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Miscanthus – for nitrogen capture

Published: Fri 12 Apr 2019 09:17 AM
Barely a day goes by without there being some item on the news or in the newspaper about nitrogen leaching contaminating waterbodies and water supplies. It helps to understand what the problem is if you have an idea of the sort of numbers that are being talked about. Indigenous forest or pine forest receiving just rainfall leaches in the order of 2 to 3 kg of nitrogen per hectare per year. In a farming sense, less than 5 is considered low, 5-15 is moderate and >15 is high nitrogen leaching. It is not unusual for some dairy farms to have nitrogen leaching greater than 30 kg/ha/year.
Because of this, some local authorities are either providing financial incentives for people to reduce the amount of nitrogen leaching from their land, or are at least talking about what they can do to get nitrogen leaching reduced without destroying their regional economy. Innovative companies who have a long-term viewpoint - admittedly this is a rarity - are already making moves to reduce their own nitrogen footprint.
Dr Jeff Brown - Senior Environmental Scientist at Fonterra - has published a study on the effect of Miscanthus on the amount of nitrogen that leaches from one of their farms in Canterbury. Fortuitously Miscanthus New Zealand Limited (MNZ) has a 2 ha stand of Miscanthus growing on this farm which is near the Darfield dairy factory. Washings water from the dairy factory is spray irrigated onto this farm with pivot irrigators. The amount of nitrogen leaching to the water table has been assessed with lysimeters and the results for the Miscanthus are nothing short of impressive.
Once established, the amount of nitrogen leaching from the Miscanthus stand was less than 0.5 kg N/ha/year. And that is with 70 kg/ha of nitrogen being applied in the irrigation water. It shows that the Miscanthus is extremely good at capturing the nitrogen that is applied, either using it for growth or for development of the rhizomes. International research supports this low leaching result. Interestingly international research also demonstrates that application of nitrogenous fertilisers to Miscanthus stands has little effect on production other than during the establishment phase.
In fact, Dr Brown said in his published paper “Given the Darfield plot received a nitrogen loading of around 140 kgN/ha/yr in the 2014/15 season and 70 kgN/ha/yr for the 2015/16 season, the recent results indicate exceptional performance.”
So why do regional councils not use this information. They could get nitrogen leaching in their regions significantly reduced. Regarding financial incentive schemes, the Lake Taupo Protection Trust was open to the idea of land-use change to Miscanthus, and at the time that was based entirely on international research. They accepted Miscanthus as a low nitrogen crop. Environment BOP is fully aware of the benefits of Miscanthus in reducing nitrogen, but political inertia has meant that nothing has actually happened yet. Ecan is becoming somewhat more aware of the benefits of Miscanthus. But despite this research having been carried out in their region, they have not made any moves that MNZ, to encourage or support establishment of Miscanthus in Canterbury.
But worst of all, Environment Waikato, which has several Miscanthus stands growing in its region is well behind the others. Their proposed plan change - for which there are hearings going on right now - could ban conversion of land to Miscanthus because of the one-off cultivation needed to get it established. Hopefully the submission that MNZ put in and our presentation to the hearing last week, will result in a change to this plan.
The opportunities go beyond simply reducing nitrogen leaching from farms. It seems to MNZ that larger opportunities, which also have positive financial ramifications for those involved, are those available to industrial food processors and district councils. For the food processors, such as dairy factories, meat works, breweries and the like, the opportunity is for them to spray irrigate their nitrogen rich effluent onto adjoining Miscanthus stands. They can then either sell the resulting Miscanthus product or else use it to generate heat, which all of these industries require. They would either make a direct return from Miscanthus sales or else save on the cost of their industrial heat.
For the district councils, the opportunity exists for them to reduce nitrogen leaching by spray irrigating their treated sewage effluent onto Miscanthus stands and to gain revenue from sale of the resulting Miscanthus product. It is probably hard for district council staff to get their heads around the idea that their sewage treatment plants might run at a profit while also reducing nitrogen leaching and being at least carbon neutral.
But the opportunity for the councils goes well beyond that. They can demonstrate that they are capable of disposing of their sewage waste in an environmentally responsible and commercially positive manner. They will then be in a very good position to be able to require industries in their district that also produce their own high nitrogen effluent, to dispose of that effluent onto Miscanthus stands. This will then save the councils further money because they will not have to treat that industrial effluent themselves. The industries will not be able to argue because of the district council setting the example. Furthermore, they will be being required to do something that will generate them a positive return. Of course if those industries require industrial heat, as most do, they can generate it themselves by using the harvested Miscanthus as fuel.

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