Growing On Compacted Soils Equals Embezzlement

Jerry with Buddy and Maggie

Compacted soils rob your bank account of cash. The theft is subtle, continuous, and forever unless, you make it a priority in your agronomic soil management practices to prevent the theft.

Except for 2003, the last several years have been very dry with record drought recorded in many jurisdictions. In 2003 however, many growers and landscape owners discovered what good drainage is all about because plants suffered due to record rainfall. I heard reports from the Carolinas where magnolias died in great numbers. Hurricane Isabel revealed that thousands of huge, old trees were anchored to earth with very shallow roots that had probably declined during the drought years. Both circumstances are in part due to problems in the soil profile.

This past spring we saw combines attempting to harvest winter grain crops in very wet conditions. Tremendous rutting resulted, which may cause a reduction in crop yields for years to come. It might have been better to wait for the right conditions, plow down the crop, and start over. Yet cash is king, and with farming generally in the tank already, current self-interest prevailed.

In my Internet study for this article I found one paper that showed heavy compaction of silty clay loam soil reduced corn yield from 200 bushels per acre to 85 bushels per acre. Is it possible that we could see a 50% decline in the productivity of horticultural crops due to soil compaction? Probably.

Productive silt loam soils will contain roughly 50% soil particles, 20% air space, 26% water, and 4% organic matter. Roots consume oxygen. When oxygen is absent because the pore space was crushed out of existence (compaction), plants will not flourish. Most plants will start to decline within 48 hours of having their roots flooded with water.

We will not be able to maintain the perfect relationship year round due to variation in weather cycles. Regardless, our goal is to do so. Anything we can do or not do that nurtures the ratio will serve our best interest. The most important factor for maintaining the relationship is to avoid soil compaction by utilizing every tool and implementing every practice that still fits into an economically viable production system.

Symptoms of Compacted Soils in Nursery Production

Surface water remains for long periods, greater than 24 hours, after rainfall or overhead irrigation.
Equipment tracks holding water.
Premature foliage drop in any season, but excessive in the fall.
Variable plant productivity in the same row or block. Inconsistent plant development such as bushy growth when not the norm, a range of leader development, the wrong foliage color, and smaller than normal leaves can all be symptoms of compaction but may also be signs of high or low nutrient values.
Increased wind and water caused soil erosion.
We find ourselves thinking the tractor is loosing horsepower when in fact compacted soils require more horsepower to work.
Previously unseen weeds start showing up and our old favorites disappear.
Irrigation water runs off prematurely instead of infiltrating to the roots where needed.
More mosquitoes than you remembered in previous years.
Increased sucker production on many different trees.
Plants show stress more readily in dry periods.
Increased denitrification in the anaerobic environment can lead to the loss of natural and synthetic nutrients. This may be difficult to detect as other symptoms may cause confusing results, but lack of plant vigor is occurring due to the lack of available nitrogen.

Two zones of compaction will impact productivity

Surface compaction caused by excessive tillage and equipment use in both wet and dry soil conditions block air, water, and nutrient penetration in the root absorption zone. This can be relieved by tillage but excessive tillage may increase the problem by reducing soil particle size. Coarse tillage by use of chisel plow type tools as compared to a rototiller will reduce damage to the soil.
Deep compaction is, in part, caused by equipment operating over wet soils. Deep compaction will prevent the soil profile from storing moisture, can cause excessive moisture to be retained from wet spells, prevents roots from penetrating greater depths to sustain the plant during dry periods and reduces the effectiveness of any manmade drainage system such as field tiles.

Some ways to prevent soil compaction

The absolute number one rule is to stay out of the field during wet periods for sure, but to also develop production systems that keep equipment out of the field as much as possible year round. Even during dry periods, soil compaction will occur to the upper soil profile.
Use equipment that provides the lowest possible pressure exerted on the soil surface. Foot traffic over the same path of lawn for several years will show up as compaction induced decline of the lawn. We have all seen this. Think about taking the tractor over the same path in all weather conditions for several years and you can begin to easily understand the level of damage we can cause unknowingly.

There is an old study of soil compaction, which seems to always surface in these discussions, that shows the compaction impact at varying soil moisture levels and the resulting depth of compaction. Note the effect even on hard, dry soils.

Effect of soil moisture on the depth of compaction.
[Sohne, W., (1958). Fundamentals of pressure distribution and soil compaction under tractor tyres. Agricultural Engineering, 39: 276–281.]
Fallow after spring digging while waiting to plant the next rotation. The fallow ground should be cover cropped with a deep rooted plant to help relieve compaction. Such crops include corn, winter wheat, sorghum and soybeans. Of these, winter wheat produces the deepest root system, up to six feet in one year if the soil profile permits. One of the significant secondary benefits of cover crops is to increase the size of soil aggregates which greatly improves water infiltration.
Plant grass in isles, low use roadways, field end turning strips and perimeter strips. This will improve soil structure, water and air infiltration, and reduce compaction. Even though this will be out of the planting zone, benefits can accrue to the land in general that translate to improved lateral root development, air exchange, and water infiltration. Importantly, grass strips have proven to be the best defense against soil erosion and nutrient run-off.

A common myth is that a one year cover crop plowed into the field will increase the soil’s organic content. Cover crops repeated for many years can slowly increase organic content but not much. Common sense says that if it took Nature 100,000 years to build a few inches of “topsoil,” we are not going to have much impact in the short term.

Subsoiling is often thought of as the panacea of soil compaction relief. It is an effective tool in the production of short term crops such as in traditional agriculture, but of limited use in horticultural production. It has long been known that the effects of subsoiling start declining immediately after the procedure and is mostly exhausted after one year. Variation in soil type and depth, severity of freeze/thaw cycles and the amount and intensity of rainfall will all play a role in the long term effectiveness of subsoiling procedures. In horticultural production, subsoiling is encouraged prior to each rotation but the grower should not believe his job is done by simply subsoiling every 5 to 8 years. Subsoiling is most effective when done during the driest season, which requires more horsepower but results in more damage to the surface soil structure.
Use drip irrigation. Drip irrigation has numerous benefits as I have mentioned elsewhere. One of which is to eliminate the pounding effect of overhead irrigation. We cannot prevent rain, but we have the power to irrigate gently. Falling water causes soil movement and reduction in the size of soil particles on the surface. The clay and silt size particles wash into the desirable airspace to reduce water infiltration and reduce the overall composition of larger soil aggregates to result in potential surface soil layer compaction.
A spading machine “tine.” It “spades” the soil by digging deep and mixing the entire zone of tillage. These machines are available in a wide range of sizes for width and depth. (Drawing courtesy of George Leidig, Imants Autusa. Inc.)

Use appropriate tillage tools and systems. Europeans have been using spading machines for years and now use the old plow as a lawn ornament. If you came to the MNLA Field Day at Waverly you saw the field demonstration of one such tool manufactured by Imants of Holland. Plows create what we refer to as the “plow layer” and the “plow pan.” Over time, the plow actually modifies the soil profile into a zone of soil that has reacted to plowing. Eventually, the profile becomes more compact at the interface of the bottom of the plow share and the soil below, the “plow pan.” This may have the effect of inhibiting roots to grow well through the compacted layer. Much U.S. acreage in small grain production is now planted by the “no-till” method to obtain many benefits, one of which is to prevent the “plow layer.” Tillage by spading machines has the benefits of deeper tillage with less horsepower, greater incorporation of subsoils into the upper soil region, the ability to deeply incorporate grown or added organics, complete planting preparation in one pass to reduce compaction by multiple passes, AND the beneficial elimination of the plow layer due to the very “coarse grind” resulting from the limited contact of the tool with the soil.

Agronomic/soil physics perfection—tracked tractor and spading machine. (Photo courtesy of George Leidig, Imants Autusa. Inc.)

Buy and use a penetrometer (soil compaction meter). Like most attempts to find improvement in our practices, measurements are required to track progress. A penetrometer is not a precise method of measuring soil compaction because it measures the resistance to inserting a probe into the soil to varying depths which will produce different results as a function of soil moisture. However, the tool can be purchased for about $200 as compared to $3000 for more effective, high-end infrared systems. For our use the penetrometer is fine in that it yields a relative measurement of different sites at the nursery. It usefulness can also be enhanced through the use of a moisture tensiometer to read the soil moisture content in relative terms. By combining both tools, we can make penetrometer tests at different times of the year or in different years when the soil moisture level is determined to be about equal.

The penetrometer measures the resistance of the soil profile to the insertion probe in pounds per square inch. By taking multiple measurements in different areas, we can judge the relative compaction of the soil. Find a plot of soil that has been undisturbed and not driven on for many years, is deemed to be well drained, and is similar to your growing fields. Record readings at 3, 6, 12, 18 and 21 inches, if possible. Then compare those readings against various sites at the nursery such as undisturbed 1, 2, 3, 4, and 5 year old planting rows. Take measurements in the planting row, and every foot or so into the isle to see if there are differences caused by equipment maintenance practices. Over time you should be able to draw some useful conclusions particularly if you start seeing big variations in troublesome areas such as where all the trees died.

It is important to note that heavily compacted but saturated soils may lead to low readings which are false relative to the compaction issue. Tests should be conducted on moderately dry soils at all depths. The tools can be obtained over the Internet. Using a search engine, type in Penetrometer and Moisture Tensiometer.

On October 19, 2003, I took a series of penetrometer readings at the farm to give you a feel for the exercise. Soil moisture was high but not at field capacity. The numbers are in pounds per square foot (psi). The soil is a deep Hagerstown silt loam. All measurements were taken within about a 50 foot radius.

Location	3"	12"	21"
5-year old heavy use grassed road	1000+	600	450
5-year old grassed isle	325	425	500
5-year old plant row	80	275	450
1-year old plant row	25	200	300

The “feel” of the probe was more or less like pushing through sand in the planting rows which I describe so that you know 200–300 psi is fairly loose soil. Note the road compaction was severe at 3 and 12 inches but about like the rest of the soils tested at 21 inches. Soil settles over time even without any manmade pressure from above which is shown as the variance in the different aged planting rows. The 1000 psi reading was greater than indicated; my gauge stops at 1000.

Do not be tempted to work soil and plant new liners when the soil is too wet. You are inviting disaster with the crop as working the wet soil will increase compaction significantly thereby preventing the newly planted liners from developing adequate root systems. We only get one chance every 5–8 years to start the liners off in the most desirable environment. It is difficult, if not impossible to repair the damage during the rotation. I believe we would be better off delaying the planting until the conditions are near perfect, rather than live with a poorly prospering planting for years into the future.

Conclusion. There have been uncounted articles written and personal stories related over time about the matter of healthy soil. This somewhat lengthy article is just “the tip of the iceberg.” Therefore, I hope if nothing else, it stimulates thought and discussion. When I typed “soil compaction” into the Google search engine, it reported over 100,000 potential responses.

Jerry