Recursos utilizados para la producción agropecuaria

Liang et al., (2013) estimated the nitrous oxide and methane emission from livestock of urban agriculture in Beijing from 2007 to 2009, it was noted that the total quantity of GHG emissions from livestock sector in Beijing was 1.67 Tg CO2e yr⁻¹, of which N2O-N and CH₄ emissions were 1.04 Gg yr⁻¹ (489 Gg CO2e yr⁻¹) and 47.25 Gg yr⁻¹ (1181.25 Gg CO2e yr⁻¹), respectively.

Browne et al., (2011) using the Australian National Inventory methodology, whole farm GHG emissions were calculated for different farm types in South Eastern Australia.

Fourteen representative farms were examined that included production of Merino fine wool, prime lamb, beef cattle, milk, wheat and canola. The study shows that dairy farms produced the highest emissions/ha (8.4–10.5 t CO2-eqv/ha), followed by beef (3.9–5.1 t CO₂-eqv/ha), sheep (2.8–4.3 t CO₂-eqv/ha) and grains (0.1–0.2 t CO₂-eqv/ha). When compared on an emissions intensity basis (i.e., t CO2- eqv/t product), cow/calf farms emitted the most (22.4–22.8 t CO2-eqv/t carcass weight) followed by wool (18.1–18.7 t CO2-eqv/t clean fleece), prime lamb (11.4–12.0 t CO2-eqv/t carcass weight), dairy (8.5–9.4

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t CO2-eqv/t milk fat + protein), steers (6.3–6.7 t CO2-eqv/t carcass weight) and finally grains (0.04–0.15 t CO₂-eqv/t grain). Christie et al., (2011) examined GHG emissions of 60 Tasmanian dairy farms using the Dairy Greenhouse gas Abatement Strategies (DGAS) calculator, which incorporates International Panel on Climate Change (IPCC) and Australian inventory methodologies, algorithms and emission factors. Total farm GHG emissions of 60 Tasmanian dairy farms, as estimated with DGAS, ranged between 704 and 5839 t CO₂e/annum, with a mean of 2811 t CO₂e/annum.

Methane production from livestock depends on the emission factors of animal management, the quantity of the manure per animal as well as quality of feed consumption are other important factors. However, emission factor selection can be influenced by regional climatic conditions. Suberu et al., (2013) provided a theoretical estimate of methane emissions from both livestock manure in Nigeria and municipal solid waste deposits in some of the country's major cities. Ten-year data obtained from the United Nations Food and Agricultural Organization (FAO) was used to estimate the methane emissions from animal residues using a mathematical approach developed by the Intergovernmental Panel on Climate Change (IPCC). The result of the estimated methane emission from livestock manure in Nigeria based on the IPCC mathematical approach from

2001 to 2010 is shown in Fig. 2.7.

Figure 2.7: Methane production from livestock in Nigeria from 2001 to 2010

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Results from this study indicated a large amount and increasing levels of methane emissions from animal residues and solid wastes, from the Figure 2.7 it obvious that there has been continual increase in methane emission in Nigeria.

Suberu et al., (2013) estimated Methane emissions from solid wastes based on the 2011 cities‘ waste generation and management data from the Renewable Energy Department (RED) of the Federal Ministry of Environment, Abuja (Nigeria). The result of the study is as shown in the Figures 2.8.

Figure 2.8: (a) Estimated methane emission in Southeastern regional state capitals (b) Estimated methane emission in the selected important cities.

From the result of the study, Onitsha city is shown to be the highest in estimated biogas emission and methane emission in some of the major cities selected in the country, while Awka Town is the highest amongs the state capital territory in the South-Eastern States of Nigeria.

36 2.7.1 Greenhouse Gases Mitigation

Methane is a potent greenhouse gas whose atmospheric abundance has grown 2.5-fold over three centuries, due in large part to agricultural expansion. The farming of ruminant livestock, which generate and emit methane during digestion (‗enteric fermentation‘), is a leading contributor to this growth (Lassey 2007). The livestock sector is one of the largest contributors to greenhouse gases (GHG) emissions globally. It is responsible for 18%–51%

of anthropogenic emissions expressed in CO₂-equivalent (Schils et al., 2007; Lassey, 2007).

With progressive increase in demand for meat products, intensive livestock husbandry is rapidly expanding. Moreover, livestock farms heavily depend on external inputs (i.e., concentrate feeds, machinery, electricity, fossil-fuel energy sources). Thus animal husbandry emits GHGs into the atmosphere almost at all production stages (Liang et al., 2013). It is important to note that proper manure management is essential for any agricultural operation because improper use of manure can lead to negative impacts on the environment. Effective control of methane and nitrous oxide emission from ruminants can raise ruminants feed utilization, energy conversion rates and productivity (Zhou et al, 2007). Nowadays, the anaerobic digestion is considered as an important option to treat different high-loaded organic wastes due to the necessity of searching for low cost treatments for wastes and at the same time for finding alternatives to reduce the use of fossil fuels and to minimize greenhouse gas emissions. (Buendı´a et al., 2007; Blanco-Canqui and Lal, 2007). It is necessary to evaluate GHG emissions at temporal and spatial scales, to identify problems and trends, and to propose strategies preventing environmental degradation.

On mitigation of greenhouse gases, Curry and Pillay (2012) asserted that where anaerobic digestion technology is applied, food waste would not be sent to landfills reducing transportation costs and greenhouse gas emissions. (Liang et al., 2013) reported

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that to reduce GHG emissions from the livestock sector, relevant strategies such as improving rearing technologies, breeding, strengthening management and developing large-scale biogas industry should be considered. Theoretically, biogas industry could offset about 80% of GHG emissions from livestock sector, yet there are some barriers, which need to be overcome to enhance cooperation among government agencies, market organizations and livestock enterprises. Beukes et al., (2011) reported that the strategy for New Zealand dairy farming formulates targets for increased national milk production and a reduction in greenhouse gas (GHG) emissions, but acknowledges these two targets conflict because GHG typically increase with increased milk output. Their objective was to determine if both targets could be achieved by implementing combinations of five mitigations. The five mitigations were: (1) improved reproductive performance of the herd resulting in lower replacement rates, (2) increased genetic merit of the cows combined with lower stocking rate and longer lactations, (3) keeping lactating cows on a loafing pad for 12 h/day for 2 months during autumn, (4) growing low protein crops of grains and/or silages of maize, barley and oats on a portion of the farm and feeding this to lactating cows, (5) reducing fertilizer N use and replacing some of this with nitrification inhibitors and the plant growth stimulant gibberellins. No single mitigation strategy achieved both targets of increasing production by 10–15% and reducing GHG emissions by 20%, but when all were simultaneously implemented in the baseline farm, milk production increased by 15–20% to 1200 kg milk fat + protein/ha, and absolute GHG emissions decreased by 15–20% to 0.8 kg CO2-equivalents (CO2-e)/kg fat and protein corrected milk, which is equivalent to a decrease from 11.7 to 8.2 kg CO₂-e/kg fat + protein. The synergies of the mitigations resulted in reduced dry matter intake and enteric CH4 emissions, a reduction in N input and N dilution in feed, and, therefore, reduced urinary N excretion onto pastures, and an

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increase in feed conversion efficiency (i.e., more feed was used for production and less for maintenance).

2.7.2 GHG Emissions Mitigation in Manure Management

Organic wastes which are potentially valuables as fertilizers or amendments must be considered as resources to be managed adequately, instead of pollutants to be removed.

Following this simple concept, manure has to be considered as a by-product of livestock production and when required processed, just for fitting the objective of an optimal management within the context of the farm (Flotats et al., 2009). Greenhouse gas emissions from manure management in the European Union (EU) in 2008 were estimated as 50.26 million tonnes CO2 equivalent, of which dairy cattle contributed 21% (EEA, 2010). The impact of anaerobic digestion (AD) technology on mitigating greenhouse gas (GHG) emissions from manure management on typical dairy, sow and pig farms in Finland was compared by Kaparaju and Rintala (2011), the results showed that enteric fermentation (CH₄) and manure management (CH₄ and N₂O) accounted for 231.3, 32.3 and 18.3 Mg of CO2 eq. yr^_1 on dairy, sow and pig farms, respectively. With the existing farm data and experimental methane yields, an estimated renewable energy of 115.2, 36.3 and 79.5 MWh of heat yr^_1 and 62.8, 21.8 and 47.7 MWh of electricity yr^_1 could be generated in a CHP plant on these farms respectively. The total GHG emissions that could be offset on the studied dairy cow, sow and pig farms were 177, 87.7 and 125.6 Mg of CO2 eq. yr^_1, respectively. The impact of AD technology on mitigating GHG emissions was mainly through replaced fossil fuel consumption followed by reduced emissions due to reduced fertilizer use and production, and from manure management.

Cuéllar and Webber (2008) observed that there is a double greenhouse gas emission benefit through the use of AD systems. Firstly, methane is captured and eventually converted to heat and carbon dioxide instead of being allowed to escape to the atmosphere

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as it does in the simple open lagoon storage of manure. Methane‘s global warming potential is 21 times that of carbon dioxide and thus the conversion of methane to carbon dioxide reduces the global warming potential. Secondly, if the AD biogas plant offsets fossil based electricity (such as natural gas fired power plants), there is a reduction in fossil fuel-related carbon dioxide emissions. Along with mitigating bio-methane gas emissions, anaerobic digestion of animal manure has the potential to reduce farm-generated odors, improve crop-based nutrient management, and produce local, renewable energy (Labatut et al., 2011). Utilisation of fossil fuels such as lignite, hard coal, crude oil and natural gas converts carbon, stored for millions of years in the Earth‘s crust, and releases it as carbon dioxide (CO2) into the atmosphere. An increase of the current CO2 concentration in the atmosphere causes global warming as carbon dioxide is a greenhouse gas (GHG). The combustion of biogas also releases CO₂. However, the main difference, when compared to fossil fuels, is that the carbon in biogas is taken up taken the atmosphere, by photosynthetic activity of the plants. The carbon cycle of biogas is thus closed within a very short time (between one and several years). Biogas production by AD reduces also emissions of methane (CH4) and nitrous oxide (N2O) from storage and utilization of untreated animal manure as fertilizer. The GHG potential of methane is higher than of carbon dioxide by 23 fold and of nitrous oxide by 296 fold. When biogas displaces fossil fuels from energy production and transport, a reduction of emissions of CO₂, CH₄ and N₂O will occur, contributing to mitigation of global warming (Al Seadi et al., 2008).