Drainage water recycling

In most areas of New Zealand, there is surplus rainfall, and associated drainage and/or runoff, during the winter and spring seasons. This drainage contains nutrients which are, therefore, lost from the farm and will contaminate the receiving water body. In contrast, most of New Zealand’s farms are constrained by soil water deficits that develop over summer and autumn. So just as farmers can harvest excess pasture in spring, store it and feed it to animals at times of slow pasture growth, farmers with artificial drainage or channels that collect large amounts of runoff can capture this water, store it and then irrigate it during dry periods.

Browse through the images below to see how water has been stored and recycled at Massey University’s Dairy Farm Four.

Drainage water recycling has two major benefits. Firstly, as mentioned above, the recycled water is a very useful source of irrigation water. In a dry climate this water can be used as part of a new irrigation system, or it may be used to replace or supplement an existing irrigation source. Secondly, it is not only the drainage or runoff water that is harvested but the nutrients, pathogens, faecal and soil material that it contains are also captured. Therefore, rather than contaminating the receiving water, these nutrients are recycled and returned to the farm system where they can be used by plants.

As drainage water recycling often involves construction of a storage facility and the installation of an irrigation systems, it can be expensive. Therefore, the key to a cost-effective drainage water recycling system is minimising the cost of storage and optimizsing the use of irrigation water. Having said this, as these systems capture all the nutrients in the harvested drainage, they can be very effective edge-of-field mitigations for nutrient loss.