ISSUED: 1-90
K. L.Wells and R.L. Phillips

Many agriculturally important soils of Kentucky percolate water very slowly through the rooting zone. This slow percolation can be caused by

high soil clay content,
naturally occurring fragipans,
seasonal high water tables,
poor soil structure
landscape position.

While many such soils are classified as imperfectly to poorly drained, some are classed as well drained. So, knowing only the drainage characteristics of a particular soil isn't enough to tell you how slowly water percolates through the rooting zone.
The more important soil series of Kentucky which are slowly permeable to water are listed in the appendix.

Why Management is Needed:
Waterlogging Can Limit Growth in Corn and Tobacco
Slowly permeable soils often waterlog after rainfall or flooding.
How - Most of the soil's pore space fills with water and stays saturated for extended periods after rainfall ceases or floodwaters recede.
When - Although such soils most often become saturated in winter due to rainfall and low evapotranspiration, they can also become waterlogged following extensive rainfall during late spring and summer.
Why - Because water moves so slowly through these soils, they dry out much more slowly in the spring than do more permeable soils and thus remain much cooler in the seed and root zone.
Problems for Corn and Tobacco - If soil gets saturated after corn is planted or tobacco is set, growth is limited. This growth limitation happens because most of the soil pore space is full of water and contains little air. Lack of air limits growth and in extreme circumstances, can actually result in death of corn and tobacco from "drowning." Since corn and especially tobacco are very sensitive to soil aeration, producing those crops is riskier on slowly permeable sods.

How the Problems Happen:
Soil Pore Space Distribution and Water Movement
The pore space in any given volume of sod is the part without solid mineral and organic matter in it. This pore space exists in the cracks, crevices, worm holes, root channels and other discontinuities in the soil. Water, air and plant roots permeate the soil through the pore space.
When a soil is completely saturated with water either from rain, flooding or a high water table, nearly all the pore space is filled with water. After rainfall stops, floodwaters recede and the water table drops, the following processes happen:

Air comes back into the large pore spaces. Gravity pulls water down through the soil, forcing water out of the large pore spaces and letting air enter.
Water stays in the small pores because it is held at a tension greater than the force of gravity. Plant roots can extract much of this water.

In a good, arable soil, about half the pore space is large enough for water to drain from it and fill with air, while the rest holds water, making it possible for plant roots to obtain both air and water.
However, these ideal conditions often do not exist. If most of the pore space in a particular soil is from small pores, water does not move through soil very rapidly and the soil's air content is greatly diminished. Soils with this situation include the following:

soils with a high clay content,
soils which have been compacted,
soils with low organic matter content,
soils with poor structure.

How Waterlogged Soil Affects Nitrogen Fertilizer Efficiency

Problem #1 - for corn and setting tobacco.
Waterlogged soil creates the potential for sizeable soil losses of fertilizer nitrogen applied at or before planting corn and setting tobacco.
Why - Under waterlogged (anaerobic) conditions, the soil's microbial population is forced to get oxygen from nitrate nitrogen (NO3) molecules.
How - In this process, called denitrification, nitrogen is reduced to a volatile form (gas) which the soil can rapidly lose.
Recommendations - Split or delay applications of fertilizer nitrogen for corn and tobacco production on slowly permeable soils. This management practice works effectively on such soils because fertilizer nitrogen is withheld until the plants are large enough to rapidly take it up in sizeable quantities. The delay also gives the soil more time to dry out and become less waterlogged, thus lowering the potential for denitrification.

Table 1 shows results of this practice on corn production from a well-drained upland soil in Central Kentucky which waterlogs easily because of high clay content.

Table 1. Effectiveness of Delayed N on Yield of No-Till Corn Grown on Hampshire Soil.
lb N/A applied
Yields (bu/A)
at planting 7 weeks after planting 1972 1973 1974 3-Yr. Av
0 0 91 78 60 76
150 0 100 106 105 104
0 150 123 142 127 131

Problem #2 - in tobacco production.
Nitrogen fertilizer losses can also be sizeable in tobacco production if all the nitrogen is applied before or at time of setting on slowly permeable soils. Much better crop utilization of the nitrogen can be obtained by applying only 1/3 to 1/2 the total nitrogen at setting and then applying the rest in 1 or 2 sidedressings.

The Effect of Turning Under Sod or Cover Crops for Tobacco
The Problem -- Turning under a heavy vegetative growth from sod or from a winter cover crop can intensify the potential problems of growing tobacco on slowly permeable soils.
Why -- This turning under adds large amounts of organic material to soils which are oxygen deficient during periods when the soil may be waterlogged. The anaerobic decomposition which takes place intensifies denitrification losses of nitrate nitrogen in the soil and it also produces organic decomposition products which are toxic to root growth. Some growers have referred to this condition as "organic matter toxicity."
When -- During growing seasons when this happens, young tobacco transplants are stunted, turn yellowish and don't produce much growth until the soil dries out enough for turned-under residues to decompose under better drained (aerobic) conditions. This effect may not occur until mid-summer and can significantly reduce tobacco yields.
(1)The best practice is to limit the amount of material turned under from sod or a winter cover crop.
(2)Early plowing also helps, particularly on a heavy sod, since doing so gives the turned-under residues more time to decompose before tobacco is transplanted.
(3)When seeding winter cover crops for erosion control, use a crop which will not produce a massive growth before being turned under in the spring. Crops like wheat, annual ryegrass or tall fescue can provide good winter cover and yet will not grow excessively in the spring, particularly during wet springs, as often happens when using a crop like rye.

Compaction Problems
Once they are waterlogged, slowly permeable soils dry more slowly than do others, so corn and tobacco producers often must work such soils under very moist conditions. This situation occurs especially in the following situations:

preparing the seedbed,
when soils are too wet at planting or transplanting,
using machinery for double cropped silage,
using machinery on fields where liquid manure is spread in winter and early spring.

Using machinery on waterlogged soil often causes compaction which can be particularly severe under wheel tracks or when disking wet land.
In-row compaction of soils, particularly those of high clay content, can be caused by planting corn when the soil is too moist. The shearing action of the furrow opener "slicks" the side of the row so that after drying, roots can't penetrate sides of the furrow. The root system is then confined to the furrow, usually resulting in stunted corn with greatly reduced yields. This most often happens with no-till planting, since surface traction of machinery is possible even though the soil is very moist below the surface.
A similar problem can occur when tobacco is transplanted into soil which is too moist. The planter's press wheels compact soil in the row, slowing root growth, often resulting in uneven growth of tobacco. And, even though tobacco fields are often cultivated under very moist conditions in hopes of improving soil aeration, tractor wheels can compact row middles, limiting the root system's expansion between the rows.
Compaction problems are intensified in soils with very poor structure. Many fields in Kentucky have been so intensively cultivated that natural structure has been destroyed. This is particularly true for tobacco fields where several diskings are usually performed before transplanting. It also can be severe on cornfields which have been intensively worked to incorporate herbicides. Loss of structure causes soils to crust easily following rainstorms. Crusting can be strong enough to cause problems in emergence of corn and to limit air movement into the soil. The latter can be very detrimental to early growth of tobacco and a cultivation is often necessary just to break up the crust.
The worst situations usually occur on soils of high clay content which have been so severely eroded that the clayey subsoil has mixed into the plow layer. This situation places the zone of reduced permeability nearer the surface.

Management practices to improve corn and tobacco production from compacted soil include:

Plowing deeply enough to shatter the compacted zone. While this can often be done with a moldboard plow, it is sometimes necessary to use one of the various types of chisel plows which can penetrate more deeply and shatter the compacted layer.
Another important practice is to minimize disking. Do not disk at all when the soil is too moist to break down from use of the disk.
Keep machinery and animal traffic off fields until they are dry enough not to be compacted. Heavy concentrations of livestock on wet fields can cause severe compaction. This often means delays in using slowly permeable soils.
Use rotations with sod crops to help improve compacted soils by improving structure.

Soils in Kentucky which are slowly permeable to water include Beasley, Bedford, Belknap, Bonnie, Calloway, Captina, Collins, Commerce, Cotaco, Eden, Falaya, Grenada, Heitt, Henry, Johnsburg, Karnak, Lawrence, Lindside, Loring, Lowell, McGary, Melvin, Mercer, Morehead, Mountview, Newark, Nicholson, Otwell, Sadler, Stendal, Tilsit, Tyler, Weinbach and Zanesville. Specific soils occurring in specific fields can be identified from published USDA Soil Conservation Service (SCS) county soil survey reports and from individual conservation farm plan maps prepared by SCS and the KY Department of Natural Resources and Environmental Protection.

To Manage Corn and Tobacco Production on Slowly Permeable Soils
1.Improve surface drainage where possible.
2.Do not use machinery or concentrate livestock on these soils while they are waterlogged at or near the surface.
3.Do not "overwork" these soils by disking and destroying natural soil structure.
4.Split or delay the application of fertilizer nitrogen.
5.Avoid turning under heavy topgrowth from sod or covercrops. When turning sod or cover crops, plow as early as possible.
6.Use slower growing winter cover crops such as wheat or tall fescue rather than rye to minimize the amount of topgrowth which must be turned under for tobacco.

About the Authors
Kenneth Wells has worked in Kentucky as an Extension Soils Specialist for the past 20 years. He has worked extensively throughout Kentucky during this time with professional and producer clientele in developing better farming programs based on better land and fertilizer use. Much of the crop response information used in these programs has been collected by Wells and other UK specialists and agents from field trials conducted on commercial farms all across the state.
Ronald Phillips, a Professor in the Agronomy Department, has conducted basic research on the effect of soil physical properties on the movement of water and solutes through Kentucky soils for the past 23 years. He also teaches and directs graduate studies in soil physics. His research in no-till agriculture has provided much of the understanding of no-till production necessary for its widespread adoption in Kentucky.