By Sam Duncan
December 5 was world soil day, so I thought I might get my hands dirty (ha-ha) and write about our most important agricultural resource, our soil.
Soil is usually a boring subject, but I’ve made my goal this year to make it sexy. As part of that I wanted to talk more about the importance of health soil across not just agriculture, but our entire economy.
I probably need to define what the term ‘soil health’ means. A lot of soil scientists I talk to despise the term because it’s so broad and ill defined. Fortunately I’m not a soil scientist and you probably don’t have all day to make your mind up about the political correctness of the term ‘healthy soil’. So to quickly summarise what it means using a summary from Agriculture Victoria:
‘Good soil health is about creating a robust soil that can withstand impacts, such as agriculture, without loss of fertility, structure and biological activity.’
So healthy soil is really about the ability for soil to sustain life (plants and microbes) in the long term, despite shocks to that system. The result of healthy soil is that we continue grow stuff, lots of stuff, generation after generation.
Similar to our health, a healthy soil can bounce back from a few blows. To use the analogy of smoking, one cigarette might not do you much harm, but the effect those cigarettes have over time build up and result in cancer and a lung transplant 30 years down the track.
Similarly the impact some of our agricultural practices have on fertility, for example tilling, may not be noticeable over a single season. But over time sustained tilling can drastically impact the productivity of that land. Take this study from 2003 that looked at sugar cane production in Queensland. It found a decline in yield of up to 33% over the course of a few decades (identified when they compared crops experiencing rotation breaks compared to the existing practices).
Fortunately zero, or no-till farming is now common place in order to prevent this from occurring. But tillage isn’t the only practice that can seriously degrade soil fertility over the long run. Sustained cropping using synthetic fertiliser without reintroducing organic matter can degrade Soil Organic Carbon (SOC) stocks. Over the course of a few years, it may not be noticeable, but over a generation the loss of SOC can have serious implications to yield and to the farmer’s bottom line. SOC helps the soil retain nutrients and water, so without it we need to replace them more frequently, and there’s a direct cost to the farm through increased fertiliser use in having to do this.
Over the course of a few years, it may not be noticeable, but over a generation the loss of SOC can have serious implications to yield and to the farmer’s bottom line.
Check out the blog post on soil carbon cycles from Soils For Life for a great summary on the different types of organic carbon, and the speed at which they get replaced. The challenge is viewing this change over time, linking it to an economic cost, and being able to forecast it out 10-20 years.
Unfortunately a reduction in soil health impacts more than just farm yield. Various studies have highlighted that over the past 70 years, the nutrient content of vegetables has declined by up to 40% or more. Some of this has been due to poor soils, whilst some of the decline has resulted from the ‘dilution effect’, which basically means crops are providing higher yields, and an increase in calorific content, without increasing the mineral or vitamin content.
So who in Australia is owning the soil health problem? A friend and mentor makes a really interesting comment, that is that soil is everyone’s care, but no one’s responsibility. To be fair, farmers need to make money, and that comes from maximising yields year after year. Governments also don’t have the data or influence (at least not Australia), to help form policy and police good soil management over the long term either. The challenge is formulating the data set and linking this to the economic benefits of long term soil management.
To get the data, and start the change in attitude towards soil health, we need to get people interested in managing soil in the first place, and that’s why we need to make soil sexy.