Edaphic Effects of Carbon Dioxide I. pH

The breathing heterotrophic in sports turf is governed by maintenance practices and has been estimated to range from 31 g C-CO2/m² and year for unmaintained turf surfaces to 922 g C-CO2/m² and year for areas with fertilisation and mowing inputs, Milesi et al., 2005. These sports surfaces produce more CO2 than agricultural soils and natural ecosystems because they contain more soil organic matter, Kaye et al., 2005.

There are records of very high CO2 values in the soil profiles of golf courses. These values, up to 3 and 4%, are much higher than the atmospheric 0.03%, and are a consequence of the intensive maintenance and high growth rates of these sports surfaces, Lee et al., 1997.

The CO2 in the soil zone has two origins: it is the result of the breathing of the roots and the mineralisation of organic matter plant. Respiration is the reverse process of photosynthesisWieko et al., 2006.

Breathing

C6H12O6 + 6 H2O + 6 O2 ⇒ 6 CO2 + 12 H2O + Chemical energy

As the roots respire and organic matter is broken down through the activity of the microbial communityCO2 is produced and the partial pressure of this gas in the pores of the soil increases, leading to a soil atmosphere with a high partial pressure of CO2. In fact, the partial pressure of CO2 in the soil zone of a soil is several times higher than the pressure of this gas in the atmosphere.

The pore water dissolves some of this CO2 until the amount of this dissolved gas (in the liquid phase) is balanced by the partial pressure of the CO2 in the gas phase. The dissolved CO2 combines with water and forms carbonic acid, which causes the pore water to become more acidic, so the more the soil breathes, the more likely it is to become naturally acidified.

Tiloom recommends measuring the pH "in situ", using standard tools. The extraction of soil samples for laboratory analysis does not take into account these processes, there is a CO2 degassing that is not taken into account, so the real information about what happens on our greens is distorted.

The pH can also be expressed as a function of carbonate forms, so respiration and the production of more CO2 can change the pH. If samples are taken directly from the soil, the CO2 in the sample equilibrates with the ambient CO2, so changing it will also change the measured pH. In other words, errors are made in the actual readings. The most efficient and accurate is the in situ measurement under the conditions of the soil environment of the green.