Is zero N a real thing?

10 Dec, 2017 04:00 AM
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Wayne and Paul Clarke, Dobies Bight via Casino, with Marguerite White, co-ordinator of the 'More Profit for Nitrogen' project with Dr David Rowlings, Queensland University of Technology, who is leading the on-farm nitrogen and pasture efficiency investigation.
Wayne and Paul Clarke, Dobies Bight via Casino, with Marguerite White, co-ordinator of the 'More Profit for Nitrogen' project with Dr David Rowlings, Queensland University of Technology, who is leading the on-farm nitrogen and pasture efficiency investigation.

Nitrogen use on-farm is getting a close inspection across a variety of cropping disciplines. So far researchers are proving less is more.

Supported by the Federal Department of Agriculture and Water Resources ‘Rural R&D for Profit’ program, the ‘More Profit from Nitrogen project’ is setting new standards on efficient use.

The Clarke brother’s dairy, located at Dobies Bight via Casino, has been the site of some of this research for the past two years, with a primary goal to justify sensible N application. Dr David Rowlings, and his team from the Queensland University of Technology, have been investigating profit drivers that involve producing efficient home grown feed while managing environmental impact.

Looking at nitrogen loss is an important quest, given that it can be dispersed through a number of pathways – into the atmosphere and through the water table – which are now better understood than in the past.

In one experiment researchers used a form of N that can be traced as it moves from application, through the soil, and up into pasture.

During one extremely wet cycle over 22 days, 22kg N/ha was sacrificed to the wider environment and more was lost over following cycles.

The knowledge bank on how to plug these losses is certainly increasing and dairy farmers are engaging in these types of projects to better manage N, as any loss from their systems is considered lost profit.

A lot of work in this field has been carried out in the dairy-intensive south, but less so in the sub-tropics.

Preventing loss

When it comes to saving time and money, minimising a farm’s fertiliser routine makes sense, say researchers.

When urea is spread to the paddock moisture will start to dissolve granules which begin to immediately gas-off. Placing fertiliser deep in the pasture will delay this loss.

By applying urea to moist soil and irrigating within 24 hours losses can be cut by 95 per cent. Soils that are waterlogged by flooding rain experience greatest loss as microbes steal oxygen molecules and convert plant available nitrate to nitrous oxide or nitrogen, which is not.

Clever tech

Applying urea coated in a breathable polymer membrane can reduce N loss by releasing dissolved urea over time, and always after rain.

Incitec sells a urea that slows the conversion from NH4+ to NO3-, at which stage microbes begin to steal oxygen and turn it into nitrogen gases, which easily escape into the atmosphere and leach through the water table.,

This fertiliser is more expensive and Dr Rowlings’ team suggests applying it at the same $/ha rate.

Allowing legumes to fix nitrogen

Biological production is a valuable source of nitrogen, as long as the farmer encourages storage of carbon in the soil. But a test plot at Dyraaba showed zero N failed to produce a winter crop of rye in a very dry winter. Once October rains came that zero N plot blossomed and pasture looked the same as fertilised blocks.

Legume production in pasture is essential in a biological system, said Dr Rowlings with clover fixing anywhere from 10-250kg N/ha . A farm with 5 per cent carbon in its soil has a lot of N in storage and can release more than 200kg N/ha per year from the organic matter.

Heavy clay rich in carbon protects organic matter whereas light sandy soil, with less carbon, allows microbes to access molecules more easily.

Not all N is available of course, with 40 per cent in North Coast heavy clay soils unavailable. Lighter soils at Gympie Qld, by comparison, recorded 10 per cent unavailable nitrogen.

Tactical application

Applying nitrogen in compost is more effective than applying straight chicken manure, for example, as most N will gas-off if manure is left on top of the soil where it has less contact with microbes.

Considering a cow’s urine patch delivers the equivalent of 970kg/ha nitrogen, researchers working under the ‘More Profit from Nitrogen’ project suggest tactical application of urea.

New technology like drones that can read photosynthesis levels in plants now provide savvy produces with a map of how their paddocks are performing, which determines how much fertiliser is needed.

Common sense stuff works too, like not applying fertiliser near gates or in cattle camps, where there is already plenty of natural nitrogen.

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