'N' curiosity sparks Qld win

Autumn 2000 nitrate depth levels on Formartin group members' properties

A GROUP of Darling Downs farmers determined to find out more about what happens to applied nitrogen brought home the Queensland TOPCROP award for 2001.

Many members of the Formartin group had wins in the form of improved on-farm information even before the TOPCROP awards, according to Ian Bach, of the Bandawing Farming Company, Bowenville.

The Formartin group's facilitator, Technical Officer Sel Rowlings of Queensland's Department of Primary Industries Agency for Food and Fibre Sciences, helped them do the research without any disruption to regular farm routine.

One of the key issues for the Formartin group, formed under the GRDC's Eastern Farming Systems project, was to answer members' concerns about the relationship between their crop management practices and what happened to the nitrogen fertiliser they applied, Mr Bach said.

Big variation in residual nitrogen

According to Mr Rowlings, the amount of residual soil nitrogen varied substantially from one farm to the next, even for soils that appeared to be nominally the same.

The group:

  • monitored the pre-plant and post-harvest soil water and nitrates to a depth of 1.5 metres on representative sites on each farm for two years
  • analysed samples from each soil core for salinity as well as pH and chloride levels
  • set benchmarks with a detailed paddock history for each of the monitored sites.

Depth of nitrogen in relation to soil conditions

A significant result of the study was that growers and researchers identified an accumulation of soil nitrogen at a depth beyond the reach of many crops. This was the case on some soils that indicated unfavourable chemical properties such as strong alkalinity, salinity and chlorides.

"In one paddock we found almost 500 kg/ ha of plant -available nitrogen in the form of nitrate nitrogen in the profile, much of it at 90-150 cm depth where crops really can't use it," said Mr Rowlings (see site 2 on the graph).

The trial results have had different implications for growers. In some cases it meant growers increased the amount of nitrogen fertiliser to lift their yields, and others actually reduced their nitrogen application rates and focused on changes to their management instead - for instance, changing from a legume to a cereal to more effectively utilise the available nitrogen in the soil

"The results assisted members to validate their own commercial soil test results and give us more confidence in soil testing as a critical crop management tool ," said Mr Bach.

"Some growers are now doing a lot more soil testing than before, on a more frequent ' basis, so they they can fine-tune the appropriate rate of nitrogen for individual paddocks."

Contact: Mr Ian Bach 07 4692 4272 Mr Sel Rowlings 07 4639 8870

Region North