• Bert Quin

Protecting our Lakes and Waterways

There is a way

Dr Bert Quin, July 2011

We have pretty much done the easy bits – fencing streams for example, to prevent direct access by stock and preventing runoff of effluent into streams being the two big ones – but nutrients continue to enter waterways from our agricultural land, simply because of the type of fertilisers we use. Why?

The traditional fertilisers used in New Zealand have been single superphosphate (‘super’) which supplies phosphorus (P) and sulpur (S), and urea for nitrogen (N).

Both have played a very important part in developing New Zealand’s pastoral agriculture. But are there better options going forward, and why?

Their biggest problems are that they are ‘leaky’ fertilisers. Super is prone to run-off of applied P into waterways in the weeks after application, leaching into shallow sub-surface drains and waterbodies on dairy farms, and being leached right through soils with low P retention such as those in Northland and the West Coast. Urea is prone to volatilisation losses as ammonia gas to the atmosphere, nitrate leaching and nitrous oxide (a serious greenhouse gas or GHG) emission.

By far the most cost-effective option for P is reactive phosphate rock or ‘RPR’. This is a natural mineral, formed on the sea floor originally, which is a very effective source of sustained-release P, ideal for maintaining high-producing pasture and extremely resistant to leaching. In the first year or two after the switch from super is made, a small proportion (25%) of soluble P such as DAP can be blended with it to maintain full production through the ‘lag phase’ as the level of plant-available P released from the  RPR  builds up.

Simply switching from superphosphate to RPR and RPR/DAP blends would reduce average run-off losses of P into waterways by 80-90%, in my estimation. This would take P losses below the trigger levels necessary to keep our lakes in a eutrophied state. In 5-10 years, water quality in the Rotorua lakes would be massively improved.

Sulphur requirements are easily met by adding in elemental S. Like RPR, this is a sustained release fertiliser. The water-soluble sulphate form of S in superphosphate is very easily leached from many soils. As this happens, it takes valuable cations such as calcium and magnesium with it.

The management of the existing ‘super’ manufacturing duopoly – ie Ballance and Ravensdown – seem to be totally focused on maximising sales tonnages of superphosphate, adopting a  ‘damn it with faint praise’ attitude to RPR, rather than promoting its real benefits.

Likewise granular urea can be made 20-40% more efficient (depending on the situation) simply by treating it with the urease inhibitor nbpt, as in (SustaiN). The cost of doing this is very low, and very cost-effective for the farmer. Until 2014, the industry hasn’t to promote this option, because 30-40% less urea will be used! Finally, Ballance is doing this, and even claiming to have invented the product, even though Summit-Quinphos released it in 2002.

But the real N news is that a massive 2-fold increase in efficiency -meaning only half as much N is necessary), at close to the same cost per kgN/ha applied, is available by using  inhibitor-treated, wetted prilled urea using the ONEsystem, with only minor changes to spreading equipment!

The time is right for people with the determination to actually do something to save New Zealand’s environment to stand up and be counted, and force change. If we do not, we will come to be viewed as the ‘gutless generation’ by our children and grandchildren. Group ONE is doing its bit.