Incorporating stubble could have big benefits
Courtesy of the Hamilton Spectator, May 2008
Text & Photographs IAN WHITING
INCORPORATING stubble with fertiliser back into the soil to build up soil organic matter will lead to improved soil health and improved soil carbon levels which could mean reducing carbon dioxide levels in the atmosphere, which in turn means farmers could actually become part of mitigating climate change.
This was the message from leading CSIRO soil scientist and researcher, Dr Clive Kirkby at the recent Southern Farming Systems paddock walk held at the Hamilton Branch trial site near Dunkeld.
Dr Kirkby was talking to farmers about building up soil organic matter. He said everybody talked about soil carbon levels, but that it should be organic matter in actual.
“We know that quite clearly. Organic matter is composed primarily of carbon, nitrogen, phosphorus and sulphur. So my message to farmers out there is that if you want to build up your soil carbon levels there is a fairly good chance that you are going to have to increase your nitrogen, phosphorus and sulphur levels as well,” Dr Kirkby said.
Dr Kirkby is proposed that farmers will need to make more inputs at the stubble incorporation stage, to effectively try to build or grow two crops.
“We are growing a crop above the soil, which is the normal crop a farmer sees, and a crop below the soil which is organic matter, and for that we need essentially the same nutrients we need for plants.
“The amount of nutrients that is actually in stubble is quite low, (while) the amount of nutrient in humus is quite high. So if you want to covert the maximum amount of stubble into humus you need extra nutrients to do it,” he said.
According to Dr Kirkby Australian soils are very low in carbon, but because of the relationships he has discovered they are also low in nitrogen, phosphorus and sulphur. He believes that all four elements are tied tightly together. Our soils are very ancient soils and have been leached for literally thousands of years so most of them are very poor nutritionally.
Dr Kirkby is not asking farmers to put their hands in their pockets just yet. He is conducting laboratory experiments in Canberra and has trial sites on commercial farms in Harden and Leeton.
“The economics is hugely important especially in this day and age so we don’t want all farmers going out there and doing all these things because it’s going to cost too many dollars. That’s what trial sites are for, to try and prove ‘yes it works’ or ‘no it doesn’t and laboratory experiments are an adjunct to that,” Dr Kirkby said.
Building up soil carbon levels is obviously a long term project but Dr Kirkby believes he may be able to improve soil carbon levels quite quickly.
“I am not sure about getting carbon levels to the right amount, but I expect that we will see changes within two or three years which is a heck of a lot quicker than most people think,” he said.
This is obviously a long term project for farmers because in big areas they are talking about significant quantities of money in order to add the required amount of nutrients.
Dr Kirkby is advising that farmers should be picking one paddock and just concentrating on building up soil organic matter there, or doing it over a larger area a little at a time which would cost a small amount of money each year.
“You certainly don’t want farmers going out there and throwing a heap of dollars at the dirt,” he said.
Dr Kirkby believes there are two major benefits. The first deals with climate change. Improving soil carbon levels could mean reducing carbon dioxide levels in the atmosphere.
“There is more carbon in the soil than there is in the atmosphere right now so there is definite possibility that farmers could actually become part of mitigating climate change.
“One of the big things I am really keen on is if farmers do that and we can prove it can be done and do it economically, there is no reason why the government shouldn’t pay a farmer to do so and that could offset the cost,” he said.
The second benefit is an improvement in soil health and if soil is in better condition than theoretically farmers should get better crops and therefore economic benefit.
“Although my science is about improving the organic matter and improving the soil carbon, the real focus is definitely on the economics,” Dr Kirkby said.
Enquiries, information and comments to:
Michelle McClure
Hamilton Branch Coordinator
Southern Farming Systems
P: 03 5572 3426
M: 0417 228 233
E: mmclure@sfs.org.au
This article appeared in the Hamilton Spectator on May 10, 2008
