Scientists drill deep into dirty dairying
Groundbreaking research into nitrogen levels well below the grass line aims to help reduce pollution and clean up our rivers.
Graeme Rogers’ tone is teasing. He rubs his calloused hands together and complains that they are ‘‘sore from having them regularly smacked’’.
Rogers is a Landcare Research technician. His job is to get his hands dirty on behalf of the research institute’s scientists. Dig their holes and come up with practical ways to implement their theories in the field. He’s a whir of industry and good humour, an indefatigable lover of machinery and science that make a difference.
The target of his fake ire can’t hear him. She’s wearing earmuffs and a focused expression. French plant-soil ecologist Dr Gwen Grelet, assisted by Colombian PHD student Jonathan Nunez, has power-sawed through a sterile PVC pipe and they are sifting through its contents. There’s anticipation in the room.
The Landcare Research science team – in collaboration with Lincoln University, Plant & Food Research and Scion – believe they’re doing something no one else in the science community has dared to do. Something big.
They’ve gathered and processed about 50 soil core samples from Ashley Dene farm near Lincoln. Collecting soil cores is Landcare’s bread and butter, even on the stony soils common to Canterbury dairy farms. But what sets this experiment apart is the size of the samples and the impressivelooking 10-tonne drilling rig. Mcmillan Drilling group designed a custom-made drilling head to plunge sterilised PVC pipes into stony Canterbury soils to a depth of 1.7 metres. The samples extracted weigh about 100 kilograms.
Generally scientists use hand-held augers to extract core sample from the top 20 to 30 centimetres of soil, where most bioactivity occurs. So this team has plumbed new depths. It was Rogers’ idea to get one of the many geotechnical rigs drilling holes in Christchurch to take the huge core samples.
If Rogers is the muscle, then David Whitehead, climate ambassador to former United States vice-president Al Gore, is the mastermind. ‘‘We are in new territory here,’’ he explains. ‘‘It is a new frontier to tell the story of nitrate leaching at this depth.’’
Scientists had assumed that all the action, in a microbiological sense, happens in the top 20cm30cm of soil. But if New Zealand is to crack how to reduce loss of nitrogen from animal waste and fertiliser into groundwater, the answer is going to come from scientists like Whitehead, who are starting to dig much deeper, spurred by the urgency surrounding the issue. Whitehead believes the solution to arresting the drainage of nitrogen into groundwater and our rivers can be found by manipulating the fungi and bacteria that live in the roots and soils of crops such as lucerne, which ‘‘fix’’ nitrogen.
The idea is that if we know more about the fungi and bacteria that thrive in soil, we can encourage farming practices that favour those that filter nitrogen.
To do this, the scientists are taking root, rhizosphere and soil samples from the deep cores. These will be processed in the lab at Landcare Research, then sent to South Korea for DNA sequencing to identify the populations of microbes and their activities.
It is research at the sharp end of
Landcare Research devotes thousands of research hours a year to study how cow poo and urine behave on grasslands and in soil in order to find a scientific solution to what is a massive concern for our agricultural economy.
Nitrogen leaching through soils is generally measured by installing giant tanks (lysimeters) in the ground, which catch seepage from what cows deposit on it. Measuring is all very well, but solutions are needed, and the focus is now moving towards encouraging fungi and bacteria to do the hard work.
According to Whitehead: ‘‘We have nitrogen coming in and nitrogen draining out the bottom of the soil.
‘‘The middle bit is the most interesting: the microbiological process, the fungi and bacteria that hold on to the nitrogen and how they prevent it draining through the soil. So we’re examining which bugs are there and which ones are actively doing the work in the nitrification process,’’ he continues.
‘‘What we are doing is extracting DNA and then sending it away for sequencing so we can identify particular parts of genes that regulate the nitrogen processes – nitrification and denitrification. And as far as I am aware, no one has ever sampled to these depths before.’’
Grelet added, ‘‘There have been studies done of mining core samples at a depth of 1 kilometre, but studies of soils where plants are grown are rarely dive down past a metre.
‘‘So we know there will be a lot of interest in our data. We’re also hoping it might shed some light on some other ideas we have formulated.’’ – Greg Ford