Greenhouse Gases in Agriculture

Greenhouse gases have become a major concern across the world. As humans living on Earth, we must look at the ways in which we can reduce our contribution to greenhouse gas emissions to the atmosphere. For example, although it is a natural occurring component of an agricultural system, farmers are committed to reducing greenhouse gas sources and increasing greenhouse gas sinks. This would lower the agricultural contribution to the total levels of greenhouse gases in the atmosphere.

In order to know exactly how much of an impact agricultural activities have on the levels of greenhouse gases in the atmosphere, scientists have developed ways in which to measure the amounts of greenhouse gas emissions and its uptake in the following ways:

1) Soil chambers are used to measure greenhouse gas emissions from the soil. The lid of the soil chamber is closed in order to trap any gasses that are being emitted from the soil. As observed in the images below, gases are measured from a syringe in the chamber. In this example, students are taking samples from an organic agricultural field shortly after manure was applied as fertilizer. Taking repeated gas samples over a certain amount of time allows the experimenter to view the rate at which gas concentrations increase; these values are used in calculating the gas emissions.

 Soil Chamber

The data obtained from soil chambers can be represented in the form of a graph. The graph below clearly shows the buildup of nitrous oxide (a greenhouse gas) over the 45 minutes being sampled. In this case samples are being taken immediately after the lid is closed and then at 15, 30 and 45 minutes later.  

Graph Soil Chamber

2) Methane production from cattle is measured using a technique called the 'sulphur hexafluoride technique'. This involves placing a small bolus into the rumen of a cow. This bolus contains sulphur hexafluoride (non-poisonous) gas, which is released at a constant rate over a specified period of time. A head halter attached with a stainless steel canister (known as an evacuated container) is then fitted onto the cow. The evacuated container hangs from the cow's neck. Next, a gas sampling pipe is placed near the cow's nostril to collect small samples of methane gas being emitted from the cow's mouth. The gas being collected by the sampling pipe is passed to the evacuated container.