In other words, the paper suggests that the amount of carbon sequestered (captured) by a lawn system is not enough to account for the amount of carbon generated by mowing, fertilizing, and taking care of a lawn. Following the publication of the UCI paper last month, two Ph.D students at NC State University studied the model used to generate the numbers in the paper and found that there were errors and therefore miscalculations. By their reckoning, for example, the CO2 generated by maintaining an ornamental lawn was 122 g m-2 yr-1 rather than > 1238 g m-2 yr-1
reported in the UCI paper. As noted by NC State, this is important, because it makes the situation with ornamental lawns carbon neutral to positive, depending on some of their other assumptions about fertilization. The NC State students also are suggesting that the paper did not take into account C speciation during combustion. Depending on the kind of mowers used, this could lower levels by another 15 to 50%.
In addition to understanding the generated numbers, it is also important to keep in mind the type of input or level of maintenance that is written into the model or equation. For example, the model may assume that all lawns are irrigated, when in actual fact they are not. The model may also assume that all lawns are fertilized four times per year and clippings removed, when in fact that is not the case. As determined by Scott's consumer studies, there are 80 million single family homes in the USA. 50% of those lawns get no fertilizer applied at all, 37.5% are fertilized 1.8 times per year, and only 12.5% are fertilized 3 or more times per year(2). Additionally, it is important to note that that much of the research is suggesting that "healthy" lawns receiving inputs from fertilizer, returned clippings and irrigation are actually showing an increase in carbon sequestration(3). This would make sense, seeing as the root system, turnover of roots, and litter biomass in a healthy turfgrass system is significant(4). So it would appear that maintenance inputs are not necessarily a bad thing! With all of this said, one can only hope that future research being undertaken is sound, that the models and calculations are right and that scientific and peer-reviewed published papers give us the the most accurate information available at the time, because there is sure to be lots more discussion (and media coverage) on this topic.
Turf managers that would like to know more about this subject can see Gina Zirkle, MS student at The Ohio State University give a talk at the Sports Turf Short Course February 24th and 25th (see front page of our website for details). Gina has developed a model for carbon sequestration in turfgrass and urban soils. Her advisor, renowned soil physicist Dr. Rattan Lal, is director of the Carbon Management & Sequestration Center at Ohio State. Gina recently presented some of her research at the annual Agronomy Meetings, entitled The Potential for Soil Organic Carbon Sequestration in Home Lawns"(5), whereby she suggested that there was a positive net sink of atmospheric CO2 in lawns.
(1) Townsend-Small, A. and Czimczik, C. I. (2010) Carbon sequestration and greenhouse gas emissions in urban turf. Geophysical Research Letters. Vol. 37.
(2) Augustin, B.J. 2007. Perception vs. Reality; how much nitrogen do homeowners put on their lawn. Presentation given at the Am. Soc. of Agron. meeting on November 2, 2007 in New Orleans, AL. 269-6
(3)Qian, Y, and Follett, R.F (2009) Carbon Sequestration Potential of Turfgrass Ecosystems.ASA-CSSA-SSSA Meetings. C5 Abtract.
(4) Lopez-Bellido, R.J., Lal, R., Danneberger, T.K., and Street, J.R (2010) Plant growth regulator and nitrogen fertilizer effects on soil organic carbon sequestration in creeping bentgrass fairway turf. Plant and Soil.
(5) Zirkle, G.N. and Lal, R. (2009) The Potential for Soil Organic Carbon Sequestration in Home Lawns.ASA-CSSA-SSSA Meetings. C5 Abtract.