Graduate Thesis Or Dissertation
 

Soil organic matter management and root health

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/w3763883k

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  • Annual applications of fresh or composted dairy manure were assessed for their effects on root rots of sweet corn and snap bean and damping-off of cucumber in a field soil. Soil biological and physical properties were measured as possible indicators of root rot suppressive potential. Regardless of amendment type or rate, soils amended for two seasons with either a high (average = 39.2 Mg ha⁻¹ year⁻¹) or low (average = 16.6 Mg ha⁻¹ year⁻¹) rate suppressed root rot of sweet corn, root rot of snap bean, and damping-off of cucumber by 54, 25 and 49%, respectively. Disease suppression was sustained for less than 6 mo after amendment, Severity of these three diseases was negatively (P<0.05) related to soil free particulate organic matter content, fluorescein diacete (FDA) activity, microbial biomass, and percent water stable aggregation. FDA activity was the best indicator of the soil's root rot suppressive potential. When FDA levels were ≥ 2.88 μg min⁻¹ g⁻¹ dry soil, disease suppression was observed. In a container experiment, amendment with fresh (10% v/v) or composted (15% v/v) dairy manure suppressed root rot of sweet corn in soils with a high root rot potential. Suppression was positively related to FDA activity in soil-i (R² = 0.70) and soil-2 (R² = 0.91). Suppression was observed at FDA levels ≥4.00 μg min⁻¹ g⁻¹ dry soil. When sudangrass and oats were grown and incorporated in a container experiment, severity of root rot of sweet corn was reduced by 22 and 18%, respectively. Annual ryegrass and cereal rye had no effect on disease severity. Disease suppression was not related to FDA activity. Host range specificity of P. arrhenomanes, Drechslera spp. and Phoma spp. was determined for crops grown in rotation with sweet corn. P. arrhenomanes and Drechslera spp. were mildly pathogenic on annual ryegrass, perennial ryegrass and cereal rye. Phoma spp. was pathogenic only to perennial ryegrass. None of the pathogens were pathogenic on sudan grass and oats. In conclusion, management of root rot of sweet corn through cover cropping coupled with soil amendment shows potential for disease suppression and should be investigated further.
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