Dr Doug Edmeades busts pH balancing myths and explains why you should try adding lime to your soil.

1. IT’S NOT THE CALCIUM YOU WANT

Lime is actually calcium carbonate, and most people think it’s the calcium that helps to balance pH, but that’s not correct says Dr Doug Edmeades, a soil scientist. “Our soils have got heaps of calcium (thanks to their young age and the high level of calcium in super phosphate fertiliser). It’s the carbonate that we add to the soil which reacts with the acid and increases the pH, so the active ingredient is the carbonate content – you should buy lime based on its carbonate content, not on its calcium content.”

2. IT’S NATURE, NOT FERTILISER THAT ACIDIFIES SOIL

Some fertilisers do acidify soil, but only in a minor way says Doug. “Organic matter contains nitrogen. Soil bugs break that down into ammonia, and then into nitrate, and that biochemical process produces acid, and there are a number of biochemical processes which produce acid in soils and that’s why the pH in soil declines slowly over time.”

3. SOIL BUGS WORK BEST IN A VERY SMALL pH RANGE

Soil is made up of mineral particles, decomposing organic matter, water, and air and is teeming with animals, from earthworms to microscopic invertebrates that help to break it all down and keep it alive and healthy. These creatures do best in a soil with a pH of 5.8-6.0 and it’s one of the biggest benefits of adding lime.

A healthy pH also increases the availability of molybdenum which can be good, or bad if your molybdenum levels are already high, in which case you will see copper deficiency in livestock. One thing liming doesn’t do is ‘unlock’ phosphorus from the soil says Doug. “There are a very few soils where that does happen… but they’re so minor.”

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Dr Doug Edmeades has 36 editions of his soil and fertiliser newsletter written over two decades available on his website for free: http://agknowledge.co.nz/publications

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