Dollar Spot Severity, Tissue Nitrogen, and Soil Microbial Activity in Bentgrass as Influenced by Nitrogen Source
- J. Graham Davis and
- Peter H. Dernoeden *
There is increasing interest in the use of bio-organic nitrogen (N) sources to suppress turfgrass diseases. The objectives of this field study were to evaluate nine N-sources for their effects on dollar spot (caused by Sclerotinia homoeocarpa F. T. Bennett) severity; to elucidate the relationship among N-sources, tissue N, soil microbial activity, and the severity of dollar spot; and to evaluate N-source effects on thatch and soil organic matter levels, and plant parasitic nematodes. Nitrogen sources included urea, sulfur-coated urea (SCU), Milorganite (Milwaukee Metropolitan Sewerage District, Milwaukee, WI), Sustane Medium (Sustane Corporation, Chaska, MN), Earthgro 1881 Select (Earthgro Inc., Lebanon, CT), Earthgro Dehydrated Manure, Ringer Lawn Restore (Ringer LR, Ringer Corporation, Minneapolis, MN), Com-Pro (Blue Plains Sanitation Commission, Silver Spring, MD), and Scotts All Natural Turf Builder (Scotts ANTB, Scotts Company, Marysville, OH). The N was applied annually at a rate of 200 kg N ha−1 yr−1 between 1994 and 2000 to a stand of fairway height ‘Southshore’ creeping bentgrass (Agrostis stolonifera L.). Data were collected between 1998 and 2000. Ringer Lawn Restore (all 3 yr) and urea (1999 and 2000) delayed dollar spot to within an acceptable threshold from May to early or mid-June, when disease pressure was low to moderately severe. Com-Pro (all 3 yr), however, enhanced dollar spot. No N-source reduced dollar spot when data were averaged over-the-season. No N-source was consistently associated with higher levels of soil microbial activity. There was a weak negative correlation between soil microbial activity and dollar spot on one date in 2000, when disease pressure was low. When disease pressure was moderately severe, there was a strong negative correlation between the amount of foliar N and dollar spot severity in June 1999, but no correlation was found in 2000. Only Sustane Medium-treated plots had higher organic matter levels in the upper 2.5 cm of soil on all rating dates, but there was no increase in soil organic matter in the 2.6 to 5.0 cm soil zone with any N-source.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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