Verdure: Organic matter matters

The age of a putting green affects its rate of soil organic matter accumulation.

|

Aggressive growth, stoloniferous growth, clippings — they all contribute to the accumulation of organic matter under bentgrass putting greens. As soil organic matter accumulates, it can create issues, including restricted drainage and gas exchange.

In the trade-off between created organic matter (by the bentgrass) and consumed organic matter (by soil microbes), researchers at North Carolina State University wanted to answer this important question: What is the rate of organic matter accumulation in a bentgrass putting green over time?

To answer this question, samples were collected from 49 golf courses all over North Carolina, with four to six greens sampled from each course (a total of 212 samples). Putting greens varied in age, from newly constructed to 25 years old. The courses all had bentgrass putting greens of medium to high quality, and all had sand-based substrates (the majority of which had been built to USGA recommendations).

A “sample” was actually a group of four to six cores collected from a small area, with the aboveground growth removed. Each core was separated into depths of 0 to 1 inch (2.5 centimeters) and 1 to 3 inches (2.5 to 7.6 centimeters). The cores were analyzed for soil organic matter content, with additional data collected on soil carbon (C), soil carbon dioxide (CO2) and oxygen (O2) contents.

Previous research by other scientists had documented that putting green permeability was restricted (drainage and gas exchange) when soil organic matter began to exceed 0.04 pound organic matter/pound of soil (35 to 40 grams/kilogram of soil), or 3.5% to 4.0% organic matter. Using that as a starting point, this new project sought to determine just how old a putting green needed to be before those potentially damaging levels of organic matter accumulation could occur.

The answer was that it occurred pretty rapidly. In the top inch (2.5 centimeters) of soil, the 4% threshold (40 grams organic matter/kilogram of soil) was reached in greens that were only 5 years old. In older greens (15 to 25 years), there was more variation in soil organic matter content in the top inch of soil, with some greens having values as high as 0.06 to 0.08 pound organic matter/pound of soil (60 to 80 grams/kilogram), while others remained below 0.04 pound organic matter/pound of soil (40 grams/kilogram) at the same age.

At the lower sampled depth (1 to 3 inches), organic matter accumulation was not an issue, and that accumulation was much slower, with values never exceeding 0.03 pound of organic matter/pound of soil (30 grams/kilogram), regardless of the age of the putting green.

Soil organic matter accumulated quickly, and many greens as young as 5 years had levels of soil organic matter that exceeded levels that could be considered deleterious to bentgrass growth and quality.

But was this decrease in quality observed? The answer was no. Interviews with superintendents found no evidence that bentgrass quality was decreased, and measured soil oxygen levels were never depressed more than 15%. This indicates that the intensive management used in bentgrass greens was successfully allowing gas exchange into the root zone.

A critical point is that this work showed that the rate of soil organic matter accumulation in the top inch changed as a result of putting green age. Basically, younger greens accumulated organic matter at a faster rate than older greens. The initial fast phase (first five years) of soil organic matter accumulation was followed by a decrease in the rate of soil organic matter accumulation, with older greens (>12 years old) accumulating soil organic matter at a slower rate.

The authors hypothesized that the reduced rate of organic matter accumulation was likely a result of increased microbial activity in older greens, which would degrade more soil organic matter, decreasing the rate of organic matter accumulation in older greens.

Source: Carley, D.S., D. Goodman, S. Sermons, W. Shi, D. Bowman, G. Miller and T. Rufty. 2011. Soil organic matter accumulation in creeping bentgrass greens: A chronosequence with implications for management and carbon sequestration. Agronomy Journal 103(3):604-610. doi:10.2134/agronj2010.0335

Editor’s note: Read all of Beth Guertal’s recent Verdure columns.


Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and the 2019 president of the Crop Science Society of America. She is a 21-year member of GCSAA.

You may also like: Verdure: Creeping bentgrass thatch, mat and coring