The correct choice of tillage system depends on climate, soils, cropping systems, and the farm’s production objectives. Some general guidelines are provided in the following paragraphs.
Conventional grain and vegetable farms have great flexibility for adopting reduced tillage systems, because they are less constrained by repeated manure applications (needed on livestock farms) or mechanical weed or rotation crop management (needed on organic farms). In the long run, limited disturbance and residue cover improve soil health, reduce erosion, and boost yields. A negative aspect of these systems is the transition period, as discussed above, and changes in weed spectrum from annual to perennial plants. This may require different timing and methods of weed control. Combining reduced tillage with the use of cover crops frequently helps reduce weed problems. Weed pressures typically decrease significantly after a few years, especially if perennials are under control. Mulched cover crops, as well as newly designed mechanical cultivators, help provide effective weed control in high-residue systems. Some innovative farmers use no-till combined with a heavy cover crop, which is mowed or rolled to create a thick cover mulch (figure 16.7).
Farmers need to be aware of potential soil compaction problems with reduced tillage. If a strict no-till system is adopted on a compacted soil, especially on medium or fine-textured soils, serious yield reductions may occur. As discussed in chapter 6, dense soils have a relatively narrow water range in which plant roots can grow well, compared to their ability to grow in uncompacted soil. When a compact soil is completely dry, roots have a difficult time making their way through the soil, and when a compact soil is wet, roots tend to have less air. Crops growing on compacted soils are more susceptible to inadequate aeration during wet periods and to restricted root growth and drought stress during drier periods. Compaction, therefore, reduces plant growth and makes crops more susceptible to pest pressures.
Readers from temperate regions may have heard of frost seeding legumes into a pasture, hayfield, or winter wheat crop in very early spring, but perhaps not of tilling a frozen soil. It seems a strange concept, but some farmers are using frost tillage as a way to be timely and reduce unintended tillage damage. It can be done after frost has first entered the soil, but before it has penetrated more than 4 inches. Water moves upward to the freezing front and the soil underneath dries. This frozen state makes the soil tillable as long as the frost layer is not too thick. Compaction is reduced because equipment is supported by the frozen layer. The resulting rough surface is favorable for water infiltration and runoff prevention. Some livestock farmers like frost tillage as a way to incorporate or inject manure in the winter without concerns for compaction from heavy equipment.
In poorly structured soils, tools like zone builders, strip tillers, and zone-till planters provide compaction relief in the row while maintaining an undisturbed soil surface. Over time, soil structure improves, unless recompaction occurs from other field operations. Crops grown on fields that do not drain in a timely manner tend to benefit greatly from ridging or bedding, because the sensitive seedling root zone remains aerobic during wet periods. These systems also use controlled traffic lanes, which greatly reduce compaction problems, although matching wheel spacing and tire widths for planting and harvesting equipment is sometimes a challenging task, as we discussed in chapter 15.
For organic farms, as with traditional farms before agrichemicals were available, reduced tillage is challenging, and full-field tillage may be necessary for mechanical weed control and incorporation of manures and composts. After all, the two greatest challenges of organic crop production are weeds and nitrogen. Organic farming on lands prone to erosion may, therefore, involve trade-offs. Erosion can be reduced by using rotations with perennial crops, gentler tillage methods like spaders and ridgers, and modern planters that establish good crop stands without excessive secondary tillage. Soil structure may be easier to maintain on organic farms, because they use organic inputs heavily.
Livestock-based farms face special challenges related to applying manure or compost to the soil. Some type of incorporation usually is needed to avoid large losses of nitrogen by volatilization, and losses of phosphorus and pathogens in runoff. Transitions from sod to row crops are also usually easier with some tillage. Such farms can still use manure injection tools with zone and strip tillage, thereby providing compaction relief while minimizing soil disturbance. As with organic farms, livestock operations apply a lot of manure and compost and naturally have higher soil health.
Rotating Tillage Systems
A tillage program does not need to be rigid. Fields that are zone-, strip-, or no-tilled may occasionally need a full-field tillage pass to provide compaction relief or to incorporate amendments like lime. But this should be done on a very limited basis. Although a flexible tillage program offers a number of benefits, aggressive tillage with a moldboard plow and harrows can readily destroy the favorable soil structure built up by years of no-till management.
Timing of Field Operations
The success of a tillage system depends on many factors. For example, reduced tillage systems, especially in the early transition years, may require more attention to nitrogen management (often higher rates are needed initially, lower rates eventually), as well as weed, insect, and disease control. Also, the performance of tillage systems may be affected by the timing of field operations. If tillage or planting is done when the soil is too wet (when its water content is above the plastic limit), cloddiness and poor seed placement may result in poor stands. Also, a zone building operation done in plastic soil results in smeared surfaces and an open slot that does not allow for good seed-soil contact. A “ball test” (chapter 6) helps ensure that field conditions are right and is especially important when performing deeper tillage. Tillage is also not recommended when the soil is too dry, because it may be too hard, clods may be very large, and excess dust may be created, especially on compacted soils. Ideal tillage conditions generally occur when soils are at field-capacity water content (after a few days of free drainage and evaporation), except for fine-textured clays, which need more drying (see chapter 15).
Because soil compaction may affect the success of reduced tillage, a whole-system approach to soil management is needed. For example, no-till systems that involve harvesting operations with heavy equipment will succeed only if traffic can be restricted to dry conditions or fixed lanes within the field. Even zone-tillage methods will work better if fixed lanes are used for heavy harvest equipment.