|Abstract or Summary
- Take-all root rot (caused by Gaeumannomyces graminis var.
tritici, Ggt) is one of the major diseases limiting winter wheat
yields in western Oregon. Losses caused by take-all (TA) can be
significantly reduced through crop management and fertilization
Results from field experiments in western Oregon show that the
use of chloride with NH₄-N is an effective tool to minimize grain
yield losses in fields with TA. This study was undertaken to
determine the effects of fall- and spring-applied chloride
fertilizers on the components of leaf water potential, grain yield
and disease severity of winter wheat with TA.
Winter wheat field plots were established on a Woodburn soil
(Aquultic Argixeroll) on 15 October 1980 at a site previously cropped
to first-year wheat after fallow. Spring fertilizer application was
on 16 March 1981. Twenty treatments were arranged in a randomized
complete block design to study the effects of source, rate, method of application and timing of chloride fertilizers on grain yield,
disease severity and leaf water potential components. Other
comparisons included rates of P and Cu plus Zn banded in the fall,
and fall and spring nitrogen rates. Grain was harvested with a plot
combine on 30 July 1981, and grain yield, test weight and 1000 kernel
weight were measured.
Disease severity was assessed using two methods, (1) visual
estimation of black root lesions on three dates, and (2) whole plant
fresh weights on 2 July 1981. Leaf osmotic potentials and plant
nutrient concentration were measured on four dates. Leaf water
potential components (turgor, osmotic and leaf water potentials) and
plant nutrient concentrations were determined during May and June on
second-year wheat and once on third-year wheat from an adjacent
site. A partial diurnal water curve for (NH₄)₂S0₄- and NH₄Cl-treated
plants was measured on 2 June 1981, on third-year wheat.
Grain yields were increased by 1000 kg/ha with the addition of
spring chloride as NH₄CI, KCl or CaCl₂. Arate of 92 kg spring Cl/ha
was adequate to achieve the highest grain yield (6633 kg/ha). Grain
yield was not significantly affected by rate, source or method of
application of fall-applied chloride, fall or spring N rates, or by
the application of P or Cu plus Zn banded with the seed at planting.
Application of 368 kg spring Cl/ha as NH₄Cl reduced severity of
take-all and increased whole-plant fresh weight when compared to
(NH₄)₂S0₄ at the same rate of N, but the differences were not
statistically significant. Disease severity was not significantly
affected by either rates or sources of spring chloride. Grain yields were negatively correlated to disease severity indices. Spring
chloride fertilizers applied as NH₄Cl or KCl significantly increased
percent total N in flag leaves sampled in late spring, while the
percent leaf chloride was increased with application of either KCl,
NH₄C1 or CaCl₂.
Osmotic potentials in flag leaves of second-year wheat were
significantly reduced (from -21.6 to -22.6 bars) over the nil CI rate
by application of spring chloride fertilizers. Ninety-two kg Cl/ha
was adequate to reduce the osmotic potential. Spring chloride at 368
kg Cl/ha significantly increased turgor potentials in both secondand
third-year winter wheat, and significantly decreased osmotic
potentials (2 bars) in second-year wheat when compared to (NH₄)₂S0₄-
treated plots at the same N rate. Potassium chloride significantly
reduced leaf and osmotic potentials at the 185 kg Cl/ha rate.
Potassium chloride did not increase turgor.
The results of this study support the recent literature
indicating that application of spring chloride in combination with
ammonium-nitrogen to moderately acidic soils reduces the severity of
take-all and increases yield of winter wheat.