Tillage is not an important management factor for increasing soybean yield and other management practices such as planting date, row spacing, and cultivar selection are more important. The key issues for deciding whether tillage is important is to have a good understanding of field conditions in terms of drainage and soilborne pathogens. Understanding these conditions is essential in determining the need for tillage in your cropping system. Even with improved plant genetics there has been basically no consistent change in response to tillage with some recent studies indicating increased yields under no-tillage conditions. Current planters and herbicides now allow us to plant and control weeds without tillage practices and variety selection and fungicide seed treatment can further enhance the profitability of no-tillage systems.
Tillage is not a requirement for high yields
Tillage is expensive, time consuming, increases soil erosion, and in many cases is not necessary to maximize soybean yield. Yet adoption of no-tillage systems has been slow because the common thought is that soybean growth and yield are reduced in these systems. Cold soils, weed control, increased crop residue, seedbed preparation and more rapid soybean emergence have been cited as reasons to use tillage prior to soybean planting. Each of these points is true; however, each has little to no affect on soybean yield.
During the 2004 growing season approximately 62.4 million acres in the United States had no tillage conducted for crop production. Specifically in Iowa there were 5.2 million acres of no-tillage production with approximately 66% of that accounted for by no-tillage soybean production. Total soybean acres in 2004 were 10.2 million and around one-third of those acres were no-tillage systems. This value has continued to increase in the past years, increasing 5% since 2002. The driving forces behind the increased no-tillage acres have been the requirements to adopt conservation practices to control soil erosion and increased fuel and labor prices. Improved planters and glyphosate tolerant soybeans have made no-tillage production practices a viable production system in Iowa.
Most of the research conducted in the Midwest has shown that soybean in general does not respond to tillage and other management practices should be given more consideration for gaining maximum yield potential. This is not to say that all tillage should be abandoned. In Iowa where some fields, particularly in the north central part of the state, are poorly drained and remain wet in the spring some tillage in the spring may be necessary to get the seed bed ready for planting. For the majority of the acres in Iowa no-tillage systems are a good management choice to reduce costs and improve erosion control without sacrificing yield.
Some of the potential problems with no-tillage are cold soils and poor seedbed conditions for planting. Research trials conducted in both Wisconsin and Minnesota have documented that soil temperatures can be four to five degrees colder than conventional systems and that emergence can be delayed and plant populations reduced. These alterations in seedling emergence have little effect on soybean yield and both studies documented that there was less than a three bushel yield difference between tillage and no-tillage systems. Eliminating tillage does have the advantage in some years of conserving moisture and research has shown that when soil moisture is limiting no-tillage systems provide a yield advantage. Poor seedbed conditions can be overcome with the proper selection of equipment that is heavy enough to plant through the crop residue.
Physiological response to tillage system
How it is that soybean is able to be competitive in no-tillage systems? Research has shown that in no-tillage environments crop growth rate is reduced early in the season prior to the V2 growth stage. The advantage that conventional tillage systems have in accumulating more biomass (higher crop growth rate) begins to decline following the V2 growth stage. By the R1 growth stage (flowering) the growth rate advantage shifts toward no-tillage systems and is maintained through the R6 growth stage (seed filling stage). This indicates that compensatory growth occurs for no-tillage systems. This growth rate advantage during reproductive stages allows no-tillage systems to remain competitive.
Tillage practices for disease management
In fields with a history of disease problems tillage is often considered a means for control. The idea is that burying crop residue or drying the soil will reduce the potential for disease incidence especially from soilborne pathogens. Using tillage to control common Iowa soybean pathogens such as Sudden Death Syndrome, Sclerotinia Stem Rot, Pythium, Phytophthora, Rhizoctonia, Soybean Cyst Nematode, and Brown Stem Rot often does not provide acceptable results. The casual organisms for each of these diseases have the ability to survive in crop residues or in soil. For fields that are prone to retain moisture early in the season, tillage my help control seedling diseases (Rhizoctonia, Pythium, Phytophthora and Fusarium). Tillage allows for improved drainage and increased soil temperatures making the environment less satisfactory for pathogen infection and more favorable for soybean growth. For most fields where these diseases have a history of occurring, management practices such as seed treatments, time of planting, crop rotation with non-host crops, and most importantly resistant varieties should be considered rather than tillage.
Other considerations for no-tillage production practices
Implementing no-tillage practices successfully requires specific types of equipment. Equipment needs to be heavier and row units need to have more down pressure to achieve proper seeding depth. Seeding depth is more critical in no-tillage systems than in conventional tillage systems and should be checked for each field as soil type changes. Seeds should in general not be planted as deep in no-tillage systems because of cooler soil conditions and the potential for more compacted seed bed. Seeding depth recommendation for soybean is 1 to 1.5 inch and never deeper than 2 inch. Seeding depth is a function of the planter and adjustment of coulters and down pressure on the closing wheels must all be made to ensure good seed-to-soil contact. Row cleaners can also be useful for removing residue from the row so that residue does not hairpin into the seed furrow.
A potential problem with no-tillage is that there is increased reliance on herbicides for weed control both before and following planting. The use of herbicide resistant soybean allows for weed control throughout the season with minimal plant stress making no-tillage a more viable option for producers. Producers with no-tillage systems should be mindful that planting can occur when weeds are still present in the field, but that weeds should be removed soon after emergence as yield potential can be reduced early in the season by weed competition. Producers should also keep in mind that excessive weeds in the field can be detrimental to proper placement of the seed in the furrow.
Nutrients, especially the non-mobile nutrients phosphorus and potassium can become stratified in no-tillage systems. This means that a higher concentration of these non-mobile nutrients exist in the top of the soil profile and are less accessible to the plant roots. Tillage can eliminate this problem by mixing the topsoil allowing plant roots to reach soil nutrients. Soil tests should be conducted to determine the nutrient levels at root depth to evaluate the need for fertilizer additions. Fertilizers can be injected into the row or banded along with the seed to improve fertilizer placement and increase availability to the plant.
Tillage is a farming practice that has traditionally been conducted each year prior to soybean planting and is difficult to give up. As production costs increase the need for tillage in cropping systems should be reconsidered as a way to reduce costs without giving up yield potential. Good management and selection of proper planting equipment will make no-tillage production a viable method of soybean production.