Minimum or No-Till Practices - Two Guides
Photo courtesy of the National Agricultural Library.
Planter Master Tiller
1. University of Nebraska, Institute of Agriculture and Natural Resources.
A. J. Jones, Extension Soil Erosion/Conservation Tillage
R.A. Wiese, Extension Soil Fertility Specialist
E. C. Dickey, Extension Agricultural Engineer-Conservation
Nature has some built-in processes that reduce soil compaction. They include cycles of wetting and drying, and freezing and thawing.
In the last 20 to 30 years, farming practices have changed drastically. These farming changes have made it more difficult for nature to rejuvenate the soil environment to an optimum condition for crops. Performing field operations on wet soils, using multiple field operations to grow the same crop continuously, and eliminating meadow crops from crop rotations contribute to more extensive and deeper compaction.
Each farmer has the opportunity to make decisions that can keep soils from becoming compacted.
Adoption of management strategies to minimize soil compaction, such as controlled traffic, may require a bit of planning; staying off wet soils may require little planning. If you have soil compaction that is limiting production, measures such as deep tillage might be needed to help loosen and shatter the compact soil layer.
Compaction of any soil is greatest when the three to six inch soil depth is near field capacity. Field capacity is only a guideline to identify optimum moisture conditions for compaction.
Clay content and organic matter content also influence the compactibility of each soil. The water content of a soil can be determined using the feel-and-appearance method (NebGuide G83-690).
You also may check the soil water content by digging up a portion of soil from the three- to six-inch depth. Mold the soil in your hand and drop the soil ball onto a hard surface. If it does not break or crack on impact it is too wet for field operations.
Perform field operations in your driest fields first. This allows more drying time for fields that tend to remain wet.
Some years field operations may have to be conducted when the soil is near field capacity to remain timely. Minimizing the axle load and increasing tire size will help reduce deep compaction in these situations. The larger tire will compact more of the soil surface, but the lower pressure will help reduce the depth to which the high compactive forces will penetrate.
Tillage for many years contributed to the breakdown of soil structure. Each individual tillage operation using a disk, chisel, sweep, harrow, moldboard plow or combination of these tools breaks down soil structure by compressing and breaking soil aggregates. A soil aggregate is a mixture of clay, silt, sand and organic matter bound together to resemble a crumb. Soil aggregates are necessary for good air and water movement and root growth. Soils that have been tilled are more susceptible to compaction than are soils receiving little tillage.
Tillage systems with a reduced number of operations leave greater amounts of residue on the soil surface. This surface residue helps prevent surface sealing, a form of compaction, by intercepting raindrops before they hit the soil surface.
Organic matter is added to the soil in the form of crop residues, animal manure, sludge, or green manure crops. Organic matter promotes the development of good soil structure and decreases soil bulk density. It helps bind soil particles together as aggregates so they are not as easily cracked, split or compressed by tillage or wheel traffic. Adding organic matter to the soil also increases soil nutrient availability for crop growth. Nitrogen, phosphorus, sulfur and trace elements especially are increased with high soil organic matter.
Fields in crop rotations that include alfalfa, clover or grass usually have soils that are less compact than soils in fields without these rotations. This is true for most soils because once these crops are seeded, 1) there generally is no tillage operation after seeding, 2) trips across the field tend to be associated with hay harvesting when the soil is dry and less likely to be compacted, and 3) the deeper rooting depth and large taproot of alfalfa and clover keeps the soil more porous (Figure 1) and removes large amounts of water which helps dry the soil and increases cracking.
Figure 1. Perennial crops such as alfalfa and clover have a taproot which is larger in diameter than most fibrous roots and usually have deeper rooting systems. (A) is dryland, (B) is irrigationd. (From Jean and Weaver. 1924.)
If you till the soil, till deeper in dry years. Vary the tillage depth in subsequent years to minimize the development of a "tillage pan" or compacted zone.
Tillage to a constant depth will cause a dense layer to develop where the implement shears the soil. A commonly used example of this is the moldboard plow pan which is created by plowing at the same depth for several years. As farmers switch their tillage system from the moldboard plow to the disk or the field cultivar, a "disk pan" can be created. This pan may be less dense than the plow pan but it is closer to the soil surface.
Compaction will be localized if all equipment tires are restricted to particular "tracks" or row middles in the field, but the rest of the field is essentially uncompacted (Figure 2). Only soil in the untrafficked row and row middles will receive compaction caused by tillage and planting equipment. Tillage systems which have different width implements make it difficult to control traffic. Controlled traffic can be practiced most easily in ridge plant and no-till systems.
Figure 2. Random wheel traffic patterns (above) create compaction over the majority of the field as compared to controlled wheel traffic (below).
Yield reductions attributed to compaction also may be associated with disease, fertility or other problems. To guarantee that any observed yield reductions are associated with compaction, soil investigations are necessary.
Soil investigations also help ensure that a deep tillage operation is successful. Deep tillage may be warranted if soil compaction is limiting yield. Subsoiling or other tillage to alleviate compaction should be needed only when crop roots have been inspected visually and shown to be restricted by a compacted zone (See NebGuide G87-331).
|Figure 3. Deep tillage can be performed with a subsoiler (shown) or other implement depending upon the depth of compaction. (32KB JPG)|
The depth of yield-limiting soil compaction will determine the required depth of tillage and tillage tool selection. If compaction occurs in the top six to eight inches of the soil, tillage tools such as a chisel plow or moldboard plow can be used to shatter the compacted layer. However, if compaction is below about eight to 10 inches, tillage tools such as a subsoiler, ripper or paraplow may be needed (Figure 3).
Many types of subsoilers are available. Most are chisel-like tools having curved or straight shanks. Each shank will require at least 20 to 30 PTO horsepower for deep tillage. It is suggested that the subsoiling depth be about 50 percent deeper than the compacted layer, and that the shank spacing be equal to the tillage depth for greatest shattering.
This tillage should be performed in the late summer or fall when the entire soil profile is fairly dry and can be shattered easily. This subsoiling operation, when performed properly below the depth of compaction, will displace and shatter a V-shaped section (Figure 4).
|Figure 4. A subsoiler shank shatters a V-shaped section of soil from the base of the shank upward toward the soil surface.|
The relative success of subsoiling will vary with soil type, soil water content,
texture, bulk density and the shape of the subsoiler shank. To ensure that the compacted
zone has been shattered properly, dig a hole and look for the V-shaped wedge of soil that
should have been loosened. Secondary tillage may be used in the spring to level the field
prior to seeding; however, slot planting without tillage also has been used successfully.
Subsoiled fields easily can redevelop a compacted layer if the loosened soil is worked too
wet or if wheel traffic is not controlled.
Search for this topic and other in publications at Univ. of Nebraska Extension Serv.
Sustainable Practices, Mary Peet, North Carolina State Univ. Extension Serv.
In conservation tillage, crops are grown with minimal cultivation of the soil. When the amount of tillage is reduced, the stubble or plant residues are not completely incorporated, and most or all remain on top of the soil rather than being plowed or disk ed into the soil. The new crop is planted into this stubble or small strips of tilled soil. Weeds are controlled with cover crops or herbicides rather than by cultivation. Fertilizer and lime are either incorporated earlier in the production cycle or plac ed on top of the soil at planting. Because of this increased dependence on herbicides for weed control and to kill the previous crop, the inclusion of conservation tillage as a "sustainable" practice could be questioned. It is included in this book for t wo reasons. First, on highly erodible soils, protecting the soil may be an overriding consideration. Second, growers and researchers are working on less herbicide-dependent modifications of conservation tillage practices, some of which are deSRCibed here.
Methods deSRCibed as no-till, minimum till, incomplete tillage, reduced tillage, or conservation tillage differ from each other mainly in the degree to which the soil is disturbed prior to planting. Even in 'no-till systems, the soil is opened by coulte rs, row cleaners, disc openers, in-row chisels or rototillers prior to planting the seed. By definition, conservation tillage leaves at least 30 percent of the soil covered by crop residues.
In another variation of reduced tillage, narrow strips are tilled and then planted with standard equipment. Where soils are compacted but subject to erosion, strip tillage is a good compromise because crops can be planted efficiently and grow well in the loosened soil of the tilled strips while the untilled portions of the field conserve soil and water and control weeds.
Advantages and Disadvantages
Reduced tillage practices in agronomic crops such as corn, soybeans, cotton, sorghum and cereal grains were introduced over 50 years ago to conserve soil and water. Crops grown without tillage use water more efficiently, the water-holding capacity of the soil increases, and water losses from runoff and evaporation are reduced. For crops grown without irrigation in drought-prone soils, this more efficient water use can translate into higher yields.
In addition, soil organic matter and populations of beneficial insects are maintained, soil and nutrients are less likely to be lost from the field and less time and labor is required to prepare the field for planting. In general, the greatest advantages of reduced tillage are realized on soils prone to erosion and drought, but significant advantages were seen in a 12-year study of Wisconsin silt-loams which were excellent agricultural soil. This study found improvements of many soil quality factors compa red to chisel or plow treatments. These included greater water-stability of surface soil aggregates, higher microbial activity and earthworm populations and higher total carbon. Soil loss was less from sprinkler irrigation than in the plow treatment.
There are also disadvantages of conservation tillage. Potential problems are compaction, flooding or poor drainage, delays in planting because fields are too wet or too cold, and carryover of diseases or pests in crop residue. Additional problems from r esidues may be caused by allelopathy and high C:N ratios. Allelopathic effects are most often seen when small-seeded vegetables, such as lettuce, are planted directly into rye residues. When the residues are incorporated, as in strip tillage, allelopathic substances break down relatively quickly and are usually not a problem. (See Weed Management for a discussion of allelopathic effects on weed seed germination.)
In vegetable crops, the difficulty of controlling weeds and the need for custom-built equipment have slowed the acceptance of reduced tillage practices. Commercial seeders which plant well into stubble have been developed for most agronomic crops, but are only now becoming available for vegetable crops. A subsurface tiller transplanter has recently been developed at Virginia Polytechnic Institute and State University that should, when it becomes commercially available, greatly increase the ability of vegetable growers to transplant their crops into stubble.
Other relative disadvantages of reduced tillage in vegetables relate to the intensive nature of vegetable production. Since inputs are high in terms of seeds or transplants, fertilizers, pesticides and harvest expenses compared to agronomic crops such as corn and soybeans, the economic return must also be high.
For example, one no-till tomato grower in Pennsylvania estimated he saved $70/acre by skipping moldboard plowing, three diskings, and two cultivations. For most growers, this represents a small percentage of total costs.
In general, vegetable growers want to harvest as soon as possible in the spring in order to get a high price and recover production costs. Without spring tillage, some no-till fields are too compacted and poorly drained for the crop to get a good start. Soil temperatures under the stubble are cooler in the spring, potentially delaying maturity of warm-season vegetables such as sweet corn, snap beans and squash. In addition, if the transplanter does not work well in stubble, the crop may be delayed and mature less uniformly.
Variable maturity is a costly problem in commercially grown vegetables especially those like cabbage where each plant is harvested once. It may not be cost-effective to bring crews in to harvest more than once or twice so late or early-maturing plants may not be harvested at all.
Another consideration in no-till production is an increased possibility of soil compaction in no-till compared to conventionally tilled soil. During one year of a four-year study, severe compaction and crusting prevented the transplanter shoe from penetrating the soil, resulting in cabbage yields 65 percent lower than conventional tillage. Planting also had to be delayed a month because the site was too wet to plant.
A further consideration is that as no-till is generally practiced in agronomic crops, the field is prepared for planting by killing the previous crop with herbicidal desiccants such as glyphosate (e.g. Roundup) or gramoxylin (e.g. Paraquat). The no-till seeders available for agronomic crops were designed to plant into these dried residues. Recently, agronomists have been developing no-till systems where cover crops are planted for weed control then killed with flail or other types of mechanical cutters instead of herbicides. No-till seeders must be modified to work on these tougher residues, but residues control weeds legumes contribute extra nitrogen. (See Cover Crops for information on cover crop cutting schedules.) Similar systems are under development for vegetable growers who want to reduce tillage operations without using herbicides.
With experience, and with the increasing sophistication and availability of no-till equipment for planting vegetables, no-till growers should be able to reach yields at least as high as with conventional tillage practices. If soil water-holding capacity improves, no-till systems may even produce higher yields. Assuming weeds can be controlled and appropriate planters found, most vegetable crops could probably be grown with reduced tillage. Asparagus, snap beans, lima beans, beets, cabbage, carrots, dry bulb onions, peas, potatoes, spinach, popcorn, sweet corn, sweet-potatoes, and tomatoes have been successfully produced in conservation tillage systems. The feasibility of using these systems without herbicides has also been demonstrated, but, as with any new technology, growers will need to experiment to develop a cover crop/vegetable crop system that works well for them.
Search on 'sustainable' at North Carolina State University (NCSU), Extension Service.
Last Modified: Wednesday, 09-Jul-97 10:12:59