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Wednesday, April 25, 2018

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11095. Smiley, R.W. and R.J. Cook. 1973. Relationship between take-all of wheat and rhizosphere pH in soils fertilized with ammonium vs. nitrate nitrogen.. Phytopathology 63:882-890.
Take-all of wheat was reduced by ammonium fertilizer supplemented with N-Serve to slow nitrification, but was severe with no added N, or with calcium nitrate at N rates equivalent to that supplied by ammonium. The addition of lime negated the control of ammonium. A good correlation existed between rhizosphere pH and disease severity, but not with bulk soil pH. The rhizosphere pH dropped with ammonium uptake, increased with nitrate uptake, and remained unchanged with no added N. Disease severity was progressively less as rhizosphere pH dropped below 7, and was greatly reduced below 6.6. In a fumigated soil, disease was controlled only when pH was below 5. Reduced disease severity apparently resulted from direct inhibition of the pathogen at pH less than 5 and indirect inhibition (possibly a biocontrol) above 5.

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