The results of the 2016 growing season suggested perennial grasses as the most profitable alternative to tillage for interrow weed control in semi-arid hop production. Barley seed was the least expensive seeding option, but ultimately provided the least benefit in weed competition after senescence. Barley also presented the possibility of becoming a weed by reseeding outside of the planted cover crop swath and into hop rows. Barley was discontinued as part of this study for the 2017 season. Of the grasses in this study, Siberian wheatgrass seed was less expensive than both streambank wheatgrass and hard fescue. However as of the 2017 growing season, hard fescue been the msot successful planting for ground cover. Further economic analyses will be performed following the completion of this study in 2018, after all soil samples have been analyzed. We will consider gains related to soil conservation, weed control, and increases in organic matter and losses related to seed cost and management (mowing). At the conclusion of the study, gains and losses attributed to other factors such as pest/disease control, fuel savings, etc. may also be included in the economic analysis.
The goal of this three-year study is to determine cover crop species that would be profitable weed control alternatives to tillage for hop producers in semi-arid climates by providing ground cover, weed competition, and soil quality benefits.
Throughout the 2016 and 2017 growing seasons, we continued to make weekly or biweekly measurements of percent ground cover and fraction of cover composed of weeds for monoculture treatments of barley (2016 only), Siberian wheatgrass, sodar streambank wheatgrass, hard fescue, and control plots of unplanted, cultivated interrows in hops.
This study took place on a mostly uniform hopyard with sandy loam soil. Cover crop species were chosen based on their tolerance to drought conditions and propensity to provide ground cover (for dust abatement). We attempted to vary the species selections among a legume (yellow-blossom alfalfa), perennial grasses (two wheatgrass spp.) and an annual grain (barley). There were also several treatments created by mixing the selected cover crop species; however after the first year of data collection, only the monocultures were evaluated because of lack of establishment among mixes. All cover crops were planted at higher recommended densities with a drill. The first evaluations began in spring of 2015. We made measurements every other week of the percentage of ground cover from planted cover crops and weeds, as well as height of the cover crop. In 2016 we began recording weed species. In 2017 we added measurements of soil temperature in each treatment (3″ depth), including the check plots. This seemed like a good metric to add, since many covers were by that time fully established and questions turned from, “Can these cover ground” to “what other effects are resulting from covered ground”. Soil samples were collected from each treatment once per growing season. These samples are being analyzed for pH, organic matter content, and complete chemical nutrients to provide a rough time-trend of changes in the driverow soil resulting from cover crops.
Results of this study were presented at the winter hop growers meeting in Yakima, WA on January 6th, 2017. Nearly 100 hop producers, researchers and other professionals attended the presentation of this project at the meeting. Of the attendees, 20% reported that the results of this study were likely to change their production practices. In March of 2017, this project was also presented at the Western Nutrient Management Conference in Reno, NV, which is attended by many professionals in agriculture. In the last year of this study, we intend to spend time producing multimedia of this project, including a YouTube production and a bulletin that can be distributed.
Results of the 2015 growing season allowed us to conclude that the sum of benefit from cover crop species mixes was significantly less than the sum of benefit from each of their monoculture treatments.
Barley plots achieved up to 95 and 80% ground cover in June of 2015 and 2016, respectively, with an average 7% of the cover composed of weeds. By Sept. of each year, and following plant senescence, barley plot ground cover decreased to an average 77%, with up to 58% of that cover composed of weeds. Barley was not replanted in the fall of 2016, and no measurements were taken of barley plots in 2017. In 2016, the well-established Siberian wheatgrass and streambank wheatgrass plots consistently achieved over 70% ground cover, and over 80% ground cover including mowed debris, with less than 10% of the cover composed of weeds. In 2017, the ratio of cover crop to weeds in Siberian wheatgrass and sodar streambank wheatgrass did not change. Progressing through the 2017 growing, Siberian and Sodar wheatgrasses seemed to senesce, dry out, and lose color and vigor, while hard fescue continued growing and remained green
By Sept. 2016, hard fescue achieved 50% ground cover following a positive trend since plant emergence, and weeds composed 10% of the cover. By Sept. 2017, hard fescue achieved nearly 80% ground cover, with weeds on average covering 8% of plots planted to hard fescue. In some replications, hard fescue has achieved 100% ground cover and 100% competition with weeds, as seen in this photo:
Alfalfa emerged minimally in 2015 and 2016 and measurements were not possible. Remarkably, the yellow-blossom alfalfa emerged with vigor in patches throughout planted plots during 2017, two and a half years after planting! Here is what the alfalfa looked like on June 23, 2017:
While it seemed to emerge, vigor of the alfalfa declined after the first mowing event on July 7, 2017. Cover crops were mowed overall much less in 2017 than in previous years. The plots with the tallest growing plants were actually the unplanted no-till control plots where weeds were left to grow. In commercial hopyards, weeds would require mowing at least once more often than a planting of any of the perennial grasses tested in this study.
Soil samples were collected from each of the plots in Oct. 2015, Nov. 2016, and Sept. 2017. Results are returning from the laboratory shortly and will be compiled into the final project report in fall of 2018.
Here are additional photos of each treatment within one replication of the trail from August 28, 2017. Listed as follows: 1. nonplanted, no-till control (weeds)
2. Hard Fescue
3. Siberian Wheatgrass
4. Sodar Wheatgrass
Educational & Outreach Activities
Several individuals and groups from different farms have visited the cover crop trail site for a more personalized tour. These are really all the same farms and people that would attend if we held a field day for the trial. A poster was produced that is currently on display at the local Washington State University Research and Education Center in Prosser, WA. The hop cover crop project was included in the overall presentations at the winter hop growers meetings in 2016, which were well-attended. At least 50 individuals from different farms and at least 24 other professionals working in the hops industry throughout the Pacific Northwest were in attendance.
Some current impacts from this research include larger scale planting of cover crops on the farm, and interest among some researchers and professionals in conducting further studies to analyze the effect of cover crops on hop pests and diseases as well as hop characteristics, yield, and quality. Many farms that have increased the acreage of cover crops planted in their hopyards have visited or discussed this project with us.
In 2018 we will be working more on producing educational outreach materials than collecting data. We plan to produce a YouTube mini-documentary and a distributable bulletin that will include the economic cost-benefit of cover crops in hopyards. We currently have three years of good data, soil sample results, images, discussions that we look forward to sharing.
This project has demonstrated an additional method for hop farmers to improve agricultural sustainability. While much remains to investigate on the effect of cover crops in hops, as well as type of crop and benefits/constraints of choosing a perennial grass over an annual grain, we pieced out the key variably of dust abatement. Cover crop treatments that effectively establish and create low-growing, dense biomass are ideal for minimal input dust abatement in hopyards. This can be considered part of an IPM program as dust is a major contributor to exacerbated two spotted spider mite populations in hops. Additionally, farmers are always working to improve sustainability practices and demonstrate those to various agencies that recognize and certify farms for their sustainable practices. Adding cover crops to the farm is recognized as an improvement to soil conservation practices, and among some agencies, possibly as an IPM strategy as a result of this study. While this study is not exhaustive of cover crop types, it has absorbed risk to farmers by demonstrating a few good options for the region.
The measurements taken in this study can be slightly subjective. For example, we determined ground cover visually. In many of the no-till control plots where weeds were left as ground cover, we were visually required to rank ground cover at a high rate, even though the cover consisted of taller, dried/senesced weeds such as mustard and kochia. Clearly these plants do not provide the same degree of dust abatement as an equivalent visual ground cover of dense, low-growing, green grass. Several more effective determinations of biomass, groundcover, or overall vegetative vigor can include NDVI imagery and direct biomass sampling. This year (2018) we will try to incorporate one of these measurement types across all treatments during the active growing season as a validation of results. Another way to get around this issue would have been to measure dust production directly. However this would have been more cost-prohibitive in materials and methods than assuming the known relationship of increased soil conservation to increased ground cover.