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).
| Increased Soil Water Storage |
||
| Stubble Treatment | Paraplow | No Paraplow |
| 1983-1984 no-till winter wheat on barley stubble (inches per top 6 foot profile) |
||
| Standing | 7.8 | 4.7 |
| Chopped | 6.9 | 3.6 |
| Burned | 3.3 | 3.0 |
| 1984-1985 winter wheat stubble | ||
| Standing | 6.1 | 4.3 |
| Chopped | 4.3 | - |
| Burned | 4.0 | 2.2 |
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.
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