16.3: Which Tillage System is Right for Your Farm?

The correct choice of tillage system depends on climate, soils, cropping systems and the farm’s production objectives. Although plowing may still be appropriate in some cases, one should strive to minimize tillage intensity and the number of passes, and to leave plentiful amounts of residue on the surface. One factor that is often not recognized: a good conservation planter (figures 16.7 and 16.8) may be your best tillage tool. It doesn’t require the preparation of a smooth seedbed, can handle a lot of residue and allows you to reduce or eliminate tillage passes. Some general guidelines for tillage selection are as follows.

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 by 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. The transition period is critical, as discussed above, including possible compaction and nitrogen availability issues as well as changes in the 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 after a few years, especially if perennials are under control, because buried weed seeds are no longer tilled up. Mulched cover crops, as well as newly designed mechanical cultivators, help provide effective weed control in high-residue systems.

Frost Tillage!

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 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 entered the soil but before it has penetrated more than about 2 inches (5 centimeters). 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 about compaction from heavy equipment (see also Figure 12.2).

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, yield reductions may occur in the first years. As discussed in Chapter 6, dense soils have a relatively narrow water range in which plant roots can grow well, compared to uncompacted soil. When it is dry, roots have a more difficult time making their way through the soil, and when it is wet, roots tend to have less air. Compaction, therefore, makes crops weaker and more susceptible to pest pressures. In highly weathered tropical soils in Brazil (oxisols), new concerns have arisen with compacted layers developing in no-till soils that are limed to correct the high acidity. The change in soil pH causes dispersion of clay in natural aggregates, washing into a lower soil layer that becomes dense and impenetrable for roots.

Tools like strip tillers provide compaction relief in the row while maintaining an undisturbed soil surface. They are generally the best approaches for farmers who plowed for many years and want to reduce tillage intensity without the challenges of transitioning to pure no-till. Over time, soil structure improves, unless re-compaction 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.

The two greatest challenges for organic farms are weeds and nitrogen. As with traditional farms before agrichemicals were available, reduced tillage is challenging and full-width tillage may be necessary for weed control and incorporation of manures and composts. 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 (Figure 16.6, right) 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 heavily rely on organic inputs to maintain fertility.

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 or 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 strip-till, 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 no-tilled may occasionally need a full-field tillage pass. Recent research in Nebraska and Australia indicates that occasional tillage, also called strategic tillage, does not have negative impacts on soil health. But it should only be done for a well-identified purpose like weed or insect control, incorporation of immobile amendments, or compaction relief (say, after a harvest during a wet period).

Tillage is one of the few practices that can decrease populations of the arthropod Symphylans. This pest feeds on root hairs and small roots of many crop plants, and uses large pores and channels to move through the soil (see box in Chapter 8). In some cases it can be controlled by making a fine seedbed, which is something we otherwise discourage because of its detrimental effects on soil crusting and water infiltration. So if strategic tillage is used, it should be done on a very limited basis (once every 5–10 years) and is best accomplished with tools that still leave surface residue. A flexible tillage program may offer benefits, but be aware that any tillage 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 to 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 strip-till or 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. A no-till system has the great advantage of saving time because there is no need for prior tillage passes before planting. However, in cool, humid climates the high residue levels and lack of soil loosening slows soil drying and warming, and may require a short delay in planting.

Tillage is also not recommended when the soil is very dry because it may be too hard, clods may be very large or 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 succeed better if traffic can be restricted to dry conditions or to fixed lanes within the field. Even strip-till methods will work better if fixed lanes are used for heavy harvest equipment.