By: Louise Cook, Owl Farm, Waikato
Waste has never been that attractive. Not to have, not to talk about and not to deal with. However, minimisation of waste is more important now than it has ever been and it isn’t a fad.
Unlike technicolour jumpsuits and leg-warmers in the 1980s, the concept of reducing our waste isn’t one that will quickly leave the human population and all of the industries we participate in.
With every passing year, the reality of just how finite our “finite natural resources” are is hitting home. We are all becoming increasingly aware of just how wasteful some practices are and we are warned of a slow decline in quality of the available resources.
The solution is multi-faceted and everyone needs to pitch in, as we all have a part to play. The challenge to all of us, is to each take steps to reduce, re-use and recycle all of the nutrients at our disposal.
This will ensure that whatever the industry, sector or population, the maximum efficiency will be extracted from the resources we choose to employ.
With nitrogen (N)-loss in the mid-40kg/hectare two years ago at Owl Farm, we are working really hard on a strategy of “reduce”. We are on a journey to reduce our N-Loss to waterways and this requires us to use multiple tools to succeed. So far this includes; controlling N fertiliser inputs, plantain in pastures and the biological interactions inside a wetland, and as more possibilities emerge over time, we’ll likely add those to our arsenal as well.
Owl Farm has a self-imposed limit of 150kg/ha of nitrogen fertilisers per year being applied to the farm. This means every application needs to be treated as precious and applied in such a way that we can get the best returns from it.
We’ve invested this year in establishing plantain in our pastures, as industry research has us convinced that this little mega-herb is absolutely a part of the solution. Seven hectares of new springsown pastures have included plantain in the sowing mix, plus we’ve both undersown and broadcast existing swards in half a dozen paddocks to see how effective those techniques might be in establishing plantain more quickly across the whole farm. DairyNZ work at Owl Farm is monitoring plantain establishment and so far there are quite varied results from each method. In the new pasture mix there are now 140,000 plants/ha versus under-sowing into an existing sward where we have 20,000 plants/ha. Broadcasting into existing pastures before grazing, led to 7000 plants/ha and after grazing closer to 13,000 plants/ha. All four methods included plantain at 4kg seed/ha.
Ongoing monitoring work will be carried out, as slow and steady emergence seems to be happening in the established swards and we hope more plants may yet spring up. More importantly, we’re really keen to see how many survive over time in a typical grazing system so we may understand what is required to keep plantain as a solid proportion of the diet.
The third tactic and the most interesting piece of the puzzle so far, involves actively intervening to stop nitrogen “flowing out the gate”. Our constructed treatment wetland is meant to act rather like a set of kidneys and filter out nitrogen, phosphate, sediment and pathogens before the water gets to the river. This sculptured wetland is designed to maximise contact time between water flowing through and plants in the wetland.
Samples have been collected from ground water wells on the edge of the wetland area, from a tile drain emptying into the wetland and lastly at the wetland outflow. This helps us get a really clear comparison of the nitrate concentration in ground water and drainage water before as it arrives at the wetland, compared to the nitrate concentration at exit after water has passed through the wetland.
Water source data shows us that generally as the ground conditions got wetter – the N concentration in the ground water increased. This is to be expected, as rainfall events and wet soils would see mobilisation of nitrate from soils away in ground water.
In January, Well 4 was so slow to refill before sampling that no sample was taken. In August a slip-up occurred meaning no outflow sample was on hand to match with the inflow samples. In terms of wetland performance, what we’ve seen so far is that the concentration of nitrogen in the outflow water is massively reduced when compared to the concentration in the water sources.
In January 2017, the outflow contained 97% less N/litre than the water that supplied the wetland. In April 2017 the average was 89% less N in the outflow compared to the water sources and in October the wetland was removing about 60% of the N by the time the water got to the outflow.
The hope, when the wetland was established, was that it would remove 30% of the N from the water flowing through the bays. However, it appears on the information so far it could well surpass this expectation.
Despite these heartening results, there is still a lot we don’t know. Monitoring will continue every two months for at least the next two years and one question in our minds that we would like to answer is: How much land is really feeding the wetland, and where does all the water actually come from?
On-going monitoring with NIWA and Waikato Regional Council will collate all of the data and create a firmer view of how this wetland behaves, and how it compares to the typical wetland areas onfarm where wet areas are planted and retired. The costs associated with creating a wetland like this are not inconsiderable, however if it improves the effectiveness in mopping up surplus N from waterways it is quite likely worth the cost.
