Wednesday, 04 September 2019 12:55

Setting Olsen P targets

Written by  Dr Bert Quin, managing director of Quin Environmentals (NZ) Ltd
New Zealand soils are mildly acidic. New Zealand soils are mildly acidic.

A new scientific article on the management of soil phosphorus makes fascinating reading, writes Dr Bert Quin, managing director of Quin Environmentals.

The article is entitled ‘A Global Perspective on Integrated Strategies to Manage Soil Phosphorus Status for Eutrophication Control Without Limiting Land Productivity’, published in Journal of Environmental Quality, July 2019.

It was co-written by 15 scientists from several countries, including Lucy Burkitt from Massey University, and Murray Hart, formerly a senior research scientist for Summit-Quinphos before moving to Australia.

Here are a few direct quotes from the article:

‘Phosphorus losses from agricultural soils are hard to mitigate because they occur in both dissolved and particulate form, and are transported from highly variable source area…. Managing soils and soil P status represents an important strategy for the mitigation of eutrophication’.

‘Modern agriculture has come to rely on maximising the availability of P in soils through [so-called] insurance application rates of highly soluble P fertilisers to build up soil P fertility and minimise risks to productivity. This makes it harder to manage resulting soil P losses’.

‘Legislation to help reduce (loss-inducing) threshold soil P test values has been generally slow to implement despite widespread eutrophication problems’.

‘Our analysis spanned three continents and catchments with different ago-hydrochemical functioning. The study areas were expected to represent variable run-off response, soil P response patterns and erosion vulnerability’.

‘All data sets showed a highly significant effect of soil P status on P runoff concentrations’.

‘Future sustainable P management within the food system must reconsider old philosophies that place undue emphasis on maintaining an artificially high level of P fertility dependent on inputs of highly soluble manufactured fertilisers towards new philosophies that concentrate on precision feeding of the crop not the soil’.

‘Our meta-analysis across three continents suggests agronomic optimum P concentrations need to be in the range of 10-20 Olsen P to match challenging eutrophication control targets being set for freshwaters (around the world)’.

In New Zealand, where all our soils are mildly acidic, we have the enormous advantage that we could maintain high pasture production levels without Olsen P levels needing to be pushed above 20, simply by avoiding the use of soluble P fertilisers such as superphosphate where sustained-release P fertilisers like reactive phosphate rock (RPR) will maintain at least as high production, with much less P run-off and leaching. 

Dairy farmers, you need to figure this reality out for yourselves soon, before you are forced to destock. Unfortunately, vested interests in a small country like ours prevent the fair and open discussion of scientific knowledge.

• Dr Bert Quin is managing director of Quin Environmentals (NZ) Ltd.

More like this

Dark ages

OPINION: Before we all let The Green Party have at it with their 'bold' emissions reduction plan, the Hound thought it wise to run the numbers through the old Casio.

Govt limits forestry conversions

Farmers have welcomed the Government’s move designed to limit farm to forestry conversions entering the Emissions Trading Scheme (ETS).

Save soil - take a pledge this 'world soils day'

OPINION: Soil is one of the most valuable assets that a farmer has. It is our collective responsibility to make use of soils without damaging either the soil or any other part of our environment, protecting them for our own use and use by future generations.

Faulty models used to measure emissions

OPINION: If you have kept your finger on the emissions pulse, none of the below information will be a surprise to you. However, if you are a farmer that has not been following New Zealand’s ruminant methane issue then you may be in for a nasty shock.

Featured

Being a rural vet is ‘fantastic’

Everyone from experienced veterinarians and young professionals to the Wormwise programme and outstanding clinics have been recognised in this year’s New Zealand Veterinary Association Te Pae Kīrehe (NZVA) awards.

Editorial: Long overdue!

OPINION: The Government's latest move to make freshwater farm plans more practical and affordable is welcome, and long overdue.

National

Lame stories from a country vet

Everyone from experienced veterinarians and young professionals to the Wormwise programme and outstanding clinics have been recognised in this year’s…

Machinery & Products

Gongs for best field days site

Among the regular exhibitors at last month’s South Island Agricultural Field Days, the one that arguably takes the most intensive…

Amazone extends hoe range

With many European manufacturers releasing mechanical weeding systems to counter the backlash around the use and possible banning of agrochemicals,…

Gong for NH dealers

New Holland dealers from around Australia and New Zealand came together last month for the Dealer of the Year Awards,…

» Latest Print Issues Online

Milking It

Less hot air

OPINION: Farmers won't get any credit for this from the daily media, so Milking It is giving the bouquets where…

Dollars go offshore

OPINION: The Advertising Standards Authority’s 2024 report revealed that not only is social media rotting our brains, it is also…

» Connect with Dairy News

» eNewsletter

Subscribe to our weekly newsletter