Fixing sub-surface acidity could improve phosphorus use efficiency
Significant improvements in sub-surface pH levels could enhance the availability of soil phosphorus – and potentially reduce fertiliser costs.
Research by the Department of Agriculture and Food shows the larger the improvement in soil pH levels, the more efficient the plant use of soil phosphorus.
The work summarises four years of trials on soil acidity and crop nutrition undertaken by department research officer Craig Scanlan and his colleagues, as part of the More Profit from Crop Nutrition: regional soil testing and nutrient guidelines – west project.
Dr Scanlan said the research revealed that moving the sub-surface pH level from below to above 4.5 resulted in a significant change in the availability of soil phosphorus and, in some cases, the efficiency of phosphorus fertiliser usage.
Trials using La Trobe barley on light to medium soils at Wongan Hills, Merredin, Northam and Doodlakine consistently found improved soil phosphorus availability to crops when there was a meaningful increase in soil pH.
The greater the improvement in pH levels, the more efficient the use of soil phosphorus and reduced yield response to phosphorus fertiliser.
While further trials to validate the results will be undertaken around the Wheatbelt this year, the preliminary thinking was that the result was due to lime applications increasing sub-surface soil pH and improving root growth.
Dr Scanlan said it seems to be more to do with root response, where plants grown in soils with a pH greater than 4.5 did not encounter aluminium toxicity and were able to proliferate to a greater depth to access more water and available soil phosphorus.
As a result, we saw improved yield responses of 1.4 tonnes per hectare.
However, the level of response was dependent on whether there were any major nutritional constraints to crop growth.
Dr Scanlan said the supply of other nutrients had a significant influence on the interaction between soil pH and soil phosphorus. He said it is not a static interaction, it is quite dynamic.
Preliminary investigations suggest that the effect of soil pH on phosphorus responses were greater at low rates of nitrogen fertiliser, compared with higher nitrogen fertiliser rates.
Dr Scanlan said the research highlighted the importance of testing for sub-surface pH to tailor liming and fertiliser strategies as it is important for growers to know where they are at.
The results so far suggest that pH is an important factor for making decisions about P fertiliser, in that predicted responses to P fertiliser is better when the soil pH has been improved.
The research also has implications for managing long term paddock responses to liming.
Further information:
- Large increases in soil pH can improve the availability of soil phosphorus if the supply of other nutrients is adequate presented at the 2016 GRDC Research Updates
- Managing soil acidity
For more information contact Craig Scanlan, Research Officer, Northam on +61 (0)8 9690 2174.