| Summary: | The effect of serial (multiple-year) organic matter (OM) amendment on
soil properties has been described in some cropping systems, although less is
known about the effect of serially amended field soils on soil-borne plant diseases.
The objectives of this study were to describe the effects of the third and fourth
years of annual, serial amendment with dairy manure solids on 1) soil physical and
biological properties and 2) severity of sweet corn root rot. Plots were amended
with five rates of separated dairy manure solids annually for three years. In the
fourth year, plots were split and only half of each plot was re-amended. Soil
physical properties [bulk density, free and occluded particulate organic matter
(POM), soil water retention, total porosity, gravimetric moisture content] and
biological properties [microbial activity (as hydrolysis of fluorescein diacetate;
FDA) and microbial biomass-C] were assessed each year in all treatments. Root
rot severity was assessed in situ and in the greenhouse with multiple sweet corn
(Zea mays L. cv Golden Jubilee) bioassays conducted in the amended field soils.
Necrosis of the radicle and nodal roots was assessed when plants reached the 6-
leaf stage. Amendment rate was positively associated with increases in soil
properties that serve as indicators of soil quality, such as POM content, total
porosity, microbial biomass, and FDA activity. In the third year after amendment,
weak root rot suppression was observed in-field and was associated with FDA
activity. By the fourth year of serial amendment this trend was no longer evident,
however evidence from the high-rate treatment that was not re-amended (3HNRA)
pointed to an emerging suppressive mechanism that persisted up to 13
months after the third amendment. Factors that may be interacting over time to
generate observed disease suppression in these serially amended soils include:
short-term post-amendment microbiostasis, soil moisture retention, inoculum
potential, and a novel suppressive mechanism. === Graduation date: 2006
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