- Response from nitrogen and chloride fertilization was measured
in field experiments on winter wheat (Triticum aestivum L. Em.
Thell. var. 'Stephens' and 'Yamhill') grown in western Oregon in an
environment with a range of susceptibility to take-all root rot
(Gaumannomyces graminis var. tritici Walker). Cropping sequences
and expected disease severity considered in the study were: first
year wheat after clover (low risk of severe take-all root rot:
Nixon I experiment), second year wheat with high disease infection
in the previous crop (high risk of severe take-all root rot: Keyt
II experiment), second year wheat with low disease infection in the
previous crop (moderate risk of severe take-all root rot: Nixon II
and Coon experiment), third year wheat (high risk of severe take-all root rot: Jones experiment), fifth year wheat (high risk of
severe take-all root rot: Keyt II experiment), and eighteenth year
wheat (take-all decline established: the pathogen is present in the
soil but does not cause damage, Evers experiment). Nitrogen
treatments were applied at 0, 67, 134, and 202 kg/ha in all experiments where wheat followed wheat and at 0, 45, 90, and 134
kg/ha in the experiment where wheat followed clover. Chloride
treatments were applied at 0, 45, and 90 kg/ha in all experiments
and a rate of 134 kg C1/ha was also used on the Jones experiment.
Nitrogen was predominantly supplied from urea while ammonium
chloride supplied chloride and ammonium sulfate supplied the crop
requirement for sulfur (about 20 kg/ha). Fertilizers were top-dressed
in split application with chloride and sulfur containing
fertilizers applied first (February) and urea applied later (March)
in all experiments but those conducted in the Nixon farm where a
single fertilizer was applied in March. Crop response was measured
through the effects of N and c1 treatments on dry matter production, plant nitrogen content, plant nitrogen uptake and plant
percent nitrogen recovery, as well as grain yield, yield
components, grain nitrogen content, grain protein content, grain
nitrogen uptake, and grain percent nitrogen recovery.
The results of the study strongly indicated that take-all root
rot was only a problem in the Jones, Keyt I, and Keyt II experiments and was most severe in third year wheat (Jones experiment).
This also was the only experiment with significant (p = 0.05)
response from rates of 202 kg N/ha.
Nitrogen fertilization was the main factor that greatly
influenced the levels of the variables studied while chloride
fertilization generally did not have a significant (p = 0.05)
influence. 134 kg N/ha was generally the rate accounting for the best levels of each variable studied in all experiments except in
the Jones experiment as precised earlier.
Crop response was also affected by a relatively long 'dry'
period (April 20th to June 20th), particularly in the experiment
where take-all root rot was a problem.
Levels of the variables studied accounted for by the optimum
rates of N were consistently higher in the experiments where take-all root rot was not a problem than where it was a problem by the
following amounts: dry matter yields-17%, plant nitrogen contents-18%, plant nitrogen uptake levels-30%, plant nitrogen recoveries-28%, grain yields-22%, grain nitrogen contents-only 4%, grain
protein contents-only 2%, grain nitrogen uptake levels-26%, grain
nitrogen recoveries-18%, and spikes/m²-24%.