A briefing note from The University of Sheffield’s Grantham Centre for Sustainable Futures has proposed a new sustainable model for intensive agriculture. The Grantham Centre argues that current crop yields are maintained through the application of large amounts of fertiliser which are unsustainable.
The application of fertiliser is unsustainable for three main reasons according to the briefing note:
- Applications consume 5% of the world’s natural gas production and 2% of the world’s annual energy supply
- They depend on non-renewable rock phosphorus which will become increasingly difficult to access (the easiest to access and highest P content ore has already been mined)
- They facilitate nutrient washout which pollutes fresh and coastal waters, leading to algal blooms and oxygen depletion
Modern crops are geared towards high nutrient artificial inputs and the chemical control of pests and diseases. As a consequence, crops have lost their reliance on microbes that extract complex nutrients from the soil and defend them against natural enemies. Over time, soil is being relegated to a substrate to support plants but nothing else. The organic carbon content of soil has declined as a result of deep ploughing, and in turn, soil is less able to retain water and supply nutrients. The pace of erosion of topsoil from ploughed fields is 10-100 greater on average than the pace of soil formation. Over the last 40 years, nearly one third of the world’s agriculturally suitable land has been lost due to either erosion or pollution. It takes approximately 500 years to form 2.5 cm of topsoil under normal agricultural conditions.
The way we use soil has important implications for climate change
Of the 3170 gigatons of total carbon in terrestrial ecosystems, approximately 80% is in the soil. The amount of carbon in soil is approximately three times more than that in the atmosphere and therefore the way we use soil has important implications for climate change.
According to the Grantham Institute, a sustainable model for intensive agriculture which combines the lessons from history and modern biotechnology is based on three principles:
- Managing soil by directly applying manure, rotating annual and cover crops, and using no till agriculture. Such practices are expected to restore the organic matter, structure, water-holding capacity, and nutrients of soil
- Biotechnology can be used to wean crops off the artificial conditions we have created for them. This will facilitate symbioses with soil microbes which will allow crops to exploit microbial biology to tap into soil organic nutrient reserves and prompt plants to better protect themselves against pests and diseases
- Inorganic fertilisers could be produced from human sewage in biorefineries at either local or regional scales. There are some technical challenges to the introduction of this idea, however they could be overcome through research
Soils that have increased biological functionality can store water and nutrients. They also support microbial communities, boosting plant health through the direct suppression of soil borne diseases, and priming plant immune systems. A re-engineering of agricultural systems would reduce the reliance on fertiliser inputs and pesticide application. It would also save water, as irrigation would not be required to the extent it is currently used.
The potential scientific, economic, cultural and political impediments of redesigning the agricultural system must be assessed. If proved feasible, we can reduce our dependence on energy intensive and non-renewable inorganic fertiliser and reduce fertiliser pollution of waterways. No model is likely to solve all problems, and different geographic, climatic or crop scenarios could benefit from the new approach more than others. Any redesign needs to be sufficiently flexible.