Why are we using up our natural resources feeding livestock?

A 2006 United Nations, Food and Agricultural Organization report has brought to light many of the problems associated with the production of meat. Increased wealth has lead to changes in food preferences, which has resulted in increased consumption of meat. During the past 40 years global per capita meat production has increased more than 60% (Tilman et al 2002). Livestock products now provide one third of humanity’s protein intake and global production of meat is projected to more than double from 1999 to 2050 with our growing population (UN, 2006). The report states that the livestock sector emerges as one of the most significant contributors to the most serious environmental problems, on a local and global scale. The meat industry contributes heavily to problems of land degradation, climate change, air pollution, water shortage and pollution and loss of biodiversity.

5 reasons why you should become a vegetarian!         

• The livestock sector is responsible for 18% of greenhouse gas emissions measured in CO2 equivalent (this is a higher share than transport). The largest share of this comes from land use change, especially deforestation (UN 2006).
• Overgrazing by cattle for meat degrades land and reduces soil productivity. Livestock production accounts for 70% of all agricultural land and 30% of the land surface of the planet. This includes the vast amount of land required to grow feedcrops for cattle which has resulted in huge amounts of deforestation (UN 2006).
• The livestock sector accounts for over 8% of human water use, mostly for the irrigation of feedcrops (UN 2006).
• The production of 1kg of meat requires between 3 and 10kg of grain, which requires vast amounts of land and many natural resources for growth (Tillman et al 2002). Therefore for the same input of resources you get a much smaller output compared to eating the grain directly, making the system less efficient.
• Meat eating adds a trophic level to the food chain and energy is lost with each trophic level, meaning that meat eating is less energy efficient than vegetarianism. Therefore meat eating increases depletion of earths natural resources (Tillman et al 2002).

Therefore increased meat consumption is not helping in the quest to feed the world’s growing population within the world’s environmental limits. 

Coastal Eutrophication – The impact of Agriculture in Chesapeake Bay

Over the past 300 years, Chesapeake estuary in mid-Atlantic USA has been converted from natural forests and wetlands into agricultural fields and urban development. Brush (2009) took sediment cores from the estuary, dating back 14,000 years ago, to look at the effects of these changes.

Sediment, nitrogen, pollen, diatom, and seed profiles from sediment cores suggest that prior to disturbance, the nitrogen cycle of this area consisted of a balance between biological nitrogen fixation and denitrification (Brush, 2009). This balance was maintained while small agricultural settlements were developed. However as land use changed to incorporate more intensive farming to support a growing population, this balance was disturbed. As agriculture grew and became more intensive, wetlands were drained, land was deforested and streams were channelized to reduce flooding of agricultural land and chemically produced nitrogen fertilizers were used to farm less fertile, marginal land. Changes to the landscape vegetation, hydrology and geochemistry resulted in a reduced denitrifying capacity of the area. This resulted in increased nitrogen loadings into the estuary, which lead to coastal eutrophication.

This diagram was produced to highlight the changes in the area over time. It is evident that many changes occurred as the population increased and with the onset of intensive agriculture (Brush, 2009).

The diagram shows how pollen types reflect the changes in land use. Sedimentation rates also increase as land was cleared for agriculture. These changes led to a shift from a benthic dominated system to planktonic dominated system, due to lack of light in the water column, which was further reduced by continued Planktonic algal growth. The increase in fertilizer purchases was mirrored by nitrogen fluxes in the sediment column. Through the process of eutrophication, this eventually led to the deep waters becoming anoxic and productivity declined (Brush, 2009).

Brush (2009) highlights how coastal eutrophication in Chesapeake Bay has significantly reduced coastal shellfish and fishery resources (especially oyster farming as shown in the diagram), which are important food sources for humans. Therefore in an attempt to feed the growing population of Chesapeake Bay through intensive agriculture, other valuable natural food resources were destroyed, and so far, all efforts to return Chesapeake Bay to its natural state have failed.

Ecosystem services as natural resources

Defra defines ecosystem services as ‘what nature gives us - Nature provides us with the very essentials of life. It gives us clean air and water; enables us to produce and gather food, fuel and raw materials from the land and sea; regulates our climate; stems flood waters and it filters pollution’. Ecosystem services provide us with natural resources. However, intensive agriculture can put many of these at risk (Tilman et al., 2002).

SOIL - plays vital roles in biogeochemical cycles and the water cycle. They provide nutrients, which enables plant growth and they play a part in flood control, and water filtration among many other processes. ‘Since 1945 approximately 17% of vegetated land has undergone human-induced soil degradation and loss of productivity’ (Tilman et al., 2002). Monocultures and continuous cropping remove nutrients from the soils and reduce soil organic matter, which reduces the stability and fertility of the soil. The reduction of this ecosystem service then results in larger fertilizer and irrigation requirements.

FORESTS- ecosystem services include - minimizing flooding, moderating regional climate, removing atmospheric carbon dioxide and aiding regeneration of fertile soils (Tilman et al., 2002). Greater food demands has led to deforestation to increase land available for agriculture. With continued population growth this will continue, with most deforestation in developing countries, which will have a major impact on the extent of tropical forests and the ecosystem services they provide (Eickhout et al 2006).

BIODIVERSITY – is vital to the maintenance of all ecosystem services. One of the main services provided by biodiversity is disease and pest resistance (Tilman et al., 2002). As previously explained, monocultures remove these protective ecosystem services. Pesticides are therefore used to reduce this problem. However, they have many adverse affects. Rachel Carson’s book silent spring explains the problems associated with increased use of chemical pesticides including the problems associated with non target species ingesting pesticides. Especially the toxic side effects of organochloride insecticides (DDT), which fueled the green revolution. The high persistence of DDT means it moves up the food chain causing more severe effects at successive trophic levels (Krebs et al. 1999). Pesticides can therefore lead to reduction of biodiversity by affecting non-target species and therefore further reduction in ecosystem services. Pollination and seed dispersal by insects and birds are vital ecosystem services that are vulnerable to destruction due to the use of pesticides. These losses would have direct adverse affects to agriculture.

FRESHWATER – has many obvious ecosystem services including water for human consumption, irrigation, power and transport. However, the use of fertilizers and pesticides in agriculture jeopardizes these ecosystem services by causing eutrophication (Eickhout et al., 2006). As shown in this very simplistic but informative video…

In turn eutrophication will reduce the availability of freshwater and the ecosystem services it provides for agriculture.

It is clear that maintaining ecosystem services is crucial for sustainable agricultural production and this is vital if we are to meet the demands of food production in the future. Some ecosystem services such as pollination or control of pests are of direct benefit to the farmer but others may be beneficial to people in general, therefore less care is taken over their preservation. Tilman et al. (2002) state that ‘Agriculturalists are the principle managers of global ‘usable’ lands’. This highlights the great control farmers have over our ecosystem services and therefore our natural resources. 

The role of Nitrogen

This video highlights how nitrogen is a natural resource that we don’t worry enough about. Nitrogen is essential for plant growth and therefore a vital agricultural input. However we are wasting it through inefficient use of fertilizers (Eickhout, 2006).

In the early 20th century the Haber-Bosch process was discovered for synthesizing ammonium nitrate (converting Nitrogen into a reactive form). This increased availability of this limiting resource enabled huge increase in food production and therefore population growth (Steffen et al., 2007).

This has dramatically altered the natural nitrogen cycle, as worldwide, more nitrogen fertilizer is now used per year than can be supplied through natural sources as agricultural inputs currently exceed inputs from natural N fixation. More nitrogen is now converted from the atmosphere into reactive forms than by all the natural processes in terrestrial ecosystems put together (Steffen et al., 2007).

This diagram shows how the flow of nitrogen has been altered by human interruption.

Figure 1. Global terrestrial nitrogen buged for a) 1890 and b) 1990 in Tg N yr^-1. (Steffen et al., 2007)

The emissions from NOy reflect those from fossil fuel combustion. Those from the vegetation include agricultural and natural soil emissions and combustion of biofuel biomass and agricultural waste. The NH_x emissions from the cow and feediot reflect emissions from animal wastes. The transfers to the fish box represent the lateral flow of dissolved inorganic nitrogen from terrestrial systems to the coastal seas.

The enormous amount of N₂ converted to NH₃ in the 1990 panel compared to 1890 represents human fixation of nitrogen through the Haber-bosch process, made possible by the development of fossil-fuel based energy systems (Steffen et al., 2007).

Artificial inputs of nitrogen mean the nitrogen cycle is no longer a closed loop, which has led to huge losses of Nitrogen from agroecosystems (Eickhout et al., 2006). This is generally due to over-application of fertilizers and the inefficient use by crops. ‘The recovery of fertilizer N in global crop production is about 50%’ (Eickhout et al., 2006). The fertilizer that is not recovered by the crop ends up in our environment, mostly in surface water or in ground water. This can then contribute to eutrophication and pollution of aquifers and can also contribute to emission of the greenhouse gas nitrous oxide (Tilman et al., 2002).

As our population continues to grow, our agricultural yields will also have to, therefore even more nitrogen fertilizer will be required. However, Tilman et al. (2002) state that increased application of nitrogen is unlikely to be as effective at increasing yields as it previously was due to diminishing returns. Figure 2 shows how efficiency declines with higher levels of addition. Therefore as more is applied to the land in the hope of increasing yields, the greater the losses and pollution of the environment will be.

Figure 2. trends in nitrogen-fertilisation efficiency of crop production (annual global cereal production divided by annual global application of nitrogen fertiliser). (Tilman et al., 2002)

Total reactive nitrogen loss will increase dramatically with the worlds increasingly intensive agricultural systems (Eickhout et al., 2006). Therefore we need to improve nutrient use efficiency so that less nitrogen is lost to the environment.

Reliance on Natural Resources

These graphs of agricultural trends over the past 40 years of a) global cereal production and b) total global use of nitrogen and phosphorous fertilizer (USSR not included). 

(Tilman et al. 2002) 

I think they show very clearly, how agricultural yields of cereal rely so heavily on natural resources - Water, Nitrogen and Phosphorous.

What a lot of water!

Intensive Irrigation

Wasting Water

Water is a renewable natural resource, yet limited access to freshwater renders it finite. Irrigation for agriculture is the largest consumptive use of water (Bouwer, 1994). The majority of our freshwater is stored in aquifers as groundwater and is abstracted for irrigation. However over-abstraction can result in aquifers becoming unproductive. Dams are often built to store water in irrigation reservoirs but these alter the natural hydrological cycle.

In 2000 agriculture accounted for ~ 75% of human water use (Wallace, 2000). Availability of fresh water is therefore a major limiting factor in population expansion. As the global population increases the demand for food increases and thus the demand for water increases. However, for the foreseeable future, ‘annual renewable freshwater resources are largely fixed’ therefore with population growth water scarcity becomes a huge concern (Wallace, 2000).

Irrigation is very inefficient, Wallace (2000) states that crops actually only use 10-30% or water put onto the land. Runoff losses and deep percolation are sources of inefficiency (Bouwer, 1994). Pimentel, et al. (1997) point out that controlling erosion can help to conserve water by reducing runoff and protecting forests and other biological resources can help maintain the hydrological cycle. As agriculture intensifies, soil erosion and deforestation are both likely to increase, therefore threatening long-term sustainability of water supplies.

Evapotranspiration is another major source of water loss from agriculture, which is likely to increase with climate change. Bouwer (1994) likens irrigated fields to evaporation pans where water is evaporated and salts are left in the soil, which can reduce the quality of the soil. The only way to reduce this water loss is to reduce the irrigated area while maintaining yields, by increasing crop yield per unit of water used (Bouwer, 1994). We need to increase the production of food for our growing population with the existing supplies of land and water (Wallace, 2000). This means agriculture must become even more intensive and even more reliant on fertilizers and pesticides. This in turn increases pollution of the limited freshwater supplies and can result in eutrophication.

            Water resource management will become increasingly complicated as the population continues to rise, especially as the areas with the largest populations to feed are often the most water scarce areas (Wallace, 2000). Wallace (2000) argues that this problem isn’t given enough attention by the scientific community. He believes that science can be used to develop the ability to grow more food with less water. Pimentel et al (1997) point out that most human activity has a negative effect on the quality of freshwater sources, as population continues to grow this effect will increase and the increased demand for water will become even more difficult to meet.