Advancing Sustainable Agriculture in the Pacific Northwest

Conservation Tillage Systems

Information Resource

Chapter 2 - Systems and Equipment, No. 13, Spring 1989

Conservation Tillage Spring Pea Production

Roger Veseth

The use of conservation tillage systems for spring dry pea production is beginning to receive some attention by researchers and producers in the Inland Northwest. The development of new management technology and equipment for seeding winter cereals under conservation tillage systems has been a major research focus. This is because runoff and soil erosion potential in the Northwest is greatest overwinter where winter cereals are conventionally-seeded into a fine, residue-free seedbed. However, substantial soil erosion can also occur on conventionally-seeded spring pea fields during heavy spring rainstorms.

In the past, most people have been under the impression that spring peas needed a residue-free, conventionally tilled seedbed to maintain production potential and harvest the crop. Consequently, few people have explored conservation tillage options in pea production. In recent years, however, several research projects involving spring peas, as well as winter and spring cereals, have demonstrated that pea production potential can be maintained or increased with conservation tillage,

The use of conservation tillage in spring pea production could have substantial impacts in this region. In 1988, there were about 176,000 acres of spring-seeded dry green and yellow pea in the Palouse region of eastern Washington and northern Idaho. Much of this production was on highly erodible land. There is also a potential of including conservation tillage practices in spring lentil production, which covered over 73,000 acres in the region in 1988, No-till seeding of lentils into bluegrass sod or other crop stubble is already becoming a common production practice for an increasing number of producers in the region.

Potential Advantages

In addition to reducing the potential for soil erosion during seedbed preparation and through the early part of the growing season, there can be additional potential benefits to using conservation tillage for planting spring peas. These could include: increased soil water storage and associated increased yield potential for the spring pea and following crop; less tillage expense; reduced potential for soil compaction; and less soil erosion during the following winter wheat crop.

Increased Water Storage

One potential advantage of using conservation tillage with spring peas is an increased yield potential due to increased soil water storage with reduced evaporation and runoff. This would have the greatest benefit on hilltops and upper slopes, where production is typically most limited by lack of water, as well as in the lower precipitation zones in the pea production region of the Northwest.

In gently-sloping field areas on lower portions of the slopes and bottomland, which typically have higher residue production, maintaining more surface residue may be a disadvantage. Slower soil drying and warming could increase existing problems of excess water and cold soils in the spring. Producers might consider different tillage systems on these areas of the field compared to the more steeply sloping areas. More intensive tillage practices could probably be used in these low areas since they usually have a lower water erosion potential.

Less Cost and Reduced Compaction

With fewer tillage operations under conservation tillage, there is a potential for lower tillage costs. An additional advantage is the potential for reducing soil compaction. Since the potential for soil compaction is greatest in the early spring, when the soil has a high water content, fewer tillage operations could help to reduce traffic and tillage compaction.

Compaction can limit rooting depth of spring peas and reduce infiltration, resulting in increased runoff potential. Soil compaction during seedbed preparation for spring peas can often remain a problem after winter cereals are seeded following the peas. In addition to increased overwinter runoff and erosion potential, the resultant reduced water infiltration rate into the compacted soil can also reduce soil water storage and thus reduce winter cereal yield potential.

The disk, a common tillage implement for seedbed preparation for spring peas under conventional tillage, can cause severe compaction at the depth of tillage under wet soil conditions. The use of a field cultivator, instead of the disk, in a conservation tillage system could help reduce the potential for this tillage compaction and maintain more surface residue. A disk buries about 45 percent of the surface residue compared to about 15 percent for a field cultivator.

Less Erosion the Following Winter

Maintaining more cereal residue on the surface through the planting of spring peas can also help reduce soil erosion potential the following winter after winter cereals are seeded. The amount of crop residue produced by spring peas is generally quite low. On steeper slopes, the pea residue alone is sometimes not sufficient to adequately reduce runoff and soil erosion, even with no-till seeding of winter cereals. Pea residue production may only be about 1,000 to 1,500 pounds per acre or less on upper slopes and hilltops. Consequently, if some spring barley residue, for example, could be maintained on the surface through the spring pea crop under conservation tillage, runoff and erosion could be reduced after the winter wheat was seeded. Increased soil water storage from the additional residue could also increase the yield potential for the winter wheat crop.

Research Efforts

Recent Northwest research projects have indicated that there may be a good potential for using conservation tillage systems for spring pea production without compromising yield. Most of the projects are part of the STEEP (Solutions to Environmental and Economic Problems) research program. Since 1975, this conservation farming research program has involved more than 100 USDA Agricultural Research Service (ARS) and land-grant university scientists in Washington, Oregon and Idaho.

STEEP Tillage/Rotation
Plots - Moscow

The 10-acre STEEP Tillage/Rotation Plots near Moscow have been sites for an extensive interdisciplinary research effort on conservation farming from 1976 through 1987, From 1984 through 1987 the research project was directed by John Hammel, University of Idaho soil scientist and STEEP researcher at Moscow. These last 4 years included a comparison of spring pea production under three tillage systems: conventional, minimum and no-till. Two crop rotations were also evaluated: (1) 2-year rotation of winter wheat-spring pea; and (2) 3-year rotation of winter wheat-spring barley-spring pea.

Seedbed preparation for spring pea production after winter wheat in the 2-year rotation and spring barley in the 3-year rotation included the following three fall and spring tillage operations:

  1. Conventional - Fall moldboard plowing, spring disking, harrowing, seeding with double disk drill (8-inch spacing), and rolling.
  2. Minimum - Fall chisel plowing, spring field cultivating with 12-inch wide sweeps, seeding with double disk drill (8-inch spacing), and rolling.
  3. No-till - Direct seeding with the UI "Chisel-Planter." a modified chisel plow with narrow Y2 -inch wide shanks (used for fertilizer placement) and double disk seed openers, both on the same 12-inch spacing.

The minimum tillage and no-till treatments resulted in similar amounts of residue remaining on the surface after planting the peas (Table 1). Surface residue levels after conventional tillage were only a small fraction of the residue under the conservation tillage treatments, although typically more than found on most conventional tillage fields in the region. Weed control and fertility practices were the same on all tillage treatments.

The 1984-87 average spring pea yields with the three tillage systems averaged over the two crop rotations were not statistically different (Table 2). Significant differences
in yields were found in only 2 years, 1986 and 1987, when yields with minimum tillage were lower than yields with conventional and no-till. Hammel points out that spring pea yields commonly varied as much or more between years as they did between treatments, reflecting yearly climatic variations. He described the crop years as follows: 1984, dry; 1985, good early spring rains; 1986, very dry; and 1987, good late spring rains.

Another factor which influenced yields was crop rotation. Hammel measured a significant increase in pea yield with the 3-year rotation compared to the 2-year rotation in 3 of the 4 years (Table 3). Where there were significant differences, yield increases ranged from 211 to 442 pounds per acre. The average 4-year yield increase with the 3-year rotation was 239 pounds per acre.

Hammel points out that in the same study, winter wheat yields averaged over tillage treatments also significantly increased with the 3-year rotation compared to the 2-year rotation. Yield increases, which were significantly different in 3 of the 4 years, ranged from 6 to 13 bushels per acre.

Table 1. Estimated average amount of residue remaining on the soil surface and percent surface cover after planting spring peas under three tillage systems after winter wheat or spring barley in two crop rotations, 1984-87, STEEP Tillage/Rotation Plots, Moscow, ID (Hammel, Ul).

Tillage System

Surface residue amount and surface cover

Winter wheat

Spring barley



(% cover)


(% cover)
















Table 2. Influence of tillage system on spring pea yields averaged over two crop rotations, 1984-87, STEEP Tillage/Rotation Plots, Moscow, ID (Hemmel, Ul).

Tillage System

Spring Pea Yields


1984 1985 1986 1987 Avg.


















LSD (0.05)1






1 Least significant difference (LSD) at the 95 percent probability level; yields within columns followed by the same letter are not significantly different.

Table 3. Influence of crop rotation on spring pea yield averaged over three tillage systems, 1984-67, STEEP Tillage/Rotation Plots, Moscow, ID (Hammel-Ul).

Crop rotation

Spring Pea Yields


1984 1985 1986 1987 Avg.












LSD (0.05)1






1 Least significant difference (LSD) at the 95 percent probability level; yields within columns followed by the same letter are not significantly different.

The fourth year increase of about 2 bushels per acre was not significantly different from the yield under 2-year rotations. Hammel feels that the yield increases for both spring pea and winter wheat with the 3-year rotation is probably due to a reduction of soilborne diseases affecting each crop. However, he points out that soil physical or chemical changes could also have been involved.

Palouse Conservation Field
Station - Pullman

An evaluation of the interactions of tillage systems and crop rotations on the production of spring pea and spring and winter cereals is underway at the USDA-Agricultural Research Service Palouse Conservation Field Station north of Pullman, WA. The tillage-rotation study is under the direction of USDA-ARS soil scientist Robert Papendick, research leader for the ARS Land Management and Water Conservation Research Unit at Washington State University, and co-chair of the STEEP research effort. It is being conducted in cooperation with Keith Saxton, ARS agricultural engineer and STEEP researcher, and Chris Pankuk, ARS research assistant.

Three tillage systems compared in spring pea production after winter or spring cereals from 1985-88 included:

  1. Conventional - Fall moldboard plow, spring rotary tillage (Rotera), seeding with a John Deere double disk drill (1985-87) or the USDA-IV Cross-Slot research drill (1988-),
  2. Paraplow/no-till - Fall subsoiling to a depth of 24 inches with minimum surface disturbance using a paraplow (now under the trade name Paratill), no-till seeding with the USDA-III off-set double disk research drill (1985-86) or the USDA-IV Cross-Slot research drill (1987-),
  3. No-till - Direct seeding with the USDA-III (1985-86) or USDA-IV (1987-) research no-till drills. The conventional seedbed prepared under rotary tillage with the Rotera in the spring-is roughly equivalent to the spring pea seedbed prepared by combinations of disk or field cultivator and harrow operations commonly used by conventional farmers in the area. The paraplow is similar to a moldboard plow except it does not invert the soil and leaves the soil surface and crop residue largely undisturbed. Its purpose is to loosen compacted soil for improving root growth, water infiltration and drainage.

Three crop rotations in the study include: winter wheat spring pea; winter wheat-spring barley-spring pea; and
winter wheat-winter barley-spring pea. Winter barley was replaced with winter wheat in Fall 1986 and then with spring wheat beginning in Spring 1988.

A preliminary summary of the results from 1985 to 1988 show that spring pea yields with the paraplow/no-till and no-till treatments were equal to or greater than yields with conventional tillage (Table 4). Differences in yield between the tillage treatments were not significant in 1985 and1986. Yields under the two conservation tillage treatments were significantly higher than under conventional tillage in 1987 and 1988, however.

The USDA-III off-set double disk drill (used in 1985 and 1986) caused some splitting of pea seed and uneven seeding depth, which consequently reduced plant populations and yield potential. The USDA-IV Cross Slot drill does not break the pea seed and provides uniform seed placement, resulting in better pea stands than with the USDA-III drill, The researchers point out that these factors may have contributed to the increased pea yields with paraplow/no-till and no-till treatments beginning in 1987,

IPM Research Plots - Pullman

An extensive Integrated Pest Management (IPM) research project near Pullman, WA, also provides a comparison of spring pea production under conservation tillage and conventional tillage. It has served as an important companion project to the STEEP effort. One of three similar IPM research projects in the United States, this research effort is sponsored by the USDA-Agricultural Research Service in cooperation with Washington State University, University of Idaho and the O. A. Vogel Wheat Research Fund.

The first crop year of field research on the IPM project began in 1986. It is scheduled to continue through 1991. Frank Young, USDA-ARS research agronomist and STEEP researcher at Pullman, is the Project Leader. More than 12 researchers from eight different disciplines are involved in the effort, most of whom are also involved in the STEEP program.

The large IPM plots cover 40 acres and are maintained with field-size equipment. Two 3-year crop rotations are used: (1) winter wheat (2 years) -spring wheat and (2) winter wheat-spring barley-spring pea. The two tillage systems are conventional tillage and conservation tillage. Conventional seedbed preparation for spring peas after spring barley includes the following tillage operations: fall moldboard plowing, two spring field cultivator operations, seeding with a standard double disk drill and rolling. For the conservation tillage system, a fall chisel plowing is substituted for the moldboard plowing, with the spring field operations remaining the same. Three weed management levels are also evaluated in addition to the rotation and tillage treatments.

Table 4. Influence of tillage system on spring pea yield averaged over three crop rotations, 1985-88, USDA-ARS Palouse Conservation Field Station. Pullman, WA (Papendick, USDA-ARS, Pullman).

Tillage System

Spring Pea Yields


1985 1986 1987 1988















LSD (0.05)1





+ Seeded with USDA III off-set, double disk no-till drill.

++ Seeded with USDA IV Cross-Slot no-till drill.

1 Least significant difference (LSD) between yields with the tillage treatments for each year at the 95 percent probability level.

Young reports that spring peas under conservation tillage have performed as well as or better than under conventional tillage so far in the study (1986-88). In 1986, pea yields under conservation tillage, averaged over the three weed management levels, were not statistically different from conventional tillage. Yields under conservation tillage were significantly higher (90 percent probability level) than under conventional tillage during the next 2 years, however. Production under conservation tillage systems was 330 and 470 pounds per acre higher than under conventional tillage in 1987 and 1988, respectively. Yields under conservation tillage ranged from 1,350 to 2,500 pounds per acre during the 3-year period.


Results of these three studies indicate that spring peas can now be included in conservation tillage systems while maintaining or increasing yield potential. This will provide an additional management tool for Inland Northwest producers to help reduce tillage costs, improve water storage and use efficiency, and reduce the potential for soil compaction and erosion.

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Hans Kok, WSU/UI Extension Conservation Tillage Specialist, UI Ag Science 231, PO Box 442339, Moscow, ID 83844 USA (208)885-5971
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