Rodweeding Frequency Effects On Seed Zone Moisture in Summer Fallow.

The winter wheat-summer fallow system dominates the dryland cropping landscape in the low rainfall (<300 mm annual precipitation) regions of Oregon and Washington because two years moisture are used to produce one crop increasing wheat yield and reducing economic risk.  In the fallow phase, tillage is used to control weeds and set a moisture line that permits timely seeding. The rodweeder is a ground-powered implement with a 2-cm square rod that rotates opposite the direction of travel that is essential to control weeds in tilled summer fallow.   We conducted a study at Lind, WA and Moro, OR to evaluate the frequency of rodweeding operations on seed-zone moisture retention and several other agronomic and environmental factors.  Soil at Lind was a Shano silt loam and the soil at Moro was a Walla Walla silt loam (Typic Haploxerolls). Average annual precipitation is 242 mm at Lind and 288 mm at Moro.  Plots received primary spring tillage plus aqua nitrogen (Lind) or urea-ammonium nitrate solution (Moro)  injection with a low-disturbance undercutter sweep implement in mid April with the following subsequent treatments: (i) no rodweeding (weeds controlled with herbicide), (ii) one rodweeding, (iii) two rodweedings, and (iv) five rodweedings. More than 30% residue cover was achieved at the Oregon site, but only the no rodweeding and 1x rodweeding treatments had 30% residue cover at the end of fallow at the Washington site. Grain yield, protein, test weight, and kernel weight were similar regardless of rodweeding frequency. Results suggest that primary spring tillage is all that is required to maintain seed-zone moisture in summer fallow and that rodweeding, although essential for weed control, is not required to “set the moisture line”.