Rotation Benefits of Canola in Wheat-based Cropping Systems
Project Investigator: William Schillinger, WSU
Collaborators: Ann Kennedy, ARS; Doug Young, WSU; and Tim Paulitz, ARS
January, 2008 Progress Report
What Is known:
Winter wheat (WW) – summer fallow has been the dominant crop rotation on 3.5 million acres of dry cropland in the low (less than 12 inches annual) precipitation in the Inland Pacific Northwest (PNW) since the land was taken out of native bunch grass and sage 125 years ago. In the 2.4 million acre intermediate (12-to 18-inches annual) precipitation zone of the Inland PNW, a 3-year winter wheat – spring cereal – summer fallow rotation is widely practiced. There is a need for alternative crops in both the low and intermediate precipitation zones to break disease and weed cycles that affect cereal production and to offer farmers economic opportunities with crops other than wheat and barley.
Winter canola (WC) has been evaluated under both dryland and irrigated conditions in the Inland PNW since the 1980s. I have conducted agronomy research on winter and spring canola for the past ten years. We know that: i) Achieving stands of winter canola on summer-fallowed soils can be difficult; ii) Grain yield potential of winter canola is much higher that that of spring canola or yellow mustard; iii) Yield potential of winter canola is often limited by hot (>900F) air temperatures during flowering stage of plant development; and iv) Winter canola extracts more water from the soil than does winter wheat. We also have some evidence that water infiltration into frozen soil is enhanced in fields with standing winter canola stubble (compared to winter wheat stubble) and suspect that this is due to preferential water flow in channels created by the tap root. One experiment conducted near Moscow, Idaho showed that spring canola provided a rotation benefit to the subsequent wheat crop yield compared to planting wheat back on wheat stubble. A farmer south of Ritzville, WA has grown winter canola for many years and claims that he obtains higher winter wheat grain yields when the previous crop is winter canola (with a year of fallow in between) compared to monoculture winter wheat.
What is not known:
We need to identify whether improved soil physical, biological, or pathological factors may account for better water infiltration and increased wheat yield as affected by having winter canola in the crop rotation
Current research:
Specific objectives are to determine the benefits of winter canola grown in (i) a 4-year WC-SF-WW-SF rotation compared to the traditional 2-year WW-SF rotation in the low-precipitation zone and, (ii) a 3-year WC-SW-SF rotation compared to a WW-SW-SF rotation in the intermediate precipitation zone on:
- Grain yield of the subsequent winter wheat (low zone) or spring wheat (intermediate zone) crop.
- Economic assessment of WC-SF-WW-SF versus WW-SF in the low-precipitation zone and WC-SW-chemical SF vs. WF-SW-chemical SF in the intermediate-precipitation zone.
- Plant diseases of the subsequent winter wheat (low zone) or spring wheat (intermediate zone) crop.
- Soil microbial changes after winter canola versus after winter wheat.
- Soil water infiltration and frozen soil runoff after winter canola versus after winter wheat.
A 6-year experiment was initiated in 2005 at the Ron Jirava farm near Ritzville, WA. Average annual precipitation at the site is 11.5 inches. Seed-zone water at Ritzville is adequate in most years for establishment of winter wheat and winter canola into summer fallow. The experiment compares the 2-year WW-SF rotation to a 4-year WC-SF-WW-SF rotation. In late August, winter wheat and winter canola are planted into summer fallow in 16 by 200-ft plots with a John Deere HZ deep-furrow drill. Seeding rate for winter canola is 3 lbs/acre and for winter wheat 45 lbs/acre. Experimental design is a randomized complete block with 6 replications (total area per site is 0.9 acres). After grain harvest, the entire experiment area is left in summer fallow for the next 13 months, then planted to winter wheat. Nitrogen and sulfur (the same rate for WC and WW), based on soil test, is applied with shanks during May of the summer fallow year. Grain yield of WC and WW is determined using a plot combine. The four corners of the experiment sites are mapped with a global positioning unit so that the precise location of all plots can be determined for the ensuing SF and WW cycles.
A similar experiment was initiated in late-August 2007 at the Hal Johnson farm located NE of Davenport, WA. Average precipitation at this site is 17 inches. The traditional 3-year WW-SW-chemical SF rotation will be compared to a 3-year WC-SW-chemical SF rotation. All crops at the Davenport site will be produced using no-till. Experimental design, plot size, and grain harvest methodology will be the same as at the Ritzville site. Fertilizer rate, again based on soil test, will be somewhat higher than that used at Ritzville. Winter canola and winter wheat will be planted and fertilized with an 8-ft-wide no-till plot drill equipped with Kyle hoe-type openers. Computerized weather stations are in place at both sites.
In addition to grain yield, soil volumetric water content is measured in all plots at time of planting in late August, in mid March, and again at grain harvest. During the winter after the harvest of WC and WW, ponded water infiltration rate is determined in each plot within a 2-foot-diameter infiltrometer ring when surface soils are partially or completely frozen. Plant diseases (Paulitz) and soil microbial attributes (Kennedy) that include pH, electrical conductivity, and dehydrogenase enzyme activity are determined each year where the previous crop was either WC or WW. At the end of the study in 2011, an economic assessment of the two cropping systems will be conducted for both the low and intermediate precipitation sites by (Young) using standard enterprise budgeting procedures.
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