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Chapter 8 - Crops and Varieties, No. 8, Summer 1988

Winter Legumes May Fit No-till Systems

Roger Veseth

A new research project is underway to develop the use of winter legumes in crop rotations for sustainable no-till farming in the Northwest. The research is part of the STEEP (Solutions to Environmental and Economic Problems) conservation farming research effort underway in Oregon, Idaho and Washington. It is also partially supported by a grant from the Tennessee Valley Authority. Dave Huggins, soils graduate student at Washington State University, and Bill Pan, WSU research soil scientist, are conducting the research effort.


In the annual cropping region of the Inland Northwest, seeding winter wheat after lower residue crops such as peas and lentils has generally been one of the most successful no-till crop rotations, Following the winter wheat crop, however, no-till seeding of spring crops has often been difficult, with less-than-satisfactory results. The large amounts of surface residues can create adverse conditions for spring crop establishment including inadequate drill penetration, delayed seeding date due to wet soils, poor seed placement and seed-soil contact and increased incidence of soilborne diseases favored by cool, wet soils. The difficulties encountered with no-till crop production following winter wheat have severely restricted the development of viable no-till cropping systems.

Producers typically have resorted to a tillage rotation along with the crop rotation. Conventional or minimum tillage has been used after winter wheat, while no-till has been limited more to seeding after lower residue crops in the rotation. To further the development of sustainable notill cropping systems, Huggins and Pan are pursuing crop rotation options designed specifically for no-till crop production.

Crop Adaptation

Based on their preliminary research results, it appears that winter legumes, such as Austrian winter pea (AWP), may have some advantages in rotations for no-till farming in the intermediate and higher precipitation areas of the Inland Northwest. Seed yields of AWP have been erratic under conventional tillage, consequently restricting their adoption in the region. Low seed yields under these conditions have often been attributed to marginal winter hardiness and to dry sea-bed conditions that adversely affected stand establishment.

Huggins and Pan propose that planting a winter legume after winter wheat under no-till may allow the large amount of wheat stubble to become more of an asset rather than a liability, Results of their first year of research indicate that the stubble may provide a microenvironment for improved AWP seedling growth during the fall and protection over the winter months, resulting in reduced winter injury and increased seed yield.

Rotation Option

A viable crop rotation for no-till must minimize weed, disease and seedbed problems while maintaining high productivity and economic return. Current emphasis in the research effort is on a 3-year rotation of winter wheatwinter legume-spring cereal. They point out that this rotation under no-till has several important features, including:

1. An emphasis on fall-seeded crops, which typically have a higher yield potential than similar spring-seeded crops under Northwest conditions.

2. Inclusion of a winter legume and a spring cereal that may help minimize some weed and disease problems commonly associated with winter wheat in short crop rotations under no-till.

3. Management of residues from each crop in the rotation to maximize the benefits to the subsequent crop while minimizing the potential adverse effects.

4. Reduced surface water runoff and evaporation which conserves available water for improved yield potential.

5. Reduced soil erosion for maintaining long term productivity.

An objective of this crop rotation is to establish fall crops into relatively high amounts of surface residue while spring crops are seeded into low amounts of surface residue, Winter wheat stubble may provide a favorable environment for stand establishment and overwinter protection of fall seeded legumes such as AWP. The winter legume crop leaves behind a relatively low amount of residue that would provide a better environment for spring crop establishment, The spring cereal would provide a medium level of surface residue that may benefit the winter survival of the following winter wheat crop and also reduce the hazard of soil erosion.

Variations of the crop rotation with combinations of minimum tillage and no-till systems could also be considered by producers. For example, a winter wheat-spring cereal-winter legume rotation might be used where the spring cereal is seeded after winter wheat under minimum tillage. Then, a no-till system is used for planting the winter legume after the spring grain, and winter wheat after the winter legume. The legume could also be used as a green manure crop incorporated with minimum tillage. However, soil erosion can be a more serious problem following the green manure crop.

Winter Legume Research

The AWP variety "Glacier" was selected as a model crop for winter legumes to investigate the effects of stubble and fertility management on winter injury, survivability and yield. Glacier peas were chosen because of their improved disease tolerance and increased grain yield potential. Field research plots were established in fall 1986 on a Southwick silt loam soil near Troy, Idaho, in a 25-inch precipitation zone. The previous crop was winter wheat, yielding 70 bushels per acre. The combine was modified to uniformly distribute the straw and chaff at harvest. Residue management treatments included: (1) no-till seeding into standing winter wheat stubble 17 inches in height, (2) no-till seeding after the stubble was clipped to a 2-inch height and removed and (3) a conventional tillage comparison with the wheat stubble incorporated by moldboard plowing followed by disking. All plots were seeded with a Lilliston double disk no-till drill at 130 pounds per acre (lb/acre) on Sept. 8, 1986.

Treatments were included to determine whether starter fertilizer placed with the seed would enhance winter hardiness and survival. Fertilizer treatments included phosphorus, potassium and sulfur. Soil tests indicated that all plant nutrients were present in adequate amounts for optimum pea production.

Winter Injury

Winter injury, measured as the percentage of the plant with necrosis (dead leaves and stems), was evaluated in April when spring growth began. Visible plant injury was markedly reduced under no-till for both standing stubble and stubble removed treatments compared to conventional tillage (Fig. 1). Winter-damaged plants in both no-till treatments most commonly exhibited O to 30 percent plant necrosis. In contrast, the majority of damaged plants under conventional tillage had31 to 60 percent or more plant necrosis. Overwinter stand survival of AWP grown under no-till with stubble was 85 percent (15 percent of the plants with 100 percent plant necrosis) as compared to 95 percent under conventional tillage and 97 percent under no-till with stubble removed.

Fig. 1. Winter Injury of Glacier Austrian winter peas measured as percent plant necrosis (dead leaves and stems) on April 21, 1986, under no-till with and without the stubble removed, and under conventional tillage after winter wheat near Troy, Idaho. Within ranges of injury, columns with the same letter are not significant differences at the 95 percent probability level (Huggins and Pan, WSU).

Pea Yields

Pea yields, averaged over fertilizer treatments, were 2,963 pounds per acre (lb/acre) for no-till with standing stubble, 3,036 lb/acre for no-till with stubble removed and 2,261 lb/acre for conventional tillage. Yields under both no-till treatments are statistically different than the yield under conventional tillage at the 95 percent probability level. Yields were not statistically different between the two no-till treatments. The higher yields under no-till may be, in part, attributed to reduced plant winter injury compared to conventional tillage (Fig. 1). Under conventional tillage, there was a greater percentage of severely-injured plants which were slower to begin growth in the spring and remained more stunted through the growing season than under the two no-till treatments.

Soil Water Content

Another factor which may have affected fall growth, winter hardiness and grain yield of AWP under the different tillage and stubble treatments was soil water content. Under the no-till treatments, soil water content was significantly higher than under conventional tillage at the O to 0.5 and 0.5 to 1.0 foot increments and again at the 2 to 3 and 3 to 4 foot increments (Fig. 2). The researchers explain that less available soil water under conventional tillage, particularly in the top foot, may have contributed to reduced fall growth and plant vigor.

The no-till environment, with higher availability of soil water in the fall and stubble for winter protection, may be more favorable for AWP stand establishment and reduced winter injury.

Fig. 2. Percent soil water content on Oct. 23, 1986, under Austrian winter peas seeded September 8 after winter wheat with no-till and conventional tillage near Troy, Idaho. Within ranges of injury, columns with the same letter are not significant differences at the 95 percent probability level (Huggins and Pan, WSU).

Fertilizer Response

Starter fertilizer treatments did not influence winter injury, survival or yield. The addition of phosphorus fertilizer significantly increased plant dry weights (measured in April) under the no-till treatments, but the response was not reflected in pea yields, No significant dry weight or yield responses to fertilizer were found under conventional tillage.

Summary and Future Plans

Huggins and Pan are encouraged by the reduction in winter injury and the improved yield potential of AWP notill seeded after winter wheat compared to seeding under conventional tillage. However, they point out that this management strategy study represents only one winter season at one location. Dry fall conditions in 1987 prevented establishment of AWP for the second year of the study. Research will continue this fall on the no-till seeding of AWP after winter wheat. A new line of winter lentil will be included in the study. Fertility management research will continue to be a part of the project.

The researchers have completed the first year of a fertility management study on hard red spring wheat under no-till and conventional tillage in 1987. The second year is in progress. Hard red spring wheat could serve as a crop option following AWP in a winter wheat-AWP-spring cereal crop rotation for no-till.


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