Iron Chelates and Supplements to Alleviate Iron Chlorosis in Soybean in High pH Soils.

High pH soils lead to iron (Fe) chlorosis in soybean (Glycine max).  The objective of this study was to evaluate Fe chelates and supplements to prevent and improve Fe chlorosis.  Greenseeker® (Trimble, Sunnyvale, CA) and SPAD chlorophyll meter readings were also evaluated as methods for identifying Fe chlorosis.  Three sites within the Blackbelt region of Alabama were tested in a randomized complete block design.  Ten treatments were used: Soygreen® (West Central, Inc., Willmar, MN) applied at 2.2, 3.4, and 4.5 kg ha^-1 in-furrow at planting; Soygreen® applied at 2.2 and 4.5 kg ha^-1 during the second trifoliate leaf stage (V3); Soygreen® at 2.2 kg ha^-1 in-furrow at planting and during V3 stage; Citraplex® (Loveland Products, Inc. Greeley, CO) at 1.1 kg ha^-1 in-furrow at planting and during V3 stage; ferrous sulfate at 4.5 kg ha^-1 during V3 stage; Citraplex® at 2.2 kg ha^-1 in-furrow at planting; ammonium sulfate at 101 kg ha^-1  in-furrow at planting; and a control without Fe supplement.  Prior to planting, soil was extracted using diethylene triamine pentaacetic acid (DTPA) and Mississippi (Landcaster) soil test methods for soil Fe.  Soil pH was also evaluated prior to planting.  Greenseeker® and SPAD chlorophyll meter readings were taken twice during the growing season, during V3 stage and 15 days later (V5) to evaluate chlorophyll content.  Leaves were collected at these times for determining Fe content.  Yield and seed weight were determined at harvest.  Ammonium sulfate had a negative effect on seed germination at most of the locations.  Although none of the supplements for alleviating Fe chlorosis increased yield, some treatments did improve seed weights.  SPAD and Greenseeker were not sensitive enough to detect differences in Fe chlorosis unless deficiency was severe.