the United States. History, Status, and Prospects. USDA-Economic Research Service. Misc. Pub. No. 1455.

Acknowledgments

This publication originally was produced through the "Sustaining and Improving the Productivity of our Agricultural Land through Water Management" project, funded by Ohio State University Extension Innovative Grant Program. Project Team: James J. Hoorman, Extension Agent, Agriculture and CNRD, Defiance and Williams Counties; and Larry C. Brown, Extension Agricultural Engineer, Department of Food, Agricultural, and Biological Engineering, The Ohio State University. Project support was provided by the Innovative Grant Program, and the Overholt Drainage Education and Research Program, Department of Food, Agricultural, and Biological Engineering.

The following reviewed the material in this publication: Art Brate (USDA NRCS); Stephen R. Workman (USDA -Agricultural Research Service); Don Eckert (Agronomy, OSU); Roger Bender (Shelby County Extension, OSU); Kristina Boone (Agricultural Education, OSU); Lynn Davis (OLICA Contractor, Defiance County);and Fred Galehouse (OLICA Contractor, Wayne County).

A special thanks to Dave Scardena and John Victor (Section of Communications and Technology) for editorial and graphic production.

The authors acknowledge Emeriti Professors Glenn Schwab, Melville Palmer (deceased) and Byron Nolte, Department of Food, Agricultural, and Biological Engineering, for their significant contribution to agricultural drainage education in the state of Ohio.


All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.

TDD No. 800-589-8292 (Ohio only) or 614-292-6181



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