Factors to Consider when Making Tillage Decisions
Selecting the best tillage system should involve a set of considerations much like those a farmer uses when selecting a hybrid. Often, certain hybrids are chosen to meet specific conditions or needs. A similar approach should be taken for tillage. Factors that should be considered in the tillage selection process are:
The amount of residue present in a field before tillage depends on the crop previously grown and the level of production. Corn generates considerably more residue than soybeans, thus it is easier to maintain higher residue levels following corn with a variety of tillage systems. The durability of the residue is also crop dependent. Soybean residue is considered to be “fragile” or in other words is easily destroyed and/or rapidly decomposed. Maintaining adequate residue cover can be a problem following soybeans, especially when planted in wide rows or if poor yielding. Corn residue, on the other hand, is considered “non-fragile” and breaks down quite slowly. Because a corn-soybean rotation generates less residue than corn rotated with most other crops, tillage flexibility is greater. In summary, both crops need to be considered when making tillage decisions for a corn-soybean rotation.
Erosion potential – Erosion potential mostly depends on the length and steepness of slope and soil texture. If erosion potential is high, conservation tillage systems are essential. Fields or acres considered to be highly erodible land (HEL) may require large reductions in tillage to minimize soil erosion and to maintain soil productivity. On the other hand, flat fields have a lower erosion potential. Sediment loss can be a problem on these fields, however, if soil detachment occurs during intense rainfall and there are open tile inlets or other channels that serve as direct conduits for the sediment-laden runoff water to quickly reach drainage ditches, streams, lakes, or other surface water bodies.
Internal drainage – Poorly drained soils warm up more slowly and usually require more tillage than do welldrained soils. With high levels of residue, the poorly drained soils often remain cool and wet too long for intolerant crops such as corn, resulting in decreased yields. System tiling helps on soils with poor internal drainage but may not be enough to ensure consistent success with little or no tillage and high levels of crop residue.
Surface soil compaction – Field activities conducted under wet conditions often result in surface compaction. Short, yellow, and spindly corn and short soybeans are evidence of this compaction, which is highly visible in field headlands, spots within fields, and wheel tracks. Primary tillage is often needed to alleviate surface soil compaction. Without primary tillage, good seed-to-soil contact and rapid root development in the spring will be more difficult when soils are compacted.
Management of fertilizer and manure nutrients is critical to the success of conservation tillage. High soil fertility levels must be established prior to initiation of a conservation tillage system. Moderate-to-low soil fertility will intensify yield loss and diminish the probability of longterm success.
Nitrogen – Nitrogen (N) is the most important nutrient for corn production. Nitrogen needs to be managed carefully for efficient use by the crop and for minimizing environmental risk of runoff and leaching. Surface-applied N fertilizer, such as granular urea and UAN (urea-ammonium nitrate) solution, should be incorporated mechanically or by rainfall within three days of application to eliminate loss of N to volatilization. Any significant loss of nitrogen to the atmosphere or by runoff or leaching will reduce yield and profitability. Alternative methods of N application in very reduced tillage systems include: (1) applying urea 4 to 6” to the side of the row with a coulter at the time of planting and (2) applying UAN 2 to 3” from the row at planting followed by coulter-injection of UAN midway between the rows at the 3- to 8-leaf stage. Anhydrous ammonia injected into the soil disturbs the soil surface and provides a minimum tillage pass without destroying the conservation tillage practice. For additional information see University of Minnesota Extension Service publications: Fertilizing Corn in Minnesota and Fertilizer Management for Corn Planted in Ridge-Till or No-Till Systems as listed in the Resource Section at the end of this publication.
Phosphorus (P) and potassium (K) – Soil testing should be used to maintain fertility at optimum levels. Fields testing low in P or K should be brought to high levels before implementing conservation tillage systems. For optimum crop production with all tillage systems, soil test P should be at least 16-20 ppm with the Bray test and 12-15 ppm when the Olsen extractant is used, and K needs to be 121- 160 ppm. Soil testing should be done every two to three years to maintain soil fertility levels in reduced-tillage fields. If additional nutrients are needed, their placement in relation to the crop is important. Placing the fertilizer close to the corn seed gives the most efficient P and K uptake. Recommended application methods include: (1) starter fertilizer or (2) banding 4 to 7” deep randomly in no till or full-width tillage systems, within the ridge for ridge tillage, or in a residue-free strip for strip-till (zonetill) systems. With no-till, ridge-till, or strip-till systems, starter fertilizer should be used for corn when Bray soil test P is <25 ppm. Broadcast applications of fertilizer are best following corn where some tillage can be used to incorporate the fertilizer and maintain adequate crop residue levels for erosion control. Soluble phosphorus can be transported to surface waters if P fertilizer is broadcast applied to no-till fields or is spread on grass waterways.
Manure – Livestock manure should be incorporated for maximum benefit. However, incorporating manure when in a corn-soybean rotation presents a real dilemma. Greatest nutrient (nitrogen) utilization occurs in corn when manure is applied after soybeans; however, the small amount of “fragile” soybean residue can be completely destroyed in the incorporation process. Incorporating manure following corn with either a chisel plow or by injection or disk-covering of liquid manure allows for good residue management, but nitrogen utilization by the following soybean crop is inferior to corn. Liquid manure offers more tillage flexibility because it can be injected or disk-covered before planting. Fall application of liquid manure to sloping no-till soybean ground is not recommended unless extreme care is taken to avoid water erosion in the tilled injection or incorporation zones. Solid manure sources offer little flexibility. They should be incorporated by chisel plowing corn ground ahead of soybean or by chiseling very level soybean ground. Solid manure sources should not be applied to sloping land following soybeans.
When a farmer begins using conservation tillage, starting with a relatively weed-free field greatly improves the likelihood of successful long-term weed management. Using reduced tillage on a weed-infested field requires greater weed management and can become very costly. In fields where tillage has been reduced and crop residue levels have increased, weed pressure may increase and shifts in weed species may occur. Post-emergence herbicide applications have become the primary weed control program. Timing of post-applications is critical and multiple applications may be needed. A wide range of effective post-emergence herbicide treatments is available today for crops grown with reduced tillage. As a result of equipment improvements, in-season row cultivation can be used with herbicides in fields with high crop residue. Row cultivation can be an effective tool for controlling problem weeds.
Many of the newer generations of planters and drills have options available to handle higher crop residue levels. Most planter tool bars sold today can be modified with row cleaners and/or coulters to ensure optimum seed-tosoil contact. Modern no-till drills are designed to clear residue while dropping and covering seeds as small as alfalfa at precise depths for exceptional contact with the soil, which results in good plant emergence. In recent years, narrow row spacing has become more prevalent and can be used with conservation tillage. Farmers can modify their planters with row cleaners and/or fluted coulters at a relatively low cost. Also, equipping the planter with starter fertilizer attachments increases the potential for success in high-residue situations.
Reduced tillage risks and benefits
Many farmers are reluctant to farm with greater amounts of crop residues on their fields. They fear yield loss and don’t like the appearance of a crop growing in heavy residue. Their perception is influenced by several factors: 1) upsetting the landlord, business partner or a family member; 2) ridicule from neighbors; 3) lack of crop management skills to adopt conservation tillage; 4) recent purchase of equipment for aggressive tillage; and 5) onfarm research results. Overcoming the aesthetics of crop emergence in a field covered with residue takes patience, time, and an understanding of the system. Farmers who have used conservation tillage learn to appreciate the "look" of a crop growing in higher levels of residue and the lower cost of production.
When evaluating potential yield loss that may result from adopting a very high-residue system such as no-till, it is important that farmers compare differences in production costs as well as expected differences in yield to arrive at a sound business management decision. Each farm will have its own production costs and risks based on equipment, management skills, and crop rotation. The long-term yield information presented later in this bulletin will help farmers decide on an appropriate tillage system(s) as they consider their field- and farmspecific factors.