WaSHI Annual Report FY25

Irrigated Columbia Basin Potato Systems LTARE

Othello, WA

A green tractor is driving through a field during harvest under a bright morning or late afternoon sun. The tractor is equipped with a front attachment for digging or lifting crops, and rows of partially harvested plants are visible in the soil. The surrounding area includes green grass on the left, farm buildings and equipment in the distance, and a clear blue sky with the sun shining overhead. The scene suggests agricultural work in progress, likely potato or root crop harvesting.
Potatoes were harvested and graded in September 2025.

The Long-Term Agroecological Research and Extension (LTARE) site in Othello, WA was reset in Spring 2025 after extensive planning. This site represents a major step forward in understanding soil health and sustainability in irrigated potato-based cropping systems in the Columbia Basin. The overarching goal of the site is to evaluate the long-term impacts of key management practices on soil health, disease dynamics, and crop performance.

Why this site matters

Growers in the Columbia Basin face unique challenges—soil-borne diseases, declining soil health, and the need for sustainable nutrient management under irrigation. The Othello LTARE trial focuses on three conservation practices identified by stakeholders as practical and impactful:

• Fumigation (+/-) using metam sodium, a common disease management tool with potential soil health trade-offs.

• Compost application (+/-) to build organic matter, improve cation exchange capacity, and stimulate microbial activity.

• Cover cropping (+/-) with diverse species mixes, including biofumigant crops like mustard, to enhance carbon inputs and soil resilience.

A table titled “All Rotation Phases Planted Each Year” showing seven treatments (Trt 1–7) with crop rotation phases and soil health practices. Columns include Phase 1 (Potato), Phase 2 (Field Corn), Phase 3 (Wheat), Fumigated, Compost, Cover Crop, and Summary. Details: All treatments have the same crop rotation: Potato → Field Corn → Wheat. Fumigation: Yes for treatments 1, 4, 5, and 7; No for 2, 3, and 6. Compost: Yes for treatments 2, 4, 6, and 7; No for 1, 3, and 5. Cover Crop: Yes for treatments 3, 5, 6, and 7; No for 1, 2, and 4. Summary column uses color-coded text showing combinations: Trt 1: +Fum Trt 2: +Compost Trt 3: +CC Trt 4: +Fum+Compost Trt 5: +Fum+CC Trt 6: +Compost+CC Trt 7: +Fum+Compost+CC The table uses shaded cells and colored text for visual emphasis.
The Othello site grows a rotation of potatoes, field corn, and spring wheat. Each crop is present every year.

These practices are tested in all possible combinations, plus a true control, across an eight-treatment split-plot design with four replications at the WSU Honey Bee Farm in Othello. The rotation includes potatoes, field corn, and spring wheat, ensuring each crop is present every year.

The site features three crop ranges and four replications aligned with irrigation spans. There are eight plots per replication, each measuring 30 ft (E–W) by 20 ft (N–S) with buffers between east-west plots. Plots are arranged in split-plot format, where main plots contain fumigation treatments and subplots contain compost and cover crop combinations. This design ensures robust statistical analysis while reflecting real-world management constraints.

A close-up view of a lush green cornfield under a clear blue sky. Tall corn plants with broad leaves fill the foreground, and a center-pivot irrigation system stretches across the horizon. The field appears healthy and well-maintained, with bright sunlight highlighting the vibrant green foliage.
Corn was planted in late May and set to be harvested in late October.

Progress in 2025

Following a 2024 test run, the trial was redesigned to accommodate a new linear irrigation system. Early challenges included low pump pressure and drought stress for potatoes and corn, prompting a major system renovation in Fall 2024. Permanent plot markers were installed, and Timothy grass was planted around the plot area to stabilize borders.

The first full season highlighted the complexity of integrating conservation practices under irrigation. In 2025, irrigation reliability improved, though hose failures in July caused temporary setbacks. Repairs required specialized equipment, delaying operations for 11 days. By late summer, a new hose system was installed to prevent future disruptions.

A close-up of a hand holding dry, clumpy soil in an outdoor setting. The soil consists of light brown aggregates and fine particles, indicating a dry condition. The background shows cracked, bare ground with a similar texture, suggesting an arid or drought-affected field. Shadows are visible on the soil surface, and the lighting indicates bright sunlight.
Infrastructure challenges resulted in irrigation delays and dry soils.

The site team led key management activities throughout the year.

  • Initial soil samples taken in February 2025
  • Crops fertilized in March 2025
  • Compost applied in March 2025
  • Crops planted May through August 2025
  • Potatoes harvested and graded in September 2025
  • Spring wheat harvesed
  • Mustard disked
  • Corn harvest is scheduled for late fall

Looking Ahead

The next steps for Othello LTARE include:

• Fumigation is lined up for late October to prepare for the next rotation cycle.

• Cover crops will be planted after cash crops, with species mixes evolving based on establishment success and stakeholder feedback.

• Comprehensive soil sampling to monitor changes in org anic matter, microbial activity, and nutrient dynamics.

• Yield and quality assessments for all crops to evaluate economic trade-offs.

• Stakeholder engagement through winter meetings to review progress and refine trial components.

A circular portrait photo showing a person wearing a light brown plaid button-up shirt over a white undershirt. The background is a mottled blue and purple studio backdrop. The image has a professional headshot style.

Tim Waters

Washington State University