Strip till for field crop production
The trend among northern Plains farmers is toward using less tillage to produce field crops with more residue left on the soil surface. Strip till is a field tillage system that combines no tillage and full tillage to produce row crops. Narrow strips, 6 to 12 inches wide, are tilled in crop stubble, with the area between the rows left undisturbed. Often, fertilizer is injected into the tilled area during the strip-tilling operation. The tilled strips correspond to planter row widths of the next crop, and seeds are planted directly into the tilled strips. Strip tilling normally is done in the fall after harvest, but it also can be done in the spring before planting.
Advantages of Strip Till
• Reduces soil erosion because most of the soil remains covered with crop residue throughout the year
• Increases water infiltration compared with full-field tillage
• Releases less carbon into the atmosphere and maintains higher levels of soil organic matter
• Promotes seed germination and plant emergence because the tilled strips warm sooner in the spring
• Conserves soil moisture because most of the soil surface area is covered with crop residue
• Results in crop yields that are similar or higher compared with other tillage systems
• Reduces expenses, including fuel and labor, by eliminating some primary and secondary tillage
Strip Till Qualifies for NRCS Conservation Incentives
Strip tillage can be used to qualify for the Natural Resources Conservation Service (NRCS) conservation management/no-till incentive programs. To qualify for NRCS no-till incentive programs, a Soil Tillage Intensity Rating (STIR) value of 10 or less is required. STIR is a numerical value calculated using RUSLE2, a computer model that predicts long-term average annual erosion by water. This model is based on crop management decisions implemented in a field. The NRCS assigns a numerical value to each tillage operation. STIR values range from 0 to 200, with lower scores indicating reduced soil disturbance. Other benefits of low STIR values include increased organic matter content of the soil and improved water infiltration rates.
Strip Till Improves Carbon Sequestration
Soil organic matter plays a critical role in the global carbon cycle. Soil can act as both a major source for carbon released into the atmosphere and a sink to store carbon. When carbon is stored in the soil, it is not released to the atmosphere as greenhouse gases, particularly carbon dioxide (CO2) and methane (CH4). Tillage increases microbial action on organic matter stored in the soil and normally increases the rate of decomposition that changes organic carbon into CO2. Soil organic matter is directly related to soil fertility and positively correlated with agricultural productivity potential.
Besides reducing greenhouse gases, other advantages of increasing or maintaining a high level of soil organic matter include reduced soil erosion, increased resistance to compaction, increased biological activity and enhanced soil fertility. Since tillage results in soil carbon loss, identifying tillage methods that reduce the amount of carbon released into the atmosphere is important.
A comparison study of soil CO2 emissions following fall moldboard plowing, disk ripping and strip tilling conducted in 2005 in Minnesota (Faaborg et al., 2005) determined that strip tillage maintained more soil carbon than moldboard plowing and disk ripping. Disk ripping and strip tillage released 53.2 and 82.6 percent less CO2, respectively, than moldboard plowing (Figure 1). Moldboard plowing disturbed and exposed the greatest amount of soil, allowing carbon previously stored as organic matter or present as CO2 in the soil atmosphere to escape into the atmosphere.
Enhance Crop Residue Management
Residue from previous crops limits evaporation from the soil surface and maintains relatively high humidity levels in undisturbed soils at 90 to 100 percent, which are ideal for seed germination. Even with excellent seed-to-soil contact, approximately 85 percent of the water entering a germinating wheat seed is in the form of water vapor. In dry conditions, reduced-tillage planting systems preserve moisture in the seedbed, enhancing uniform germination and plant establishment.
Crop residue is also a food source for beneficial fungi, bacteria and insects. Managed properly, the beneficial aspects of maintaining high levels of crop residue with conservation tillage systems outweigh the negative aspects.
Strip till leaves most of the previous year’s crop residue on the soil surface, protecting new crop plants from wind damage during establishment and continuing to protect the soil if the crop fails to establish due to drought or flood. Crop residue readily decays and is incorporated into soil by earthworms and other invertebrates when the growing crop canopy covers the space between the rows.
Equipment components and functions
Several strip-tillage equipment manufacturers offer a variety of designs and features. Most equipment manufacturers market machines with similar features, including coulter blades, row cleaners, tillage shanks, berm-building disks and packing wheels or conditioning baskets. Some strip-till equipment designs include paired coulters or a large disk without a tillage shank.
Most strip-till equipment manufacturers in the northern Great Plains produce strip tillers with 30-inch or 22-inch row spacing. Coulter blades cut through the soil and residue ahead of the tillage shank. The coulters require mounting that allows flexible movement over stones. Some manufacturers use fluted coulters and designs with depth-control features with the coulters. Coulter size influences operation in residue; larger-diameter coulters function better in heavy residue. Parallel linkages on each row unit are desirable on strip tillers operated on soil with large stones or rolling topography because this linkage system allows row assemblies to move over stones or uneven surfaces without interrupting accurate fertilizer placement on adjacent row assemblies.
Row cleaners function to clear residue away from the front of the tillage shank and berm-building disks, leaving a clean, tilled strip. Various manufacturers use unique proprietary designs to clear the tilled area. The row cleaners usually are mounted behind the cutting coulter and a few inches ahead of the tillage shank.
Strip-till equipment needs to be designed to meter accurately and correctly place appropriate amounts of fertilizers in the tilled strips. The ability to apply one or more liquid, gaseous or dry fertilizers is an important design feature of strip-till equipment. The tillage shank penetrates and loosens soil and normally is designed with a fertilizer injection tube to allow application of gaseous, liquid or dry granular fertilizers during the strip-tillage operation. Tillage depth is dependent on the soil type and conditions and the specific crop to be planted.
Berm-building disks are mounted on each side and 6 to 8 inches behind the tillage shank. The disks can be mounted to mound the strip to promote moisture runoff and facilitate soil drying in the spring or, alternatively, mounted to create a slight depression in the soil to catch snow and rain to increase soil moisture for the next crop.
Conditioning baskets are mounted behind each shank to break soil clods and smooth the soil surface. Some manufacturers use rubber packing wheels instead of conditioning baskets. Large clumps likely indicate that the soil is too wet for tillage or adjustments are needed on equipment. Some system of smoothing the soil and breaking clumps is important, particularly if the strip tilling is done immediately prior to planting. Smoothing the tilled strips is less important if strip tilling is done in the fall because winter weather conditions smooth the soil naturally. All components of strip-till machines usually are mounted on three-point tool bar attachments directly to tractors or assembled as pull-type units with wheels. Pull-type designs are more common because they can be used with wider units. Power and
The power requirement of strip-till equipment varies depending on the equipment design, number of row units, components used, soil properties, shank depth, field conditions and operator adjustments. The power requirement listed in the equipment specifications by several strip-till equipment manufacturers ranges from 12 to 30 horsepower per row unit. However, since only about one-third of the field surface is tilled with strip-till equipment, the energy requirement is less than with conventional tillage systems.
Strip Till and GPS Guidance
Accurate equipment guidance is important for strip tillage and the subsequent planting and spraying operations, particularly in irregularly shaped fields. Strip-tillage machines can be equipped with markers to facilitate accurate spacing of rows on each new round in the field, or global positioning system (GPS) guidance can be used without markers. GPS positioning accuracy of greater than 6 inches pass-to-pass is recommended. Real-time kinematic differential correction (RTK) GPS is recommended for positioning accuracy for strip tilling.
Crop Production With Strip Till
Strip-till systems move crop residue from the soil surface over the seedbed, resulting in soil temperatures similar to conventional tillage systems. No-till systems leave residue on the soil surface over the seedbed, resulting in lower soil temperatures compared with tilled soil. University of Minnesota research in southern Minnesota (Stahl, DeJong-Hughes) shows an aggressive strip-till machine can clear away sufficient residue to promote soil warming similar to moldboard plowing in a continuous corn rotation.
In a corn-soybean rotation, soil temperatures were similar for strip till and chisel plow and lower for no till. Similarly, research in the Red River Valley (Prosper, N.D., and Moorhead, Minn.) in 2007 indicated comparable temperatures between conventional tillage and strip till (Overstreet et al., 2007). The soil temperature advantage with strip till compared with no till promotes faster plant emergence and development. This advantage is enhanced when soil temperatures are lower and approach the lower threshold for crop seed germination.
For example, early planted strip-till corn or soybeans likely will emerge sooner than in a no-till system. Earlier plant establishment normally increases crop yield and quality. Earlier emergence and stand establishment also promotes earlier crop canopy closure, reducing mid- and late-season weed seed germination, and providing a better chance for young plants to establish and withstand disease and insect pressure.
Conserves Soil Moisture
Strip tillage on the northern Great Plains in the United States conserves soil moisture by trapping winter snow and reducing evaporation and transpiration losses, resulting in more soil moisture available for plants, particularly later in the growing season during the plant reproductive stages.
When to Strip Till?
In the northern Great Plains, strip tillage with fertilizer application usually is performed in the fall after harvest, followed by planting in the spring. Fall tillage allows time for the soil in the berm to smooth during the winter and warm in the spring before crop planting. Strip tillage operations can be performed in the spring, particularly in regions with coarse-textured and lower organic matter content soils. Research conducted in 2007 on loam soil at Carrington, N.D., indicates similar crop yield between fall and spring strip tillage.
Strip-till Practices for Crop Production
Research indicates strip tillage works well with crops grown with 30-inch row spacing; however, narrower row spacings also work, but residue management is more difficult with less space for residue. Mounting strip-till units on staggered bars allows residue to flow between strip-till units in narrower row spacing. Strip tillage is used with row crops, such as corn, sugar beets, soybeans, dry beans and sunflowers.
North Dakota and Minnesota research shows corn yields are similar or higher when strip till is used compared with other tillage methods. The University of Minnesota Extension compared four tillage systems for corn following soybeans on farm fields in 2004 and 2005 (DeJong-Hughes and Vetsch, 2007). The average daily temperatures were below normal in 2004, resulting in higher corn yields with strip till compared with no till and conventional till. The 2005 growing season was warmer than average, resulting in all tillage methods producing excellent corn yields while maintaining adequate residue cover to protect the soil from erosion.
Another ongoing study started in 2007 in southern Minnesota with a continuous corn rotation shows corn yields grown in strip-tilled soil were similar or higher than with other tillage systems in all situations except when soil conditions are too wet to properly operate strip-till machines in the fall. This research uses moldboard plowing, disk ripping and strip till on a continuous corn field to study the effects of residue placement on seedling emergence, soil temperature and grain yield. The soils at the site ranged from loam to heavy clay loam, with poor internal drainage and no tile drainage.
Four years of North Dakota corn research conducted at Carrington and Fargo in 2007-10 (Endres, Franzen and Overstreet) on fall strip till shows yields were 6 bushels per acre greater than with conventional till. At Carrington, corn was grown in 30-inch rows on a loam soil, and at the Red River Valley sites in 22-inch rows.
Dry edible beans
Dry edible bean production using strip till significantly reduces soil erosion potential compared with conventional tillage. Moisture conservation is an additional benefit in arid areas. The obvious disadvantage with strip-till beans is changing harvest strategies. Strip-till edible beans require direct harvest, which potentially increases harvest loss. However, reduced harvesting equipment, time and labor, and potentially improved seed quality may offset increased harvest losses.
Preliminary data in 2007 and 2009-10 by NDSU researchers at Carrington with fall strip-till pinto beans indicate potential for similar seed yield compared with conventionally tilled bean, and greater than with no till.
Production advantages may be gained with strip till for soybeans in arid areas because of moisture conservation, or if the crop is planted early because of warmer soils compared with no till. NDSU research during 2005-10 indicated soybean yields of 2 bushels more per acre with strip till compared with conventional till or no till (Endres, Franzen and Overstreet).
The University of Minnesota Extension conducted research in southern Minnesota comparing soybean yields in a rotation following strip-tilled corn in chisel-plowed, no-till and strip-till fields (DeJong-Hughes, Stahl). The yields in 2006 and 2008 were similar, reflecting soybean versatility in various tillage systems. In 2007, the no-till fields yielded less than the chisel-plowed and strip-tilled fields.
NDSU strip-till research with sugar beets grown in 22-inch rows was conducted during 2005-07 at several Red River Valley locations (Franzen and Overstreet, 2007). Sugar beet yields were similar among tillage systems in two of the three years. Strip-till yields were approximately the same as conventionally tilled plots.
Sunflower production using strip till is limited in the northern regions of the United States. Strip-till research trials and commercial production in Kansas show some success for sunflowers (Olson et al., 2005). Four years of NDSU strip-till research at Carrington during 2006-09 by Endres have indicated similar sunflower performance for seed yield and quality among tillage systems, including strip till.
General Fertilizer Considerations
Phosphorus and potassium can be band-applied during strip-till operations. Banding phosphorus and potassium allows for a rate reduction of one-third compared with broadcast application on a medium or low-testing soil (University of Minnesota Fertilizer Recommendations, 2001). Phosphorus and potassium also can be applied to crops as starter fertilizer with the planter.
Nitrogen also can be applied using strip-till equipment. However, fall nitrogen application is not recommended in sandier, lighter soils.
Nitrogen can be applied as a starter fertilizer and side dressed later in the growing season. Carrington, N.D., research conducted in 2010 (Endres, Hendrickson, Glatt) show similar plant emergence and stands among tillage systems and fertilizer placement methods. However, among strip-till treatments, in-furrow fertilizer had lower plant densities compared with other methods of applying fertilizer. Grain yield and quality were similar among treatments. However, among strip-till treatments, seed yield was higher with fall deep-band followed by spring in-furrow fertilizer compared with other fertilizer treatments.
The Oakes Irrigation Research Site conducts research on growing continuous corn and corn following soybeans in a strip-till system to determine efficient nitrogen fertilizer rates. Results from these studies can be used to evaluate likely corn yield and quality for various fertilizer rates (W. Albus, L. Besemann and H. Eslinger. 2010). More information is available online at www.ag.ndsu.nodak.edu/oakes/oakes.htm.
Economics of Strip Till
Investment costs vary depending on the type of equipment, size and accessories purchased. Total investment will run between $3,000 and $4,000 per row. Based on machine width, the investment will run from $1,600 to $2,000 per foot.
Ownership costs are heavily influenced by the amount of use per year and the number of years the equipment can be used. The annual ownership cost of a 24-row tiller is estimated to be $6,306, or $6.31 per acre, based on an estimated annual use on 1,000 acres per year. The estimated annual ownership cost of a six-row tiller would be $1,951, or $4.88 per acre, based on annual usage of 400 acres.
Operating costs include fuel, lubrication, repairs and labor. The total would be $3.16 per acre for a 24-row machine and $4.75 per acre for a six-row machine. The total cost per acre for the 24-row equipment, including the power unit, is estimated to be $11.74 per acre. The total cost for the six-row equipment and power unit is estimated at $12.34 per acre. The smaller equipment has higher operating and tractor ownership costs but lower fixed costs.
Converting to a strip-till method of production from conventional tillage will eliminate expenses associated with primary and secondary tillage. If the other tillage equipment is not sold, you need to include the depreciation and interest costs on that equipment when calculating the true cost of strip tilling.
Additional costs to strip tillage include machinery ownership and operation costs, chemical burn-down and a ground-spraying operation. Cost reductions include eliminating chisel plowing and field cultivation. The estimated change in per-acre costs to convert to strip tilling using these costs indicate an increase of $10.63 per acre for a 24-row machine and $11.63 per acre for a six-row machine.
Management Tips for Strip Tillage
• Match the strip-till row width with the planter row width.
• Leave corn stubble standing for maximum air movement and less matting of residue. Build strips between the previous crop rows.
• For the greatest soil warm-up and seed-to-soil contact, strip tillage should be performed in the fall.
• In cooler, fine-textured soils, strip-till equipment should clear the berm to less than 10 percent residue for faster soil warming in the spring.
• In high-moisture conditions, build berms approximately 3 inches high in the fall so they are at least 1 inch high by planting. In arid conditions, berms can be depressed to collect winter snow.
• The economic advantages of strip till are improved if banding phosphorus and postassium fertilizer with the fall strip operation.
• Avoid slopes of more than 7 percent without contouring; otherwise, risk of soil erosion can occur in tilled strips.