[ 8/April/21 Tim’s Facebook page]
If you are going to allow 100Kg of nitrate/Ha to leach, then you have to budget sufficient water going to groundwater to keep that below 0.5mg/l. Doing the numbers, gives 10g/m2, and that takes 20,000l of water per m2 of land to get to 0.5mg/l (20m depth of water – even Fiordland doesn’t get that much rain).
So you are correct – there is no way this is sustainable.
There is no way that nitrogen forcing production is sustainable.
To avoid nitrogen forcing, then we would need to drop stocking rates from the current roughly 4.0 stock units/Ha to something less than 1.8 stock units, and radically alter the pasture mixes, in order to reduce nitrogen losses.
Current levels of agricultural practice are not sustainable long term, yet they are demanded by our economic and political systems.
We need to look seriously at the economic systems that create these incentive structures, and not demonise the farmers that are doing exactly what treasury has asked them to do.
Competitive systems that do not have a strong cooperative base to them cannot survive long term – the mathematics and logic of that is beyond any shadow of reasonable doubt for anyone who has taken the time to seriously investigate such depths of mathematical and biological complexity.
And our existing economic systems are deeply complex, and transitioning them to something sustainable is not trivial or simple, and it is doable and it is demanded of us by the dictates of survival.