|Return Tillage Handbook|
Conservation Tillage Handbook Series No. 27
|Date||Conventional tillage||Minimum tillage||Delayed minimum tillage|
|Aug||Sweep - 12 in. shank spacing, 14-in.-wide sweeps, 5 in. depth. Sweeping was not conducted in 1996, 1997, and 1998.||Herbicide - 6 oz. glyphosate + 32 oz. 2,4-D/a in 1993; 32 oz./a glyphosate in 1994 and 1995. Not required in 1996, 1997, and 1998.||Herbicide - 6 oz. glyphosate + 32 oz. 2,4-D/a in 1993; 32 oz./a glyphosate in 1994 and 1995. Not required in 1996, 1997, and 1998.|
|Nov||Chisel - 24 in. shank spacing, straight point, 10 in. depth.||Chisel - 48 in. shank spacing, straight point, 10-to-16 in. depth. Not conducted in 1996. Rotary subsoiler, 16 in. depth in 1997 and 1998.||Chisel - 48 in. shank spacing, straight point, 10-to-16 in. depth. Not conducted in 1996, 1997, and 1998.|
|Feb||Herbicide - 12 oz./a glyphosate.||Herbicide - 12 oz./a glyphosate.||Herbicide - 12 oz./a glyphosate.|
|Mar , ||Primary tillage - cultivator, overlapping 7-in.-wide sweeps, 5 in. depth + 5-bar spring-tooth harrow (two passes). Tandem disk, 5 in. depth (one pass) in 1997 and 1998.||Primary tillage - undercutter, overlapping 32-in.-wide V-blades, 5 in. depth + rolling harrow.|
|Apr||Anhydrous NH3-N injection @ 40 lb/a.|
|May||First rodweeding, 4 in. depth.||First rodweeding, 4 in. depth.||Primary tillage - undercutter, overlapping 32-in.-wide V-blades, 5 in. depth + rolling harrow.|
|June||Second rodweeding, 4 in. depth.||Second rodweeding, 4 in. depth.||First rodweeding, 4 in. depth.|
|July||Third rodweeding. 4 in. depth.||Third rodweeding, 4 in. depth.||Second rodweeding, 4 in. depth.|
|Sept §||Sown to winter wheat @ 40 lb/a.||Sown to winter wheat @ 40 lb/a + aqua NH3-N injection @ 40 lb/a.||Sown to winter wheat @ 40 lb\a + aqua NH3 injection @ 40 lb/a.|
sown to hard red spring wheat in March 1995 because winter wheat failed
due to dry seed zone conditions in September 1994.
Skew tread to cut and incorporate high quantities of residue in all treatments on 1 March and again on 15 May in 1998.
§ MT and DMT treatments first "blind sown" in 1997 with just the drill's packer wheels in order to pass through 1785 lb/A residue without plugging during actual sowing.
in the 6 ft soil profile were made immediately after grain harvest in
late July-early August (beginning of fallow), in March prior to primary
tillage, and again in late August-early September just before sowing winter
wheat. Soil volumetric water content in the 1-to 6-ft depth was measured
in 6-in. increments by neutron attenuation. Volumetric water in the 0-to
1-ft depth was determined from two 6-in. core samples using gravimetric
procedures (Gardner, 1986). In addition, volumetric water content in the
seed zone was determined in 0.8-in. increments to a depth of 9 inches
just before sowing winter wheat in early September of 1994, 1995, and
1996 using an incremental soil sampler (Pikul et al., 1979). All soil
water measurements were obtained from three locations in each plot.
Surface soil cloddiness
was determined at the end of the fallow cycle in 1994, 1995, 1996, and
1998 by measuring the diameter of individual soil clods within a one-yard diameter sampling hoop randomly positioned at three locations in each plot. Wheel tracks were avoided. All clods with diameters equal or greater than 2 inches were sorted into 0.5-in. size increments and the mass of each size group measured in the field with a battery-powered digital scale. Clod mass was not measured in 1997 because clod structure was dispersed during an intense rain shower. Subsurface soil cloddiness was measured by gently dry sieving 0.35 ft3 of soil from the 0-to 4-in. tillage mulch layer through stacked 2 in.2, 1 in.2, and 0.5 in.2 mesh screens. Clods not passing through each of the three mesh screens were then weighed. Subsurface clod measurements were obtained from the same one-yard diameter area where surface clods had just been removed, therefore surface clods greater than 2 in. diameter were excluded from subsurface samples. Oriented roughness in all plots was measured soon after sowing in September using the chain method (Saleh, 1993).
Surface residue remaining
from the previous crop cycle was measured several times throughout the
fallow period by clipping and gathering all aboveground dry matter within
a one-yard-diameter hoop. Three samples were always obtained from each
plot. Wheat straw and dead Russian thistle plants were separated, placed
in paper bags, and allowed to air dry in a low-humidity greenhouse before
Winter wheat stand
establishment was determined by counting individual plants in one-yard-long
row segments 21 days after sowing. Grain yield was determined in mid-to-late
July by harvesting a 20-ft swath through each 150-ft-long plot with a
commercial-size combine and auguring grain into a weigh wagon.
recorded at a standard U.S. Weather Bureau shelter located < 0.5 mi
from the experiment site (Table 2). A frost depth tube (McCool and Molnau,
1984) was installed in undisturbed winter wheat stubble near the weather
shelter and freeze-thaw status of the soil was recorded daily throughout
Analysis of variance
was conducted for total soil water content in the 6 ft profile, seed-zone
water content, quantity of surface residue, surface cloddiness, subsurface
cloddiness, surface roughness, wheat stand establishment, and grain yield.
The procedure used to compare treatment means was Fisher's protected least
significant difference. All statistical tests were done at the 5% level
Table 2. Precipitation during six 13-mo-long fallow cycles compared with the 80-year average at Lind, Washington.
|Time period||1993-1994||1994-1995||1995-1996||1996-1997||1997-1998||1998-1999||80-yr avg.|
--------------------------------------- inches ---------------------------------------------------------------------
RESULTS AND DISCUSSION
Residue at the beginning of fallow (just after harvest) ranged from 2000 to 5000 lb/A during the 6-year period, and was lowest after a spring wheat crop (1993-1994 and 1995-1996 fallow cycles, Table 3). Russian thistle produced more dry matter by the time of grain harvest than dry matter for the spring wheat crop. The important contribution of dead Russian thistle plants as residue during fallow after low crop production years in this study has been reported (Schillinger et al., 1999). By using herbicides instead of tillage for post-harvest Russian thistle control, and non-inversion undercutter V-sweeps for primary spring tillage, significantly greater quantities of surface residue were maintained with MT and DMT when compared with CT on all sampling dates (after the onset of tillage) during all years (Table 3). Retention of sufficient residue for government farm program compliance (> 350 lb/a) during fallow was not a problem, even with CT, when the previous winter wheat crop produced 3500 lb/A or more straw.
Surface Clods, Subsurface Clods, and Roughness
years, the mass of surface soil clods 2 in. or more in diameter at time
of sowing in September was 9, 16, and 20 tons/a for CT, MT, and DMT, respectively
(Fig.1). The DMT treatment generally resulted in the greatest surface
clod mass because the undercutter V-sweep did little mixing or disturbance
to the surface soil layer, which was dry when primary spring tillage occurred
in mid-May to early-June. The greater mass of surface clods in 1996 compared
with other years is likely due to extensive and prolonged freezing of
the soil during the 1995-1996 winter (data not shown) which generally
promotes a more stable clod structure. The skew treader tillage operations
in March and May of 1998, to cut and incorporate large quantities of surface
residue into shorter lengths, resulted in a major reduction in surface
clods compared with other years when the skew treader was not used (Fig.
1). Quantities of blowing dust collected from portable wind tunnel (Pietersma
et al., 1996) tests on soils at the Lind Dryland Research Station (Horning
et al., 1998), and on the tillage management experiment at Lind(K.E. Saxton,
unpublished data), were significantly reduced with increasing levels of
residue, clods, and roughness.
Table 3. Quantity of surface residue as affected by conventional, minimum, and delayed minimum tillage during the 13-mo-long fallow cycle. Values in parenthesis for 1993-1994 and 1995-1996 fallow cycles are the percentage of total dry biomass comprised of dead Russian thistle plants.
------------------------ lb/acre ----------------------------------------
|5 Sept.||3020a (56%)||3005a (57%)||2980a (55%)|
|7 Nov.||655b (29%)||2705a (56%)||2595a (52%)|
|10 May||455c (12%)||1005b (29%)||1400a (38%)|
|17 Aug||275b (16%)||780a (31%)||890a (36%)|
|12 Sept.||3080a (57%)||3100a (58%)||3225a (59%)|
|18 Dec.||1005b (34%)||2140a (43%)||2215a (44%)|
|5 April||560c (17%)||1225b (28%)||1680a (37%)|
|12 June||500b (16%)||910a (25%)||1045a (27%)|
|29 Aug.||390b (15%)||750a (28%)||770a (26%)|
Within-row means followed by a different letter are significantly different at P < 0.05.
Figure 1. Mass of surface soil clods 2 inch diameter or larger at time sowing in early September for 1994, 1995, 1996, 1998, and the 4-year average as affected by conventional, minimum, and delayed minimum tillage during fallow. Within year, averages followed by a different letter are significantly different.
In the subsurface
(0-4-in.) tillage mulch layer, masses of 0.5-to 1.0-in. and 1.0-to 2.0-in.
diameter clods in 1995 and 1996 were greater in MT and DMT treatments
compared with CT, but there were no differences for subsurface clods 2
in. and larger (Fig. 2). Growers feel that finely divided soil aggregates
within the subsurface tillage mulch layer are desirable for retarding
evaporative water loss from summer fallow, thus there is a perception
that CT is required for optimum soil water conservation. Similar to surface
clods, the skew treader implement used in 1998 reduced subsurface clod
mass compared with previous years and there were no differences in subsurface
clods among treatments (Fig. 2).
There were no differences in oriented soil roughness between MT and DMT measured just after sowing winter wheat. Both MT and DMT had rougher surfaces than CT, except in 1998, when there were no differences among treatments (data not shown), presumably due to use of the skew treader on all plots.
Figure 2. Subsurface (0-to 4-in. depth) soil clods in 1995, 1996, and 1998 as affected by conventional, minimum, and delayed minimum tillage during fallow. Within year, averages for each subsurface clod size group followed by a different letter are significantly different.
Soil Water Content
Figure 3 shows that
there was little or no difference in soil water content among treatments
immediately after grain harvest (beginning of fallow) during any year.
Less than 6 inches of water remained
in the 6 ft soil profile at the beginning of fallow, except in 1993 (Fig. 3a) when 2.1 in. of rain fell in July after wheat had reached physiological maturity and was no longer extracting soil water.
efficiency (SE) is defined as the percentage of precipitation occurring
during the fallow cycle that is stored in the soil. Over-winter SE (from
late-July to March) was extremely low (range 3 to 14%) in 1993-1994 (Fig.
3a) because: i) water from the 2.1 in. July rainfall event likely evaporated
after beginning-of-fallow soil water measurements were obtained, and ii)
only 4.1 in. of over-winter precipitation occurred, the least for any
year of the study and well below the long-term average (Table 2). Over-winter
SE was significantly improved with MT and DMT compared with CT in 1994-1995
(Fig. 3b) when several January and February precipitation events occurred
when surface soil was frozen to depths as great as 12 inches (data not
shown). The 16-in.-deep channels created by wide-spaced chiseling in MT
and DMT likely allowed precipitation to infiltrate into unfrozen soil,
whereas infiltration was probably impeded in the CT treatment because
the soil was frozen below the 10 in. chiseling depth.
Figure 3. Soil water content in the 6 foot soil profile during the 6-year (1993-1999) study period: i) at the beginning of each fallow cycle in early August, ii) in early spring after over-winter soil recharge had occurred, and iii) at the end of the fallow cycle in early September as affected by conventional, minimum, and delayed minimum tillage. Averages for each sampling date followed by a different letter are significantly different. Numbers above bars show storage efficiency (SE), i.e., the percentage of precipitation occurring during the fallow cycle which was stored in the soil. NS=Not significant
During the 1996-1997
fallow cycle, when no fall chiseling was conducted in the MT and DMT treatments,
several winter precipitation events occurred on frozen soil, or on thawed
soil overlaying a frozen layer, extending as deep as 9 inches (data not
shown). The CT treatment stored significantly more water in the soil than
MT or DMT (Fig. 3d). This was presumably due to frozen soil restricting
water infiltration in non-chiseled soils while channels in the chiseled
soils extended below the depth of frost. The 1995-1996, 1997-1998, and
1998-1999 winters were relatively open and mild, and there were no over-winter
SE differences among treatments (Figs. 3c, 3e, and 3f). Averaged across
6 years, over-winter SE was 51, 54, and 57% for CT, MT, and DMT, respectively.
These over-winter SE values are considerably higher (61, 62, and 65% for
CT, MT, and DMT, respectively) if 1993-1994 is excluded from the data
Water remaining in
the soil profile at the end of fallow cycle was always in the same relative
ranking among treatments as measured over-winter, i.e., highest for MT
and DMT in 1995 (Fig. 3b) and for CT in 1997 (Fig. 3d), but not different
in the other years (Figs. 3a, 3c, and 3e). The 5-year average end-of-fallow
SE was 24, 26, and 26% for CT, MT, and DMT, respectively.
There were no differences in seed zone water content among treatments in 1994, 1995, and 1996 (Fig 5). Sowing of winter wheat was attempted in 1994, but the deep-furrow drill could penetrate no deeper than 8 inches, which was not adequate to reach the minimum soil water content (11% by volume, Fig. 4a) required for emergence from deep sowing conditions on silt loam soils (Lindstrom et al., 1976). Seed zone water content was adequate in 1995 (Fig. 4b) and 1996 (Fig. 4c) as well as in subsequent years (comparative measurements not taken) in all treatments. Many growers feel that it is necessary to create a fine "dust mulch" on the soil surface to retard evaporative soil water loss from fallow during the summer. These data, however, show that the greater mass of surface clods (Fig. 1) and sub-surface clods (Fig. 2) in the MT and DMT treatments did not adversely affect seed zone water content compared with CT.
Figure 4. Seed-zone soil water content at time of sowing in September 1994, 1995, and 1996 as affected by conventional, minimum, and delayed minimum tillage during fallow. There were no water differences among treatments at any depth (0-to 9-inch) in any year.
and Grain Yield
Winter wheat seedling stand establishment was not affected by tillage treatment, except in 1996, when CT stands were greater than in MT and DMT (data not shown). Differences in 1996 are likely due to the larger quantities of surface clods in MT and DMT compared with CT (Fig. 1), as many seedlings were unable to elongate around clods that rolled into the furrow during sowing. These stand differences in 1996 did not affect grain yield.
There were no differences in grain yield among treatments during any year or when averaged over 5 years (Fig. 5). Due to generally favorable precipitation and growing conditions, grain yield averaged across treatments and years in this study was 52 bu/a compared with the long-term (30 year) average winter wheat grain yield at Lind of 35 bu/a. Janosky (1999), who conducted an economic analysis of this study over the 6-year period, reported that MT and DMT slightly out performed the CT system in terms of net returns over total costs.
Figure 5. Yearly and 5-year average grain yield of wheat as affected by conventional, minimum, and delayed minimum tillage during the preceding fallow cycle.
1. Surface residue
retention during fallow was consistently and significantly increased using
minimum tillage (MT) and delayed minimum tillage (DMT) compared with conventional
tillage (CT). When wheat straw production was low, the minimum quantity
of surface residue (350 lb/a) required for highly erodible soils for government
farm program compliance could not be achieved or was marginally met using
CT, whereas ample surface residue was always present in all years with
MT and DMT.
2. On average, twice
the surface soil clod mass and a rougher surface was achieved with MT
and DMT compared with CT.
3. Chiseling in late
fall with straight-point shanks benefited over-winter precipitation storage
efficiency (SE) in two out of six years when water runoff or snowmelt
occurred on frozen soils, but had no effect during open winters when runoff
was not a factor. Creating deep tillage channels at wide spacing in late
fall with MT and DMT was equal to or greater for over-winter SE than with
CT, where chisel shanks were more closely spaced and operated at a shallower
depth. The best option to maximize over-winter water storage with minimal
residue disturbance may be to create narrow pits about 16 inches deep
with a long-tooth rotary subsoiler, with approximately one pit every 8
4. Seed-zone water
at the end of fallow (measured 3 years) was not affected by tillage treatment.
This suggests that finely divided soil particles within the tillage mulch
may not be as important for retarding evaporative water loss during the
summer as previously thought. Rather, creating of an abrupt break between
the tilled and non-tilled layer with primary spring tillage, which severs
capillary channels from the subsoil to the surface, appears to be the
dominant factor regulating over-summer evaporative water loss.
5. Delaying primary
spring tillage until mid-May and beyond had no adverse agronomic affects
compared with MT and CT. The late winter application of a nonselective
herbicide provided excellent control of downy brome (Bromus tectorum)
and broadleaf weeds until at least 1 May in all years in the DMT treatment.
Downy brome, the most problematic grass weed in the region, was well controlled
in all tillage treatments during all years of the experiment.
6. Surface residue in excess of 1800 lb/a at time of sowing in MT and DMT treatments plugged the deep-furrow drill in 1997. This problem was easily remedied by 'blind sowing' (with only the drill packer wheels) prior to actual sowing. Several implements, such as the coil packer, rotary hoe, and skew treader will bury, align, or otherwise cut straw to allow effective drill operation in heavy residue; but these implements also pulverize soil clods and, therefore, are not recommended in low-residue situations.
In conclusion, conventional tillage during fallow held no agronomic or economic (Janosky, 1999) advantages over MT or DMT in this 6-year experiment. The CT system had distinct environmental disadvantages, especially when straw production from the preceding wheat crop was less than 3,000 lb/a. This research showed that, with judicious use of herbicides, tillage operations during fallow can be effectively reduced from eight (CT) to as few as three (DMT). If MT and DMT fallow management were widely practiced on Shano soils in the Columbia Plateau of eastern Washington, it is reasonable to expect a sharp reduction in wind erosion and suspended dust emissions, with associated benefit to air quality. Minimum tillage and delayed minimum tillage practices, as outlined in this paper, can be implemented by wheat growers with little or no hardship to their livelihood.
Information Center. 1997. 1997 National crop residue management survey.
pp. 81. Cons. Tech. Info. Center, West Lafayette, IN.
Gardner, W.H. 1986.
Water content. p. 493-544. In A. Klute (ed.) Methods of soil analysis.
Part 1. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI.
Hammel, J.E., R.I.
Papendick, and G.S. Campbell. 1981. Fallow tillage effects on evaporation
and seedzone water content in a dry summer climate. Soil Sci. Soc. Am.
Horning, L., L. Stetler,
and K.E. Saxton. 1998. Surface residue and soil roughness for wind erosion
protection. Trans. ASAE 4(4):1061-1065.
Horning, T.R., and
M.M Oveson. 1962. Stubble mulching in the Northwest. Agric. Info. Bulletin
No. 253. USDA-ARS and Oregon Agric. Exp. Station, Corvallis, OR.
Janosky, J.S. 1999.
An economic analysis of conservation tillage cropping systems in eastern
Washington. M.S. thesis, Washington State Univ.
R.I. Papendick, and F.E. Koehler. 1976. A model to predict winter wheat
emergence as affected by soil temperature, water potential, and depth
of planting. Agron. J. 68:137-141.
McCool, D.K., and
Molnau, M. 1984. Measurement of frost depth. p. 33-41. In B.A. Shafer
(Ed.) Proc. Western Snow Conf., 17-19 April, Sun Valley, Idaho.
Papendick, R.I. (Ed.).
1998. Farming with the wind: Best management practices for controlling
wind erosion and air quality on Columbia Plateau croplands. Washington
State Univ. College of Agric. and Home Econ. Misc. Publ. MISC0208.
Pietersma, D., L.D.
Stetler, and K.E. Saxton. 1996. Design and aerodynamics of a portable
wind tunnel for soil erosion and fugitive dust research. Trans. ASAE 39(6):2075-2083.
Pikul, J.L., Jr.,
R.R. Allmaras, and G.E. Fischbacher. 1979. Incremental soil sampler for
use in summer-fallowed soils. Soil Sci. Soc. Am. J. 43:425-427.
Saleh, A. 1993. Soil
roughness measurement: Chain method. J. Soil Water Cons. 48(6):527-529.
and F.E. Bolton. 1993. Fallow water storage in tilled vs. untilled soils
in the Pacific Northwest. J. Prod. Agric. 6:267-269.
and R.I. Papendick. 1997. Tillage mulch depth effects during fallow on
wheat production and wind erosion control factors. Soil Sci. Soc. Am.
Schillinger, W.F., R.I. Papendick, R.J. Veseth, and F.L. Young. 1999. Russian thistle skeletons provide residue in wheat-fallow cropping systems. J. Soil Water Cons. 54(2):506-509.
Conservation Tillage Handbook Series publications are jointly produced
by University of Idaho Cooperative Extension System, Oregon State
University Extension Service and Washington State University Cooperative
Extension. Similar crops, climate, and topography create a natural
geographic unit that crosses state lines in this region. Joint writing,
editing, and production prevent duplication of effort, broaden the
availability of faculty, and substantially reduce costs for the
Northwest Conservation Tillage Handbook is a large, three-ring binder
handbook that is updated with new and revised Handbook Series publications.
It was initiated in 1989 as a PNW Extension publication in Idaho,
Oregon and Washington. Updates to the Handbook are provided when
the updating card is returned. By the end of 2000, 55 new PNW Conservation
Tillage Handbook Series had been added to the original 98. Copies
of the complete Handbook are available for $20 through county extension
offices in the Northwest or ordered directly by calling state extension
publication offices: Idaho -- (208) 885-7982; Oregon -- (541)-737-2513;
Washington -- (509) 335-2999 (some shipping and handling charges
and sales tax may apply).
It's now accessible on the Internet! All of the PNW Conservation Tillage Handbook and Handbook Series are on the Internet home page (http://pnwsteep.wsu.edu) Pacific Northwest STEEP III Conservation Tillage Systems Information Source. The home page also contains recent issues of the PNW STEEP III Extension Conservation Tillage Update, listings of other conservation tillage information resources, coming events and much more. For more information on the Handbook or other Web site information, contact Roger Veseth, WSU/UI Conservation Tillage Specialist, Plant Soil and Entomological Sciences Department, University of Idaho, Moscow, ID 83844-2339, phone 208-885-6386, FAX 208-885-7760, e-mail (email@example.com).
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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