High rainfall OVERSEER calibration trials underway

Two OVERSEER calibration trials commenced in April this year, both on dairy farms owned by Collective members. One trial is on a pumice soil and the other is on a podzol soil. The trials will run for three years and are being managed by Dr Stewart Ledgard from AgResearch. Project funding is from BOPRC, DairyNZ and AgResearch itself. Each trial includes over 100 ‘suction cup samplers’ which are buried 60 cm below the soil surface. These devices are used to sample water as it moves down the soil profile, carrying nitrogen with it.

The sampling method being used in this research is similar to the Parekarangi trials.

“It’s really exciting to have this research underway. The need for this trial work has been identified by farmers and supported by the LandTAG. As a result Ag Res approached us with initial funding to establish the trials.  Having two trial sites will help us understand nitrogen leaching under high rainfall conditions.  It’s also great to have industry support  from  DairyNZ and AgResearch” says Andy Bruere, Bay of Plenty Regional Council Lakes Operation Manager.

The OVERSEER® nutrient budget model is used to assess nitrogen loss levels under Rule 11 and the proposed ‘PC10’ rules for the Lake Rotorua catchment. The field trials used to calibrate OVERSEER have been in locations like Ruakura with annual rainfall up to about 1200 mm. There is a clear need for additional trials on high rainfall sites, something recognised by both the Bay of Plenty Regional Council and Rotorua farmers. Parts of Mamaku can receive as much as 2500 mm annual rainfall, nearly double the 1300 mm or so at Rotorua airport.

There is national interest in this calibration work given its potential to improve high-rainfall calibration of OVERSEER. Watch this space!