9. Should We Go Organic?

“If everybody switched to organic farming, we couldn’t support the Earth’s current population – maybe half”

Nina Federoff

My last post identified that synthetic fertilizers can successfully maintain and enhance soil quality, but at a significant environmental cost. Organic agriculture aims to avert this ‘cost’ by only using organically fixed nitrogen incorporated into the soil via techniques such as crop rotation, companion planting and compost addition. Organic agriculture is generally perceived to be the 'environmentally friendly' choice.

Fig. 1 Pro-organic slogan from American smoothie company claiming “100% organic, no harm to nature” (Source: Organic Greenfix)

However, as I explained in my last post organically fixed nitrogen is limited. Humans can intentionally increase biological N-fixation but this requires time and space. Furthermore, some argue that organic farming is only half as productive as conventional farming. Therefore, to maintain/increase agricultural production using 100% organic methods we would need to expand agriculture onto new land. Yet land use change to make way for agriculture (particularly deforestation) is one of the primary causes of soil degradation (see my third post) and biodiversity loss (see Ruth's blog). Is organic agriculture actually environmentally superior or is this just an urban myth?

Fig. 2 Agriculture is responsible for around 80% of deforestation worldwide. This photo shows deforestation in the Papua Province Forest, Indonesia (Source: Archaeology News Network; Credit: Geografika Nusantara)

More recent studies have challenged these low productivity claims. They have found that organic yields are highly context specific and may only be 3% lower than conventional ones if at all. Thus the debate continues… 

8. Fertilizer: The Good, The Bad and The Ugly

“Turning stones into bread”

Fritz Haber

Nutrient depletion is the second main cause of global soil degradation (see my second post). Fertilizers can restore, maintain and enhance chemical soil quality depending on the quantities in which they are added. They can restore/maintain productivity by replacing the nutrients lost through harvesting. They can then enhance productivity if nutrients are added beyond natural baseline levels (although this only translates into increased plant growth if these nutrients were naturally limiting). This post investigates the use of artificial nitrogen fertilizers, covering both their revolutionary agricultural benefits and also their significant environmental threats.

Natural N fixation
Nitrogen is the most important nutrient for plant growth. Yet, it is also the most naturally limiting. Atmospheric nitrogen (N₂) is abundant, comprising 78% of the air we breathe, but unavailable to plants. There are only two ways that atmospheric nitrogen is naturally converted into plant available nitrogen (i.e. fixed): (1) via lightning or (2) via specialized ‘Rhizobium’ bacteria found in the root nodules of certain ‘leguminous’ plants. No wonder it’s in short supply! 

Fig. 1 Elemental nitrogen: essential to life

Artificial N fixation
In 1909 Fritz Haber invented a process (outlined in Fig. 3 below), which allowed humans to artificially fix atmospheric nitrogen to produce biologically available ammonia. In the 1930s, Carl Bosch then developed this process on an industrial scale and by the 1950s synthetic ammonia fertilizers were being mass-produced all over the world. 

Fig. 2 Fritz Haber (left) and Carl Bosch (right)

Fig. 3 Diagram showing the Haber-Bosch process for converting unreactive atmospheric nitrogen into plant available ammonia. (Source: Gulf Coast Environmental Systems)

The Good: 
These fertilizers allowed farmers to replenish the nitrogen lost through harvesting and increase its availability beyond natural levels. As a result, global agricultural productivity dramatically increased and this 'detonated the population explosion'. In fact, the Haber-Bosch process is now responsible for feeding almost 50% of the world's population, as demonstrated in the graph below. As such, it has been deemed the most important technical invention of the twentieth century.

Fig. 4 Trends in human population and nitrogen use throughout the twentieth century. Of the total world population (solid line), an estimate is made of the number of people that could be sustained without reactive nitrogen from the Haber–Bosch process (long dashed line), also expressed as a percentage of the global population (short dashed line). The recorded increase in average fertilizer use per hectare of agricultural land (blue symbols) and the increase in per capita meat production (green symbols) is also shown (Source: Erisman, 2008)

The Bad & The Ugly: 
Whilst the production of artificial fertilizers has clearly been good for humanity, it has also begun to cause serious environmental problems. Because biologically available nitrogen is so rare in nature, ecosystems are highly sensitive to it. Nitrogenous fertilizers (that have not yet been incorporated into crop plants) can wash off fields and into watercourses, where they stimulate blooms of algae. These blooms trigger a process called ‘eutrophication’, which depletes the water column of oxygen to a point where no life is possible, as shown in the diagram below.

Fig. 5 Fertilizer washes into a water body causing eutrophication. At the end of the eutrophication process the oxygen levels in the water are so low that no life can exist. (Source: BBC Bitesize)

   
Eutrophication is creating areas of hypoxia (low oxygen) and anoxia (no oxygen) in surface waters all over the world. These areas have grown exponentially since the 1960s and threaten all the ecosystems that depend on them. Hypoxic 'dead zones' are particularly common at the mouths of large rivers, near major population centres, where nutrient rich waters pour into the sea. For example, the extensive Gulf of Mexico dead zone has developed near the mouth of the Mississipi. Globally, coastal dead zones now cover more than 245,000 km², an area the same size as the UK!

Fig. 6 Map showing location of major dead zones (where marine life cannot survive) caused by in washing of excess reactive nitrogen (Source: NASA, 2017)

Production and use of synthetic fertilizers can also contribute to climate change. Firstly, because the Haber-Bosch process is energy intensive and emits millions of tonnes of CO₂ every year. Secondly, because more reactive nitrogen in the environment increases the abundance of nitrous oxide (N₂O). This is an extremely powerful greenhouse gas (300 times more powerful than CO₂) that remains in the atmosphere for over 100 years! Nitrous oxide can also deplete the ozone layer, which creates another whole set of problems. 

The Nitrogen Boundary:
In 2009, a group of scientists proposed 9 'planetary boundaries' (PBs) that humanity must not cross if we are to continue to support life and our civilization. These scientists deemed the side-effects of increased nitrogen-fixation to be significant enough for nitrogen to have it's own boundary. The PB framework was updated in 2015 and the original nitrogen boundary amalgamated intro a more holistic 'biogeochemical flows' boundary. Nevertheless, both frameworks identify that we are already WAY beyond the safe zone for nitrogen use, as shown in the diagram below. The flow of human-fixed nitrogen must be reduced by about a third of its current value (from ~150 million tonnes to ~62 million tonnes per year) to return to the ‘safe zone’. 

Fig. 7 Current status of the control variables for seven of the planetary boundaries. The green zone is the safe operating space, the yellow represents the zone of uncertainty (increasing risk), and the red is a high-risk zone. The planetary boundary itself lies at the intersection of the green and yellow zones (Source: Steffen et al., 2015) 

A question of distribution?
The transgression of the global nitrogen boundary is mainly due to a few agricultural regions where fertilizer application rates are so high that nitrogen is often actually in excess. Perhaps a redistribution of nitrogen from these areas to areas where the soil is still nitrogen-poor could maintain global crop production whilst reducing the need for nitrogen-fixation. Unfortunately, this is not as simple as it sounds because artificial fertilizers are expensive and many of the regions with low usage (e.g. Sub-Saharan Africa) are unable to afford them. Therefore, the next few posts investigate other ways we could reduce artificial nitrogen-fixation.

Fig. 8 Map of global nitrogen fertilizer application in Kg/ha. (Source: adapted from Potter et al., 2010)