MANAGING SLOWLY PERMEABLE SOILS FOR TOBACCO AND CORN PRODUCTION IN
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
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
||7 weeks after planting
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
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.
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
• using machinery for double cropped
• 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
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
To Manage Corn and Tobacco Production on Slowly Permeable Soils
1.Improve surface drainage where
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.