Below are the performance indicators used in Table 2 to summarize the tillage recommendations for various cropping systems in the two sub-regions of the basin: the eastern "loess (Karst)" area where loess soil overlies fractured bedrock, and the western "loess-cap (till)" area where loess soil overlies glacial till deposits.
1) Recommended with good management
No yield penalty is expected if the farmer observes all relevant recommended management practices for high residue systems.
2) 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.
3) Reduced yield potential
The potential exists for substantially reduced yields, especially on poorly drained soils in wet years.
4) Inadequate residue to minimize erosion
Less than 30 percent of surface is covered after planting. Highest yield may be obtained, however.
Table 2 shows the residue management/yield performance indicators for continuous corn and a corn-soybean rotation using the different tillage systems described earlier. Management to maintain adequate levels of surface residue is more difficult for the corn-soybean rotation. This is clearly shown by the "1/4" indicator for the chisel plow-plus and one-pass systems; in these cases 1 indicates "recommended following corn" and 4 indicates "inadequate residue following soybeans." However, yield potential is likely to be compromised more easily in continuous corn with some of the very reduced tillage systems.
Table 2. Matrix of residue management/yield performance indicators for continuous corn and a corn-soybean rotation grown on loess (Karst) soils and on loess-cap soils over glacial till.
1/ For corn following silage corn, inadequate amounts of surface
residue will exist for all tillage systems.
2/ No data specific to these soils. Estimates are based on information from somewhat similar glacial till soils.
3/ Tillage recommendations for these soils are also appropriate for the soils just to the west of MLRA 104.
Annual residue production is high and some degree of tillage is needed to prevent excessive build-up of surface residue, especially in more poorly drained areas. After corn that is harvested for silage, very reduced or no-till systems are needed to maintain adequate surface residue cover.
In the more well-drained Karst region, spring disk, strip-till and Rawson tillage systems produce yields comparable to chisel plowing. All these tillage systems leave adequate residue for erosion control. In the Karst region, a no-till system may result in an average yield penalty of 2 to 6 percent, but cost-savings from a well-managed no-till system may offset the yield penalty. In the loess-cap till region, moldboard plowing produces the highest yields, but leaves inadequate residue cover. This tillage system, in combination with riparian buffers and grass waterways as needed to retard runoff, may sometimes be appropriate on level fields with poor internal drainage where the potential for erosion is relatively low. Slight yield reductions occur with the chisel plow system, which may be partly offset by lower production costs ($7/A to $12/A, according to 1996 University of Minnesota data). More significant yield reductions result from no-till and strip-till systems in continuous corn in this loess-cap till region.
Maintaining 30 percent surface soybean residue after planting corn often is a challenge. Strip-till and the Rawson system leave adequate residue and prevent yield losses if managed well. If the field cultivator is used for one-pass spring tillage before planting, equipment must be carefully outfitted and operated to avoid burying too much soybean residue. In the more well-drained Karst region, yield penalties associated with very reduced tillage are generally small or nonexistent. However, substantial yield reductions can occur in some years, especially under cooler and wetter growing conditions or after several years of continuous no-till farming. On more poorly drained soils in the loess-cap till region, results show slightly lower corn yields (3-8%) with no tillage compared to chisel plowing, the highest-yielding treatment. Savings in production costs with excellent management of a no-till system might offset slight yield reductions. Very small yield differences occurred among the chisel, strip-till and field cultivation systems.
Very reduced tillage and no-till systems can be used to maintain high surface residue levels without incurring significant yield reduction in the Karst region. However, excellent management is needed to optimize performance of ridge-till and no-till systems. In the loess-cap till region, chisel plowing and spring disking produce yields very similar to moldboard plowing, while leaving much more crop residue on the surface. No-till systems resulted in average yields similar to other tillage systems in long-term field studies in Nashua, Iowa, within the same soils region. However, field trials in Waseca indicate that a very slight yield penalty (maximum of 5%) may result from no-till planting or drilling on glacial till soils.
Fall-killed alfalfa that was later planted to corn using no-till methods produced yields comparable to corn planted following primary tillage. However, where alfalfa was not fall-killed, no-till corn planting resulted in large yield losses compared to tilled treatments, while use of the chisel plow or disk in the spring resulted in small yield reductions compared to moldboard plowing.
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