Solutions for intensive farming on stony soils

Irrigation has enabled the expansion of intensive farming – particularly dairying – on shallow, stony soils, but these properties increase the vulnerability of nitrogen leaching, potentially affecting water quality. Landcare Research is collaborating with several research organisations at a Canterbury research farm to find solutions.

Graeme Rogers uses the term soil loosely when referring to the earth at Lincoln University’s Ashley Dene Research and Development Station.

“We always call it soil, but in actual fact it’s a lot of stones,” the research technician at Landcare Research says.

However, this makes the 190-hectare converted dairy farm near Lincoln perfect to research what management systems are best suited for intensive farming on stony soils, which are particularly vulnerable to nitrogen leaching.

The findings from this new research facility will have widespread significance – particularly in Canterbury, where 70 per cent of productive land is on shallow, stony soils, as well as large parts of the lowlands in Otago, Southland, Hawke’s Bay, and the Wairarapa regions.

Landcare Research is working with a number of research organisations at the Lincoln University research station to find solutions to help farmers operating on these types of soils to minimise nitrogen losses from leaching and greenhouse gas emissions.

The Crown research institute has established three sites on the farm, each with large lysimeters – a buried container that measures how much and how quickly nitrogen, water and nutrients from fertiliser, dung and urine drain through the soil. One site has irrigated lucerne, the second dryland lucerne, and the third different winter forage crops.

Supersized lysimeters:

Rogers has been at the forefront of installing the 16 large lysimeters.

The lysimeters are unique, not only set apart by their size, but by their material. Plastic pipes (2 m wide x 1.5 m deep) and a shipping container (6 m long x 2.4 m wide) have been repurposed for the job – an innovative idea of Dr Sam Carrick, a soil scientist at Landcare Research.

Carrick is working alongside scientists from DairyNZ, Plant & Food Research, and Lincoln University to help farmers reduce their nitrogen footprint, and as a result improve nutrient efficiency and water quality.

Carrick said the large lysimeters were needed to allow an “even representation” of the soil type, as well as to accommodate the deep roots of lucerne.

The lysimeters will allow various farming systems to be compared. For example, nitrogen and drainage losses under a dryland regime will be compared with an irrigated system at the lucerne sites.

Different forages are another option researchers are looking at to help reduce nitrogen leaching. This research is part of the DairyNZ-led Forages for Reduced Nitrate Leaching programme.

Integrated approach:

But it’s not just nitrogen leaching levels being measured.

The association of carbon and water with nitrogen losses is also being closely analysed.

These cycles have typically been studied in isolation. However, researchers believe studying all three will reveal innovative new ways to tackle nitrogen leaching. This is something that’s never been done before on stony soils.

Keith Cameron, Lincoln University professor of soil science and head of Centre for Soil and Environmental Research, said Ashley Dene provided an unrivalled opportunity for this “integrated approach” to take place.

“Often our science teams have worked exclusively in carbon or nitrogen so what we’ve done here is bring those research experts together and link those critical cycles and therefore try and find ways to reduce the environmental footprint of agriculture with enormous benefits for farmers,” Cameron said.

Importance of carbon:

Landcare Research is particularly interested in the potential of carbon in reducing nitrogen leaching.

John Hunt, a researcher at Landcare Research, said it was not only important to know not only how much carbon is in the soil but also how different management practices affected changes in soil carbon.

“Carbon in the soil is good because it’s organic matter, which means it holds more water and it holds more nutrients, so it’s better for the plants, it’s better for the farmer, and it’s better for stopping nitrogen leaching.

“Some other long-term work in New Zealand has shown that irrigation results in carbon losses from the soil, so this is also an important area for the research to further develop our understanding of the processes involved."

Hunt is using ultra-high-speed instruments at the dryland and irrigated lucerne sites to measure the exchange of carbon and water between the pasture and the atmosphere, or as leaching, under the two different farming systems. These instruments continuously measure the exchange over the whole paddock. He is also measuring how much carbon is being taken up by the plants in order to tell if the systems are losing or gaining carbon, and how much water is being lost from the plants and the ground.

Data loggers are also being used to record meteorological information (measuring sunlight, wind speed and direction, humidity and temperature).

Manipulating carbon inputs:

A new and exciting approach being explored at Ashley Dene to reduce nitrogen losses – from leaching and the potent greenhouse gas – is through manipulating carbon inputs.

The innovative 5-year project, led by scientist Dr David Whitehead and in collaboration with scientists from Lincoln University, Plant and Food Research and AgResearch, was recently awarded $8million funding from the Ministry of Business Innovation and Employment’s (MBIE) Endeavour Fund.

Whitehead said: “Stony soils are particularly important because that’s where most of the conversion from dryland to irrigated farming is taking place.

“Those are the soils that are the most fragile and most likely to allow water to drain through and for nitrate leaching to occur as well. What are the long-term impacts of dairying going to be on those systems? We’re very concerned about maintaining the quality of those soils as well and that’s principally around retaining soil carbon.

“If we can reduce nitrate leaching on these stony soils and at the same time increase soil carbon then that would have an enormously beneficial effect and that’s again why our work is focused on carbon and nitrogen dynamics at the same time,” Whitehead said.

“We propose to manipulate soil carbon inputs by growing different crops, changing the composition of animal urine (through different feeds) and using irrigation scheduling to reduce nitrogen losses. We are anticipating a breakthrough by using new molecular techniques.”

Sequestering carbon to offset climate change:

At the research station, Landcare Research is also investigating how to keep more carbon in the soil to help offset climate change.

Landcare Research scientist Dr Peter Millard said the international project, funded by the Global Research Alliance, is looking at how land management impacts soil carbon levels, and exploring what practices could stabilise soil carbon.

“We’re trying to understand what drives the turnover of soil organic matter,” he said.

“If we could sequester just 0.1 per cent more carbon in the soils globally than the amount present now, this could more than completely offset all the greenhouse gas emissions from human activity because there’s a lot of soil and that would equate to a huge amount of carbon.”

Long-term aims:

Data, collected from all of the studies at the new Ashley Dene Research and Development Station, will be used in models to forecast the impacts of management practices and climate change on soil carbon turnover and nitrogen losses, enabling farmers to adopt improved practices to enhance soil carbon and reduce nitrogen losses.