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Thursday, 25 April 2019 14:55

Managing nutrients in waterways

Written by  Greg Campbell, Ravensdown chief executive
Waterways are crying out for better nutrient management. Waterways are crying out for better nutrient management.

OPINION: Most of us are under the impression that all of New Zealand has fertile soil that’s great for growing food. It’s more or less a fairy tale.

We do have some good soils, but not enough. Only about 5% of our soils are fertile enough to grow food without some sort of human assistance. 

As a nutrient management cooperative, Ravensdown tries to help farmers aim for soil conditions that are ‘just right’ for growing food whether it’s carrots for kids in Pukekohe or clover for cows in Culverden. This Goldilocks approach has started to pay dividends. 

Over the course of a decade, our laboratory has conducted nearly a million soil tests for farmers which look at things like phosphate levels in the soil or its acidity. 

In that time, about 25% have shown fertility levels below the optimum for growing food and where farm nutrients would have an effect. Twelve per cent of the soil test results have been above the optimum and so don’t need any more fertiliser or nutrients until they drop back to the optimum levels.

To successfully grow the grass needed to feed livestock, or the fruit and vegetables we buy from the supermarket, we need to put nutrients used by the growing plants back into the soil, or introduce those which were not there in the soil in the first place. 

This is true even if, as the recent EAT-Lancet Commission’s global report suggested, the world consumed less meat protein and ate more vegetables. Because fertiliser would still be required to grow all those plants. 

The UN’s Global Environmental Outlook states that in 30 years, 10 billion people will be wanting to eat and to feed them will require a 50% increase in food productivity. 

So replenishing what the soil and plants need is vital. 

But we can all agree that what our waterways are crying out for here in our backyard is better nutrient management. 

Good advice and smarter farming practice is starting to deliver some progress.  The National Science Challenge Our Land and Water has found that phosphorus has decreased at 40% of measured sites in streams and rivers since 1994 and at 65% of sites since 2004. 

The second national LAWA trend report on river water quality between 2008 and 2017 showed that, at 60% of the sites measured, improvements in the amount of ammonium (nitrogen) were being seen. 

Over the past year 2,110 square kilometres have been assessed by Ravensdown consultants for environmental mitigations. 

Nobody is getting complacent as there is still a massive task ahead and there are lag effects that mean some data could show things getting worse before they get better. 

Other countries’ farm nutrient sectors are dominated by global corporations chasing shareholder profits. 

New Zealand is mainly served by two local cooperatives who are not here to maximise profits at the expense of the environment. 

The awareness of what constitutes a ‘just right’ approach to fertiliser for the sake of the soil, plants and waterways of New Zealand has come on in leaps and bounds in the past 10 years. 

Combined with scientific research, smarter technology and a field-based team of certified advisors advocating changes in farming practice, this approach is starting to have an effect. 

There’s no reason why there can’t be a happy ending to this story. 

• Greg Campbell is Ravensdown chief executive

More like this

No silver bullet for phosphorus

In New Zealand’s soils, phosphorus does a great job at growing plants but unfortunately it does the same thing if it makes it into our water.

Fertiliser use in spring

The refreshed National Policy Statement for Freshwater Management increases the pressure on farmers to improve their nutrient management. 

Getting spring pasture covers right

Managing pasture surpluses or deficits in spring is the key to maintaining quality and persistence going into summer, says Ravensdown agronomist Tim Russell.

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