AMMONIUM AND NITRATE IN THE RHIZOSPHERE OF SPRING BARLEY, HORDEUM-VULGARE-L AND TAKE-ALL DISEASE

The incidence and severity of take-all disease, due to Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici Walker, was observed on spring barley plants growing in soil in two glasshouse experiments. Soil amendments of NH+4-N significantly increased the number of diseased plants and roots during the first month after germination in comparison with controls unamended with N (P < 0.05). No significant difference in the incidence of take-all disease was detected between more mature barley plants growing in soil amended with either NH+4 or NO-3-N and unamended controls. The least take-all disease in 3 month-old barley plants was observed when N was supplied as foliar sprays of urea at 0.5 mg N kg-1 soil (P < 0.01). There was no significant correlation between the degree of infection and the NH+4-N to NO-3-N ratio in the rhizosphere soil. © 1979.