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By P.W. Burton

At a recently held farmer information day on the coming changes to soil fertility programmes, soil tests from a highly productive intensively farmed pastoral property were presented.

The tests were taken prior to the introduction of a biologically based soil fertility programme, and comparative tests 5 years later.

A farmer in attendance objected on the basis that the data was misleading.  His concern was around the Olsen P tests results.  The initial test showed an Olsen P of 4, the subsequent test showed an Olsen P of 7.

The property is primarily used for lamb finishing and the performance of the stock is carefully monitored and the results have been, and still are, as good as those achieved anywhere.

Photos from the block showed masses of both red and white clover, along with plantain and chicory. Grasses are not planted but appear of their own accord, we assume from seed that has accumulated in the soil over many years.

In my visits to the property since 2012, along with the reports of pasture and animal production, at no time has a capital input of phosphorus been seriously required or considered.

There are historic long-term measures (trials) that show maximum pasture production from sites with an Olsen P of 10 or slightly lower.  It is this data that brought about the rule-of-thumb that clover survival requires an Olsen P of ten.

The significance of this is that because clovers require higher levels of plant available nutrient than grasses, where clovers thrive the same conditions are suitable for high fertility grasses.  It is only where clover is the provider of nitrogen that Olsen P levels are of serious consideration.

The question that requires answering is why have recommended Olsen P levels been steadily ratcheted up over the last thirty years.

Having been involved in the phosphorus industry for over ten years the answer is that no-one actually asks for supporting data, and because everyone believes that their neighbours and colleagues properties have higher Olsen P levels, it’s an easy sell.

There is a secret to maximising both crop and pasture yield with low Olsen P levels, and inputs, that only a very few highly successful operators understand.  This allows them to apply approximately half the normally recommended phosphorus and never be concerned about performance.

At the meeting mentioned earlier, photos of the knee-high crops of clover were shown, and it was obvious to all including those from Lincoln that there was no obvious phosphorus deficiency.

There are three letters that all students of soil fertility understand the significance of and they are ROC, the abbreviation for Rapid Organic Cycle.  It is the speed at which phosphorus cycles that is more important than the amount contained in the soil.

And the key to increasing the speed of phosphorus cycling is having outstanding physical soil structures.  Soils should ideally contain 25% air, and 25% moisture.  Under the pressure exerted by feet during intensive grazing soils compress.

It is when the soil does not rapidly regain its ideal structure after animals are removed that compaction has occurred, and compaction is rated as the number one issue by those involved in practical soil fertility work.

Compacted soils grow less total feed in a season although during periods when all conditions are favourable exceptional growth is possible.  Desired plant populations decrease rapidly after establishment and renewal is necessary within five years.

Feed quality is compromised due to plants photosynthesising less efficiently which means feed is less palatable and animal performance suffers.

The ability of soils to maintain their ideal structures is dictated by the amount of biological activity taking place and this to a large degree is related to the calcium content of the soils.

It’s been long known that earthworm numbers increase after the application of lime and where earthworms thrive other beneficial soil dwellers also flourish.

Functional Fertiliser specialises in calcium rich total nutrient programmes that provide outstanding performance on all soil types throughout New Zealand.  As the pressure mounts on farmers to reduce fertiliser costs and become more efficient these programmes are poised for much wider acceptance.

For more information contact Peter on 0800 843 809.

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