Winter wheat-summer fallow rotation. Moro, OR. Photo provided by Stephen Machado.

No-till cropping systems can replace summer fallow in north-central Oregon and south-central Washington

Issue: Annual cropping, necessary for soil organic matter maintenance or buildup, is difficult to implement in most parts of north-central OR and south-central WA, where annual precipitation is less than 280 millimeters. Most wheat growers in these regions are still practicing the traditional winter wheat–summer fallow rotation using some form of tillage. Previous studies have shown that this cropping system depletes soil organic matter, exacerbates soil erosion, and is not biologically sustainable. Some growers remain skeptical about alternative cropping systems such as the wheat–fallow system using no-till or chemical fallow that have the potential to alleviate the negative impacts of the traditional wheat–fallow system.

Action taken: To inform growers transitioning from the traditional winter wheat–summer fallow system to no-till systems, we established a long-term experiment in the 2003–04 crop year to identify no-till fallow systems and annual cropping systems that could replace the traditional wheat–fallow system without sacrificing grain yield. After six years of study, average grain yields of winter wheat in the no-till winter wheat–chemical fallow rotation (3.43 megagrams per hectare) and winter wheat–spring barley–chemical fallow rotation (3.76 megagrams per hectare) were not significantly different from wheat grain yields under the traditional wheat–fallow rotation (3.56 megagrams per hectare). Notill fallow systems continued to yield more than traditional fallow systems in the 5-year period that followed. Water use efficiency was very similar among the three fallow systems. Results also show that no-till annual cropping of winter wheat, spring wheat, and barley, although risky, can be practiced in this region. Weeds were easier to control in the annual cropping rotation compared to other rotations.

Results: Given the benefit of no-till systems to soil conservation, adoption of no-till winter wheat–chemical fallow or the more-intensified winter wheat–spring barley–chemical fallow rotation in place of the traditional winter wheat–summer fallow system is recommended. Annual cropping of spring wheat and spring barley under no-till is also recommended if deemed profitable. Annual cropping was observed to increase soil surface residues and soil organic matter, factors essential for enhancing grain yields, supporting agricultural sustainability, and developing climate-resilient cropping systems.

Prilled biochar from Walking Points Farms. Photo provided by Howard Boyte, CEO, Walking Point Farms LLC.

Biochar builds soil organic matter and raises soil pH

Issue: Up to 60% of soil organic matter has been lost since the 1800s, when cultivation started in wheat–fallow lands of the Pacific Northwest. Soil organic matter has become depleted because of limited biomass production, which is due to low precipitation and fallowing every other year. In addition, the continued use of ammonium-based fertilizers has increased soil acidity to less than pH 5.0 in the top 15 centimeters of soil. Soil pH below 5.2 interferes with wheat growth, biomass production, and yield. Increased soil organic matter and favorable pH levels (pH 6 to 7) are essential for improved crop productivity and sustainable agriculture under a changing climate.

Action taken: Biochar, charcoal produced from pyrolysis and resistant to decomposition, has the potential to improve soil health. Adding biochar to soil sequesters carbon that would otherwise be lost to the atmosphere as carbon dioxide through burning or natural decomposition, where it would contribute to global warming. We evaluated the effects of biochar derived from forest wastes on crop yields, soil pH, and nutrient dynamics. Biochar was applied to field plots under a winter wheat–spring pea rotation and to soil samples with or without fertilizer in a greenhouse experiment.

Results: In the field, application of biochar increased grain yield, and the yield increase has persisted for three years even without further biochar applications. Biochar increased pH by 0.42 units (5.76 to 6.18) but did not influence other nutrients. In the greenhouse study, biochar increased wheat shoot biomass and root biomass as well as soil pH. Applying biochar to soil samples also increased phosphorus, potassium, and sulfur, but not nitrate and ammonium.

Results indicate that biochar has the potential to increase crop yields from wheat and spring peas while sequestering carbon. Increasing pH may have increased nutrient use efficiency, resulting in higher crop yields. The positive effects from biochar have persisted for three years, and the study continues to monitor yield without any further applications of biochar. 

Spreading biosolids on a wheat field in Douglas County, WA. Photo by Craig Cogger.

Building soil organic matter with biosolids

Issue: Building soil organic matter levels in the inland Pacific Northwest has proven to be challenging in our traditional cropping systems. The one management factor linked to substantial soil organic matter increases, as documented in long-term trials at Pendleton, OR, is the addition of organic amendments such as animal manure.

Action taken: We conducted a comprehensive review of biological soil amendment research. In addition, we analyzed soil samples from a 20-year experiment conducted near Okanogan, WA, where a wheat–fallow system has been fertilized with either King County, WA, biosolids or commercial anhydrous ammonia. We analyzed archived soil, plant, and biosolids samples to assess carbon and nitrogen balances in the system over 20 years.

Results: Total soil organic carbon and nitrogen more than doubled over 20 years during biosolids application, while sufficiently fertilizing the wheat–fallow system. Anhydrous ammonia mostly contributed to grain nitrogen production. Gains in soil organic matter included stable organic matter fractions, providing further evidence that adding organic amendments like biosolids should be credited as an effective way to sequester carbon and reduce greenhouse gas emissions. Studies of long-term biosolids application on sequestration of carbon and nitrogen in other systems such as perennial grass pastures are continuing beyond REACCH.

Crop diversification at WSU Wilke Farm

Issue: The low- and intermediate-rainfall zones in the dryland cropping region of eastern WA often rely on a tillage-based, summer-fallow system to produce winter wheat. Yet reducing fallow and improving crop diversity are important to reduce erosion and improve long-term soil health.

Action taken: The Washington State University Wilke Research and Extension Fam is a 320-acre direct-seeded facility located in the intermediate-rainfall zone. The farm has been divided into eight large plots (22 to 67 acres each). One plot is in a continuous crop rotation, three plots are in a 3-year rotation (no-till fallow–winter wheat–spring cereal), and four plots are in a 4-year rotation (no-till fallow–winter wheat–broadleaf crop–spring cereal). We collected agronomic and economic data each year comparing the performance of the three rotations.

Results: There has been no difference in returns over production costs between the 3-year and 4-year rotations, and both of these rotations have outperformed the continuous crop rotation. Our findings have helped farmers stretch their rotations and reduce the overall amount of summer fallow and especially tillage-based summer fallow. Since the inception of this project, an estimated 25 farmers within a 20-mile radius of the farm have purchased direct-seed drills. These farms represent significant acreage under a no-till or direct-seed farming system.

Soil organic carbon (SOC) and total nitrogen (N) levels and their relationship to mean average temperature (MAT)/mean average precipitation (MAP) × 0.01 at present and under future climate scenarios for 2050 and 2100 across four dryland sites.

Climate change could negatively impact soil organic matter

Issue: Predicted future climate scenarios for the inland Pacific Northwest (PNW), including warmer temperatures relative to precipitation levels, could negatively impact soil organic matter and associated soil health.

Action taken: Using long-term experiments throughout the dryland cropping region of the inland PNW, we assessed the relationship between soil organic carbon and the climate ratio—mean annual temperature divided by mean annual precipitation—as well as cropping intensity and soil disturbance. We alsocalculated future projections of the climate ratio to assess climate change impacts on soil organic carbon.

Results: We discovered a strong relationship between soil organic carbon and the climate ratio, where soil organic carbon declines as the climate ratio increases. The climate ratio was the dominant driver of soil organic carbon compared to both cropping system intensity and soil disturbance. Using future climate projections, we calculated that the climate ratio would increase throughout the region in response to climate change. Therefore, climate change could reduce overall soil organic carbon levels throughout the region. If this occurs, future soil health within the region would also decline.