Tillage Recommendations for South-Central Minnesota
Below are the performance indicators used in Table 1 to summarize the tillage recommendations for both corn and soybeans in south-central Minnesota based on the research described in this publication.
1) Recommended with good management
No yield penalty is expected if the farmer observes all relevant recommended management practices. Surface residue coverage may be inadequate following soybean, however.
2) Excellent management required
A slight yield penalty is possible, even if all recommended management practices are observed. Above average crop management is needed to ensure good performance.
3) Reduced yield potential
None of the tillage systems shown in Table 1 fit into this category in a corn-soybean rotation. However, the potential exists for substantially reduced yields when multiple years of corn are coupled with one year of soybean, i.e., a corn-corn-soybean rotation.
Table 1. Residue management/yield performance indicators for corn and for soybeans in a corn-soybean rotation on soils with slopes <4% and >4% in southcentral Minnesota.
4) Inadequate residue to minimize erosion Less than 30 percent of the soil surface is covered after planting. Greatest yield may be obtained, however. Table 1 shows the residue management/yield performance indicators for both corn and soybean on soils with slopes <4% and slopes >4% using the different tillage systems described earlier. Maintaining adequate levels of surface residue with tillage management is more difficult for corn after soybean than for soybean after corn. This is illustrated by the “4” indicator appearing frequently for corn, especially on slopes >4%. Because of logistical and practical reasons, SFC, DZT, and ST are not applicable (N/A) for soybeans following corn.
Corn following soybeans
Maintaining 30 percent surface coverage after planting corn is challenging whenever full-width tillage practices are used before planting, especially if soybeans are planted in 30” rows. The MP+, CP+, and SD tillage systems will not leave adequate residue to minimize soil erosion and will often not result in greater yields than other tillage systems. Thus, these tillage systems are not recommended with the exception of when broadcast manure needs to be incorporated on 0-4% soils or if severe surface soil compaction occurred during the last year. In those situations, using a CP+ tillage system may be helpful. The SFC system is commonly used to destroy earlyemerging weeds, and level the field to prepare the seedbed. To avoid burying too much residue, the field cultivator must be carefully configured and operated. The SFC tillage system is appropriate on very level fields where vulnerability to erosion is minimal, but as slope increases and erosion potential increases, SFC tillage becomes problematic. Strip tillage, RT, and DZT leave adequate amounts of residue and prevent yield losses if managed well, and thus are recommended on fields with slopes of preferably <4%. No tillage maintains excellent surface residue coverage, but yield penalties can occur, especially if NT has been practiced for both corn and soybeans the previous few years and a dense residue mat covers the soil surface. Our experiments suggest that some form of minimal residue disturbance in a continuous NT corn-soybean rotation is necessary to optimize yield without compromising residue cover. Practices such as inseason row cultivation, coulter carts on soybean drills, fullwidth rolling coulters that slice the residue and surface soil, or full-width rolling harrows that stir the residue and surface soil may be the “extra” management step that enables more consistent, better performance of the continuous NT system across a range of soil environments and past tillage systems. They may also enable the soil to warm slightly faster and break surface sealing, a concern often expressed by NT farmers.
Residue management to achieve high corn yields and minimize soil erosion is a major challenge in a corn-soybean rotation on slopes >4%. First, the amount of soybean residue is not sufficient to limit runoff and erosion in many instances. Second, any simple tillage practice results in some “downhill” movement of soil and over the long term, this “erosion” reduces soil productivity. Thus, NT is the system of choice for greatest soil productivity and profit on these steeply sloping fields. But with excellent management, ST and RT may also work on some landscapes. When slopes exceed 6% or are sufficiently long, growers are encouraged to employ other conservation practices, i.e., terraces and grass waterways with NT, or switch to cropping systems that produce more residue or maintain season-long ground cover.
Soybeans following corn
Because substantially more residue exists following corn, there is somewhat greater flexibility in tillage choices. Moldboard plow-plus is not recommended, but full-width CP+ and SD are appropriate for slopes <6%. When fertilizer P and K or manure are to be incorporated, CP+ is recommended with care not to chisel directly up and down the slopes. Residue coverage can also be maintained with RT and NT, with NT having the advantage of narrow rows, more row-direction flexibility, and perhaps higher yields. On slopes >4%, NT is highly preferred. Similar to corn following soybeans, some minimal form of surface residue/soil disturbance may be helpful to achieve optimum performance of continuous NT.