A paper published in the Journal of Agricultural Research based on data collected from AgResearch’s Ballantrae Hill Country Research Station in Manawatu shows earthworms thrive and proliferate in soil treated with phosphorus and sulphur fertilisers.
Areas not treated with those elements had less than half the number of earthworms as those that did, showing there was less food available to sustain the population.
AgResearch scientist and paper co-author Nicole Schon says earthworms are a sign of good soil health and have long been considered a barometer for healthy soil biology.
In short, fertiliser stimulates pasture production, which generates food for soil and earthworms.
The earthworm population in the trial that has not received fertiliser since 1979 was about 219 a square metre, about half the number found in areas getting an annual application of superphosphate.
Worm numbers increased with higher application rates.
The populations at the sites treated annually with 125kg/ha were 384/sq m and 428/sq m where 375kg/ha of superphosphate was applied.
Schon says some farming critics contend fertiliser is too toxic for earthworms but 35 years of research shows that is not true.
If the fertility is kept within the appropriate range for the geography and soil type the worms will flourish.
The study also found a greater abundance of worms in soil at the foot of slopes compared to steeper gradient, reflecting better pasture quality and quantity. Poor pasture had low worm counts.
Across all areas measured worm abundance was closely associated with greater pasture production and improved soil health, especially at the foot of slopes where sheep camped and transferred manure and urine.
“There’s a very strong correlation between pasture performance and earthworm abundance.”
A greater density of worms increases pasture production but it is also stimulated by the action of worms in the soil improving both nutrient availability and soil physical structure.
The more worms the better the soil structure and their burrowing allows easier transfer of water and air.
At Ballantrae the number of earthworm species has increased from two in 1979 to nine in 2014, the result of both accidental and deliberate anthropogenic earthworm introductions.
The research focus is now shifting to the roles of each variety and there appear to be benefits from having a variety, Schon says.
Some are deeper burrowing, which has obvious benefits to a plant’s root structure but could also play a role in taking carbon deeper into the soil profile.
The 35-years of research gave confidence in the accuracy of the findings but that could all be about to come to an end.
A proposed new road bypassing the slip-prone Manawatu Gorge road will dissect the Ballantrae farm, leaving its future up in the air.
