Final crop yield is the most definitive indicator of soil health, according to Prof. Mike McLaughlin, from the University of Adelaide in Australia.
McLaughlin took part in a recent edition of the Tillage Edge podcast.
“In these circumstances carbon is bring pumped below ground. The plant is the overall bioassay of the soil in which it is growing,” he said.
“It is showing that the soil is both fertile and capable of producing high crop yields.”
He referred to the role of soil organisms and the impact on them by fertilisers as a contentious issue.
There are current streams of thought, suggesting that the inclusion of molasses with liquid nitrogen (N) would mitigate the impact of the high levels of added chemical on soil microbial populations.
The addition of commercially manufactured humic acids with artificial fertilisers has been mooted in a similar context.
“In my opinion, the inappropriate use of N fertiliser can lead to conditions that can affect the microbial health of the soil,” he continued.
“There is no doubt about that. So, too much N, too much leaching is going to acidify the soil. And that’s going to impact on the microbes.”
“If there is too much N applied and no leaching, this will cause salt-related problems, which will also impact on soil microbes.
Fertiliser impact on soil health
McLaughlin explained that the proper use of N, in terms of crop production, can actually improve soil health.
“Producing more crop adds more carbon to the soil. This is on the plus side of fertiliser application,” he stated.
“In my opinion, adding small amounts of materials to overcome inappropriate N use is not appropriate. The first priority must be to fix up the inappropriate use of the fertiliser.
“Well managed fertiliser additions will always be the priority. After that, it’s a case of assessing what can be added with the fertiliser applications.
“I don’t think the additions of humic acids with fertiliser will particularly help. The reality is that there is lots of similar material already in the soil,” he said.
Trials
McLaughlin acknowledged that molasses is a carbon source and might stimulate microbiological activity.
“This is not a bad thing; it may even work to retain nutrients in the soil. But with all new products, multi-site and multi-year field trials must be carried out,” he added.
“These must be scientifically verified on an independent basis. And a mode of action must be identified.”
McLaughlin concluded by reflecting on a number of fundamental steps that Irish farmers can take to maximise soil health and productivity.
These are:
- Keep soil pH values at the appropriate kevels;
- Add lime to acidic soils when appropriate;
- Keep the nutrient balance correct within a soil;
- Keep an eye on micronutrients;
- Soil test regularly;
- Tissue sample a crop if a possible micronutrient deficiency is identified;
- Boost soil carbon levels;
- Minimise compaction issues.