Soil Respiration

The breathing of a soil gives us the measure of carbon emissions (C - CO2), coming mainly from the decomposition of organic matter through the aerobic pathway (microbial respiration), from grass roots and soil fauna, and even from the dissolution of carbonates. It is a measure of the soil health as it gives the level of microbial activity, organic matter content and its mineralisation. The measure of C - CO2 release is given in kg/ha/d. In this process, organic phosphorus, nitrogen and sulphur are converted into inorganic forms. This process is also known as carbonic mineralisation.

There are a number of variables on which respiration depends, such as temperature, humidity, and aeration. The respiration rate doubles every 10 degrees, until it reaches 35 - 40 degrees, above which temperatures are limiting; it is also limited below 5°C. The respiration rate also increases with increasing VWC up to saturation levels, where this rate begins to decline and anaerobiosis with denitrification and sulphur volatilisation begins to occur.

In situations of saturation, micro-organisms start to use NO3, nitrates instead of O2 for the decomposition of organic matter, leading to denitrification and losses of N2 in gaseous form. The C/N ratio also plays a fundamental role in these processes, with C/N ratios of 8 being optimal for a good mineralisation of organic matter.

Field devices are available for determination or laboratory testing. These test kits consist of "in situ" devices with chemical agents, which change colour depending on the presence of CO2. An example is the Draeger-tubes®.

In profiles of sports surfaces the CO2 produced is much higher than in other types of environments due to the high density, porosity and intensity of maintenance.