Epidemiology of wheat take-all as influenced by soil pH and temporal changes in inorganic soil N

Abstract

Soil pH, NH 4 + and NO 3 − concentrations in soil, and take-all root rot of winter wheat grown in the field were measured concurrently from sowing to anthesis in order to relate disease development to liming and N fertilization practices. Experimental variables included soil pH (5.5 and 6.0) and three N sources (NH4NO3, (NH4)2SO4, NH4Cl) banded with the seed at sowing in factorial combination with the same three N sources topdressed in the spring. Take-all severity was increased by increasing soil pH and by fertilization with NO 3 − . Disease severity on crown roots increased exponentially following spring N fertilization and was affected more by soil pH and N-form than was severity on seminal roots. Grain yield ranged from 4.70 Mgha−1 with spring NH4NO3 at soil pH 6.0 to 7.65 Mgha−1 with spring NH4Cl at soil pH 5.5. Sixty-six percent of the variability in grain yield was explained by the number of take-all infected crown roots per tiller at anthesis.