Companion and Cover Cropping for Eastern Washington Dryland Grain Farms
Innovative dryland grain farmers in Lincoln and Spokane Counties, WA want to include a cover crop or companion crop in their rotation to raise soil organic matter levels, break disease cycles, suppress weeds, penetrate soil compaction layers, and improve soil fertility by fixing atmospheric nitrogen.
In addition, they want to make this system work with the winter precipitation (Mediterranean climate) of the area. So far, seeding cover crops in the spring in place of fallow results in excessive loss of soil moisture so that getting a crop germinated that fall has proven tricky. Consequently, the group is exploring other options.
The model for this project is that the farmer-collaborators develop the ideas for which cash cover crops to try, and they grow a demonstration block on their farms. The Extension professional repeats these tests in replicated strips (about 18 feet wide by 200 feet long) on the WSU Wilke Research Farm at Davenport, WA.
The project began (prior to funding from Western SARE) in the spring of 2011. While interest in the project from around the region has been high, we do not yet have “proven recipes” to share with other growers. It is truly a work in progress.
While the Wilke Farm and most of the farmers in the group use direct seeding/no-till farming, we believe that these cover crop methods should benefit any type of farming system.
Despite above average rainfall in August-September 2013, the rest of the 2014 crop season in the intermediate precipitation zone of eastern Washington was marked by drought (Figures 1 -3). This had a negative impact on our cover/companion crop trials at the WSU Wilke Farm. For this reason, we were not able to do any fall seeding in 2014, therefore 2015 will be all spring crops.
- Experiment with cover crop cocktails and companion/intercropping to develop mixtures and places in the rotation where they benefit soil health and moisture retention.
- In all the following trials, take soil tests each season to track changes in soil moisture, organic matter, and nutrients.
Wilke Cover Crop A
The group started the project in 2011 by growing a cover crop cocktail that was a nine-way mix: oats, peas, crimson clover, hairy vetch, mustard, safflower, sunflower, purple top turnip, and a sorghum-sudangrass hybrid. Details of the trail at the Wilke Farm are included in the table for Wilke Cover Crop A (Table 1).
Table 1. Schematic of Wilke Cover Crop Trial A
The cover crop plots were seeded in the place of no-till fallow, and there was a fallow check. The crop grew well but did not canopy enough to prevent evapotranspiration. It was terminated at flowering.
We tried to use a roller-crimper that will crush the stems of the plants and prevent further moisture loss (compared with mowing). However, the oats were so resilient that by the next day they were standing vertical and brought everything else back upright with them. So we sprayed out the crop with glyphosate.
In 2012 the plots were seeded to a winter or spring wheat (Table 1). The cover crop removed so much moisture from the soil that seeding winter wheat into it was delayed compared with the winter wheat on fallow ground. The disparity in wheat development resulted in herbicide damage when this was applied – thus the zero yield for that treatment. The spring wheat following cover crop yielded average for the area, so did not appear to benefit from the previous cover crop.
In 2013, the plots were all seeded to spring mustard. The intent was to harvest them separately but this did not happen. In 2014, the plots were all seeded to spring wheat. The intention was to seed some sort of cover crop in the fall of 2014, but this was not possible due to dry conditions.
We took extensive soil samples of each trial, each sample point being from several sample points within a plot and the plot data averaged over three or four repititions per trial. Here are a few of the charts developed.
Treatments for Trial A are as follows (Table A):
Figures 4a to 4c show how the cover crop treatments removed moisture from the soil initially. Treatment 1 then had slightly higher moisture at all depths shown in 2013, then the levels converged in 2014 as the effect of the cover crop diminished.
Figure 4a. Wilke Trial A moisture top 6 inches
Figure 4b. Wilke Trial A moisture 6 to 12 inches
Figure 4c. Wilke Trial A moisture 12 to 24 inches
Figure 5. Total nitrate levels following cover crops grown in treatments 1 and 2 in 2011.
We also charted soil sample data for organic matter (%), pH, and Total Nitrate (lbs). Figure 5 indicated that the cover crop provided extra nitrogen in 2012 over the previously fallow treatment (3) in the 6 to 12 inch zone. Caution should be taken in interpreting these data as absolute differences are small (6 lb)
Wilke Cover Crop B
In 2012 we used a five-way cover crop mix – per the recommendation of Jill Clapperton to have fewer species in this drier (than the Midwest) climate. There were more warm season species in the mix – proso millet and buckwheat – as well as faba bean, flax, and crimson clover. The treatments and details are shown in the table for Wilke Cover Crop B.
The summer of 2012 was the closest to a “summer rainfall” that we have had in the past 20 years, as evidenced by widespread incidence of stem rust across the region. Stem rust depends on summer moisture for development and spread. The cover crops grew well and canopied better at the Wilke Farm than the mixture the previous year (Trial A).
In 2013, the plots were seeded to winter and spring wheat (see Table B). The winter wheat following cover crop was lower than that seeded on fallow ground – but it wasn’t horrible.
In 2014, we grew spring barley across the plots and harvested them separately to continue to track the effects of the cover crop (Table 2).
Table 2. Schematic for Wilke Cover Crop Trial B
We have also collected soils data for this trial but no trends are obvious at this time.
Wilke Cover Crop C
After 2011, the farmer group decided we need to focus on growing cover crops that fit with our rainfall patterns and do not detract from establishing cash crops.
Prior to the development of synthetic fertilizers, farmers in the area grew yellow sweet clover (legume) to provide nitrogen for their soil. The plant fell out of use due to insect infestations, but it has naturalized in the region and grows in ditches and waste areas. We decided to try growing it as a companion crop, as used by Bob Quinn at Big Sandy, MT.
Yellow sweet clover (YSC) is a biennial. In 2012 we seeded YSC (broadcast with a hand-held fertilizer spreader) and cross-seeded the field with barley using a direct seed drill. Details are in the table for Wilke Cover Crop C.
The barley grew and was harvested as normal, except we used no fertilizer (we should have done) and there was no in-crop herbicide (field was very clean). The YSC was short under the barley. It went dormant in the fall and winter and started growing again the next spring (2013).
We sprayed the YSC out at two treatment stages: bolting and flowering. The theory is that rhizobia nodules slough off the roots of legume crops at flowering so they stop fixing nitrogen. We wanted to compare the effects of delaying the crop termination.
In 2014 we compared winter and spring cereals across these treatments (Table 3).
Table 3. Schematic for Wilke Trial C.
Wilke Cover Crop D
This trial was a repeat of YSC interseeded with barley, with details in the table for Wilke Cover Crop D (Table 4). We seeded the block in 2013, broadcasting the YSC as before. But as too much expensive seed was being buried by the barley seeding operation, we came in later (barley at 4-leaf stage) and cross-drilled more YSC into the stand. One of the farmers in the group (Ed Warner) recommended this from his experience.
We did not, however, use inoculant. We should have done so, as even though the YSC grows naturally in the area it does not nodulate well. We should use species-specific inoculant with every legume grown.
In 2014 we planned to spray out the YSC at bolting and flowering and compare subsequent crops in 2015. However, the overwintering stand of YSC was poor and weeds were prevalent in the plot, so we sprayed out the whole trial.
Table 4. Schematic for Wilke Trial D
Wilke Cover Crop E
In the fall of 2013 we seeded a companion crop mixture with winter canola, following the lead of farmer-collaborator Charles Gross. Details are in Table 5.
The idea here is that the companion crop: buckwheat (makes phosphate available), tillage radish, and peas will grow in the fall then die out over winter and hopefully not detract from the cash crop. We used a Roundup Ready canola, but that might not be the best choice and they are not as well adapted to the area as other varieties. We should have stuck to the belief that the companion crops will winterkill and no spraying out be necessary.
The fall was the best in years for seeding and the plots looked fabulous going into the winter.
Table 5. Schematic for Wilke Trial E.
The winter of 2013/2014 had some harsh periods. The RR winter canola on its own had a poor, spotty stand. It would have been better to use a better adapted variety that was hardier.
The companion crop completely choked out the winter canola it was seeded with. We need to use lower seeding rates for companion crops. However, the companion crop also choked out any weeds. The companion crop winter-killed completely, as intended. So those plots actually looked very clean in the spring. Although we had planned to continue this study, we ended up taking it out.
Following are two of the soils charts from Wilke Trial E (Figures 6 and 7).
Figure 6. Soil moisture tests from Wilke Trial E taken spring 2014
The most interesting sample was the 6-12 inch zone that had more moisture in the spring in plots that had a fall planted crop. It is possible that the decaying tap roots of canola and tillage radish did allow moisture penetration and storage over winter.
Figure 7. Total nitrate levels in Wilke E soil tests
The nitrate levels indicated that the canola plus companion crop was capable of mining nitrogen from the soil.
- Figure 4c. Wilke Trial A moisture 12 to 24 inches
- Table A. Treatments by year for Wilke Trial A
- Figure 1. Drought index January 2014 showing Lincoln County, WA, experiencing extreme drought.
- Figure 3. Drought index July 2014 showing Lincoln County, WA, experiencing extended drought.
- Figure 4a. Wilke Trial A moisture top 6 inches
- Figure 5. Total nitrate levels following cover crops grown in treatments 1 and 2 in 2011.
- Figure 6. Soil moisture tests from Wilke Trial E taken spring 2014
- Table 2. Schematic for Wilke Cover Crop Trial B
- Figure 7. Total nitrate levels in Wilke E soil tests
- Table 1. Schematic of Wilke Cover Crop Trial A
- Table 3. Schematic for Wilke Trial C.
- Table 5. Schematic for Wilke Trial E.
- Figure 4b. Wilke Trial A moisture 6 to 12 inches
- Figure 2. Drought index April 2014 showing Lincoln County, WA, experiencing extended drought.
- Table 4. Schematic for Wilke Trial D
Impacts and Contributions/Outcomes
We have learned the following so far:
- Always inoculate when seeding legume with species-appropriate inoculant.
- With companion crops, use seeding rates that won’t “smother” the cash crop.
- Use starter fertilizer at least with cover or companion crop seedings.
- Legume companion crops may not provide nitrogen to the current crop (only to subsequent crops).
- Cover crops seeded in the spring may reduce moisture availability for germinating the subsequent fall cash crop.
Regional interest in this project has been high, especially as NRCS is offering EQIP contracts for cover crops. We recommend that growers start out with small areas (less than 30 acres) of cover crops, as this is not a proven methodology for the area.
In 2014, we spoke at three field tours, reaching 101 participants. We spoke at three workshops, including the tristate (WA, OR, ID) Pacific Northwest Direct Seed Association conference, with a total of 130 participants. A survey at the PNDSA conference showed that 70% of attendees were interested in trying cover crops prior to the talk, and this level rose to 75% after that talk. Sixty-two percent rated continuation of the research Highly Important (5) and 23% rated it Fairly Important (4) on a ranking scale of 1 to 5.
One of the grower-cooperators on the project seeded 25 acres of yellow sweet clover as a companion crop with barley. We will evaluate this seeding in subsequent seasons.
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