New Minimum Tillage Systems for Legume-Winter Wheat Cropping Sequence

Chapter 2 – Conservation Tillage Systems and Equipment, No. 20, May 1997

Authors: Roger Veseth, WSU/UI Conservation Tillage Specialist; Stephen Guy, UI Crop Management Specialist; Donn Thill, UI Weed Scientist; John Hammel, UI Soil Scientist; Tim Fiez, WSU Soil Fertility Specialist, Joe Yenish, WSU Weed Scientist

Some revolutionary changes in tillage practices for spring dry pea, lentil and other spring grain legumes are underway in the Inland Northwest. They offer exciting potential benefits in soil erosion control, soil quality, yield potential and profitability. Innovative growers and university scientists have combined efforts to develop integrated management systems for the use of minimum tillage in legume-winter wheat crop sequences. The following is a brief description of why a change is needed and the new management systems that are being developed.

The Problem

In the Palouse region, soil erosion can be a serious problem in crop rotations with grain legumes followed by winter wheat. Intensive tillage has traditionally been used to bury the previous cereal crop residue, incorporate herbicides and prepare a finely-tilled, low-residue seedbed for spring grain legumes. Spring field operations when soils are wet can result in significant soil compaction from tractor traffic and tillage implements. The combination of little or no cereal crop residue retained on the soil surface after legume planting and soil compaction from the spring tillage operations can leave legume fields vulnerable to soil erosion during intense rainstorms in the spring and early summer. Soil compaction also can directly reduce crop yield potential.

Grain legumes produce relatively little crop residue, which is fragile and shatters easily during dry harvest conditions, and decomposes rapidly under moist conditions. Even though Palouse growers have made a significant shift towards minimum tillage or direct seeding of winter wheat, surface residue cover from the legume crop alone is often inadequate for erosion control. Without carryover cereal residue preceding the legume crop and prevention of soil compaction often associated with the legume production, a winter wheat crop after grain legumes can be highly vulnerable to erosion during the critical November to April period, when about 70% percent of the yearly precipitation occurs. Winter wheat is usually seeded in October to reduce the risk of a number of weed, insect and disease problems, and/or because of dry soil conditions earlier in the fall. Consequently, the wheat crop usually over-winters as small plants and provides little erosion protection.

Surface runoff and soil erosion can both cause yield losses in grain legume and winter wheat crops. Water running off the fields is water not stored for grain production. The greatest impact would occur on upper slopes and ridgetops where yields are most limited by available water. Erosion can reduce current crop yields by loss of plant stands and reduced plant vigor. Soil loss will also reduce the yields of future crops due to loss of soil fertility, water holding capacity, rooting depth and other soil quality and productivity factors.

Solutions To the Problem

Some innovative growers in the Palouse are beginning to plant spring legumes with direct spring seeding, with or without minimum fall tillage systems. An important development in direct spring seeding of grain legumes is the recent availability of herbicides that offer weed control without soil incorporation or that are applied post emergence. A 3-year research project by scientists from University of Idaho and Washington State University was initiated in 1996 to assist growers in developing integrated management systems for these production practices. It is an interdisciplinary team project coordinated by Stephen Guy, UI Crop Management Specialist. The project is partially supported by grants to UI and WSU from the STEEP III (Solutions To Environmental and Economic Problems) conservation farming research program in Idaho, Oregon and Washington.

The goal for growers and scientists is to develop integrated management systems for direct spring seeding of grain legumes. This would retain more of the previous cereal crop residue on the surface and minimize spring soil compaction, thus reducing the potential for runoff and soil erosion, and improving water infiltration. The crop and pest management systems for grain legumes must optimize yield, quality and residue production. In addition, winter wheat planting systems must then continue to retain surface residue from the legume and previous cereal crops, and maintain soil physical conditions for effective water infiltration. The overall goal is to improve erosion control, yield potential and profitability in the legume-winter wheat rotational cycle.

The research effort focuses on the following management considerations:

1. Surface residue retention, surface roughness, and other soil physical properties affecting water infiltration and erosion potential in minimum and intensive tillage systems for establishing legumes and winter wheat
2. Crop yield, quality and profitability of the legume and winter wheat crops under the minimum and intensive tillage systems
3. Effectiveness of current and prospective herbicides for weed control in legumes under minimum and intensive tillage systems.
4. Incidence of weeds and diseases in the legume-winter wheat rotational sequence under minimum and intensive tillage systems
5. Surface retention of spring wheat versus spring barley residue through the following legume-winter wheat cropping sequence under minimum and intensive tillage systems
6. Residue production and decomposition rate differences between legume species and varieties
7. Effects of fertilizers, fertilizer placement and other crop management options on legume yield, quality and residue production under minimum and intensive tillage systems

Need for a 3-Year Rotation — An important point to keep in mind is that minimum tillage establishment of spring legumes will be much more successful in a crop rotation of three years or longer, such as winter wheat-spring cereal-legume, than in a 2-year winter wheat-legume rotation. The additional year of spring crop in the rotation is very important in reducing the potential for soilborne diseases and winter annual grass weeds that can be problems under a minimum tillage system in a 2-year rotation. Residue levels are much lower after spring cereals than winter wheat, making minimum tillage systems more feasible for grain legume establishment.

Preliminary Results

Two growers are currently involved in large scale on-farm tests of minimum tillage establishment of pea and lentil with their field equipment. Preliminary results of a 1995-1997 on-farm test by Wayne Jensen, near Genesee, ID, show the success of minimum tillage for planting spring pea after spring wheat compared to conventional tillage (Table 1). This trial began in the fall of 1995 after a 90 bu/A spring wheat crop. Three tillage systems being evaluated include 1) conventional tillage system of fall moldboard plow – two spring cultivations for herbicide incorporation – seed with conventional double disc drills; 2) minimum tillage system of fall chisel – fall cultivate – spring herbicide application without soil incorporation – direct seed with a John Deere 455 minimum tillage drill with off-set double discs; and 3) fall flail before the system in number 2 above. The trial was seeded to Antigo pea in mid-March 1996. The entire trial was direct seeded to winter wheat with a Yielder no-till drill in October.

The two minimum tillage systems retained over 52% surface cover from the spring wheat residue through pea seeding compared to 10% with conventional tillage. Minimum tillage pea yields were slightly higher than yields with conventional tillage, but the difference was not statistically significant. Erosion protection overwinter was much higher in the two minimum tillage systems with over 46% surface cover compared to 21% in the conventional tillage system. A substantial portion of the surface residue in the minimum tillage systems was carryover spring wheat residue. Trial data collection will continue through winter wheat harvest in 1997.

Table 1. Surface residue retention and pea yield in 1996 under minimum tillage and conventional tillage in a spring wheat-pea-winter wheat rotation, Wayne Jensen, Genesee, ID grower.

A repeat of Jensen’s 3-year trial (except for the flail treatment) was established in the fall of 1996 in a nearby field after 70 bu/A spring wheat and will continue through the 1997 pea crop and winter wheat harvest in 1998. Overwinter surface residue cover was 11% with conventional plow system and 47 percent with the minimum tillage system.

A 1996-98 field trial was initiated with Art Schultheis near Colton, WA. A field of spring barley stubble was lightly disced in early fall 1996 and chiseled in late fall. Overwinter residue cover was 55%. After a tine harrow operation to smooth the field in spring of 1997, and a herbicide application, the trial was established to compare direct spring seeding after fall tillage versus the traditional system of two field cultivator operations for herbicide incorporation before seeding lentils. The trial will be direct seeded to winter wheat and data collection will continue through winter wheat harvest in 1998.

The UI Kambitsch Research Farm south of Moscow is the site of a large-scale trial to compare the effects of fall tillage practices after spring wheat and spring barley on surface residue retention and spring pea production. The following are surface residue levels (%) from spring barley in April 1997 for four fall 1996 tillage practices: 1) moldboard plow – <1%; 2) chisel-plow – 22%; 3) flail/ Paratill subsoiler – 21%; and 4) flail/no-tillage – 62%. Residue cover after spring wheat was not significantly different than after spring barley. The trial will continue through the spring pea crop in 1996 and harvest of winter wheat in 1998. A repeat of this trial will begin in 1997 with fall tillage treatments after harvest of spring wheat and spring barley.

Another large-scale trial at the UI Kambitsch Research Farm will begin in 1997 to evaluate the residue production of two spring pea and spring lentil varieties. The longevity of the residue on the soil surface will be compared under four tillage systems for establishing winter wheat. These will include: 1) Direct seed and fertilize with a no-till drill; 2) Direct-shank fertilize – conventional drill; 3) Direct-shank fertilize – cultivate/harrow – conventional drill; 4) Direct-shank fertilize – 2X cultivate/harrow – conventional drill. The trial will be monitored through winter wheat harvest in 1998. A repeat of the trial will be initiated in 1998.

Research on management options for herbicides to control weeds in minimum tillage systems for legumes was initiated in 1997. Trials to evaluate fertilizers and other crop management options to improve legume grain yield and residue production will begin in 1998. Both of these research efforts will be part of grower-managed on-farm tests on minimum tillage legume systems in the region.

Pacific Northwest Conservation Tillage Handbook Series publications are jointly produced by University of Idaho Cooperative Extension System, Oregon State University Extension Service and Washington State University Cooperative Extension. Similar crops, climate, and topography create a natural geographic unit that crosses state lines in this region. Joint writing, editing, and production prevent duplication of effort, broaden the availability of faculty, and substantially reduce costs for the participating states.

For herbicide application recommendations, refer to product labels and the Pacific Northwest Weed Control Handbook, an annually revised extension publication available from the extension offices of the University of Idaho, Oregon State University and Washington State University. To simplify information, chemical and equipment trade names have been used. Neither endorsement of named products is intended, nor criticism implied of similar products not mentioned.

Cooperative Extension programs and policies comply with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. The University of Idaho Cooperative Extension System, Oregon State University Extension Service and Washington State University Cooperative Extension are Equal Opportunity Employers.