Samuel D. Evans
West Central Experiment Station
University of Minnesota
now Emeritus Professor at Morris, Minnesota
John F. Moncrief
Department of Soil, Water, and Climate
University of Minnesota
Gyles W. Randall
Southern Experiment Station
University of Minnesota
William E. Lueschen
Department of Agronomy and Plant Genetics
University of Minnesota
formerly Head of the Southwest Experiment Station at Lamberton
Copyright © 2002 Regents of the University of Minnesota. All rights reserved.
Management of crop residues with reduced tillage is the most cost-effective method of controlling sediment losses and reducing farming impacts on water quality. Crop residues can also help reduce wind erosion and can enhance snow entrapment. One of the primary water quality concerns for the Minnesota River and its tributaries is sediment, which contributes increased phosphorus (P) to the system. This increased P stimulates algae growth, which is followed by an increased biological oxygen demand when the algae die and decompose. This can deplete dissolved oxygen levels, resulting in game fish stress or kill.
In addition to affecting sediment loss, tillage influences many interacting physical, chemical, and biological properties of soils that can have major impacts on crop production. These properties include temperature, moisture, aeration, bulk density, structure, nutrient distribution, organic matter levels, and microbial populations. Various crops respond to these changes differently. The range of these changes can be amplified by extremes in tillage reduction associated with some residue management alternatives. Small grain is insensitive to temperature changes but may respond to changes in the seed furrow environment and to differing weed species present.
Small grain is a prominent part of the agriculture in the upper Minnesota River basin. Following is a discussion of residue management tillage system effects on small grain production.
On soils classified highly erodible land (HEL) the general requirement is 30 percent residue cover after planting. On non-HEL soils the steepness and length of the slopes will indicate the potential for significant erosion. A second soil factor that must be considered is internal drainage. Poorly drained soils warm up more slowly than well-drained soils, so may require more tillage. Tile drainage may improve this situation, but in some cases this may not be enough to insure consistent success with little or no tillage. A third factor is soil fertility level. Having a high level of fertility is necessary if reduced tillage systems are to perform well. Low fertility conditions offer too many obstacles and generally limit yields in reduced tillage systems. It is important to effectively control sediment at high soil test P levels. Research has shown that this can be done effectively with crop residues in conjunction with other conservation techniques.
The amount of residue present in a field depends on the crop rotation and the level of production. Corn generates more residue than small grains or soybeans; thus it is easier to maintain higher residue levels with a variety of tillage systems. The durability of the residue is also crop dependent. Soybean residue is classified as "fragile," or in other words is easily destroyed. Corn and small grain residues, on the other hand, are classified as "non-fragile."
Spring wheat and soybeans appear to be a viable crop rotation in a no-till system for Minnesota conditions. Other crops that fit well in a small grain rotation are sunflowers, sugar beets, and field beans. Maintaining a sufficient residue cover may be a problem following these crops. Soybean yields after small grain have generally not been affected by tillage. With more intensive tillage systems, crop sequence becomes less important. In summary, both the crops in the rotation and the sequence of the crops are important in tillage management.
Tillage for small grain production requires the management of residue to allow for effective stand establishment. Planting when surface crop residues are relatively dry and are cut more easily with coulters is advisable. Experience has shown that planting in the direction of stubble orientation reduces the effectiveness of coulters and disk openers. Small grain residue pushed into the seed furrow by coulters "cradles" the seed and often results in stand loss and delayed emergence. This is primarily because of slower absorption of soil water due to poor seed-to-soil contact and allelopathic inhibition. Small grains are not as temperature sensitive as corn, so residue effects are mainly due to in-furrow seed-soil contact or phytotoxicity.
Do not surface-apply urea sources of nitrogen (N) without incorporation unless air temperatures are cool or rain is imminent. Urea left on the surface in proximity to residue has a high potential of volatilization losses. With residue management tillage systems, less N is released from soil organic matter due to less physical disturbance. In addition, soil organic matter may increase under some reduced tillage systems, and this will act as a sink for nitrogen. Anhydrous ammonia has been the most consistent source of N. Drill-applied diammonium phosphate (18-46-0) places N and P below the soil surface and close to the seed. This has been very effective in the western Minnesota River basin with calcareous soils that can tie up P. In addition to being a very efficient method of P fertilizer application, it also minimizes the risk of erosive losses of P.
The effects of tillage on the development and severity of crop diseases are variable, depending on the disease, the specific type of tillage system used, and the effectiveness of the other disease management practices used. Conservation tillage usually reduces soil temperatures, conserves soil moisture, and leaves crop residue on the soil surface. Of particular concern are crop diseases that are favored by cool, wet soils. Diseases most troublesome in high-residue tillage systems are those that have inoculum associated with crop residues left on the soil surface. In many cases the diseases are most noticeable when monoculture cropping is practiced. Diseases of most concern are scab and tan spot, both of which are associated with plant residue. However, in addition to the disease inoculant supplied by residue, the proper environment and susceptible varieties must be present for economic infestations.
Controversy exists over what type of seed openers (disk vs. hoe vs. sweep) deal with small grain residue most effectively. Generally, hoe openers work better in drier soil. Hoe-type openers operate below residue, making "in furrow" residue less probable. Sweep or air seeders, placing seeds below sweeps, also reduce the probability of intimate contact of seed with crop residue. Depth control is the challenge with sweep seeders. Press wheels should also be used for good stand establishment under dry conditions. Disk-type openers require the most caution in this respect, but work better under wet conditions. If considering no-till small grain production, it is essential to use a properly designed, heavy duty drill that can cut through the residue, place seed in contact with the soil without incorporating residue, and firm the soil over the seed. Selecting a drill with fertilizer capability is also important.
Various factors including soil characteristics, crop rotation, residue management, disease problems, seeding equipment, and management ability must be considered when selecting a residue management system including small grains. In rotations with moderate amounts of residue, many systems will work on a variety of soils. With higher residue levels, the importance of proper residue management and heavy duty reduced tillage drills will ensure proper seed-to-soil contact without significant residue in contact with the seed. In the upper Minnesota River basin, higher levels of residue may contribute to increased soil moisture and subsequent yield increases in dry years. Crop rotation is a major factor in minimizing the disease problems in small grains.
The results of studies in Douglas, Norman, and Becker Counties are shown in Table 1 . In these studies tillage plots were split, with winter and spring wheat planted into barley stubble.
On average, spring wheat yields following barley were not affected by tillage. Only in one site year (1986 in Becker County) did tillage significantly affect spring wheat yields. A bindweed problem at this site was the likely cause. At most sites an increase in foxtail (pigeon weed) was associated with chisel and no-till systems.
Results of some recent studies near the headwaters of the Pomme de Terre River in Ottertail County are shown in Table 2. Tillage affected spring wheat yields at only one site year out of five (in 1994). The yield reduction in 1994 was linked in part to stand reduction with the no-till system. The drill used had a single disk opener. At the other site years spring wheat yields following soybeans were not affected by tillage.
The Paraplow is a unique type of subsoiler which leaves surface residue minimally disturbed. Even though soils were very dense in the fall of 1993, subsoiling that fall reduced spring wheat yields the next year. Paraplowing reduced stand compared to a chisel plowing system. On average there was a 4 bu/acre yield reduction with the no-till system compared to the chisel plow-based system.
In a continuous wheat study on a Barnes loam near Morris ( Table 3 ) there were no significant effects of tillage on yield in the three years measured. Sometimes protein content can be used as an indicator of reduced N availability. For this reason it is presented in Table 2 and Table 3 . Protein contents appeared to be more affected by environment than by tillage system. Protein differences between tillage systems were very small.
Traditionally there has been very little winter wheat grown in Minnesota. This is primarily due to the harshness of the winters. In some years lower prices (vs. spring wheat) and the lack of a suitable crop sequence may also be a factor. In most years, with a clean-tillage system there will be substantial winter kill. This limits varietal selection to only the most winter hardy. In some instances this is at the expense of intrinsic yield potential, protein content, and disease resistance.
The studies in Table 1 illustrate the potential for winter wheat production when stubble is managed for snow catch in an effort to insulate the soil. North Dakota research has shown that if 4 inches of snow are caught by stubble, winter wheat is protected to -30° F. In the three-year study at three locations, winter wheat yields were slightly higher than spring wheat and there was little effect of tillage. Disease management is more important with winter wheat, however.
Data from six trials in northwestern Minnesota where barley was grown after soybeans with spring-applied urea showed no difference in yield or protein due to tillage ( Table 4 ).
Success of reduced tillage approaches to small grain production have been higher when preceded by a low residue crop such as soybeans. Spring wheat and barley following soybeans have generally not been affected with most alternative tillage approaches. A no-till system resulted in more variability in yields (higher or lower than a moldboard plowing system). No-tillage sometimes posed challenges in stand establishment, N management, and weed control.
By catching snow with barley stubble, no-tillage systems allow winter wheat to be grown in Minnesota with less "overwintering" risk. Winter and spring wheat resulted in comparable yields, although performance was more variable for winter wheat. This provides an opportunity for growers to reduce their labor during peak labor demand periods (spring and fall). It also allows for more flexibility to accommodate variations in weather.
Tillage passes with different implements can be used very effectively to create various levels of residue remaining on the soil surface. Four tillage systems shown below are categorized in the following Tables 5-8 according to the residue management/yield performance indicators also shown below:
Moldboard Plow: Fall moldboard plowing followed by one or two secondary spring tillage operations before seeding.
Chisel Plow: Fall chisel plowing plus secondary spring tillage before seeding. Special attention should be paid to use of proper shaped/width shovels and implement speed in order to maintain proper residue cover.
Spring Disk/Field Cultivator: One or two passes in the spring prior to seeding.
No-till: All seedbed preparation is performed by the drill.
Inadequate Residue to Minimize Erosion
(less than 30 percent of soil surface covered after planting).
Where erosion is not a concern, fall moldboard plowing may be the best practice.
Recommended with Good Management.
No yield penalty is expected if the farmer observes all relevant recommended management practices for high-residue systems.
Excellent Management Required.
Slight yield penalty is possible, even if all recommended management practices are observed. Above average crop management will be needed to ensure good performance.
Reduced Yield Potential.
The potential exists for substantially reduced yields, especially on poorly drained soils in wet years.
A number of tables have been developed which estimate residue management/yield performance of various crop rotations involving corn, soybeans, and/or small grains. Continuous corn and corn-soybean sequences are discussed in other publications. In those publications the Minnesota River basin was divided into high annual rainfall (>28 inches) and low rainfall (<28 inches) areas. This north-south line is approximately halfway between Highways 71 and 15. Since most small grain is grown in the low rainfall segment of the Minnesota River basin, indices were developed only for that section of the basin. In each crop sequence, separate indices were developed for glacial till (deposited in place by melting glacier, poorly sorted) and lacustrine (deposited in glacial lakes, well-sorted) soils.
Moldboard Plow: This systems generally results in high yields but leaves inadequate surface residue to minimize soil erosion. For this reason it should not be used except on level soils where erosion is not a concern, to alleviate surface soil compaction, to incorporate P and K fertilizer, or to incorporate manure.
Chisel Plow: This tillage system generally results in high yields but care must be taken to insure adequate surface residue cover. In most cases straight chisel shanks should be used to achieve 30 percent residue cover. For small grain following soybeans this system will result in less than 30 percent cover, so it is not recommended.
Spring Disk/Field Cultivator: On glacial till soils this tillage system will result in good yields and will leave adequate residue if the implement is properly set. On lacustrine soils this system will probably result in some yield loss due to delayed planing for small grain following soybean. It will also require a high level of management on other crop sequences with higher residue production.
No-till: On glacial till soils this system will work well for small grain following soybeans or soybeans following small grains. For corn following small grain or small grain following small grain, some yield loss would probably result. On the lacustrine soils the no-till system will likely result in yield loss (even with good management) for small grain following soybean or soybean following small grain due to delayed planting. For the other crop sequences substantial yield loss would occur.
To order other publications in this series, contact your Minnesota County Extension Office, or outside of Minnesota, contact the Extension Store at (612) 625-8173. Titles in this series include:
This set of publications was the result of a joint effort between Minnesota Extension Service, Minnesota Agricultural Experiment Station, and Minnesota Pollution Control Agency. This information was first presented February of 1995 at the Sediment Control Solutions Conferences in Mankato and Montevideo, Minnesota.
In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.