Field crops, pastures and rangelands and their contributions to climate change
Soil management, cultivation (soil disturbance) and fertiliser use are significant emission contributors within the agricultural sector.
A few facts:
- Soil organic carbon is important as it maintains the soil's chemical, physical and biological fertility, which allows good-quality crops and pastures to grow.
- If soil is disturbed through clearing for land use changes, or by the burning of remaining crop stubble after harvesting, some of the carbon is lost to the atmosphere.
- In 2006 carbon contributions by agricultural soils and the field burning of agricultural residues contributed 20% of agricultural greenhouse gas emissions in NSW1.
- Livestock grazing on pastures and rangeland contribute methane to the atmosphere, yet good grazing management of perennial pastures increases soil carbon.
Fertilisers
Fertilisers are used in agricultural production of crops and pastures to provide additional nutrients that are not present in the soil, or not present in large enough quantities in the existing soil. Nutrients required in the largest quantities in agriculture are nitrogen, phosphorus and potassium. The fertiliser requirements for every crop and pasture are different, due to different soil types, soil depth, the pasture or crop type itself, and the previous paddock history.
The production of fertilisers requires a large amount of energy and generates considerable greenhouse gas emissions. Therefore, applying fertilisers so that the nutrients are available particularly during the plants' main growth period, and assessing the nutrient content of soils before applying fertilisers, helps to reduce fertiliser use. This reduction in usage means reduced nitrous oxide (N2O) emissions during production, and less expense for farmers.
1Department of Climate Change, 2009 State and territory greenhouse gas inventories 2007; Australian national greenhouse accounts. http://www.climatechange.gov.au/~/media/publications/greenhouse-acctg/state_territory_inventory.ashx