Advancing Sustainable Agriculture in the Pacific Northwest

Conservation Tillage Systems

Information Resource

Chapter 2 - Systems and Equipment, No. 5, Winter 1987

Tillage System Comparisons

Roger Veseth

In discussions about the advantages and disadvantages of conservation tillage systems compared with conventional tillage, a common question is . . . How do they compare in yields? That is usually a very difficult question to answer because there are so many growing condition and management variables which influence yield potential. Caution must be used in "neighboring field" or "across the road" comparisons because differences in soils, crop rotation history, seed treatment, fertilizer rate or placement, seeding date or many other factors can easily overshadow the effects of the particular tillage systems.

STEEP and related conservation farming research projects have provided the opportunity to compare tillage systems. A cross-section of these research projects will be highlighted hereto compare winter wheat yields. Keep in mind that technology has changed dramatically in the past few years and continues to change. Higher yield potentials from new developments in equipment design, fertilizer placement, disease and weed control strategies, combine residue distribution, varieties and other factors can quickly outdate the results of tillage system comparisons. Yield comparisons must be based on the latest technology.

Davenport, Washington

A research project which focused on fertilizer placement comparisons has also provided yield comparisons between conventional tillage and no-till. Fred Koehler, Washington State University soil scientist and STEEP researcher, has conducted the research under an annual cropping, winter wheat-spring wheat rotation near Davenport, a 16-inch precipitation area.

The conventional tillage system, with primary tillage by a Calkins cultivator and flex-tine harrow, was compared with a one-pass fertilizer and seed operation using a specially designed research drill. Fertilizer shanks banded fertilizer 2.5 inches below the seed row. Double disk seed openers followed each fertilizer opener on a 12-inch spacing. The drill was used to seed both the conventional and no-till plots. In all treatments, except the non-fertilized checks, phosphorus fertilizer was placed below the seed row. Nitrogen and sulfur fertilizer was either broadcast before seeding or deep banded with the phosphorus at seeding. Table 1 compares the winter wheat and spring wheat yields between the two tillage systems and fertilizer placement options from 1978 through 1985.

In both tillage systems, banding nitrogen and sulfur fertilizer increased spring wheat yields about 10 bu/acre and winter wheat yields 4 bu/acre when compared to broadcasting. While spring wheat yields were about 4 bu/acre higher under conventional tillage than under no-till, winter wheat yields were about 3 bu/acre higher under no-till. Koehler felt the higher winter wheat yields under no-till reflected a reduction in soil water evaporation compared with the fall tillage operations under conventional tillage. Winter wheat yields under this annual cropping experiment were lower than typical yields under the winter wheat-fallow or winter wheat-spring grain-fallow rotations commonly used in the area. Crop yields were higher with annual cropping, however, when the fallow year is taken into account.

Table 1. Effect of Nitrogen and sulfur fertilizer placement on yields of spring wheat and winter wheat under conventional tillage and no-till, 1978-1985, Davenport, WA (Koehler, WSU)

N and S fertilizer 1

Spring Wheat

Winter Wheat





















NT is no-till; CT is conventional tillage.

1 90 lb/acre N and 18 lb/acre S was banded 2.5 inches below the seed row or broadcast at seeding; 60 lb/acre P2O5 was banded 2.5 inches below the seed row in all treatments except in the non-fertilized checks.

Pullman, Washington

An evaluation of tillage systems and crop rotation is underway at the Palouse Conservation Field Station north of Pullman under the direction of Robert Papendick, USDA-ARS soil scientist and STEEP researcher. Three tillage systems are being compared: (1) conventional tillage - fall moldboard plow, Roterra (rotary tiller) for secondary tillage and seedbed preparation, seeding with John Deere double disk drill; (2) Paraplow/no-till - Paraplow subsoil tillage in the fall before a spring crop (not before winter cereals), no-till seeding with the USDA III (Yielder research drill); and (3) no-till - direct seeding with USDA III drill. The Paraplow is similar to a moldboard plow except it does not invert the soil and leaves the soil surface largely undisturbed. Its purpose is to loosen the surface soil and compacted plow pans or other restrictive soil layers for improved root growth, water infiltration and drainage.

Three crop rotations include: (1) winter wheat-spring barley-spring pea; (2) winter wheat-spring pea; (3) and winter wheat-winter barley-spring peas. In all treatments, winter wheat is planted after spring peas. Production inputs are the same under all treatments, except for fertilizer placement. Under conventional tillage, 100 lb N/acre of dry nitrogen fertilizer is broadcast and plowed under before planting. In no-till treatments, the same rate of liquid nitrogen fertilizer is deep banded 2.5 inches below the seed depth between pairs of seed rows 5 inches apart on a 5: 15-inch paired-row spacing. No starter fertilizer is applied with the seed in any treatment.

Table 2. Winter wheat yields under three tillage systems and three crop rotations, 1984-86, Pullman, WA (Papendick, USDA-ARS).

Crop Rotation

Tillage system



Paraplow/No-till 1


Winter wheat-Spring barley-Spring peas




Winter wheat-Spring peas




Winter wheat-winter barley-Spring peas




1 Paraplow used in the fall before spring crops but not before winter wheat

In a 3-year summary of results from 1984 through 1986, yields under no-till averaged about 10 bu/acre higher than under conventional tillage in the three rotations (Table 2). Possible reasons suggested by Papendick for the higher no-till yields include reduced soil water loss to evaporation and runoff, increased winter survival and increased plant vigor because of early access to deep banded fertilizer. The Paraplow was not used in the fall before winter wheat seeding (only the fall before spring crops). Its impact on no-till winter wheat yield the following year has been inconsistent.

Moscow, Idaho
Another STEEP tillage-rotation study is underway just north of Moscow under the direction of John Hammel, University of Idaho soil scientist. Three tillage systems are being compared. For winter wheat establishment these consist of the following equipment sequences: (1) conventional - moldboard plow, disk (2X), harrow (2X) and double disk drill with 7-inch row spacing; (2) minimum tillage - chisel (12-inch spacing) and double disk drill with 7-inch row spacing; and (3) no-till - UI "Chisel-Planter" with 12-inch spacing and double disk seed placement. The Chisel-Planter was developed through the UI Agricultural Engineering Department under the STEEP research program.

Winter wheat is always seeded after spring peas. Three crop rotations used in the study include: (1) winter wheat-spring peas; (2) winter wheat-spring barley-spring peas; and (3) rotation 2 with a one-time Paraplow tillage operation in the fall of 1983. Tillage sequences for spring crops in the rotation are nearly the same as for winter wheat.

All treatments received the same rate of fertilizer (100 lb/acre N, 45 lb/acre P2O5, 15 lb/acre S), although fertilizer type and application method varied. In conventional treatments, dry fertilizer as 27-12-0-5 was broadcast applied and incorporated with the disk. Liquid fertilizer as Solution-32, 10-34-0 and Thiosol was shanked 2 to 3 inches below seeding depth with the chisel for minimum tillage and the UI Chisel-Planter (directly below the seed rows) for no-till. No starter or pop-up fertilizer was applied with the seed.

Results of the last 3 years of winter wheat trials are shown in Table 3. Yields have tended to be highest with conventional tillage, intermediate with minimum tillage and lowest with no-till, however, differences were not always statistically significant. Differences between tillage systems were also smaller under a 3-year rotation than a 2-year rotation, especially in the last 2 crop years.

Wheat yields are listed separately by year to reflect the impact of yearly variations in precipitation, particularly with respect to the Paraplow treatment. In the "wet" 1983-84 crop year, the fall 1983 Paraplow operation did not increase yields. However, the effects of the Paraplow operation appear to be important in the "dry" 1984-85 crop year in the minimum and no-till. Averaged over all tillage treatments, there was a 10 bu/acre increase in yield in 1984-84 with the Paraplow treatments (least significant difference of 8.4 bu/acre). A 15 bu/acre increase in notill wheat yield occurred in the "dry-average" 1985-86 crop year where the Paraplow was used in 1983. There has been no spring crop response to the Paraplow.

The reason for the minimum tillage and no-till winter wheat yield response to the 1983 Paraplow treatment is not clear. Soil water measurements in 1986 indicate that a larger amount of water was extracted to a greater depth in minimum tillage and no-till where the Paraplow was used. Hammel points out that this probably reflects an improved root growth environment. Possible factors stimulating root growth include: (1) reduced compaction and resistance to root growth; (2) improved soil aeration, drainage and water infiltration; and (3) less favorable environment for some soilborne diseases such as Pythium root rot.

Table 3. Winter wheat yields under three crop rotation and three tillage systems, 1984-88, Moscow, ID (Hammel, Ul).

Crop rotations 1

Tillage System Winter wheat-Spring peas Winter wheat-Spring barley-

Spring peas

Winter wheat-Spring barley-

Spring-peas + Paraplow

1983-84 crop "wet year"

Conventional 116.4a 116.2a 120.6a
Minimum 94.0b 107.4a 89.3b
No-till 79.6b 83.8b 84.9b

1984-85 crop "wet" year

Conventional 66.8a 69.5a 73.2a
Minimum 55.0b 54.2b 76.0ab
No-till 49.3b 52.4b 62.5b

1985-86 crop "wet" year

Conventional 89.5b 93.0a 88.1b
Minimum 74.5b 97.7a 100.0a
No-till 66.9c 76.7b 91.8ab

1 Statistical comparisons are only between tillage systems in each rotation, each year, not across rotations or years. Yields followed by the same letter are not statistically different at the 95 percent probability level.

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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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