8 Oct 2015

Science of stony soils and water

From Our Changing World, 9:06 pm on 8 October 2015

By Alison Ballance

“We’ve an integrated research project using lysimeters to quantify how our management activities affect both the performance of crops and also how water and nutrients leach out the base.”
Sam Carrick, Soil Scientist, Landcare Research.

Different size lysimeters in the ground

The barrel lysimeters (left) are 50-cm across and filled with very stony soil. The very large lysimeters (right) are made from a 2-meter diameter sewer pipe (in the foreground) and a shipping container (in the background in front of Sam Carrick) Photo: RNZ / Alison Ballance

A cut-away of a lysimeter

A cut-away of a lysimeter showing how the barrel is dug into the soil, enclosing a core of soil, and water draining through can be measured at the bottom. Photo: RNZ / Alison Ballance

What do a 50-cm diameter barrel, a 2-metre diameter sewer pipe and a shipping container have in common? They are all being used to study stony soils in Canterbury, to see how water and animal urine move through the soil, affect plant growth and contribute to the emission of greenhouse gases such as nitrous oxide. They have been turned into lysimeters, which enclose an undisturbed plug of soil that can be fitted with scientific instruments so it can be studied in detail. The smaller lysimeters can even be dug up and moved to a new location, while keeping the soil structure intact.

Sam Carrick is a soil scientist from Landcare Research at Lincoln, and he is involved in a six-year research programme called ‘Forages for Reduced Nitrate Leaching’. The project, which is being run by a number of organisations at the Lincoln Hub, including  Lincoln University, Dairy NZ, and Plant and Food as well as Landcare Research, aims to ‘reduce nitrate leaching losses by 20 percent by delivering proven, adoptable and profitable pasture and forage crop options.’

A number of lysimeters have been installed on research farms around Lincoln. One contains 24 of the smaller lysimeters, and has a moveable greenhouse that can slide over the lysimeters to keep them dry during a rain storm. This is because irrigation rates are being studied in this experiment, and natural rain would upset the calculations. Different kinds of irrigators deliver water at different rates, and even a centre pivot irrigator delivers differing amounts of water at different points along the irrigator. Sam says it’s important to know the best flow rate and the optimum interval to irrigate at to ensure that the greatest amount fo water stays in the soil and doesn’t flush straight through.

In other experiments lysimeters are variously treated with a nutrient-rich amount of water that mimics a natural urine patch left by a cow.

These lysimeters (marked by circles of vigorous plant growth) are in situ in a paddock

These lysimeters (marked by circles of vigorous plant growth) are in situ in a paddock that is grazed by diary cows, and different kinds of forage are being grown in the lysimeters. Photo: RNZ / Alison Ballance

The 50-cm diameter barrels are the same size as an average urine patch, so some lysimeters can be treated while others are left as controls.

The exercise is being scaled up using the Christchurch rebuild-inspired lysimeters made from a piece of sewer pipe and the shipping container. These lysimeters are large enough to grow crops on, and a number of urine patches can be applied across the surface. Previous research has shown that in the course of a year about cows deposit urine on about half a paddock.

2015 is Year of Soils, and we have already featured stories about New Zealand's rich diversity of soils and Earthworms.

A lysimeter set-up with a travelling cover, and Sam Carrick with a complex computer control box with

The 24 lysimeters on either side of the trench can be covered by a travelling greenhouse to keep the rain off. Sam Carrick (right) is next to the computer controlling all the instrumentation monitoring the soil in the lysimeters. Photo: RNZ / Alison Ballance

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