Wednesday, November 15, 2006

Manure and nutrient supplements effect on iron-deficiency chlorosis in soybean.

Lori Scott, Southwest Research & Outreach Ctr., 23669 130th Street, 23669 130th Street, Lamberton, MN 56175, United States of America

Anecdotal evidence suggests that manure application may improve or worsen iron-deficiency chlorosis symptoms in soybeans.  We planted five soybean varieties with four supplement treatments including application of liquid hog manure, application of K, application of P, and a control treatment with no supplement applied at five locations.  The supplements were applied in two 12-inch bands about six inches from each side of the hill plots at the time of emergence.  Application rates were 2.36 g TSP per strip (80 lb P2O5/ac), 1.86 g potash per strip (86 lb K2O/ac), and 300 mL manure per strip (2800 gal/ac).  Subsequent nutrient analysis of the manure indicated that the P content in the manure was lower than anticipated and the actual rates of P2O5 and K2O applied as manure were 40 and 94 lb/ac.  Chlorosis symptoms were scored visually on a 1 (no chlorosis) to 5 (severe chlorosis with necrosis or death) scale.  Chlorosis scores for varieties were significantly different from each other but supplement treatment effects were less significant.  Compared to the control treatment having no supplement, manure worsened IDC scores and P or K alone improved IDC scores – control vs. manure (P = 0.06), control vs. P2O5 (P = 0.14), control vs. K2O (P = 0.06).  If neither the P nor K component in the manure is associated with worsening of chlorosis that the manure itself is associated with it may be the N content or another component of the manure affecting IDC.  The presence of nitrate may discourage nodulation, reducing the iron-uptake siderophore activity that would otherwise be present with the root nodules.