Dairy farms in clover not nitrogen
Greenpeace says its wants to ban nitrogen fertiliser. What it really wants to do is stop dairy farming. I can understand wanting to halt the growth of dairy cows in New Zealand. I do too.
But it’s quite likely that banning nitrogen fertiliser will result in more dairy cows rather than less.
I’m well and truly on the organic farming train, so this column is not a pro nitrogen fertiliser campaign. But we can’t ignore how important nitrogen fertiliser is to the current global food supply.
Unless you are actively involved in growing something, like a vege garden or a full-scale farm, you don’t have any cause to think about fertiliser very often and it’s easy to underestimate its importance.
According to an Our World of Data report, nitrogen fertiliser alone enables the lives of between 3 billion and 3.5 billion people.
The report draws on numerous sources including a paper published in Nature Magazine. They all point to a similar conclusion – roughly 30 per cent to 45 per cent of the global population is dependent on nitrogen fertiliser.
Prior to the 1920s, most crops’ growth was restricted by a lack of nitrogen. Between 1903 and 1910 Fritz Haber and Carl Bosch invented a process that converted nitrogen from the air into a synthetic form of nitrogen that plants could absorb.
There was no longer any excuse for a plant to lack nitrogen. From then on, crop yields of every kind increased dramatically. Mechanisation, breeding, irrigation and improved farming practices also helped.
Consumers benefited, British households would typically spend 33 per cent of their household income on food in the 1950s. Today its closer to 10 per cent.
Obviously, all this synthetic fertiliser has had negative environmental impacts too. It’s well documented and it is a big problem.
The important thing to understand is that synthetic nitrogen fertiliser is not a small insignificant tool, it’s a fundamental part of the global food system.
But it’s not a fundamental part of the New Zealand dairy farming system. Sure, dairy farmers use some nitrogen fertiliser, but NZ dairy farms are pasture-based and 70 to 80 per cent of nitrogen inputs on dairy farms comes from clover or other legumes.
The Haber–Bosch process takes nitrogen out of the air and puts it into pellets at a cost of $1.40 a kilogram, clover does it for free.
Good farmers are not going to pay for something when they can get it for free.
As dairy conversions have increased so has the amount of nitrogen fertiliser applied in New Zealand. But it has gone from a low base of almost no nitrogen fertiliser on sheep and beef farms to about 150kg per hectare once converted to dairy.
Greenpeace’s campaign email states ‘‘there’s one thing that industrial dairying can’t live without. Synthetic nitrogen fertiliser’’.
Greenpeace has a point about increased fertiliser use. But removing nitrogen fertiliser from dairy farms is more likely to have a minor reduction in stocking rate on dairy farms, simply because most of the nitrogen needs comes from clover for free.
This is not the case for dairy farms in the northern hemisphere though.
According to the Nature Magazine paper northern hemisphere farmers apply 230kg to 331kg of nitrogen a hectare a year and almost no natural nitrogen fixation from legumes was taking place.
That’s because they mainly feed their cows crops like maize and grain. Once these crops are harvested the farmer needs to replace the nitrogen absorbed by the crop somehow.
The same problem applies to crops such as wheat, barley and vegetable growers in New Zealand. How do they replace the nutrients absorbed by the previous crop?
This can be done in a number of ways such as manure, mulches or adding livestock to a cropping rotation.
But the quickest, cheapest and easiest way to do it is to apply synthetic nitrogen fertiliser.
The economics of the global food system is based on the cheap, easy and quick methods of nitrogen fertiliser.
If we ban nitrogen fertiliser, it will make nitrogen a scarce resource.
This will require cropping and vegetable farmers to make radical changes to their systems.
They will essentially have to become organic farmers. Many people will say this is a good thing but it’s a big change that is not as simple as it seems.
What are the possible unintended consequences of a nitrogen ban?
The cost of New Zealand-grown vegetables and bread will probably increase. Retailers may import cheaper products from overseas countries which don’t have a nitrogen ban. New Zealand growers may not be able to compete and decide to subdivide their land for housing.
Or, they could convert their land to dairy because it’s not hard to run a profitable dairy farm with no nitrogen fertiliser.