ISSUE 7 June 21, 2007
WET WEATHER, CARBONATES AND IRON DEFICIENCY
Growers of soybean in eastern North Dakota are well acquainted with iron deficiency chlorosis (IDC). As the figure of soybeans shows, the deficiency will appear when the first trifoliate leaf appears, if the soil has carbonates and if there is sufficient moisture to dissolve the carbonates and make bicarbonate ions (HCO3-1). Soil, climate, and cultural practices that increase its severity are: high soil moisture, elevated levels of soluble salts, high soil nitrate, cool weather, thin stand, susceptible varieties, herbicide applications. Soil, climate, and cultural practices that decrease severity are: dry soil conditions, low salt, low nitrate, warm soils/air temperatures, planting in wider row widths, use of less harsh herbicides, more tolerant varieties.
Soybean affected by IDC
Other crops are also susceptible to IDC, although its presence is not as common as in soybean. Look for bright yellow color on leaves of monocot or dicot. On closer inspection, leaves will have interveinal yellowing, as in the wheat samples below. These plants will be in wet areas usually surrounding submerged soils, and the soils will be high in carbonates, with the possible presence of higher soluble salts. Most crops will recover some yield potential after the soil dries out and green color returns to the plants. The longer the crop suffers from this affliction, the higher the yield toll. In soybean, merely showing IDC symptoms for a short time will reduce yield by 5 bu/a. Soybeans that never green up all season usually yield less than 10 bu/a and often die out. Sprays of Fe products sometimes help the crop green up temporarily. However, the yield enhancement of the use of these products, especially in our region with higher soluble salts has not consistently helped economically. Products are being tested that have the potential to reduce susceptibility to IDC, but they need to be applied at seeding.
Wheat showing IDC symptoms, from western ND,
Dickinson area. Note that newer leaves are affected,
and show varying degrees of intervienal chlorosis or
N AND S DEFICIENCIES IN HIGH RAINFALL AREAS
There are continued reports of N and S deficiencies in high rainfall areas, especially in sandier soils. These mobile nutrients have leached out of the root zone and are preventing normal crop development. Topdress and sidedress will help alleviate these problems if the crop is not too far along. In small grains, the critical yield stage is jointing, or about 6 leaf stage. Application after this window may result in a bushel or two advantage, but not enough to pay for the application. In wheat, application later can result in a protein improvement. Spring wheat deficient in N will struggle to achieve 12% protein grain in most varieties. Improvement in protein may pay for the application if dockage for low-protein wheat is high.
In row-crops, particularly corn and sunflowers, yield determinations are made a little later on in the season relative to spring wheat. Still, earlier application allows the use of cheaper anhydrous ammonia as a knifed-in side-dress application. Other products, such as urea or 28% can also be knifed in or cultivated in if the soil dries. Later on when the crop is too big to allow subsurface application, dribbling on 28% between the rows is the most effective way of late-season N application, and S also. Liquid S products include dilute ammonium sulfate, or ammonium thiosulfate (12-0-0-26S), with ammonium thiosulfate being the most commercially available choice.
Dr. Dave Franzen
NDSU Extension Soil Specialist