Canola versus wheat rotation effects on subsequent wheat yield

Authors: SCHILLINGER, WILLIAM - Washington State University; Paulitz, Timothy

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2018
Publication Date: 6/15/2018
Citation: Schillinger, W., Paulitz, T.C. 2018. Canola versus wheat rotation effects on subsequent wheat yield. Field Crops Research. 223:26-32.

Interpretive Summary: Canola is becoming increasingly important as a rotation crop in the wheat cropping system of the Pacific Northwest. It is used as a biofuel and oilseed crop, and acreage has increased over the last 10 years. One of the advantages of canola is the rotation benefits in wheat, with higher wheat yields reported after a winter or spring canola crop. In a 6 year field study, we grew spring wheat after a winter canola or winter wheat crop. Contrary to expectations, we found significant yield reductions after winter canola. We ruled out any differences in nutrients, water, weeds, and pathogens. We hypothesize that a change in soil microbes may be responsible for this effect.

Technical Abstract: Winter canola (Brassica napus L.) (WC) is considered the most promising, domestically-produced oilseed feedstock for biodiesel production and for diversifying wheat (Triticum aestivum L.)-based cropping systems in the Inland Pacific Northwest, USA (PNW). A law passed in 2006 requires that at least two percent of diesel sold within Washington State must be biodiesel. This law further mandates that at least five percent must be biodiesel when in-state production of oilseed feedstock can satisfy this requirement. Canola serves as a break or non-host crop for many important soilborne pathogens of wheat and helps farmers control weeds. Most studies in the literature on cereal-based cropping systems report that canola has a positive effective on subsequent cereal crop yield. We conducted a 6-yr field experiment near Davenport, WA to measure the effects of WC versus winter wheat (WW) on the subsequent production of spring wheat (SW). Averaged over the years, there were no differences between WC and WW in soil water use or overwinter water recharge into the soil following these crops. Subsequent SW had excellent plant stands, was weed free, was adequately fertilized, and had no foliar or root diseases. Average SW grain yield following WC was 3292 kg/ha versus 3897 kg/ha following WW; a 17% reduction (p<0.0001). Visual differences in SW treatments were also apparent. Spring wheat grain yield differences could not be attributed to the variables measured. Soil cores were collected and archived each year in the WW, WC, SW phases and we plan future comprehensive laboratory analysis of these cores to determine any soil microbial differences that may contribute to SW grain yield reduction following WC versus WW. This study provides novel information for ongoing efforts to promote and expand oilseed biodiesel feedstock production in the PNW and the influence of brassica crops on the subsequent performance of wheat.