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Earthworms have been the measure of the value of land for the last thousand years. In the Sahara, the price of land is often determined by the amount of worm casts on the soil surface. Here in New Zealand, farmers still talk of getting good livestock under the ground before they can get good livestock above the ground.
We all know earthworms are important. They rapidly recycle dung, urine, run-off and dead vegetation, purifying the soil and assisting in the manufacture of humus – the end product that feeds the plant. They also provide aeration in the soil, help store moisture, and supply vermacasts. Hatuma clients have also proven that in large numbers earthworms assist in smoothing the soil after being stressed – on a survey farm in the Manawatu during 2003 on Marton silt loam soil, after heavy rain, very bad pugging, and a severe drought, it only took a matter of weeks after the first rain before the soil had smoothed itself out. The speed in which the farm recovered was amazing; a feat thought impossible by many authorities considering that soil type is synonymous with becoming dense and heavy once soil degradation has occurred, often taking years to fully recuperate. This incredible resilience was largely due to the farm’s hefty population of earthworms at the time (1,125 per sq/m) moving masses amounts of dirt – a phenomenon that could only come from a combination of excellent soil management and approximately thirty years of conditioning the soil with dicalcic and lime (remarkably, scientists have traditionally recommended this soil type does not require lime). With all these benefits in mind, it is easy to see why the earthworm’s role in productive farming is crucial. But in this modern era of intensification, their function of being a simple indicator of true soil fertility is being ignored. |
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Olsen P levels have taken their place as a primary indicator of soil fertility instead, and farmers are encouraged to have high P levels for production and high farm re-sale. Hatuma clients have always known the true worth of having a fertile soil, yet their soils often have Olsen P levels in single figures, despite high production, and more importantly, good profit. Does their secret lie in nurturing the soil life?
Preliminary Hatuma trials on their farms and neighbouring farms are showing fascinating trends. Even with apparently low Olsen P levels (75% of sites under 13), dicalcic and lime farms are showing on average over 50% more earthworm numbers than across the fence where acididulating phosphatic and nitrogenous fertilisers are being applied. The initial average number of earthworms found on farms using dicalcic and Cropfine blends is 1,070 per sq/m. This equates to over ten million earthworms per hectare, significantly above the number of earthworms found on the neighbours’ property. The most earthworms found so far during the trial was on a dicalcic/Cropfine farm. Sixty-five earthworms were found in a 20cm cube of soil, which equates to over 1,600 per square metre, or approximately 16,250,000 earthworms per hectare!
How was this measured? Visual Soil Assessment tests were conducted by its developer, soil scientist Graham Shepherd, throughout the central and lower North Island on different soils ranging from clay to pumice. The VSA, an official test, is a very easy and useful tool for farmers to gauge how their management practices are affecting the soil’s condition and health. Among other aspects, part of the VSA criteria is to count earthworms in a 20x20cm cube of soil; something every farmer can quickly and effectively do. Preliminary results also indicate that, while not statistically significant, farms receiving dicalcic also tend to have higher overall Visual Soil Assessment scores indicating better soil condition, even though their Olsen P levels are notably lower.
By creating an environment where the earthworms can thrive in abundance, farmers are giving their farming operation a huge advantage; a massive workforce running twenty-four hours a day. They are also an excellent indicator of soil health, so when they are found in abundance, like the average number above, farmers can have confidence that the rest of the soil is fertile with life. Unlike Olsen P levels though, there is no limit of earthworms you can have in your soil where it starts to becomes wasteful – the higher the number the better! |