Soil Health and Deep Zone-Tillage
Jude Boucher, University of Connecticut
reprinted from Croptalk v4.1
Roadmap to a healthy soil
A “healthy soil” is one that is capable of sustaining crop productivity. It has to have adequate depth, drainage and nutrients, large populations of microbes and other beneficial organisms, low levels of pest organisms, adequate oxygen for root growth, few harmful chemicals, and be able to resist natural and artificial adversities.
If we take a closer look at the factors that make up a healthy soil we see that it is a balance of soil chemical, biological and physical attributes that makes a soil productive. Important chemical properties of the soil include things such as macro and micro nutrients, pH, organic matter (carbon), toxins or pollutants (herbicide carry-over), and cation exchange capacity. Biological properties include adequate populations of beneficial microbes, nematodes, mites, insects and worms for nitrification, decomposition of organic matter, and just to compete with and occupy niches that pest organisms might otherwise occupy. Many of these organisms are also critical in maintaining the proper physical attributes of the soil. Fungi, earthworms and organic matter (OM) are particularly important in the formation and durability of soil aggregates, which provide both small and large pores for drainage, airflow, and water holding capacity. Earthworm channels also help transport air and water deep into the soil profile. Important physical properties of the soil include such things as surface hardness, subsoil compaction, aggregate stability, and porosity, which are all influenced by OM content and tillage practices.
What is the problem with conventional tillage?
The extensive tillage practices used on vegetable farms in the Northeast are expensive and result in problems with soil degradation, soil compaction, and soil erosion. Multiple tillage trips across the field are expensive and are becoming cost prohibitive as fuel prices continue to rise. There is also a substantial investment in machinery and labor associated with tilling.
Between plowing, harrowing (several times), subsoiling, cultipacking or bedding, and cultivating (several times), we are literally working the life out of our soils. Constant tillage oxidizes soil organic matter away as CO2. With conventional tillage, more organic matter is lost than can be replaced by incorporating crop residues and through the use of winter cover crops.
As the organic matter (OM) disappears, so do the earthworms and other beneficial organisms that depend on OM to survive. Many of these organisms provide the “glue” that hold the soil aggregates together to give us good soil structure. As the aggregates are broken down by tillage, and not replaced due to loss of OM and soil organisms, the soil air pores associated with the aggregates disappear too. This chain reaction leaves the soil devoid of oxygen and with an inability to hold water, nutrients and pesticides (which may run off and become pollutants). Obviously, plant root health suffers in such a scenario, as do crop yields.
Loss of organic matter can also cause the soil on the surface to plate or crust, making an almost impenetrable barrier, which prevents seed emergence and leads to water pooling, low oxygen conditions and even lower biological activity. The horizontal pressure at the bottom of a plow or disk-harrow can produce sub-surface plow and disc-pans over time. Compacted plow pans often prevent root growth beyond 8-12 inches deep and lead to drainage problems, disease problems (think Phytophthora, etc.), reduce yields and additional tillage costs. A compacted soil depleted in OM retains too little water during dry weather and floods and ponds during wet periods.
Of all the problems associated with tillage, the most important problem is erosion, because soil lost, can not be replaced. The average U.S. farm losses about 3.1 tons of soil per acre each year. Contrary to what this statistic implies, there is not a constant loss of soil. As few as 5 major rainfall events over a 25 year period may cause 75% of the soil erosion. This illustrates why it is best to have the soil covered at all times.
Due to the hilly terrain in New England, high land values and urban sprawl, we have some other unique problems with tillage in our region. As the farms are handed down to new generations and divided among siblings, some of whom may or may not want to farm, new vegetable growers are often pushed off the bottom land and onto the slopes, where they continue to use bare-cultivation practices that result in severe soil loss. In 2006, one Connecticut grower actually resorted to building rock “bridges” every 100 yards or so, across four-foot-deep erosion ditches, so that he could spray his sweet corn for insect pests, and then ended up rebuilding the bridges when they washed out.
As land trusts buy up open land in Connecticut, they often institute policies that prevent farmers that rent the land from using conventional tillage techniques to help prevent damage to the property. Such policies limit future vegetable production in a state where land is expensive and land trusts control much of the open space.
As urbanization spreads across New England, farmers also have trouble with new neighbors along the farm boundaries who object to the dust and noise. Reduced-tillage systems are capable of reversing soil degradation and compaction problems, halting erosion, and even solving some of our urban/land value issues.
Why deep zone tillage?
Reduced-tillage is not new. It has been successfully used on farms in the mid-west and west for over 40 years and is currently used on more than 36% of the U.S. farmland. Of the different types of reduced tillage, deep zone tillage seems most appealing for our climate. This is a combination of strip tillage and zone building or subsoiling. Deep zone tillage systems can address all of the problems mentioned above and more. Unlike no-till, which relies on a heavy blanket of plant residue to protect the soil and delays the warming of the soil and crop growth in Northern climates, deep zone tillage uses a 5-inch-wide tilled strip to simultaneously break up plow pans, warm the soil and prepare a seedbed. A deep shank or subsoiler (zone-builder) breaks up the plow-pan while fluted coulters cut and prepare a strip in the killed residue/cover crop, and rolling baskets help break up soil clods to prepare the narrow seedbed. Crop roots grow deep through the slit made by the zone builder rather than just spreading out in the top few inches of soil. Coulters or (finger-like) residue managers in front of the planting shoe on the planter provide a finished seed bed.
Most of the ground between the crop rows retain the heavy surface residue from the killed cover crop. The 5-inch-wide tilled strip is slightly raised, warms faster than covered soils, and does not allow water to build up enough speed to erode a slope.
Residue that is allowed to buildup on the surface between rows does not break down as fast as when it is mixed in the soil, so OM levels tend to rise slowly over time. With the return of OM, comes the return of beneficial organisms, better soil structure and a healthier, more productive soil.
What can deep zone tillage do for you?
When combined with the use of cover crops, deep zone tillage helps replace lost OM, reverses the deterioration of the soil, improves soil drainage, increases soil water and nutrient holding capacity, and allows beneficial soil organisms to thrive. A Connecticut vegetable grower that switched to zone tillage in 2007, made fewer trips across the field with his tractor, saved on fuel, reduced dust and noise when preparing fields near a crowded neighborhood, and had his best yields ever, despite a prolonged drought. He also preserved soil moisture which allowed his sequential corn plantings to go in the ground and emerge on time, had better plant stands than his bare-ground fields, prevented dry tips on his sweet corn (without irrigation), had his cleanest winter squash and pumpkins ever, and acquired new rental land from a nearby municipality that will no longer rent to farmers that use conventional tillage. Although the following benefits were not obvious in such a dry year, he also improved the drainage on his land and helped reduce his potential Phytophthora problem by breaking up the plow pan, added to his soil organic matter (instead of mining more away), created more soil aggregates and pore spaces, and provided insurance against soil erosion and the necessity of building “stone bridges,” had it been a wet year. In short, he took the first step back to a healthy soil.
What are some of the secrets to converting to deep zone tillage?
As with any new system, there are a few details one must learn that help make it successful. Conversion to deep zone tillage begins by measuring the depth of the plow pan using an instrument called a penetrometer. A penetrometer is a steel soil probe with a gauge at the top which measures resistance as the tip of the probe is pushed into the soil. Plant roots will not penetrate compacted layers that register over 300 p.s.i. Therefore, it is important to identify the depth and the firmness of the plow pan, so that the subsoiler/zone builder on the deep zone till equipment can be set two inches below the compacted layer, to help break it up. The second season, planting rows are prepared midway between the rows of the previous year to continue the process of breaking up the plow pan throughout the field. Eventually, the compacted layer is destroyed and the zone builder is raised to approximately the 5” depth. This further reduces the drag, horsepower and fuel required to prepare ground to plant.
With silt, loam or sandy-loam soils, the deep zone till strips can be prepared in the fall, spring or throughout the summer as needed. With clay soils, fall preparation is usually recommended to allow the soil time to settle after the zone building and before planting. Growers usually find that preparing the seed bed “off-season” gives them more time during the season to attend to other chores. Some sandy soils do not need zone building and just a surface strip-till system is sufficient.
Deep zone tillage is most commonly used with large-seeded crops such as sweet corn, pumpkins, winter squash, beans and transplants such as cabbage and tomatoes. A team of Cornell researchers are working on refining systems for small seeded crops, root vegetables and for organic farms.
For early-season plantings, winter rye cover crops should be killed with herbicides (glyphosate or paraquat) when it is less than four inches tall so that the roots do not become too big and gnarly. Growers in NY have reported that paraquat is more successful at killing the rye during cool, wet springs. Roots from large rye plants (10-12”) tend to pile up in the planting strip causing seeds to bounce off, rather than entering the soil, at planting. On late-planted crops this is not a concern because even large rye roots seem to break down or soften adequately if killed 2-3 weeks before the deep zone builder is used to prepare the seed bed, eliminating seeding problems.
Coulters or finger-like residue managers on the planter that clear the planting strip of excessive cover crop residue are important for proper placement of the seed and high yields. Residue managers tend to clear surface rocks from the seedbed as well, making it easier to transplant crops, although care should be taken not to remove too much soil, or water can accumulate in the depressions left behind and rot seeds. Some brands (i.e. Dawn) of residue managers have finer depth adjustments than others and may be preferable.
Growers should adjust the residue managers so that they remove debris and not soil to achieve the best plant stands.
I plan to conduct a penetrometer and soil survey on farms across Connecticut this summer as part of a grant from the Sustainable Agriculture Research and Education (SARE) program. The goals of the survey are to assess how common plow and disk pans are in Connecticut and what OM levels are like on our conventionally-tilled vegetable farms. Also, for farms converting to zone tillage, I will be taking additional soil samples to send off to Cornell University for the new Soil Health Tests. The Soil Health Tests go beyond the normal pH, macro/micro nutrient and OM measurements and also assess soil physical characteristics such as porosity, soil aggregate stability and root health. Results will be used as baseline data to help document changes over time for zone-tilled fields.
Duiker, S. W. and J. C. Myers. 2005. Better Soils with the No-Till System. Pennsylvania Conservation Partnership.
Gugino, B. K., O.J. Idowu, R.R. Schindelbeck, H.M. van Es, D. W. Wolfe, J. E. Theis and G. S. Abawi. 2007. Cornelll Soil Health Assessment Training Manual. NYSAES, Geneva, NY
Idowu, J., A. Rangaranjan, H. van Es and B. Schindelbeck. Reduced Tillage Fact Sheets: Fact Sheet #1 Zone Tillage. Cornell University, Ithaca, NY.
Magdoff, F. and R. R. Weil. 2004. Soil Organic Matter in Sustainable Agriculture. CRC Press, NY, NY.
Cornell University Reduced Tillage Project Team Website, http://www.hortcornell.edu/reducedtillage
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