Cover Crops for Hop Production in Semi-arid Yakima Valley, Washington

View the project final report

• 2016 annual report

Commodities

• Agronomic: hops

Practices

• Crop Production: alley cropping, cover crops

The goal of this three-year research project is to determine a cover crop species or mixture that will be economically viable for hop growers in dry climates to conserve topsoil, control weeds, and improve soil fertility between hop rows or in rows as a mowed green manure. The study will take place in the Yakima Valley, a semi-arid region of central Washington that produces 29,021 acres of hops (USDA NASS), a staggering 76% of all hop production in the United States. This region receives eight inches or less of annual precipitation and wind gusts, leaving fine-textured topsoil prone to wind erosion when left bare and dry. Hops in the Yakima Valley are commonly grown in rows that are one to two feet wide and spaced 14 feet apart. Interrows are usually left bare and soil is managed by tilling after harvest, controlling weeds with herbicides and mowing, and using dust abatement measures of spraying water or spreading mulch on soil throughout the growing season. Dust is controlled not just to conserve soil but also to prevent its accumulation on the webbing of a severe hop pest, the twospotted spider mite (Tetranychus urticae Koch), which creates an insulation barrier against pesticides and natural predators. Herbicide options registered for hops have also recently become very limited, especially those that target grasses. Therefore, new weed control measures are of high interest. According to ongoing research and publications in central Washington orchards and vineyards by David Granatstein (WSU Center for Sustaining Agriculture and Natural Resources) and Joan Davenport (WSU Prosser Irrigated Agriculture Research and Extension Center), planting interrow cover crops could be an effective way to mitigate dust, suppress weeds, scavenge and reuse nutrients, retain soil moisture, increase biodiversity, and have many other unforeseen advantages; however, we estimate that only 10% of Yakima Valley hop growers utilize cover crops successfully. Many hop growers have indicated in casual conversation that they want to plant cover crops, but they are leery of options that could risk their limited time, water, and nutrient resources. Past cover crop studies specifically for hops have taken place in different climates or in production systems that provide supplemental overhead irrigation (i.e., SARE projects FNE11-711, FNE12-742, GNE12-033, and SW09-050), which is not always economically viable for hop growers to emulate in arid, water-limited regions such as the Yakima Valley. This project team, led by hop agronomist, Sarah Del Moro of John I. Haas, Inc. (Haas) and Technical Advisor, Joan Davenport of WSU, aims to take some of the time and resource risk out of deciding to use a cover crop for hop farmers. We will compare several drought tolerant crops in non-irrigated interrows to determine a species or mixture and best management practices that will be sustainable for hop farmers at large in dry climates. We are proposing this project for three years in order to gain confidence in measurements given variability of weather from year to year and time required for changes in soil properties to occur. We selected five main cover crop species to plant as monocultures and mixes with a control of bare, tilled soil for comparison. Crops were selected based on their potential to tolerate drought, shade, and heat while providing excellent ground cover to conserve soil and compete with weeds. The treatments span three 700-foot interrows each and are randomly replicated four times within a 30-acre hop field that we chose for uniform drip irrigation distribution, topography, and soil type (classified as Umapine silt loam with average pH of 8.3). The field is also split into two management regimes: one that uses mowed cover crops as a green manure in the hop rows, and the other that leaves mowed clippings in the interrow. Differences between these management zones and between all cover crop treatments and the control will be determined by a comprehensive array of measurements and an appropriate statistical analysis. For grower education outreach and materials, we will demonstre this project every year as a stop on the Washington hop industry field day, held in the Yakima Valley. Annual results will be presented at meetings and conferences, and open-access progress of the research will be updated on the company website and social media. Final results will also be published in a free “Cover Crops in Hops” guide and possibly as an article in a journal.

1. 1. To research the propensity of selected cover crops to conserve soil, increase soil fertility and retain soil moisture (Years 1-3)

1. 1. To investigate changes in pest, weed, and disease occurrence resulting from cover crops (Years 1-3)

1. 1. To construct a cost-benefit analysis for hop growers that includes expenses and gains related to cover cropping based on three years of data (published in Year 3)

1. 1. To deliver and demonstrate results of Objectives 1-3 to hop growers and encourage the adoption of likely sustainable cover crops as determined from our research (Years 1-3)

1. 1. To evaluate the impacts of this project using responses from other hop producers and industry professionals (Years 2-3)

We will begin Objective 1 in spring of 2015 by evaluating crop establishment and percent ground cover as an indicator of soil conservation potential between cover crop treatments and management zones. Soil in hop rows and interrows of treatments will be sampled each spring and fall throughout the study to quantify changes in soil pH, mineralized and total nitrogen, phosphorous, potassium, and other nutrients and soil properties over time. Objective 2 will be achieved by counting weed species and numbers from a subset area, while both harmful and beneficial insects and disease incidence will be counted from the total treatment area every week throughout the growing season.

For Objective 3, we will work with the Haas farm manager to assign costs and gains to factors related to each cover crop treatment, such as planting, maintenance, and contributions of water, nutrients, and pest control, together with general farming practices and weather changes between years. Treatment options that result in a net gain by the third year will be compiled into a summarized cost-benefit analysis and distributed to growers. This data and other results will also be used to demonstrate and promote the use of sustainable cover crops at field days, conferences, and through media, reports and publications to accomplish Objective 4. For Objective 5, we will use Western SARE Program Outreach Surveys from every event to analyze and respond to producer changes of opinion about adopting cover crop practices.

We have great confidence in attaining these goals based on a successful first step: in October 2014 we planted 11 cover crop monocultures and mixes, all of which were chosen to represent a range of characteristics in addition to drought tolerance. Planted crops consisted of ‘Vavilov II’ Siberian wheatgrass, ‘Sodar’ Streambank wheatgrass, ‘Henry’ hard fescue, ‘Don’ falcata alfalfa, and ‘Alba’ winter barley. As of June 2015, most crops were established (Figures 1 and 2), which will allow us to continue with the objectives and timeline outlined above.

• Figure 1. Spring 2015 barley establishment
• Figure 2. Spring 2015 wheatgrass establishment