Ohio Agronomy Guide, 14th Edition

Bulletin 472-05

Chapter 1: Ohio’s Climate and Soil

By Dr. Jim Beuerlein

Because no mountain ranges exist between Ohio and the polar regions, no effective barrier prevents the southward spread of Arctic air from northern Canada. Similarly, warm tropical air masses move freely northward in the summer. Storm systems form along the boundary between major cold and warm air masses, and storm paths frequently cross the Ohio Valley and the Lower Great Lakes.

The climate of Ohio varies significantly throughout the state. Mean annual air temperatures range from 49°F in the northeast to 57°F in the extreme south. Normal annual precipitation ranges from a low of less than 30 inches at Put-in-Bay to a high of more than 44 inches in parts of Clinton and Highland Counties. Ohio’s climate is continental, with a wide range of air temperatures, higher precipitation in the spring and summer, and lower precipitation in the fall and winter.

Average length of the freeze-free period (number of growing season days) ranges from a high of 200 days along the Lake Erie shore to a low of 140 days in east central Ohio (Figure 1-1). The earliest dates with a 50% or less chance of frost (32°F) range from April 20 for areas immediately adjacent to Lake Erie to May 15 in east central Ohio (Figure 1-2). The earliest freezing temperatures in the field generally occur around September 30 in east central Ohio and October 20 along the Lake and in southern Ohio (Figure 1-3).

Figure 1-1. Average number of days without killing frost.

Figure 1-2. Dates in spring after which the chance of temperatures falling to 32°F or lower is less than 50%.

Figure 1-3. Dates in fall by which the chance of the first 32°F temperature will have occurred is 50%.

Most soils in Ohio are saturated during March and early April. Although growing season rainfall varies from a low of 18 inches to a high of 26 inches (Figure 1-4), it may not be adequate for maximum yield unless effective water management practices are used throughout the growing season. Soil moisture declines during June, July, and August; by the end of August, available soil moisture is usually reduced by 80% or more.

Figure 1-4. Long-term average rainfall (inches) for growing season, April through September.

For additional information on climate and its influence on crop production, refer to: www.usda.gov/nass/pubs/staterpt.html

Some agronomic crops (such as corn) progress through the various growth stages in response to heat units or growing degree days (GDD). Table 1-1 shows the GDD for several sites in Ohio starting at various dates in May through the 10% frost date in the fall. The information in this table is useful in predicting when corn hybrids with varying heat unit requirements will reach various growth stages.

Soil Formation and Soil Properties

Soils are continuous over the earth’s surface, except on steep and rugged mountains, areas of perpetual ice and snow, extreme deserts, and salt flats. Soils are formed by the weathering of parent materials that are deposited or accumulate by geological activity. The two major stages in soil formation are the accumulation of parent material and the differentiation of horizons within the soil profile.

Soil characteristics depend on the interrelationships of five soil-forming factors:

• Physical and mineralogical composition of the parent material.
• Climate under which the material was accumulated and has existed since accumulation.
• Plant and animal life in and on the soil.
• Relief, or lay of the land.
• Length of time weathering has acted on the soil material.

Because different factors dominate in different regions, many different kinds of soil are formed. Four basic changes occur in the soil system—additions, removals, transfers, and transformations. The intensity of soil-forming processes, now and in the past, has determined the degree of layer or horizon differentiation and the soil properties and characteristics we observe today. Soils are identified, described, and classified by their physical and chemical property characteristics which are measured and determined by using laboratory tests.

Soil Properties and Crop Management

The physical and chemical properties of a soil greatly affect crop yields. The soil properties that determine how well a crop performs on a given soil and the best cultural and management practices to use for its production are listed here.

• Organic matter content
• Soil texture
• Subsoil pH
• Water in the soil available to plants
• Slope of the topography
• Natural soil drainage

Organic Matter Content

Excluding muck and peat soils, the amount of organic matter in mineral soils ranges from about 1% to 20% in the topsoil. Most Ohio soils range from 1% to 6%. The organic matter content in most light-colored soils is between 1.5% and 3%, while a large proportion of the dark-colored soils contains between 3% and 6%. Organic matter content decreases markedly with soil depth.

In light-colored soil, the organic matter content below the plow layer is usually between 0.5% and 1%, and at depths of 20 or 30 inches only trace amounts exist. In dark-colored soils, the organic matter content is commonly between 1% and 3% immediately below the plow layer and decreases with depth to less than 0.5% at 24 inches of depth.

Soil organic matter provides nitrogen, phosphorus, and some micronutrients for crop production as the organic matter is oxidized or decays. The level of organic matter in the soil cannot be changed easily. Most crops produce less than four tons of dry matter per acre annually, which is less than 0.4% of the total soil mass in eight inches depth over an acre. Only a small portion of the crop dry matter will actually become organic matter. If large volumes of manure—200 to 300 tons per acre—were applied annually, a significant change in organic content might be achieved, particularly in coarse-textured soils.

Historically, when forages were part of the crop rotation, nutrient release and soil tilth increased due to the season-long production of roots. Currently, well fertilized, high-yielding grain crops return large volumes of residue to the soil and are a source of nutrients. On medium-textured soils low in organic matter, crop residues are usually more beneficial when left on the surface than when incorporated. During the growing season this surface residue reduces the formation of soil crusts and results in increased water infiltration and higher crop yields. Crop residue on the surface of fine-textured soils such as silty clay loam or clay loam may delay planting by delaying soil drying.

Soil Texture

The relative amounts of sand, silt, and clay in the soil determine soil texture. The soil texture classes, in order of decreasing particle sizes (coarse to fine), are as follows:

Sand Loamy sand Sandy loam Loam Silt loam Silt Sandy clay loam Clay loam Silty clay loam Sandy clay Silty clay Clay
		Figure 1-5: A guide to soil texture.

Figure 1–5 shows the ranges of sand, silt, and clay in each soil texture class. Sand is the largest soil particle, ranging in diameter from 0.08 to 0.002 inch; clay is the smallest particle, with a diameter of less than 0.00008 inch. The soils on Ohio farmland predominately have textures classified as loam, silt loam, clay loam, and silty clay loam as seen in Table 1–2.

The surface area of soil particles is also important and varies with soil particle size as indicated in Table 1-3. As the soil particle size decreases, surface area in a given volume of soil increases. Soil surface area determines the amount of nutrients that can be held in the soil. Clay has a large surface area and has negatively charged particles. These negative charges are measured as exchange activity for cations such as Ca++, K+, and others, and collectively is called the Cation Exchange Capacity (CEC).

Soils containing more than 50% silt usually have a weak structure and crust easily. This crust contributes to water runoff, sedimentation problems, and reduced gas exchange. A rough soil surface or a residue cover, however, can mitigate this problem. Crop residues should remain on the surface during the fall and early winter to improve water intake and recharge soil moisture on adequately drained soils. During the growing season, runoff will occur if the soil surface is not porous enough to allow water intake. Shallow cultivation of row crops reduces soil crusting and increases water intake and gas exchange where residue cover is absent. A residue cover on at least 80% of the surface is more effective than cultivation for these purposes.

Clay or fine-textured soils may crust, but the crust typically fractures on drying because some types of clay change volume when they dry, which improves water infiltration and air exchange. Soil moisture recharge on clay-textured soils usually produces no serious problem. However, plowing late in the spring, when soil moisture is high, may produce soil clods and prevent the preparation of a desirable seedbed. In the absence of weeds, cultivation of these fine-textured soils during the growing season is not necessary for rapid water intake and gas exchange.

Soil texture also influences plowing depth. If the soil texture is fairly uniform to a depth of 12 inches, little alteration of the soil’s physical condition may be gained from deep plowing. If the soil texture changes considerably from a silt loam to a clay texture at eight to 10 inches, some caution should be exercised in increasing the plowing depth. Gradually plowing deeper and mixing these two materials is more desirable than plowing an additional depth of three to four inches in one year.

Subsoil pH

Naturally occurring alkaline parent materials become acidic as a result of leaching over long periods of time. Water moving through the soil, particularly in late winter and spring, removes soluble cations (such as Ca++ and Mg++) from the soil profile. After the cations have been leached, the removal of these basic elements exceeds the rate of production by weathering, and the soil becomes acidic. The degree of soil acidity is, therefore, a result of the reaction of the soil parent material, the amount of water moving through the soil, and the length of time the water has been moving through the soil.

Soil reaction, commonly expressed as pH, is a measure of the intensity of acidity or alkalinity. Most Ohio soils have values ranging from pH 4.0 to pH 8.5. In soils of strip mine spoils in southeastern Ohio, the pH may be as low as pH 2.0. The pH, or degree of acidity, of subsoils varies greatly among Ohio soils. Soils formed from similar parent material tend to have similar pH values (Table 1-4). Terms commonly used to describe soil pH are as follows:

Plowing deeper than seven or eight inches on the light-colored Blount soil often lowers the pH of the plow layer due to the incorporation of the more acidic layer below. The pH of the new plow depth will be somewhat lower than the original plow layer because of the mixing of two soil layers having two different pH values.

Materials from which the Ohio soils developed had a wide range in pH. The parent materials in western and northwestern Ohio have high pH values and contain as much as 50% calcium carbonate or its equivalent. Eastern and southeastern Ohio soils, however, have developed mainly from acidic sandstones and shale, which have pH values as low as 5.0. Some bedrock strata associated with coal beds contain iron sulfates and are strongly acidic when first exposed to air. This oxidation of the iron sulfates may result in soil pH values as low as pH 2.0.

Soil Water Available to Plants

Water in the soil is held in voids, or pore spaces, and as thin films on the surface of soil particles. Normally the soil consists of about 50% pore space. When this pore space is completely filled with water, the soil is saturated. When no more water will drain from the large soil pores—which occurs within one or two days after rainfall—the moisture level is described as being at field capacity. Much of the moisture held in the soil at this level is available for uptake by growing plants.

Soil moisture is considered low when it is present only in very small pores. Because water in small pores is held tightly, the energy available to roots for removing water is not sufficient to extract it at the rate that it is being transpired. When this condition exists, the plant leaves wilt or curl, and this soil moisture level is called the wilting point. The amount of soil water between field capacity and the wilting point is the available water-supplying capacity of the soil. Available water-supplying capacity is designated as inches of water per inch of soil, or as a percent by weight. This water is available to plants when root development and aeration are adequate for optimum plant growth.

An acre inch of water is approximately 27,000 gallons. Soils have available water capacities of from four to eight inches in four feet of soil. As shown in Figure 1-6, texture influences the amount of water held in the soil. In this chart, the vertical distance between the wilting point and field capacity for each soil texture determines the available water-supplying capacity. A silt loam or loam texture soil holds the largest amount of available water per inch of soil.

Figure 1-6. Available water capacity for 10 soil textures—inches of water/foot of soil.

The moisture available for crop use includes the amount of water held by the soil as well as factors that influence how water moves into and through the soil. During the growing season, high-intensity rainfall infiltrates slowly into soils with textures having the greatest water-holding capacity. Fine sandy loam and silt loam soils, for example, have low infiltration rates. A lack of adequate clay, which is important for the development of a durable structure, contributes to low infiltration. Other factors that reduce infiltration include continued tillage of these soils, an increase in rainfall, and a sealing of the soil surface (which also increases runoff). Figure 1-7 illustrates the rate of infiltration of both fine- and medium-textured soils on corn seedbeds when the soils are initially dry.

Figure 1-7. Soil texture and rate of infiltration (OARDC).

Blount and Canfield are medium-textured soils with weak structure. The breaking down of the soil structure by raindrop impact greatly reduces the water infiltration rate. Hoytville soil, a fine-textured soil containing considerable clay and organic matter, maintains a high infiltration rate at the soil surface. The infiltration rate of the fine-textured soil is adequate to enable the infiltration of essentially all water from rainfalls of high intensity and short duration.

Slope of the Topography

The topography of an area influences soil movement, soil depth, internal soil drainage, and other soil properties. Topography must be considered when determining the soil management practices and conservation measures for farming operations. Most agricultural soils in Ohio are on slopes ranging from nearly level to 18% (18 feet of height per 100 feet horizontal distance).

Movement of materials applied to the soil surface is directly related its slope. Sloping topography contributes to movement of surface-applied material primarily because of low infiltration rates and surface runoff, either from frozen or crusted surfaces lacking adequate residue cover or surface roughness. Nearly level topography, where soil usually drains poorly, may also result in surface movement of materials by water when a saturated condition in the soil causes low infiltration and high runoff.

Slope aspect or direction of exposure may also influence surface runoff. Southern exposures have fluctuating temperatures, which affect freezing and thawing, while slopes with a northern exposure have more uniform temperatures during winter and spring. The slope also influences vegetative growth during summer. Southern slopes are warmer and drier, while northern slopes are cooler and have higher soil moisture contents.

Natural Soil Drainage

Most Ohio topsoils hold one to two inches of water in the plow layer. When the downward rate of water movement is restricted by fine-textured subsoils, hard pans, or other impervious material, a saturated zone develops in which voids in the soil, normally containing air, fill with water. Saturated soil or poor drainage causes many problems and limits the uses of many soils. In the early history of Ohio, approximately 200 years ago, the extensive Black Swamp of northwestern Ohio was covered by swamp vegetation. After large ditches were used to drain this part of the state, it became an important agricultural area. Adequate soil drainage is the largest soil management problem in Ohio agriculture. Approximately 57% of the soils used for cropland in Ohio have a natural drainage limitation.

Not all Ohio soils, however, are poorly drained. The rate of water movement through some soils is adequate to prevent the buildup of a saturated zone of water within the root zone. These soils are commonly called “well-drained soils.” In “moderately well-drained soils,” saturated zones are present only during short periods in the spring. Other soils are referred to as “somewhat poorly drained,” depending on the location of the saturated zone in the soil and the length of time it is present. Figure 1-8 shows the occurrence of saturated zones in well-drained, moderately well-drained, somewhat poorly drained, and poorly drained Ohio soils during winter and spring.

Figure 1-8. Saturated zones of water in Ohio soils by depth and season. (Adapted from Summary of Soil and Water Studies, Ohio Department of Natural Resources, Division of Lands and Soil.)

For crop production to be profitable, soil drainage problems must be eliminated, using appropriate drainage measures, such as land smoothing and tiling. Recommendations for drainage improvements are available in the Ohio Drainage Guide, 1973 and on the Internet at: www.ag.ohio-state.edu/~agwatmgt/.

Ohio Soil Regions

Ohio is divided into eight soil regions (Figure 1-9). These regions are principally delineated by parent material properties and glaciation. Soil properties of Region I have been influenced by water impoundment during glaciation, which resulted in deposits of fine sediment in deeper areas of historic lakes and coarse sediments near lake margins. Textures of these soils range from fine (clay) to coarse (sand). Soils of Region II were developed in glacial till containing considerable limestone material and clay. Textures of these soils range from medium (silt) to fine (clay).

Figure 1-9. Ohio soil regions.

Soils of Region III reflect a lesser influence of clay compared with the fine-textured soils of Region I and II. The glacial till is medium textured. The amount of silty material in these soils increases from the north to the south, with values of 65% to 70% silt in the plow layer being common in the southern part of this region.

Region IV is the oldest glaciated area in Ohio. The soils in this region are extensively weathered and extend to a considerable depth. Topsoil usually extends to a depth of 10 to 12 inches; total soil depth may exceed eight feet although soil below the five-foot depth contributes little to plant growth. The topography in many areas of this region is relatively flat and has inadequate drainage, which results in slow or very slow water movement through the subsoil.

Soils in Region V have been influenced by successive levels of impounded water. The lake-plain soils of northeastern and northwestern Ohio were deposited at about the same time. The lake-plain soils of northeastern Ohio range from fine to coarse texture but are generally more acidic than northwestern Ohio soils.

The glacial till in Region VI is predominately medium textured, with some areas of fine texture. Calcium carbonate (lime) content of the glacial till increases from east to west, with the eastern area containing mostly sandstone and shale fragments, and the western area containing considerable limestone. Two soil properties peculiar to some of the soils in this area are the high content of extractable aluminum, which increases lime requirements, and dense, medium-textured subsoil “pans.”

Region VII is the largest residual soil region in Ohio. Glaciation has had little influence on the soils in this area, with the exception of the alluvial or terrace soils formed from the movement of glacially derived material down stream valleys. This soil region is in the foothills of the Appalachian plateau, and topography ranges from nearly level to extremely steep. The soils are developed on weathered materials derived from sandstone, shale, and limestone. Because considerable mass movement of material has occurred on these slopes, many of the soils are mixtures of bedrock materials.

Region VIII soils are found in parts of Adams, Brown, and Highland counties. These soils were developed on sloping to steep, rolling topography in unglaciated areas of limestone and shale bedrock.

Available Data on Soil Properties

Approximately 400 soil series exist in Ohio. Soil survey reports, published by the Natural Resources Conservation Service (NRCS), formerly the Soil Conservation Service, contain soil property information for each series on a county-wide basis. The soil surveys also contain maps identifying the locations of the various soil series. Soil surveys have been completed for all 88 Ohio counties and are available from local NRCS offices. Complete descriptions of the physical and chemical properties of each Ohio soil can be found on the Internet at: soils.usda.gov/technical/classification/osd.

Another web site with useful information about Ohio’s soils is: www.dnr.state.oh.us/soilandwater/soils/soilreg1.htm.

This site is maintained by the division of soil and water conservation and contains information on coastal nonpoint pollution control, environmental education, Ohio soils, Soil and Water Conservation Districts of Ohio, stream morphology, watersheds, and more.