What Does Winter Wheat Decomposition Have to Do with Climate?

by Georgine Yorgey

Managing crop residue is essential to reduced and no-till farming systems. These farming systems store more carbon than conventional farming systems, thereby mitigating climate change, enhancing soil health, and reducing soil erosion. In work described in a recent project report, Arron Carter and colleagues have been working to make it easier for growers with diverse needs across the Pacific Northwest to manage wheat residues. While the work is still in progress, it is an illustration of the kind of creative, applied work that is needed to make reduced-tillage systems easier to manage, and more widely adopted across the region.

Wheat growing in a field, with residues remaining from last year's harvest between the rows.
Wheat residue in a field in early July near Bickleton, WA. This area is part of the drier winter wheat-fallow area, where slower decomposing residues are preferred. Photo: Hilary Davis.

Growers in different parts of the dryland Pacific Northwest are seeking different residue characteristics. In most areas with less than 12 inches of annual precipitation, wheat is grown every other year, and land is fallowed in between to conserve moisture. Having a cultivar which has a slow straw breakdown would help reduce soil erosion by wind and retain more of the scarce water in the soil. In contrast, where annual rainfall exceeds 18 inches, wheat yield, and residue production, is much higher. As a result, when growers try to direct seed into the winter wheat stubble in the spring, it can oftentimes be difficult due to the high amount of remaining residue. Growers in these areas are searching for cultivars with residue that decomposes quickly.

Growers, and the seed dealers they work with, regularly request information on residue decomposition of winter wheat cultivars, but none is currently available. Arron Carter and colleagues’ therefore aimed to develop efficient methods to provide this information, and lay the groundwork for future breeding efforts that select for wheat varieties with the decomposition characteristics that growers want. The project explored the degradability characteristics of wheat, and how degradability might be dependent on both genetic and environmental factors. It is also seeking to identify regions of the wheat genome involved in degradability, and to develop new, faster methods for evaluating degradability, work that I don’t discuss in detail in this post, but that are covered in a longer post on WSU’s Center for Sustaining Agriculture and Natural Resources website.

The team analyzed a set of 151 lines created by crossing two varieties with very different decomposition characteristics (Eltan and Finch). Their initial results indicated that repeating the work with a population that had more genetic diversity would generate more conclusive insights. They are now in the process of repeating the work with a large diversity panel of 480 soft white winter wheat lines from the Pacific Northwest, that represents maximized allelic and phenotypic diversity.

The results from these studies indicated that both genetic and environmental factors are important for determining degradability, but not all lines respond to the environment in the same way. Thus, recommendations for growers in one location who want a degradable wheat residue are likely to be different than recommendations for growers in another location who want a degradable wheat residue. Using the results the team acquired from the diversity panel, which includes a large number of wheat varieties currently being grown, Carter is now able to give recommendations to growers across the region about varieties they should consider based on their residue needs. He has also discovered that this information is of interest to researchers working on other types of more sustainable systems across the region, for example, those seeking to develop approaches for using wheat straw to produce cellulosic ethanol.

This post is adapted from a longer blog post on Washington State University’s Center for Sustaining Agriculture and Natural Resources website, and the 2018 WSU CSANR Annual Report. The full grant report PDF is available online.


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