Authors: Karie Boone, Center for Sustaining Agriculture and Natural Resources (CSANR) at WSU; Dane Elmquist, University of Idaho
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Farmers have been planting winter peas in the Inland Pacific Northwest since the 1930’s. While the practice may not be new to dryland farmers, our growing understanding of how incorporating winter pea rotations impacts subsurface soil biology is just starting to blossom. The underground, subsurface world functions as a soil factory to help plants grow and is gaining increased attention.
Ongoing research is examining dryland wheat systems that include a winter pea in rotation in place of fallow or spring-planted legumes. Continued fallow use has negative implications for soil health, increasing the potential for erosion, decreasing soil organic matter content and biological activity. Spring-planted crops are subject to water and heat stress. University of Idaho entomologists are uncovering the impacts of this alternative crop on belowground arthropods (e.g., mites, beetles, springtails, centipedes) that dominate the soil ecosystem. Planting winter peas increased the abundance and biodiversity of beneficial soil fauna, like predators and decomposers. These critters contribute to soil health and crop productivity in agroecosystems by breaking down and incorporating crop residues into the soil, improving the cycling of nutrients through interactions with soil microbes, and controlling undesirable soil pests/pathogens (for example, root feeding insects or pathogenic nematodes). Using crops like winter pea to support soil arthropod biodiversity promotes these vital, naturally regulated, soil processes.
Knowing how different crop rotation choices impact soil health is important for making management decisions. Soil is a living ecosystem and using soil arthropods as biological indicators can reveal a lot about the condition of a soil. These arthropods were used to gauge how soil health was impacted when winter peas were incorporated into cereal rotations at two climatically distinct sites on the Palouse: St. John, Washington and Genesee, Idaho. Genesee typically has a wetter climate (24.5” mean annual precipitation) compared to St. John (17” mean annual precipitation). After a 3-yr rotation in both climates, incorporating winter pea improved soil health relative to rotations that used fallow or spring legumes. Soil health measurements used arthropods and their level of adaptation to the soil habitat as a bioindicator. This consistent response across climates contrasts with other diversification options, like cover crops, which have variable impacts on soil health across the region.
We know there are soil health benefits to increased rotational diversity and that these can have long-term benefits for soil productivity but what about the economic considerations? The economics of winter pea rotations have been a substantial barrier to adoption. Until 2009, peas planted in the autumn could only be marketed as ‘feed-quality’ and the farm gate value of feed peas is 50-60% less than that of food peas. US marketing regulations were changed in 2009 so that peas could be marketed based on their seed characteristics, not the season they were planted. When the marketing regulations were changed, breeders started developing food-quality winter peas – peas with large, smooth seeds and clear seed coats. In 2021, the USDA-ARS released the first three food-quality winter pea cultivars, USDA Dint, USDA MiCa, and USDA Klondike, and this may make fallow replacement more profitable. Switching from spring-sown to autumn-sown has many benefits for farmers in areas with similar annual precipitation to the study areas (17’’ and 24.5’’) including higher yields, shifting field work from unpredictable springs to autumn, and less water use than wheat.
Increasing the abundance and biodiversity of beneficial soil arthropods influences agricultural productivity in ways we are just starting to understand. “Listening” to what soil arthropods tell us about management decisions will help us continue to develop cropping strategies that improve the sustainability and productivity of dryland agroecosystems. We know management practices aboveground have significant and measurable impacts on the belowground soil factories and these practices come full circle as the driving engine of what we see growing (or not) on the surface. In the case of alternative crops, such as newly developed food-quality winter pea cultivars, the underground soil factory is functioning better.
The work that resulted in this timely topic was funded by the U.S. Department of Agriculture National Institute of Food and Agriculture grant No. 2017-68002-26819, Inland Pacific Northwest Wheat-based Systems: Landscapes in Transition.