Term Paper on Agriculture and GHG Emission | Geography

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Term Paper # 1. Agriculture and GHG Emission:

While the increasing concentrations of GHGs are associated primarily with fossil fuel consumption, a significant share (estimated in the range of 12 to 42 per cent) is believed to be caused by changes in land use, including deforestation and the expansion of agriculture. The GHGs can be reduced in the atmosphere by reversing some of the processes associated with land use changes and adopting appropriate agriculture management practices.

Agriculture is a significant emitter of GHGs, particularly methane, nitrous oxide, and CO₂. Thus policies designed to reduce emissions need to be targeted to these agricultural sources.

The IPCC (1996) estimates that globally agriculture emits about:

i. 50 per cent of total methane, sources includes rice, ruminants and manures;

ii. 70 per cent of nitrous oxide, sources includes manure, legumes and fertilizer;

iii. 20 per cent of CO₂, sources include use of fossil fuels, soil tillage, deforestation, biomass burning, and land degradation.

Emissions can vary substantially, between developing and developed countries. Deforestation and land degradation mainly occur in developing countries. Agriculture in developed countries uses more energy, more intensive tillage systems and more fertilizer, resulting in fossil-fuel based emissions, reductions in soil C and emissions of nitrous oxides. In addition animal herds emit methane from ruminants and manure.

Term Paper # 2. Agriculture and Land Use Change as Source of Carbon Flux:

Agriculture and forests are mentioned as both emitters of and sink for GHGs in the Kyoto Protocol.

Annex A of the Kyoto Protocol lists agriculture as an emission source in terms of:

i. Enteric fermentation,

ii. Manure management,

iii. Rice cultivation,

iv. Soil management,

v. Field burning, and

vi. Deforestation.

In agriculture, carbon flux is mainly due to methane (CH₄) & nitrous oxide (N₂O).

Carbon flux of CO₂, CH₄, & N₂O, can occur due to land-use change and forestry as follows:

i. Forest carbon flux.

ii. Liming of agricultural soils.

iii. Urban trees.

iv. N₂O from settlement soils.

v. Non- CO₂ emissions from forest fires.

vi. Landfilled yard trimmings and food scraps.

The Kyoto Protocol also lists agriculturally related sinks of afforestation and reforestation. Additional sources and sinks which are under consideration include agricultural soil carbon and water. Some of the important sources of GHGs in agriculture and the ways to minimize emissions. Emissions of GHG from waste food and related control are also included.

i. Enteric Fermentation:

Fermentation that occurs in the digestive systems of ruminant animals is termed as enteric fermentation. It is one of the factors responsible for increased methane emissions. Ruminant animals are those that have a rumen, a special stomach found in cows, sheep, and water buffalos that enables them to eat tough plants and grains which monogastric animals, such as human, dog and cat cannot digest. Enteric fermentation occurs when methane (CH₄) is produced in the rumen as microbial fermentation takes place.

Over 200 species of microorganisms are present in the rumen, although only about 10% of these play an important role in digestion. Most of the methane so produced in the rumen is belched by the animal. In Australia, ruminant animals account for over half of their green house gas contribution from methane. Australia has implemented a voluntary immunization program for cattle in order to help reduce methane production in rumen.

ii. Manure Management-Manure as Resource:

a. Using Manure as a Nutrient Source in Crop and Garden Production:

The separation of animal agriculture from crop production has led to accumulation of excess manure on livestock farms. Crop farms can benefit from this manure as a source of nutrients and organic matter, if the manure is suitable for their needs and shipping does not make the cost prohibitive. Nutrient values of different sources of manure are being assessed with respect to their suitability for crop production. Guidelines to use manure as fertilizer for crop farmers are available.

b. Horse Manure and Soil Nitrogen:

Horse manure is an abundant, locally available source of organic matter for soils. A major concern about horse manure is that it can cause a nitrogen deficiency when added to soils, leading to stunted, yellowed crops.

c. Managing Dairy Manure:

Water quality problems, changing herd management patterns, and increased regulation have made manure management a critical issue for dairy farmers. The immediate goal is to help dairy farmers improve the use of manure to increase agronomic benefits and reduce the risk of over-application, runoff, and leaching. Manure application rates have traditionally been based on nitrogen, but phosphorus has emerged as the nutrient of concern in many watersheds.

iii. Rice Cultivation:

a. Methane Emissions from Flooded Rice Cultivation:

By 2020, the world will need to produce 350 million tons more rice per year to feed an anticipated 3 billion more people than in 1992. The rice field methane emissions have been identified as a major source of atmospheric methane. During flooding of the field in wetland rice soils, the oxygen supply from the atmosphere stops and leads to anaerobic fermentation of soil organic matter.

Methane, a major end product of anaerobic fermentation, is released from submerged soils to the atmosphere through the roots and stems of rice plants. Estimates of global methane emission rates from rice fields range from 20 to 100 Tg per year (1 Tg = 1 million tons), which corresponds to 6 to 29 percent of total annual anthropogenic methane emission.

b. Methane emission from rice field was found to be affected by various factors some of which are as follows:

i. Exogenous organic matter appears to be the largest contributor to methane production from flooded rice soils.

ii. In coastal rice fields of Texas, it was found that as the rice growing season progressed, methane production at lower depths and farther away from the plants increased in proportion with root density.

iv. Agricultural Soils: Source of Emission & Carbon Sequestration:

In some places (e.g. North Carolina), soils are naturally acidic and need lime, which neutralizes the acidity, for optimum growth of crops, forages, turf and trees. Soils become more acid due to the leaching of calcium (Ca2+) and magnesium (Mg2+), or acidification by hydrogen added to soils by decomposition of plant residues and organic matter and during the nitrification of ammonium added to soils as fertilizer.

Agricultural lime (Agilime) includes crushed limestone (CaCO₃) and dolomite (Ca-,Mg- CO₃). Following IPCC that all carbon in agrilime is eventually released as CO₂ to the atmosphere, the US-EPA estimated that 9 Tg (1Tg = 10 ¹² g = 10 ⁶ metric tons) of CO₂ was emitted from an application of 20 Tg of aglime in 2001.

Globally, soils are estimated to contain approximately 1,500 gigatons of organic carbon, more than the amount in vegetation and the atmosphere. Modification of agricultural practices is a recognized method of carbon sequestration as soil can act as an effective carbon sink offsetting as much as 20% of 2010 carbon dioxide emissions annually.

Scientists estimate that about 80 percent of global carbon is stored in soils, and that a substantial proportion of carbon that was originally in soils has been released due to human land use, implying that there is a large technical potential to sequester carbon in soils Agriculture may enhance the soil’s capacity to absorb GHGs by creating or expanding sinks.

This may be achieved through a variety of changes in land use and management practices. The adoption of agroforestry practices like windbreaks and riparian forest buffers, which incorporate trees and shrubs into ongoing farm operations, represents a potentially large GHG sink nationally.

In addition, agricultural practices such as conservation tillage and grassland practices such as rotational grazing can also reduce carbon losses and promote carbon sequestration in agricultural soils. These practices offset CO₂ emissions caused by land use activities such as conventional tillage and cultivation of organic soils.

The carbon sequestration management processes should basically cover the followings:

i. Land retirement (conversion to native vegetation or reversion to wetlands),

ii. Afforestation,

iii. Residue management,

iv. Less-intensive tillage,

v. Changes in crop rotations, and

vi. Conversion of cropland to pasture and restoration of degraded (or highly eroded) soils.

Some of these management practices are:

a. Agricultural Land Use Changes:

The agricultural land use changes to cater for the increasing demand of bio-fuels can result in increased carbon emission thereby negating the climate change mitigation programme. Recent Oxfam studies indicate that by 2020, carbon emissions resulting from land use changes in Europe because of rising demand of bio-diesel derived from palm oil would be between 3.1 to 4.6 billion tonnes, which is 46 to 68 times higher than the EU hopes to be achieving by then from bio-fuels.

Also the carbon emissions from global land use changes due to US corn-ethanol programmed will take 167 years of climate mitigation programmed to pay back. In addition to increased emission the land use changes for biofuel has also resulted in an estimated increase in food price by 30 per cent.

However the proper management practice can make the biofuel as carbon neutral. Burning biomass based fuels not only reduces carbon emission in comparison to fossil fuels, but also can reduce net CO₂ emissions to nearly zero, if the growing plants can absorb equivalent carbon in their photosynthesis process for biomass growth.

b. No-Till Soil Management:

During tilling, soil is turned; the organic matter is exposed to the atmosphere and can quickly oxidize into carbon dioxide. This is bad for the soil and is thought to be an important emission source driving global warming. Less organic matter in the soil means less water retention, less nutrient release and less clod formation.

Along with encouraging the oxidation of organic matter, plowing physically breaks up pre-existing clods (lumps) and exposes them to the direct force of rainfall. The force exerted by rain drops is enough to break up the remaining clods and form a structure less soil “crust” on the field surface.

This crust has virtually no pores and as a result, plant roots do not get the water and oxygen that they need, and surface runoff and soil erosion become a large problem. The crust can also be strong enough to make it difficult for seedlings to push through to the surface. In no-till agriculture, the farmer uses a disk or chisel plow to prepare the field for seeding.

Rather than turning the field, these plows create a narrow furrow, just large enough for the crop’s seeds to be injected. Tractor attachments inject a band of fertilizer in with the seeds, thus negating the need to fertilize the whole field, and close up the furrow after the seed and fertilizer have been planted. With these new plows, the farm field can be seeded with minimal disturbance of the soil.

Advanced field management coupled with modern no-till plowing can actually increase the fertility of a farm’s soil. The use of cover crops and green manures during the non-growing season are two popular forms of such field management. A cover crop is any sort of vegetation that is grown between commercial plantings.

The cover crop holds the soil in place with its roots, preventing erosion. Green manures are any type of crop that is incorporated into the soil while still green or soon after flowering. In many cases, cover crops become green manures just before commercial planting resumes.

The benefits of no-till farming are economic as well as environmental. The no-till farmer will see an increase in the organic matter of the soil, and a decrease in the amount of erosion. More organic matter and less erosion mean more fertility, less fertilizer, and higher yields. Additionally, with the advances in cover crops and green manures, the no-till farmer can greatly reduce the use of high-cost herbicides.

According to Prof Johan Rockstrom, an environmental scientist and the director, Stockholm Environment and Stockholm Resilience Centre, India with its agro-based economy has around 30% of carbon emission from old farming technique of ploughing and need to go for no till practice. Some Latin American countries have gone for no-till practice. In USA, around 40% of farming has been using no-till practice.

The various management practices can lead to following percentages in carbon savings:

i. 49 per cent of agricultural carbon sequestration can be achieved by adopting conservation tillage and residue management,

ii. 25 per cent by changing cropping practices,

iii. 13 per cent by land restoration efforts,

iv. 7 per cent through land use change, and

v. 6 per cent by better water management.