13 February 2004 Science Behind eco-n Research All a Matter of Positives and Negatives

The chemistry of livestock urine as it interacts with naturally occurring bacteria in the soil of grazed pastures has been used by Lincoln University scientists to develop a "clean green" means of reducing water pollution, helping cut global warming and ozone layer depletion, and improving the environmental sustainability of intensively farmed grassland agriculture.

This new breakthrough technology, known in its commercial form as eco-n, has been launched by Ravensdown Fertiliser Co-operative Ltd at a Focus Day at the South Island Dairying Development Centre, Lincoln University. (12 February)

At the heart of the Lincoln scientists' research leading to the development of eco-n is the principle of retaining animal urinary nitrogen at the top layer of the soil and limiting its conversion from ammonium into nitrate. Nitrate is easily leached from the soil and can contaminate aquifers and groundwater, whereas ammonium is retained by the soil.

More than that however, by stalling the production of nitrate, more nitrogen remains in the soil for plant use.

At the same time, there is less nitrogen emitted as nitrous oxide. Nitrous oxide is a powerful greenhouse gas and this new eco-n technology will therefore help New Zealand to meet its commitment to reducing greenhouse gas emissions under the Kyoto Protocol.

Central to the conversion process are soil bacteria known as nitrosomonas. They're the bacteria that start the conversion of the urinary-sourced nitrogen from ammonium to nitrate.

The idea of using an agent of some sort to inhibit this process of nitrification by reducing the activity of the nitrifying bacteria has been used overseas with the aim of reducing nitrate leaching from nitrogen fertilisers. However in grazed pasture systems in New Zealand, most nitrate leaching comes from animal urine rather than from fertilisers.

The uniqueness of the Lincoln work is therefore the development of a new soil treatment technology that can be used to reduce nitrate leaching from animal urine patches rather than from fertiliser.

The scientists, Professor Keith Cameron and Associate Professor Hong J. Di of Lincoln University's Centre for Soil and Environmental Quality have had a long association researching the movement of solutes through soil and the Centre with its unique campus-based lysimeter laboratory, has an international reputation for the quality of its soil studies.

The basis of their eco-n work has been an exploitation of the positive and negative charges on the ions of the various elements involved in the process – within the compounds ammonium and nitrate – and utilisation of the fact that soil can retain positively charged ions (such as ammonium) but not negative ones (such as nitrate).

When livestock urine hits the pasture surface a process of nitrification begins. The nitrogen in the urine, mostly in the form of urea and ammonium, combines with oxygen to form first of all nitrite and then nitrate. As mentioned, the bacteria mediating this process are the soil-based nitrosomonas.

In the untreated situation, as the negatively charged nitrate ions move down through the soil they usually take with them other positively charged ions (cations) of beneficial elements, such as calcium, magnesium and potassium. However, under eco-n, with less nitrate leaching there is also a cut in the leaching loss of these other useful elements. Ultimately then, with more calcium, magnesium and potassium being retained for soil health and plant growth, farmers might be able to look at making reductions in fertiliser usage.

The product, as developed by Ravensdown, is a suspended solution and is applied by spray technology with two applications a year recommended – one around April-May covering the winter period and the other around August-September, covering spring.

The cost, announced by Ravensdown, is $63 per hectare per application, $126 per hectare for the full 12 months.

The scientific research behind the product has spanned more than six years and it has been published in international, peer-reviewed science journals.

Professor Cameron describes it as "solving a New Zealand problem" where stock are grazed outdoors all year round with a resulting return of urine derived nitrogen to the environment.

The Lincoln University scientists have demonstrated that through the processes they have been researching it is possible to –

• reduce nitrate leaching by 60 percent, thus reducing the impact on groundwater quality

• reduce potassium, calcium and magnesium leaching by more than 50 percent

• reduce emissions of the greenhouse gas nitrous oxide by 75 percent

• increase pasture production by up to 15 percent per year.

The traditional view has been that fertiliser, particularly nitrogen fertiliser, has been largely to blame for nitrate contamination of groundwater. However, data now shows that urea, even at high rates of application such as 400kgN/hectare, has minimal impact on what is draining through pasture soil to groundwater.

Indeed the livestock urine patch, particularly that of the lactating cow, has been identified as the main cause of nitrate leaching. The rate of nitrogen can be the equivalent of between 700-1000kgN/ha, and for sheep urine it can be around 300-500kgN/ha.

Ian Collins, Journalist, Lincoln University, Canterbury, New Zealand