Taming the nitrogen elephant in the room

08 Mar, 2015 01:00 AM
Precision Agronomics Australia technical development manager Frank D'Emden (left), discusses the new soil water initiative with Moora-Miling Pasture Improvement Group respresentatives Brad Tonkin and Kristin Lefroy who participated in last year's GRDC Regional Cropping Solutions 'Probes and Prophets' initiative. Photo: Rachel Walmsley.
We're interested in creating a plant available water map..
Precision Agronomics Australia technical development manager Frank D'Emden (left), discusses the new soil water initiative with Moora-Miling Pasture Improvement Group respresentatives Brad Tonkin and Kristin Lefroy who participated in last

THERE seem to be plenty of elephants in the room when it comes to agriculture.

And Precision Agronomics Australia (PAA) technical development manager Frank D'Emden has another one to join the herd.

Its name is nitrogen (N) and it relates to making N decisions in June, July and August while attempting to forecast rainfall.

"In those months farmers can sit on a knife edge trying to work out how much N to put on in their efforts to gain optimum crop yield and quality," Mr D'Emden said.

"Forecasting spring rainfall is inherently difficult so we need to know how much moisture we've got in the soil to make better N decisions.

"That's why PAA is involved in a Soil Water Champions panel with the Department of Agriculture and Food (DAFWA), CSIRO, farmers and consultants in a soil water initiative to measure and manage soil water.

"We're interested in creating a plant available water map that would give us a better idea of what areas of a paddock carry more risk with less water availability than other parts.

"Basically we want to identify each paddock bucket and its levels within the paddock throughout the season.

"It has been in the too-hard basket for too long because it requires a more forensic approach taking into account things like soil type variability.

"Knowing what soil moisture is available is meaningless if you don't have any understanding of the variability of soil types.

"We now have the technology available through electromagnetic (EM) and gamma radiometric (GR) mapping which has broadened our knowledge base.

"By ground-truthing EM and GR we know how to create prescription maps for various inputs, and the aim is to create water maps with which we can make better use of in-crop nitrogen decisions."

In the past two years, PAA has installed 25 real-time soil moisture probes throughout the Wheatbelt alongside on-line production model Yield Prophet.

In total 80 probes have been established by the Soil Water Champions panel.

They were installed as part of GRDC-funded projects, by grower groups as well as privately installed.

Most installations use one or two probes on a particular soil type in a given paddock, with the exception of nine probes installed in one paddock in Dalwallinu, which are part of a stubble management trial managed by the Liebe Group.

The soil water probes measure the soil water at 15 minute intervals and at 10-20cm (4-8in) increments down the profile.

Probes are generally installed at 20cm depth, to be away from sowing machinery, with some sites also including a removable surface probe for the 0-10cm measurements.

Soil water probes are ideal for continuous soil water measurement and are often linked to a weather station at that site, which also provides valuable information.

The probes may, over time, be used for the soil water characterisation at that site.

Researchers use the soil water probes on trials to see the effect of management or amelioration on the crop's ability to extract water from the soil at depth and over time.

Soil moisture data is wirelessly transferred to a computer and data is presented on a graph format to track seasonal moisture variability.

"It's cutting edge stuff and you need at least two years of data to assess meaningful soil moisture interpretations," Mr D'Emden said.

Mr D'Emden said the app developed by Esperance farmer Mick Fels was another tool to be used in conjunction with water maps.

Called iPaddock Yield, it is designed to give growers a reliable forecast of yield and takes less than an hour for each user to set up, with no need for field inspections or tests.

The iPaddock Yield concept has been tested on farms in low, medium and high rainfall zones, and has consistently made yield forecasts, as early as June, that have matched up with results at harvest.

Soil water is now monitored throughout WA, using soil water probes and using tools such as Yield Prophet, however there are still large gaps in the network.

The Soil Water Champions panel and the GRDC-funded "Measuring and managing soil water" project will collate this resource across the industry to improve co-ordination and dissemination of soil water information.

The project will improve farmers' and consultants' understanding of how to use of soil water information in farm decision-making and the project will determine whether the current tools meet the industry's needs.

Training will be provided to help participants increase their base soil and soil water knowledge.

The project will characterise 105 soils in WA over three years, targeting regional gaps and the heavier soils, and gravel and duplex soils often considered difficult to characterise.

This will be facilitated by using linkages with existing trials (ie, Focus Paddocks) and grower group efforts.

Ken Wilson

Ken Wilson

is Farm Weekly's machinery writer


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