Bring autumn color to turf

Karl Danneberger, Ph.D.

Autumn is the best time to work on a golf course. The days are shorter, the mornings cooler, the air clear. The colors on a course are the most striking. The green turf contrasts strikingly with the changing leaves of trees and ornamentals. For those who enjoy photography, the morning sunrise brings these colors into focus.

Fall leaves provide a color contrast — reds to burgundy to orange — but what do we do with them once they fall to the ground? In golf, leaves are nuisances that can cover a golf ball. In conjunction with the leaves, the low sun angle causes a lighting effect that makes finding a ball more difficult. There’s only one thing worse than looking for your golf ball, and that’s looking for someone else’s.

Superintendents spend considerable time and effort collecting and removing leaves, and there are agronomic advantages to doing so. Leaf removal reduces potential shading of turf. The microclimate effect of shading can reduce turf photosynthesis and make annual bluegrass susceptible to certain types of winter injury.

Reduced light limits photosynthetic potential, resulting in lower carbohydrate storage, which plants might need to survive the winter. Internally, especially with annual bluegrass, plant mechanisms that play a role in cold tolerance can be affected by leaf cover, resulting in a loss of cold and freeze tolerance.

The problem with collecting and removing leaves is what to do with them. You can haul them off, burn them or recycling through composting. All these methods take time and effort.
Because most leaves fall in the rough, mulching is a possibility. Several manufactures sell mulching attachment kits for rough (rotary) mowers. Besides not having to deal with large leaf collection, mulching returns leaves into the turf (if done frequently enough) and nutrients, primarily nitrogen, are recycled.

Nitrogen being released and returned for turf growth depends on the carbon-nitrogen (C-N) ratio. Soil microorganisms use carbon for energy and nitrogen for maintenance and growth. Within microbes, a C-N ratio of 8-to-1 is ideal for living. For soil to acquire the carbon and nitrogen necessary to maintain an internal 8-1 ratio, the microorganisms ideally are at a C-N ratio of 24-to-1.

If we add organic material to be degraded by these soil organisms, it’s the C-to-N ratio that determines whether nitrogen is released or captured. For example, if we add wheat straw with a C-N ratio of 80-to-1 to our turf, soil microorganisms will consume the carbon but will need to find extra nitrogen in the soil. The result of consuming extra nitrogen is known as immobilization. Immobilization ties up extra nitrogen in soil, making it unavailable for plant growth. This may lead to a temporary nitrogen deficiency.

In contrast, if we were to add grass clippings with a C-N ratio of 19-to-1, soil microorganisms would consume the leaves and release extra nitrogen (mineralization), resulting in a temporary soil nitrogen surplus. With grass clippings having a C-N ratio close to 24-to-1, the amount of excess nitrogen immediately released might be minimal (although the nitrogen eventually would be released). However, because of the C-to-N ratio, grass clippings are readily broken down in a short time.

In general, if the C-N ratio is greater than 30-to-1, nitrogen immobilization occurs as maximum biological activity is reached. With C-N ratio less than 20-to-1, we reach mineralization of nitrogen with maximum biological activity.

The C-N ratio in leaves is around 50-to-1. The breakdown of leaves is considered intermediate between grass clippings and wheat straw. Leaves range from sugars (quickly broken down) to cellulose (intermediate) to lignin (slowly broken down).

Because roughs are to some extent fertilized, leaves especially mulched or repeatedly chopped with a mower can break down rather quickly. Where rough areas exist that accumulate leaves, mulching is a sustainable method of management.