PNW
CONSERVATION TILLAGE HANDBOOK SERIES
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 |
CT |
NT |
CT |
|
| (bu/acre) |
||||
| 0 |
16.5 |
18.1 |
16.9 |
17.1 |
| Banded |
41.4 |
45.2 |
46.3 |
43.5 |
| Broadcast |
30.8 |
35.7 |
42.4 |
39.7 |
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 |
||
| Conventional |
Paraplow/No-till 1 |
No-till |
|
| Winter wheat-Spring barley-Spring peas |
70.7 |
77.9 |
83.1 |
| Winter wheat-Spring peas |
69.9 |
81.1 |
81.5 |
| Winter wheat-winter barley-Spring peas |
74.0 |
89.7 |
78.2 |
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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