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July 1, 2019 – June 30, 2020 Annual Report: Visual ratings for iron-deficiency chlorosis

Principal Investigator: Dr. Ted Helms, Department of Plant Sciences, North Dakota State University

Iron is less available to the soybean plant on high pH soils. The symptoms of iron-deficiency chlorosis (IDC) include leaves that are yellow in June and sometimes through July. Soybean growers with fields that have a past history of IDC need information to aid them in comparing varieties from many different companies in side-by-side comparisons. There are genetic differences among cultivars for tolerance to IDC. Even a small amount of yellowing in the soybean leaves can reduce final yield by twenty percent. We measure the tolerance to IDC by the amount of yellowing in the leaves. For fields with IDC, visual yellowing has been shown to be closely correlated to yield. This data provides unbiased information that enables growers to choose the best variety for their IDC prone fields. Choice of variety has been shown to be the most important factor to increase yield on fields where IDC is present.

The objective was to screen all private company varieties that have been entered into the Langdon Research and Extension Center (REC), Carrington REC, Minot REC, Williston REC and Fargo Main Station yield trials for visual ratings of IDC at multiple field locations with a past history of IDC symptoms. A second objective is to provide visual IDC screening of advanced NDSU breeding lines. Comparing soybean varieties from different companies requires that all varieties be evaluated in side by side comparisons in the same field. Otherwise, a fair comparison is not possible.

In 2019, four locations on farmer-cooperator fields with a past history of IDC symptoms were later planted with hill-plots. Four replicates of each genotype were planted at each test site. There were 257 Roundup Ready company varieties tested and 39 non-GMO company varieties tested. Also, the NDSU soybean breeder evaluated 90 advanced NDSU breeding lines for visual IDC symptoms. Those locations included Leonard, Erie, Hunter and Colfax, ND. Iron-deficiency chlorosis was not detected at the Hunter and Colfax, ND sites in 2019. A total of 6,304 hill-plots were planted.

This is the largest data set with the most comparisons of many different company varieties. Roundup Ready, Enlist, Xtend, and non-GMO cultivars were evaluated to provide data for soybean growers in North Dakota and western Minnesota. The 2019 data was averaged across both the Leonard and Erie, ND test sites with two locations and four replications per location. The data is quite reliable in aiding growers to select the best varieties for their IDC prone fields. This data enables growers to increase their yield on their IDC prone fields because those varieties with the least amount of yellow IDC symptoms will yield the best on those fields that have that problem. Data was analyzed and reported in the NDSU bulletin entitled ‘North Dakota Soybean Performance’ and was posted online. Relative rankings of the IDC ratings of the check cultivars were consistent with previous years.