Updated December 2, 2016:
Final Progress Report is downloaded in the File (optional) below

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From the Ground Up: How Salinity Gradients Damage Soybeans, Contribute to Arthropod Pest Infestations, and Impact Soil Nitrogen Reserves

Principal Investigators:
Abbey Wick, Dept. of Soil Science; Tom DeSutter, Dept. of Soil Science; Jason Harmon, Dept. of Entomology; Deirdre Prischmann-Voldseth, Dept. of Entomology, NDSU

Technical Support:
Kirsten Butcher, Graduate Student, Dept. of Soil Science
Jackie Eichele, Graduate Student, Dept. of Entomology
Chandra Langseth, Extension Research Technician, Dept. of Soil Science

FY Year End Report: June 30, 2016; Executive Summary

Approximately 1.2 million acres in the Red River Valley are classified as slightly saline. Soybeans are very salt sensitive, so even low levels of salts can significantly hurt yields. For soybeans, this results in crop losses of $57 million annually. Much of the existing information on soybean response to salinity does not apply directly to North Dakota soils or the types of soluble salts we have here. From 2013-2016, a series of greenhouse and field studies were conducted at NDSU to look at soybean response and resulting pest pressures to low levels of salinity in conditions specific to North Dakota.
Soybean grown in sandy loams soils were found to be considerably more sensitive to soluble salts than previous studies suggest. We found soybean yields began to decline at a soluble salt level of 1.1 mmhos/cm, instead of 1.9 mmhos/cm originally identified in other studies not conducted in North Dakota. Fifty percent yield reductions occurred at soluble salt contents of 2.2 mmhos/cm (Figure 1). No yield reductions at low levels of salt (< 3 mmhos/cm) were observed for a silty clay loam soil texture.

Increased pest numbers on plants grown in higher salinity soils has been consistently observed in our greenhouse studies and was also found in our field study. In general, pests can do better on plants grown in more saline soil (Figure 2). However, there is some variation in this results from field to field which suggests there may be other factors involved in determining how salinity affects the pests. In the greenhouse we have also been performing detailed studies to better understand how pests, like the soybean aphid, benefit from being on plants in saline soil. In addition to having more babies and producing large populations, we have found that aphids on plants grown in saline soil live longer and make babies for longer. Plus, they will preferentially move toward plants grown in saline soil, which means that may be able to find and take advantage of high salinity areas within fields.

These results are extremely important for soybean growers in North Dakota experiencing yield reductions as a result of salinity. We are finding that it is not just the yield loss that growers need to consider when selecting a crop for saline areas, they need to also consider the pest pressures. Managing saline areas differently (for example, tillage management, crop selection, fertilizing, pest scouting and spraying) from the remainder of the field not affected by salts becomes important for the grower’s bottom line.