Summer Decline=OM Content

Dr. Robert Carrow at the University of Georgia credits OM Accumulation as the Source of Summer Decline. Dr. Robert Carrow at the University of Georgia studied organic matter (OM) dynamics on Bermudagrass and bentgrass USGA golf greens. While this research was done in a golf turf situation, highly managed sand athletic fields suffer the same problem of surface OM accumulation.

He hypothosized that too much organic accumulation or rapid death of surface roots could result in reduced infiltration, a higher water content, and a decrease in both the total oxygen within this zone and movement of oxygen within this zone.

In addition, when OM >4.5% by weight, macroporosity declined substantially and it was more likely that a massive root dieback from hot, humid weather would occur. Surprisingly, prolific root growth during periods of optimum temperatures (soil 55-65ºF, air 60-75ºF) also plugged macropores and reduced oxygen levels.

In summary, OM dynamics were thought to be influenced by:

* Grass type & density

* Anaerobic conditions (oxygen within 0-2 inches) caused by too-frequent irrigation

* Acidic conditions in the top 1-inch possibly caused by acidic nitrogen fertilizers

Secondary Problems:

* Limited root depth because OM has reduced oxygen diffusion

* Root & crown injury

* Inhibition of nutrient & water uptake

Preventing &/or curing this OM accumulatiom problem is achieved by surface management (verticutting, scarification), and regular aeration and topdressing. Keeping the top 0-2 inches of playing surface free-draining and with adequate levels of oxygen appears to be the key to surviving summer stress.

Authors: Dr. Karl Danneberger