Sunday, 16 March 2014

Talk : From Soil to Supper

A recent Cafe Sci Event featured a fascinating talk by Dr Duncan Cameron (Department of Animal and Plant Sciences, University of Sheffield). The talk was entitled "From Soil to Supper: how microbes can help feed the world" and gave an insight into the interactions between plants and the microbes that surround them in the soil, as well as some uncomfortable facts about the future the lies ahead for food production if present trends continue.

This post is based on the talk, with a few added comments and linkage.

Dr Cameron, a plant and soil scientist, introduced himself by explaining that he had only recently became interested in soil and food and had soon found himself heading up the agri-industry focused "P3 centre of excellence in sustainable agricultural technologies".

To set the scene, Dr Cameron related this quote from Franklin D Roosevelt, which comes from a letter written to all state governors in the aftermath of the Dust Bowls of the mid 1930s

"The nation that destroys its soil destroys itself"
Franklin D Roosevelt-
 Letter to all State Governors on a Uniform Soil Conservation Law.
February 26, 1937 

The scene was set further with a few pertinent facts:

- Soil is the least understood and most degraded part of the ecosystem
- One third of arable land has been lost in the last 30years (see here)
- Erosion of arable land is at 30 -100 times the rate at which is can be replaced
- It is often the most important parts of the soil (the clay and organics) that are lost first.
- It takes some 2500years to produce a 1" layer of topsoil (see here)

Intensive ploughing progressively reduces the amount of organic matter in the soil, which eventually results in soil erosion. The process by which this happens is very clearly described in this UN FAO document and also here.

Dust Storm, Texas, 1935

Modern intensive farming techniques (especially in Europe) have tried to compensate for this loss in soil quality by increased use of fertilizers. Indeed, intensive agricultural practices have effectively sterilized the soil – leaving a material that is essentially just a support to the plants, with all nutrients being supplied by fertilizers.

Two key elements that plants need to grow are Nitrogen and Phosphorous.

With Nitrogen comprising about ¾ of the atmosphere, one might think that plants could have as much of this as they need, but it turns out that the Nitrogen in the air is in a very stable form, with chemical bonds that are very strong. Instead, plants are reliant on obtaining Nitrogen from the soil via compounds that are easier to break down

A breakthrough came in the early part of the 20th century, when the Haber process was developed to economically produce ammonia (which contains useable Nitrogen) on an industrial scale. The ammonia was critical to the WW1 German military as it was a key ingredient in the manufacture of explosives. After the war it the process also allowed for a rapid increase in Nitrogen based fertilizer production and played a major part in the "green revolution". Indeed, some 2% of global fossil fuels used in the Haber process to produce Ammonia, more than for any other process.

It's worth reading this history of fertilizers and also downloading this utterly fascinating map showing which countries are the major global manufacturers and consumers of fertilizers. These two trends of reducing arable land availability (per capita), and increased fertilizers are shown to dramatic effect in the chart below:

World Percapita Fertilizer Use & Available Grain Area
Derived and simplified from USDA data

In contrast to Nitrogen, which can now be extracted on a virtually limitless scale from the air, Phosphorous is a non-renewable resource which is mined from the ground. Depending on whose figures you believe, it may become increasingly hard to obtain in 50-100years time (see here, here and here) , or reserves may last over 300years. (see here)

Globalised food transport has severely disrupted the Phosphorus cycle, as the element is transported (in food plants) from one part of the world to another. Meanwhile, excessive use of Phosphorus fertilizers can result in devastating Eutrophication of waterways (often characterised by algal blooms)

Soil Biology
Dr Cameron described how fungi and bacteria play a vital and complex role in healthy soil by breaking down organic matter so that it is available for use by plants. Indeed part of his research looks at the 80% of plants that have a symbiotic relationship with fungi – a relationship the developed at the time when plants first colonised the land.

In these "Mycorrhizal" relationships the plant provides the fungus with carbohydrates, while the fungus provides the plant with nutrients and with more water than it could obtain via its roots alone

Flax root cortical cells containing paired arbuscular mycorrhizal fungi

Another critical role that fungi play is to erode rocks, thus releasing nutrients for uptake by plants. Research on this topic is currently being undertaken at Sheffield (see here)

Regarding the role of organic farming, Dr Cameron commented that "I'm not going to tell you that organic farming will feed the world, because it won't " but added that there were many organic movement principles (e.g. reduced inputs) that were of value in reducing farmings dependence on fertilizers.

Indeed, many parts of the world (especially the US and Australia) have already swapped intensive high tillage forms of agriculture for low tillage approaches, as described here.

However, when a farmer switches from high tillage to low tillage processes, there is an initial period of a few years when yields drop. This occurs because it takes time for the complex ecosystems to return to an area – some three years for earthworms for example. It is during this time period that state support – and political will – may be required to subsidise the farmers while their yields are recovering as the soil improves.

Dr Cameron described how there was a need to "close the loop" of phosphorus use by returning the phosphorus taken up by plants back to the earth - by using human and animal waste as fertilizer (see here), a practice which used to be common in the UK, with the waste being knows as "Night Soil"

The 1,500kg of liquid and solid waste produced per person could produce 20kg of fertilizer, which would help to produce 200kg of crops

Regarding GM technology, Dr Cameron suggested the people needed to distinguish between the marketing policies of some companies (which could certainly be criticised) and the technology as a whole. In particular he commented that it was increasingly difficult to draw a line between GM and non GM technology and that GM technology offered the chance to dramatically reduce development times for new plant strains – something that may be critical given the pace of climate change. Exchange of DNA is very common in the plant and soil ecosystem, one example being that of agrobacteria, who insert genes into plants to make tumours.

An overview of much of what the Plant Sciences department is doing in this area can be found in this article

Image Souces
Atbuscular Mycorrhiza
Night Cart
Texas dust storm in 1935

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