High rainfall nitrogen leaching trials update

The aim of these trials is to provide N leaching data from high rainfall sites for use in OVERSEER® calibration and to provide a better understanding of the differences in N loss from the root zone in pumices compared to podzol soils. These trials started in May 2016 and will run for three years, funded by BORPC, DairyNZ and AgResearch.

Dr Stewart Ledgard and Mike Sprosen from AgResearch provided an update last week for the Rotorua farmers who are hosting the trials. The meeting was held at the Butterworth’s Mamaku dairy farm (thanks Shelley for all the food!). There is a matching trial at the Paterson’s Kaharoa dairy farm which has pumice soils.

Each farm has about 150 samplers buried 60 cm below the soil surface. Stewart and Mike demonstrated how a syringe is used to periodically suck out a sample of soil water so it can be tested in the lab for its nitrogen concentration. Lots of samples are needed because of the variable pattern of animal urine patches which are the main drivers of nitrogen leaching on pastoral farms. Both trial farms have five 50 cm diameter soil cores called ‘lysimeters’ that are used to measure the volume of soil water drainage.

The trial is progressing well, with a few practical modifications needed to handle the high rainfall conditions. This included adding surface runoff samplers, bigger containers under the lysimeters and shifting some samplers that were affected by elevated groundwater levels. It’s too early to draw any conclusions yet but everyone is keen to see the final trial results and recommendations.