Influence of No‐Till on Soybean Cultural Practices

Soybean [ Glycine max (L.) Merr.] no‐till culture has greatly expanded with implementation of conservation provisions of the 1985 Farm Bill. Compared with other tillage systems, no‐till requires burndown or early preplant herbicides to control weed growth occurring before planting. Other unique requirements are combine attachments to uniformly spread residue and a rugged enough planter to provide precise seed placement. Most other cultural practices are similar to those used with full‐width tillage systems. No‐till does have some tendency to require higher seeding rates and a greater need for seed treatment pesticides. Injection of nutrients or occasional use of tillage can also make no‐till nutrient management much easier. In 18 locations throughout the USA, no‐till yields were highest on soils prone to early season drought, while yields were less on more favorable soils. In none of these locations did yield response to no‐till improve significantly with advancement of time. No‐till is often the least‐cost system where highly erosive lands mandate extreme erosion control or where yields are higher without tillage. On soils yielding less with no‐till, economics favor use of tillage. A downside of no‐till has been use of greater amounts of pesticides that are more vulnerable to surface runoff. Integrated weed management systems offer potential to greatly reduce herbicide use if combined with small amounts of row cultivation. Incorporation of herbicides, while maintaining surface cover, offers much of no‐till's soil erosion control, yet provides greater potential for reduced herbicide runoff. Research Question Farmers interested in reducing soil erosion and increasing profits have been growing soybeans with no‐till culture for over 20 yr. As Conservation Provisions of the 1985 Farm Bill have been implemented, use of no‐till soybean culture has greatly expanded. Questions arise as to what cultural practices have to change with the switch to no‐till; which soils and crop rotations are most suited to no‐till; what impacts no‐till has on economic returns; and what future management challenges exist as farmers adopt less intensive tillage systems? Study Approach Over 40 research reports published during the past 6 yr were reviewed. These reports centered around no‐till and included small plot agronomic research results as well as survey research reporting on actual farmer‐use patterns. Studies from throughout the major North American soybean production regions were included. Applied Questions What cultural practices have to change when tillage is eliminated? No‐till weed programs include normal herbicide treatments to control weeds in the growing soybean crop. In addition, no‐till requires burndown or early preplant herbicides to control weed growth occurring before planting. Combine attachments to uniformly spread residue and planters or drills rugged enough to provide precise seed placement in firm soils are other unique requirements. Most other cultural practices are similar to those used with full‐width tillage systems. If planting into high residue and cool seedbeds, it may also be wise to consider using seed treatment pesticides and to increase seeding rates to 200 000 to 225 000 seeds/acre. Injection of nutrients or occasional use of tillage will make no‐till nutrient management much easier. Which environments are most suited to no‐till? Using crop rotation will increase the range of soils adapted to no‐till. In research plots from Minnesota to Alabama, no‐till produced yields 2.5 bu/acre higher than reduced‐till and nearly 5 bu/acre higher than mold‐board plow on sandy soils or soils having a restrictive pan near the soil surface. In contrast, on deep favorable soils, no‐till yields averaged about 3 bu/acre below moldboard and 2 bu/acre below reduced‐till. In none of 18 locations examined did yield response to no‐till improve with the number of years no‐till was used. Thus, there is little evidence that soils not initially favorable to no‐till will “adapt” to no‐till. What impact does no‐till have on profits? Eliminating tillage reduces tillage, fuel, and time costs while herbicide and other variable costs increase. Where yields are higher with no‐till or Full scientific article from which this summary was written begins on page 43 of this issue. where extreme erosion control is mandated, no‐till is generally the most profitable tillage system. On soils yielding less with no‐till, economics generally favor use of tillage. How much is pesticide use in no‐till increased, and can it be reduced? Growth in no‐till acreage has caused a parallel increase in pesticide sales. Compared with farmers using moldboard tillage, no‐till northern soybean producers used 27% more pounds of active herbicide ingredient while no‐till southern producers used 41% more. Number of pesticide applications also increase as farmers move toward less intensive tillage systems. These trends run counter to public and legislative mandates asking for less pesticide use. Integrated weed management systems in rowed soybeans show strong promise to reduce herbicide use by 50 to 75% yet provide equal or higher yields (Fig. ). These systems combine minimal mechanical cultivation with herbicide banding or with reduced herbicide application rates. Are there management options to conserve soil yet reduce chemical contamination? Two‐year average soybean yields obtained with herbicide treatments of full‐rate broadcast, half‐rate broadcast, full‐rate band, and half‐rate band treatment. All were used with 0, 1, or 2 cultivations. image Many important agricultural chemicals, particularly herbicides, move off‐site in soil solution rather than attached to soil particles. No‐till requires surface application of chemicals and is more vulnerable to surface runoff than systems using incorporation. New tillage machines now provide the option of thoroughly incorporating chemicals while maintaining high levels of surface cover. These limited tillage systems eliminate the need for burndown herbicides, provide considerable soil erosion control, and mix chemicals in the soil profile where they are less suceptible to runoff. This concept can be used with drill as well as rowed soybeans. Effect of tillage system on soybean yields when grown in a corn/soybean rotation. Summary of 18 research reports published in the last decade. Tillage system Favorable soils Droughty/Pan soils ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ bu/acre ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Moldboard plow 44.0 33.2 Reduced‐till 43.1 35.6 No‐till 41.1 38.1 Locations 11 7 Location‐years 86 53 This moldboard yield is based on only four locations, but if the number of locations is restricted to four for all tillage systems, mean yields are essentially the same as shown.