What is crop production?
Crop production activities are the result of a system of practices used to grow or harvest agricultural crops, including land that is set aside or temporarily in fallow (not in use for crop production). At present, approximately 11% (1.5 billion ha) of the world’s land surface (13.4 billion ha) is used for crop production. Land-use change due to the conversion of natural habitat for agricultural expansion has been one of the largest sources of greenhouse gas (GHG) emissions historically, as burning and decomposition of forests releases carbon into the atmosphere. Historically, croplands have lost more than 50 petagrams (Pg) – or 50 trillion kilograms – of carbon (C) but some of this lost soil C can be returned to the soil via improved cropland management, thereby decreasing atmospheric carbon dioxide (CO2) concentrations.
According to IPCC Guidelines for National Greenhouse Gas Inventories (2006), GHG emissions from cropland are defined as “emissions and removals from arable and tillage land, rice fields, and agroforestry systems where vegetation falls below the thresholds used for the forest land category.” Following the IPCC, C or CO2 accounting for croplands is considered under forestry and other land use (FOLU), and not agriculture, within AFOLU as the CO2 emitted from agriculture is considered to be neutral.
CO2 emissions occur in cropland due to the disturbance of mineral soil (e.g., erosion, tillage), flooding or drainage of organic soils for crop production (e.g., histosols, peatlands, paddy rice), residue management (e.g., crop residue burning, manure management) or land-use change. Other management practices that occur in croplands (e.g., soil nutrient inputs, liming, residue management, paddy water management) that produce methane (CH4) or nitrous oxide (N2O) are accounted for under “agriculture” and are considered here in line with IPCC Guidelines (2006). Other associated activities in the supply chain include fertilizer production, processing and transport, and food loss and waste management. Land-use change due to the conversion of natural habitat for agricultural expansion has been one of the largest sources of emissions historically.
Emissions by source
Human-induced emissions from crop production originate from five principal sources:
|Nutrient application (CO2 and N2O)||
|Drainage of organic soils (CO2 and N2O)||833 Mt CO2e globally in 2019|
|Paddy rice (CH4)||533 Mt CO2e globally in 2017. See Flooded Rice|
|Land-use conversion to cropland (CO2, CH4, and N2O)||See Open Burning|
|Burning crop residues (CO2, CH4 and N2O)||31 Mt CO2e globally from maize, paddy rice, sugar cane, and wheat in 2017. See Open Burning.|
|Soil disturbance (CO2)||Although global estimates from soil disturbance, such as conventional tillage via moldboard plow, are not available, it is generally accepted that soil disturbance stimulates soil C losses through enhanced decomposition and erosion. See Soil Carbon.|
Emissions by commodity and emission intensities
Emission intensities are a way to compare the emissions of different commodities on a per-product basis (e.g., Mg CO2e per kg of grain), per total kilocalorie production (“production intensity”; Mg CO2e M kcal−1), or emissions from production per kilocalorie available as food (“food intensity”).
From Carlson et al. (2016):
- Rice accounts for 48% of total crop emissions (Fig. 1a) because of high CH4 emissions associated with flooded rice cultivation (Fig. 1e).
- Coconut has high overall production intensity (Fig. 1b) due to 2.2% of its cultivated area located on peatlands (Fig. 1c).
- Fertilizer production intensity is high for rapeseed and potato (Fig. 1d).
- Total country emissions (Fig. 1f) are greatest from China, with extensive flooded rice systems and high fertilizer application rates. Vietnam’s triple-cropped rice and Indonesia’s peatland development generate high overall GHG production intensity (Fig. 1g). Peat production intensity (Fig. 1h) exceeds fertilizer (Fig. 1i) and rice (Fig. 1j) intensities, demonstrating the importance of preserving peatlands.
Land management practices for GHG mitigation regarding crop production include the following partly overlapping categories:
- Using improved crop varieties.
- Extending crop rotations.
- Avoiding or reducing fallow periods by using cover crops.
- Nutrient management
- Tillage/residue management
- Adopt minimal- or no-tillage practices to reduce soil disturbance and subsequent soil C losses as well as reduce emissions from fuel use. No-tillage practices should be adopted on well-drained soils to avoid increases in N2O emissions.
- Residue retention tends to increase soil C sequestration.
- Water management
- Expanding the use of irrigation or using more efficient irrigation techniques can enhance soil C sequestration due to increased crop production and residue returns.
- Draining croplands in humid regions can also promote productivity and soil C sequestration, and potentially suppress N2O emissions by improving aeration.
- Energy use reduction, more efficient energy use, and substitution of fossil fuels.
- Agroforestry can greatly reduce erosion and nutrient leaching while building soil C
- Land cover change management
- Avoid the conversion of high C stock ecosystems to cropland by intensifying productivity on existing cropland.
- Convert surplus agricultural land, or croplands with marginal productivity, to ecosystems with a high C storage capacity (e.g., grasslands, wetlands, forests).
- Open burning reduction
- Minimizing food waste