Over the last year, four farms in the Ballinderry catchment have been trialling systems that will allow them to capture and recycle nutrients and minerals that would otherwise be leeched into nearby waterways.
It’s part of an innovation project that involved dairy, beef, pig and poultry farms. The challenge was to find solutions that would improve the farm as well as the environment. That meant it needed to be low enough cost that it could be easily replicated on other farms, not take up too much productive land and it had to yield some kind of benefit for the farm.
There’s an awful lot of rain that falls on Northern Irish farms and, as it makes its way inevitably to the rivers and loughs, it will pick up nutrients from silage pits, farmyards and any areas where there is heavy animal traffic.
The first thing to tackle was reducing the volume of water by diverting clean water before it joins any contaminated water. Checking gutters and drainpipes to capture rain coming off roofs is a good start and for some of the farms natural springs had to be captured and piped away from the farmyard.
Swales
The next step was to introduce swales – two types; open and pebble-filled.
Open swales are widely used in urban drainage systems as a way to carry stormwater and treat run-off. For the pilot, swale systems were carefully designed with a suitable gradient so that dirty water from the farmyard could run very slowly through the system, diffusing the water and the nutrients into the soil.
Pipes run between the swales which can be easily opened and closed. On two of the farms, the swales have already provided a failsafe when slurry was accidentally spilt. It was captured in the swales and recovered before any damage was done.
Pebble swales are trenches two-thirds filled with pebbles with a pipe at the top of the pebbles to keep the water flowing. The top third is backfilled with topsoil so farm machinery can travel over the whole plot. Pebble swales use about 40% of the land required for open swales but they have less flexibility and carrying capacity.
The power of plants
Using plants for bioremediation is nothing new. AFBI has been at the forefront of much of the research into the use of Short Rotation Coppice Willow for treating wastewater for years.
This project incorporates the same thinking. Willow is a profitable and harvestable crop which can be used for biomass and there happens to be a local farm which will buy and harvest the crop.
Willow planted in the pilot scheme shows the impact of planting where there is a source of nutrient-rich water – the willow planted in the dirty water path is twice the size of the rest. The golden willows planted beside each fence post are growing well and will provide attractive living fence posts when the existing ones rot.
The secret weapon in the system is Comfrey. This incredible plant acts as a nutrient recycler. Comfrey can be found growing wild around the countryside. It’s a brilliant absorber of nitrogen, phosphorous and potassium so a very useful plant in situations where we need to mop up nutrients before they get into waterways.
