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Severe Iron Deficiency Chlorosis (IDC) Causes in Eastern North Dakota (6/29/17)

Dr. Goos is a wonderful chemist in the NDSU Soils Department and it is his work that resulted in the first years of the regional IDC screening of varieties that Dr. Kandel now administers along with Dr. Helms, the NDSU soybean breeder.

Severe Iron Deficiency Chlorosis (IDC) Causes in Eastern North Dakota

Dr. Goos is a wonderful chemist in the NDSU Soils Department and it is his work that resulted in the first years of the regional IDC screening of varieties that Dr. Kandel now administers along with Dr. Helms, the NDSU soybean breeder. Varieties are much more tolerant now than they were 20 years ago, thanks to the work of Dr. Helms and other breeders working for commercial seed companies.  Research in the NDSU soil department showed that North Dakota/NW Minnesota IDC problems are different than those in Iowa.

IDC is impossible if pH is below 7. At least I haven’t seen it. That’s because carbonates dissolve when the soil is moist/wet and form the byproduct bicarbonate, which neutralizes the acidity soybean roots form in their immediate vicinity (rhizosphere), inactivating the pH sensitive enzyme that reduces oxidized iron (the iron present in topsoil) to reduced iron (the iron form in ground water which is a trillion times more soluble than oxidized iron). The soybean then responds by trying to decrease the rhizosphere pH and /or exuding more reducing enzyme, both requiring substantial additional plant energy at a time when iron supply into the plant is low. For a better description of this process, see the narrative in the NDSU soybean fertility circular.

In Iowa and other central soybean growing states, IDC is a minor temporary problem, because additional stresses to the plants are few. In our region, soluble salts are present in all but our most sandy upland topography landscapes. A colleague last year came up from Missouri to operate a Veris EC sensor across two of our plots where we had mutual protocols between 8 states in an N rate project, and was distressed that the site had soluble salts. I told him if you wanted a site in North Dakota, it was going to have soluble salts. He was astonished. Once there are carbonates in the soil, salts are a stress that is going to make the problem worse. This was first documented in the paper available at this link https://www.ndsu.edu/fileadmin/soils/pdfs/Plant_Nutrition.pdf .                                       

This season, in northeastern North Dakota, from Grand Forks north to Canada, water tables were high following last year’s high rainfall and salts moved to the surface with the shallow water table. This spring, although the northeast received a little more rain and snow than south, rainfall has been generally below normal; that’s good because the crop could be planted, but it also means that soil water is being pulled to the surface along with the salts it contains, leaving more salt near the surface than last year. The same is true for the rest of the state, although the initial water table in east central and southeastern North Dakota was lower than it was in northeast North Dakota.                

In addition, despite educational programs last fall and winter by me and other colleagues, urging growers to pay more attention to field soil EC (salt) readings before deciding to plant soybean, soybean was seeded in more acres than normal. Some of those acres should not have been seeded to soybean given their high EC levels. Also, though some growers pay attention to Dr. Kandel’s and Dr. Helms soybean IDC tolerance charts, significant numbers of farmers and their seed salesmen do not. I also think that seed was short because of higher demand for North Dakota maturity groups. A million extra bushels of seed is a lot of pressure on supply and it would tend to make salesmen sell varieties to fit maturity at the expense of IDC tolerance.

In addition, we are beyond the age of glyphosate as a stand-alone weed control option. We are almost back to the soybean world I grew up with, in which the question wasn’t whether the herbicide would injure the crop, but how much. Also linked is a paper from herbicide/IDC work I conducted with Dr. Zollinger before the world of glyphosate illustrating that the herbicide choices interact with IDC affected soybean.

Earlier in the season, the soil was dry at the surface, which was an agronomic worry because of what the crop would do, but at the same time it limited moisture that would solubilize bicarbonate and result in IDC. Then it began to rain a couple weeks ago. At my Absaraka site and Rutland site, where I have interactive weather stations, each has received 3 inches of rain during the past 2-3 weeks, right at the time when the soybean is most sensitive to IDC. The moisture dissolved carbonates, releasing bicarbonate, and the result is as you see, with astounding IDC.  In addition, last year was a great soil N mineralization year. I estimate that over 150 pounds N per acre were supplied by the soil in eastern ND during this most perfect year, 2016. The winter was relatively dry, or certainly not wetter than normal except for northern Walsh, and Pembina counties in NE North Dakota. The extra N applied in 2016, that wasn’t necessary and remaining after the wheat or corn crop, was not revealed in soil tests before soybean, because who would want a nitrate test before soybean? So there were vast acres of soybean seeded into land where the residual N was probably greater than 100 pounds N per acre. Although nitrate taken up by soybean does not limit iron uptake, it plays havoc within the plant cells, rendering iron in the cells unavailable. Work in Minnesota, led by North Dakota and also conducted in South Dakota, showed that the use of an oat cover crop seeded at the same time as soybean helped dry out the topsoil and used a little nitrate, greatly decreasing the effect of IDC on soybean. For nice images of the results of treatments from a Minnesota location, see my soybean fertility circular previously referenced.

Solid-seeded soybeans are much more susceptible to IDC than soybean planted at the same seeding rate, but in wider rows. A good example of that can be seen near the SHARE farm operated by Dr. Wick, soil scientist at NDSU, and her excellent cooperator. Their soybean is an IDC tolerant variety, because the field, particularly the west half, is high in EC and very susceptible to IDC. Their soybeans, with the tolerant variety in 30-inch rows, are perfectly green, while north across the road in similar soils are solid seeded soybean, and they are as yellow as any IDC bean in the country.

As Dr. Goos wrote in last week’s Crop and Pest Report, there is no satisfactory rescue application for this condition. However, it should prompt growers and suppliers to work out a better strategy for 2018. Field Selection/Tolerant Variety/Wider Rows/Cover Crop at Seeding/o-o-FeEDDHA at planting in furrow.

 

Dave Franzen

NDSU Extension Soil Specialist

701-799-2565

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