Updated July 4, 2018:
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Water Stress Development and Mitigation in West-Central North Dakota
R. Jay Goos and Jeremy Wirtz, Dept. of Soil Science, NDSU, and Eric Eriksmoen, North Central Research Extension Center, NDSU
Soybeans are being grown further and further west in North Dakota. Water stress is a common yield-limiting factor. The purpose of this research was to monitor the development of water stress in soybeans grown at Underwood, Cole Harbor, and Minot. Another objective was to determine if "anti-transpirants" could be used to slow water use earlier in the season, to make more water available later in the season.
Anti-transpirants slow water use by plants. Modes of action include hormonal or growth regulator effects, film or barrier anti-transpirants (which physically slow water escape from the leaves), and reflective anti-transpirants (which reflect light, making the leaf cooler). Our experiments had twelve treatments, with the treatments applied before flowering, after flowering, or both. Leaf water status was monitored using a reliable technique called the "Relative Water Content," which consists of measuring the water content of the leaves, allowing the leaves to take up water and rehydrate, and weighing again.
In general, our experimental treatments did not work. The year 2017 was an extremely dry year in western North Dakota, with water deficits (potential water use minus rainfall) greater than 10 inches. At Cole Harbor and Minot, the growth regulator ethephon did give some indication of increasing plant water status, but yields were not increased by anti-transpirant use at any of the three sites.
The patterns of water stress were different at the three sites. At the Underwood site, the plants were under only a slight to moderate water stress at the end of the growing season, and yields were acceptable, given the harshness of the growing season, at 28 bu/A. The Minot site was under a slight to moderate water stress for the entire last month of the growing season, and the yield was 16 bu/A. The Cole Harbor site was more vigorous than the Minot site for most of the growing season, but essentially "burned up" at the end of the season, and the yield was only 10 bu/A. Relative Water Content measurements less than 80% were observed, indicating severe stress.
This research is important to North Dakota soybean farmers, as a greater understanding of water stress, and how water stress affects yields will be important as soybean production moves west.