Soil Nitrogen reserves decline

There seems to be a trend in falling soil nitrogen and organic carbon levels across the cropping regions of Victoria, New South Wales, Queensland and South Australia. This overview of soil reserves is based on soil tests conducted by Nutrient Advantage Laboratory Services.

Many of eastern Australia’s winter crop paddocks may not have adequate nitrogen for crops to reach their potential in 2013, based on soil tests analysed by the Nutrient Advantage® laboratory from 13 October 2011 to 5 June 2012.

Jim Laycock, Technical Agronomist with Incitec Pivot Fertilisers, compiled an overview of soil nitrogen reserves in January 2013, mapping the decline in soil nitrogen levels since 2005.

In more than 2,300 deep nitrogen soil tests analysed, 81 per cent had less than 60 kg/ha of nitrogen in the sampled profile.

The soil samples tested were collected in cropping regions including the Darling Downs and Maranoa in Queensland, the New South Wales Slopes and Plains, Victoria’s Wimmera, Mallee, Western District and North Eastern District and the South East, Mallee, Mid North and Peninsulas of South Australia.

Mr Laycock’s findings showed that in 2011, 71 per cent of the deep soil nitrogen tests showed less than 60 kg/ha of nitrogen, and in 2010 it was 66 per cent. He compared this with 2005 results, which showed only 37 per cent of samples with less than 60 kg/ha of nitrogen.

He said a soil test result of less than 60 kg/ha of nitrogen meant growers could expect cereal yields to be no more than 2.5 t/ha, even assuming mineralisation of 40 kg/ha of nitrogen.

Mr Laycock said falling soil nitrogen reserves could be linked to low grain protein levels at harvest in many grain growing regions over the past three seasons.

“We keep seeing growers getting caught out by low soil nitrogen and these soil test results tell us the situation is not getting any better as we head into the 2013 season,” he said.

“With deep soil nitrogen reserves dropping as low as less than 30 kg/ha of nitrogen in many paddocks tested, growers need to work through their nitrogen budgets and make decisions regarding nitrogen fertiliser requirements or crop choice.

“There may be a fit for a pulse crop or legume based pasture phase to improve organic nitrogen levels for the future,” he said.

Mr Laycock said there were many possible reasons for individual growers to see falling soil nitrogen levels on their farms.

He said there has been a growing trend to remove pulse crops and legume pasture phases from cropping rotations and this was contributing to the depletion of soil nitrogen levels.

“Over the past few seasons it appears that the removal of nitrogen in cereal and canola grain has been exceeding the nitrogen input, contributing to a decline in soil reserves,” he said.

“We have also had some very wet summers, resulting in nitrate leaching and denitrification on some soil types, particularly in the summers of 2010/11 and 2011/12.”

He advised growers to soil test their paddocks this autumn to determine how much nitrogen should be applied by the time of sowing.

“If soil moisture is adequate, aim to supply a proportion of the crop’s total budgeted nitrogen requirement pre-plant or at plant if suitable equipment is available,” he said.

“Where moisture is available, but soil nitrogen levels are relatively low, there is little risk in applying nitrogen early.

“If growers do not make adequate nitrogen available to developing cereal and canola crops, they may struggle to achieve the targeted shoot densities in cereals and dry matter in canola needed for budgeted yields.

“Based on these soil test results, a large proportion of crops will need early season nitrogen applications in 2013, so talk to your adviser to ensure nitrogen will not limit your crops’ potential.”

Soil nitrogen reserves have fallen across the cropping regions of Victoria, South Australia, New South Wales and Queensland.

Source: Nutrient Advantage Laboratory Services, 2004-2012. 2005 results from 5506 deep N tests analysed between 13/10/2004 and 5/6/2005. 2008 results from 3669 deep N tests analysed between 13/10/2007 and 5/6/2008. 2010 results from 2001 deep N tests analysed between 29/10/2009 and 30/9/2010. 2011 results from 2146 deep N tests analysed between 1/10/2010 and 21/9/2011. Tests include 0-60cm, 10-60 cm, 15-60cm and 0-100cm from Queensland, New South Wales, Victoria and South Australia.

 

Soil test results

Source: Nutrient Advantage Laboratory Services. Results from 2,316 samples analysed between 13/10/2011 and 5/6/2012. Tests include 0-60cm, 10-60 cm, 15-60cm and 0-100cm from Queensland, New South Wales, Victoria and South Australia.


Source: Nutrient Advantage Laboratory Services. Results from 2,146 samples analysed between 1/10/2010 and 21/9/2011. Tests include 0-60cm, 10-60 cm, 15-60cm and 0-100cm from Queensland, New South Wales, Victoria and South Australia.

 

Source: Nutrient Advantage Laboratory Services. Results from 2,001 samples analysed between 29/10/2009 and 30/9/2010. Tests include 0-60cm, 10-60 cm, 15-60cm and 0-100cm from Queensland, New South Wales, Victoria and South Australia.

 

Source: Nutrient Advantage Laboratory Services. Results from 3,669 samples analysed between 13/10/2007 and 5/6/2008. Tests include 0-60cm, 10-60 cm, 15-60cm and 0-100cm from Queensland, New South Wales, Victoria and South Australia.

 

Source: Nutrient Advantage Laboratory Services. Results from 5,506 samples analysed between 13/10/2004 and 5/6/2005. Tests include 0-60cm, 10-60 cm, 15-60cm and 0-100cm from Queensland, New South Wales, Victoria and South Australia.


Source: Nutrient Advantage Laboratory Services. Results from 2,569 samples analysed between 13/10/2002 and 31/12/2003. Tests include 0-60cm, 10-60 cm, 15-60cm and 0-100cm from Queensland, New South Wales, Victoria and South Australia.

Organic carbon test results

Source: Nutrient Advantage Laboratory Services. Results from 6,818 samples analysed between 4/1/2012 and 31/12/2012. Tests include 0-10 cm and 0-15 cm soil carbon from Queensland, New South Wales, Victoria and South Australia.

 

Source: Nutrient Advantage Laboratory Services. Results from 8,324 samples analysed between 4/1/2011 and 31/12/2011. Tests include 0-10 cm and 0-15 cm soil carbon from Queensland, New South Wales, Victoria and South Australia.

 

Source: Nutrient Advantage Laboratory Services. Results from 4,361 samples analysed between 4/1/2010 and 31/12/2010. Tests include 0-10 cm and 0-15 cm soil carbon from Queensland, New South Wales, Victoria and South Australia.

 

Source: Nutrient Advantage Laboratory Services. Results from 8,794 samples analysed between 4/1/2009 and 31/12/2009. Tests include 0-10 cm and 0-15 cm soil carbon from Queensland, New South Wales, Victoria and South Australia.

 

Source: Nutrient Advantage Laboratory Services. Results from 8,485 samples analysed between 4/1/2008 and 31/12/2008. Tests include 0-10 cm and 0-15 cm soil carbon from Queensland, New South Wales, Victoria and South Australia.

 

 

Source: Nutrient Advantage Laboratory Services. Results from 1,734 samples analysed between 4/1/2007 and 31/12/2007. Tests include 0-10 cm and 0-15 cm soil carbon from Queensland, New South Wales, Victoria and South Australia.

 

Source: Nutrient Advantage Laboratory Services. Results from 2,571 samples analysed between 4/1/2005 and 31/12/2005. Tests include 0-10 cm and 0-15 cm soil carbon from Queensland, New South Wales, Victoria and South Australia.