Hayden and Jessie Dorman are in search of practices which will ensure the long term sustainability of their farm. This 2014/15 season they have begun to utilise the Electromagnetic (EM) soil survey data of their farm (by Agri Optics NZ Ltd) and their Growsmart Precision VRI technology in order to demonstrate environmental efficiency and improve soil health. Their 640m centre pivot with Growsmart Precision VRI installed is estimated to save them an average of $148 in power per application while decreasing water usage by 3,300m³ in comparison to applying a uniform application rate.

The initial investment in their precision agriculture technology was made a few years earlier by the farm’s previous owner and was largely un-utilised. However since taking over management of the farm the Dormans are aiming to employ full use of the system. Requiring ongoing time to review and learn from the process this season has marked the start of the Dormans’ precision agriculture journey and they hope to dedicate more time to it in the following year.

Alongside this technology the Dormans also employ HydroServices to carry out weekly soil moisture readings on their farm and are involved in a joint NIWA and ECAN trial which involves a weather station and a soil moisture sensor that provides continuous moisture data. Soil moisture monitoring locations were chosen using the farm EM soil survey data to identify zones of similar soil type. These activities are all part of their long term goal of farm sustainably while maintaining their high production system.

Figure 1 – EM soil survey of Riverstone Farm showing the VRI pivots and location of soil moisture sensors

Figure 2 – Riverstone Soil Moisture Probe, Heavy

Figure 3 – Riverstone Soil Moisture Probe, Light

The operation on Riverstone farm totals 180 hectares and is serviced by a single centre pivot with Growsmart Precision VRI installed, irrigating 136 hectares. Located near the mouth of the Rakaia River they are not restricted by water availability. However, as progressive farmers, they would like to reduce their water usage and improve overall efficiency by aligning soil moisture data with their EM soil survey data and using these tools to guide variable rate irrigation application primarily during the shoulders of the season.

The Dormans already utilise their Growsmart Precision VRI technology to avoid watering over laneways saving water, pumping costs and laneway/track maintenance costs. Furthermore this season they have been investigating further utilising the variable rate irrigation technology through dividing their farm into three management zones and delaying water application to those soils with a greater ability to retain water. This is expected to decrease their water usage and pumping costs by an overall total of 3,300,000 litres and $148 respectively per application.

As a previous ECAN employee, Jessie is well aware of what future nitrate leaching restrictions will involve. Soil moisture monitoring on the farm shows the Dormans when drainage events are occurring through the soil profile and allows them to modify their irrigation accordingly to minimise leaching. Data from the NIWA lysimeter also allows them to see leachate collected and this has been recorded as minimal over the 2014/15 irrigation season. Through this trial they have access to telemetry (live) soil moisture data and are able to view soil moisture at increasing depths down the profile, to 50 cm. Any sharp spikes in soil moisture at this depth, which is at the bottom of the rooting zone, would also indicate drainage occurring. The Dormans have begun to successfully utilise this data over the season and their soil moisture content has stabilised since the previous year.

In upcoming seasons the Dormans’ goal is to monitor their soil moisture data and use this to guide their Growsmart Precision VRI irrigation schedule combined with weather forecasts, times of the season and pasture cover. Hayden admits that investing the time is the hardest part but realises that the long term benefits are there and is determined to increase their use of the system in the future.

Figure 4 – NIWA soil moisture reading from the high EM zone

Figure 5 – Soil pit at Riverstone Farm showing soil characteristics