PNW CONSERVATION TILLAGE HANDBOOK SERIES
Chapter 2 - Systems and Equipment, No. 2, December-January 1986

STEEP research conducted with a subsoil tillage implement, called a Paraplow, indicates that it may have potential value for conservation farming systems in the Northwest. The Paraplow, manufactured by Howard Rotavator Company, is a slant-shank chisel plow developed and used successfully in England. Fig. 1 on the next page shows the unusual shank design.

The Paraplow can effectively fracture and loosen the soil to a working depth of 12 to 16 inches. The soil surface is left smooth with virtually no disturbance of the standing stubble (Fig. 2, next page). Because the stubble is left anchored and upright, the Paraplow can fit into a "no-till" planting system. Other tillage implements, such as a standard chisel or disk, loosen the stubble and create plugging problems and other difficulties for most no-till drills.

The purpose of the Paraplow is to loosen compacted soil layers and surface crusting, and still maintain surface residue, As the Paraplow lifts and fractures the soil, it creates a higher percentage of larger soil pores (macropores). These large pores help maintain higher water infiltration rates into the soil, even when the soil is frozen.

Compaction of soils, such as the formation of a dense plow pan just below the tillage depth of the moldboard plow, is commonly an important contributing factor in the high runoff and soil erosion problem in the Northwest. Traffic compaction with heavy equipment, particularly on wet soil, also adds to the problem. A compacted soil layer directly increases runoff by restricting water infiltration rates into the soil. The reduced internal soil drainage can also cause a temporary "perched" water table to form above the layer. When this wet soil layer freezes, it becomes impermeable to water movement into the soil. Nearly all of the subsequent precipitation can be lost as runoff before this dense frozen layer thaws.

Producers changing from conventional tillage to no-till still face the problems associated with plow pans or other compacted soil layers inherited from previous conventional tillage operations. The Paraplow could offer a solution while allowing full use of crop stubble for soil water storage and erosion protection.

Research Results

Soil Compaction

One of the first Paraplows imported to the U.S. is being tested by many researchers in the STEEP Program. John Hammel, University of Idaho soil scientist, and Robert Papendick, USDA-ARS soil scientist at Pullman, have evaluated the effectiveness of the Paraplow in loosening a compacted plow pan. They used a cone penetrometer, a probe instrument which measures the soil's resistance to penetration, to estimate the relative soil density or degree of soil compaction. In Fig. 3, the high soil resistance measurement (850 lb/in²) at about 8 inches depth indicate the compacted plow pan present before Paraplowing. After paraplowing, the soil resistance measurement at 8 inches was only about 450 lb/in². This shows that the plow pan has been loosened, allowing increased downward water movement and root penetration. The comparison was made in the Palouse silt loam soil near Pullman, WA.




Soil Water Storage

Keith Saxton, hydrologist, and Lloyd Elliott, soil microbiologist with the USDA-ARS at Pullman, and other researchers have been evaluating the Paraplow's effect on overwinter soil water storage. At a field site west of Colfax, WA, the researchers measured increased stored soil water during the past two winters under different stubble treatments. Standing, chopped and burned stubble treatments were used, with and without the Paraplow. Table 1 summarizes the average amount of increased soil water in four replications of the different treatments over two winters.

Table 1. Increased soil water storage from November to April, 1983-84 and 1984-85, with the Paraplow and different stubble treatments west of Colfax, WA (Saxton, Elliott, USDA-ARS, Pullman).

In the 1983-84 study period, winter wheat was no-till seeded into spring barley stubble after the Paraplow and stubble treatments were in place. The same treatments were conducted on winter wheat stubble in 1984-85. The site was then no-till seeded to barley in spring 1985.

The cereal stubble alone had a significant beneficial effect on soil water storage. On the non-Paraplowed treatments, standing stubble increased stored soil water about 2 inches over the fall burned treatment with no surface residue in both winter seasons. The chopped stubble treatment was intermediate in soil water storage. When the Paraplow was combined with the standing stubble treatment, an additional 2 to 3 inches of soil water was stored.

Soil water storage varied with yearly precipitation levels and runoff conditions. Precipitation amounts in the November and April monitoring periods were 11.75 inches in 1983-84 and 9.18 inches in 1984-85. The largest increase in soil water storage with Paraplowing and standing stubble was in 1983-84 when several runoff events occurred on frozen soils. However, little benefit was achieved in the burned treatment without surface residue. With little runoff occurring during the 1984-85 winter season, Paraplowing increased soil water storage about 2 inches on both the standing stubble and burned treatments.

Under these winter climatic conditions, the study indicates that Paraplowing, with standing stubble, can increase stored soil water by 4 to 5 inches compared to no surface residue as with fall burning. With an increased wheat yield potential of 5 to 7 bushels per acre for each additional inch of available water, Paraplowing in conjunction with surface crop residue can have a significant impact on production. STEEP research on the Paraplow and other conservation tillage equipment is being continued in the 1985-86 winter season.

NOTE: Beginning in 1987, the Tye Company began manufacturing and distributing the Paraplow under the trade name of Paratill.

Fig. 3. Measurement of the soil's resistance to a cone penetrometer before and after using the Paraplow (Hammel, Ul; Papendick, USDA-ARS).

Use of Trade Names

To simplify the information, trade names have been used. Neither endorsement of named products is intended nor criticism implied of similar products not mentioned.

Contact us: Hans Kok, (208)885-5971 | Accessibility | Copyright | Policies | WebStats | STEEP Acknowledgement
Hans Kok, WSU/UI Extension Conservation Tillage Specialist, UI Ag Science 231, PO Box 442339, Moscow, ID 83844 USA Redesigned by Leila Styer, CAHE Computer Resource Unit; Maintained by Debbie Marsh, Dept. of Crop & Soil Sciences, WSU