Initiation of a Winter Canola Early-Fallow Seeding Date StudyMegan Reese, W. Pan, W. Schillinger

Variables Measured1) Soil profile moisture throughout the growing seasons• Decagon soil temperature, moisture, and

EC sensors, 2 hour increments• Neutron attenuation to measure

volumetric water content incrementally down to 6 feet, every other week

• First foot soil cores by AMS sampler for gravimetric analysis, every other week

2) Plant nutrition and soil fertility • Initial and post-harvest soil ammonium and

nitrate by KCl extraction• Biomass samples for N, C content by LECO

combustion analysis, every fourth week3) Winter kill• Stand counts in fall and spring4) Various yield parameters when harvested in the summer

Future ResearchThis experiment will be conducted for several seasons. Statistical evaluations

and other practical analysis – such as plant available water calculations – will becompleted. Next season, Russian Thistle and insect ecology will be monitored aswell, to determine if planting date affects these pest pressures.

Experiment and Site Details• 4 planting dates of Flagstaff winter canola

• June 10, June 26, August 5, and August 12, 2013• 8’ x 100’ plots direct-seeded into fallow• 4 replications of each date, and fallow for comparison• Ritzville silt loam, pH 6.0-6.5, bulk density 1.35 g/cm3

• 30-year average annual precipitation of 11.85 inches

IntroductionWinter canola can introduce diversity into the traditionally winter

wheat-fallow rotations of Washington state’s low rainfall zones. Previousstudies have established late July through late August as the optimumplanting window, contingent upon forecasted cooler weather. However,stand establishment and winter-kill can be major impediments, so earlierplantings may be beneficial. There may be a relationship between plantingdate and soil available moisture throughout the season – which in turn canbe correlated to canola yield. Therefore, soil available moisture andextraction depths are main focuses of this research. The ultimate objectiveof this experiment is to clarify an optimum winter canola planting windowby determining canola responses to variable temperature and moistureregimes. This multi-year study was initiated in the summer of 2013.

Special thanks to Decagon Devices for their contributions to this project

Preliminary DataFigure 3 shows volumetric water content on 2-Dec. At this time, canola foliage

had just frosted, so no further plant influence is anticipated until spring regrowth.Data indicate that the earliest canola plantings (10-June, 26-June) have extractedwater at a depth beyond the measured six feet. On the other hand, the mostrecent canola planted (12-Aug) did not extract appreciably more than the fallowplots, apparently utilizing precipitation.

Figure 3. As measured on 2-Dec, average volumetric water content down to six feetfor each planting date. The 0-12 inch depth was determined from two 6-inch coresamples and analyzed using gravimetric procedures. From 12-66in, data wasobtained in 1 foot increments by neutron attenuation.

Figure 4. Average volumetric water content as measured at five different times forthe 5-Aug planting date. Values obtained in the same manner as Figure 3.

The volumetric water content of the 5-Aug planting date plots at differenttimes is shown as a representative example in Figure 4. It is clear that more water– and water deeper in the soil profile – is utilized as time progresses. However,this extraction appears to stabilize, with similar readings occurring from 21-Octuntil 2-Dec (later dates omitted).

Questions to Ponder- Have the earlier plantings extracted more fallow summer moisture than can be

recovered by winter recharge? Will they face water shortages before harvest?- Will the later plantings have poorly-established root systems and therefore be

more susceptible to winter-kill?

Figure 1. Downloading datafrom a Decagon data logger.

Figure 2. The left picture depicts a slide hammer used to obtainone-foot cores. An arrow shows a neutron probe access tube.Seen on the right is the neutron probe, which is incrementallylowered down to 6 feet.

10-June 26-June 5-Aug 12-Aug

Photos taken 11-Nov