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. 

Are corporations ruining food? – A lecture by Rob Lyons.

Last night (23/11/11) I attended a UCL Current Affairs Society lecture by Rob Lyons - deputy editor of spiked-online.com, writer on science and risk and author of Panic on a Plate: how society developed an eating disorder.

Short but thought provoking, the lecture revealed Lyons’ views that modern agriculture has enabled us to achieve all that we need to, in terms of food production. He stated that “for most of human history, the politics surrounding food was simply 'will there be enough'. Now such fears are absent from the developed world, the politics of food now focuses on who produces it and how”. Lyons took a historical view from when food was local and organic but expensive and scarce, making the current food system look far more successful! Food is now cheaper and more varied (due to trade) therefore people in the developed world eat a better, more varied diet. – So far intensive agriculture is looking good.

When questioned about the environmental impacts of these practices in terms of soil erosion and eutrophication, Lyons stated that our rivers and lakes are much cleaner today than they have been in the past - ok fair enough. Regarding soil erosion, he compared the desertification occurring in developing countries, where small-scale subsistence farming methods deplete nutrients, with soil in developed countries where fertilizers and irrigation maintain soil quality- I see his point here too. Lyons seemed positive that there will always be ways to improve environmental conditions with advances in technology and understanding in the future, therefore we need not worry about damaging it now.

            However, when I questioned Lyons on the long-term sustainability of intensive farming in terms of fossil fuels and phosphorous depletion, required to maintain the agricultural inputs, he simply suggested that fossil fuels aren’t really running out. He named a couple of newly found fuel reserves and explained that the viability of the extraction of shale oil is increasing. Similarly with phosphorous, Lyons stated that new reserves have been found therefore availability of phosphorous is no longer a problem. He explained that as we get close to the depletion of a resource, the value of that resource will increase and therefore more effort will be made to find new reserves. Lyons seemed pretty sure that we wouldn’t run out of these vital resources for at least 100 years – so there’s no need to panic!

            I do agree that maybe the depletion of fossil fuels is often dramatized, however, I think that continuing our reliance on them even longer is just going to increase our vulnerability by enabling the population to grow even more. We will never produce fossil fuels as quickly as we are using them so we will inevitably run out at some point and we need to prepare for this. Similar to the green revolution – I believe that finding more resources to rely on is just ‘postponing the day of reckoning’.

I left the lecture feeling intrigued but frustrated. I felt like the environmental impact of modern agriculture had been dismissed, as if it didn’t really matter because Lyons wasn’t concerned about it.

Other issues raised in this lecture will be discussed in later posts.

Monoculture Wheat Crop

Monoculture Wheat Crop - Montana (National Geographic)

MONOCULTURES

A summary of Altieri's report (University of California) on the problems associated with monocultures. 

Monocultures are agricultural land areas ‘devoted to single crops and year-to-year production of the same crop species on the same land’ (Altieri, University of California). Development of monocultures was enabled by agricultural mechanization, the improvement of crop varieties, and the development and increased availability of pesticides and fertilizers. Governments have encouraged this as monocultures can contribute significantly to the ability of national agricultures to serve international markets.

Intensive farming has enabled farmers to become more integrated into international economies. As a result, monocultures are ‘rewarded by economies of scale’ (Altieri, University of California). Therefore farms today are ‘fewer, larger, more specialized and more capital intensive’. However, monocultures are highly vulnerable and dependent on many chemical inputs, as the lack of rotations and diversification has taken away key self-regulating mechanisms.

Problems

-       The move from crop rotation to harvesting the same crop type each year means the same nutrients are removed from soils year after year and nutrient depletion and soil degradation becomes a huge problem and is highly unsustainable.

-       Crop types have been selected for their high yields, ‘sacrificing natural resistance for productivity’; this makes them more susceptible to pests. This is overcome by increasing the use of pesticides, however, many argue that the negative impacts of pesticides, including the reduction of beneficial insects, outweigh the positives. (As shown in Rachel Carson’s, Silent Spring, which I will look into further at a later date)

-       Monocultures are also more vulnerable to disease, as populations of the same species will have the same resistance to certain diseases, therefore whole populations can be wiped out by one disease outbreak. Protecting monocultures and treatment of disease requires a further increase in inputs, occasionally to the extent that, ‘the amount of energy invested to produce a desired yield surpasses the energy harvested’ (Altieri, University of California).

Intensified chemical controls are required to overcome the limiting factors reducing the productivity of monocultures, such as high pest potential, limited soil moisture, or low-fertility soils. The efficiency of the many inputs required to maintain monocultures are decreasing and crop yields in most key crops are leveling off, making the whole practice highly unsustainable.