Precision Moving from Cropping to Dairy

Successfully using precision agriculture technnology already on two of their cropping centre pivots, it was an easy decision for the Mitchell and Webster Group to invest again this time on their dairy farm.

The Group is owned and operated by two families, the Mitchell and the Webster families with 1400 hectares of cropping land around North Otago. In the last two years have converted 200 hectares of cropping land to dairy and have invested in Growsmart Precision VRI technology (Lindsay International) and Electro-magnetic maps (Agri-Optics NZ Ltd) for two centre pivots on the dairy farm covering 100 hectares of the farm.

The use of precision agriculture technology on the dairy farm has allowed the Mitchell and Webster Group to irrigate more efficiently through their pivots. They have been able to reduce the amount of water they apply through their pivots, while still maintaining soil moisture levels for pasture growth, and the water they have saved they now use to irrigate an additional 15 hectares wtih K-lines. By irrigating this additional area they are able to increase pasture production by 6 tonnes DM per hectare giving them an additional 90 tonnes DM per season and resulting in a subsequent increase in MS production. Given a long term payout average of $6/kg MS their expected increase in revenue is $40,0001, a 40% ROI. In addition the VRI pivots have meant that the Group is able to apply effluent in accordance with consent conditions and avoid application over drains on the property.

With an annual rainfall of 400-500 mm and a range in Summer rainfall from 10 mm – 240 mm (October – April)2 irrigation is central to achieving production targets and the Group aims to increase cow numbers to 750 cows in order to attain an output of 300,000 kg MS. However water is also expenisve and financial returns are dependent on efficient irrigation and minimising the number of irrigation shares required by the operation.

The Group has been able to increase their irrigation efficiency by creating avoid zones, areas where no irrigation is applied, over a total of 2.1 hectares of gates, laneways and troughs across the farm. While still ensuring there is enough water for optimum plant growth the Group have also been able to decrease application rates depending on soil texture (defined by their EM map) and the responses from their soil moisture sensor. As a result they have been able to spread the water available to them, through irrigation shares, across more land, increasing pasture production and revenue.

Fast Facts:
 Peter Mitchell, Nick Webster & Jock Webster
Farm: Hillbrook Dairies Ltd Farm
Type: Dairy
Location: Weston

– 650 cows
– 285000 kg MS
– 200 hectares
– Second season since conversion from cropping farm
– 2 VRI pivots, 500 meters and 460 meters in length irrigating 100 hectares
– EM survey carried out for the area under VRI irrigation
– Cost for precision agriculture system of $100,000.

1 – Assuming 15% DM wastage and 11.4 kg DM eaten to produce 1 kg MS 2 – Rainfall data from Grow Otago and NIWA regional rainfall recordings

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Figure 1 – VRI map of the Webster and Mitchell dairy farm showing the two VRI pivots, Dog Town and Hillbrook with a soil moisture sensor under the Dog Town pivot.

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Figure 2 – Soil moisture sensor under the Hilbrook Dairies VRI pivot showing that soil moisture levels for the first 3 weeks in February are within the desired range

An interesting feature of the farm is the presence of springs that make themselves known through the lime rich, calcareous parent material and mean that the already heavy, clay soils become water logged as they shrink and swell. Precision technology means that ongoing farm maintenance costs can be reduced as irrigation is avoided over areas that are identified as more prone to waterlogging, helping to maintain soil structure and reduce pugging damage.

To assist with the problem of waterlogging and try to remedy the presence of springs on the property the Mitchell and Webster Group has installed Novaflow drains which they can also create avoid zones for on their VRI programme. By creating avoid zones for a total of 12.6 hectares, of drains and other sensitive areas across both the pivots, the Group is able to apply effluent through their system in accordance with their effluent consent conditions from the Otago Regional Council (ORC).

From a nutrient leaching perspective the ORC has defined nitrate leaching limits as 20 kgN per hectare per year, for areas surrounding sensitive aquifers, and 30 kgN per hectare per year for the rest of Otago. Co-owner Peter Mitchell describes the benefits of precision agriculture as “savings both environmentally and financially”. He believes that the system will help the Group to meet these environmetal restrictions on their dairy property. Given the high costs of water in the region Peter notes that “the main driver for precision technology is financial however we also want to do what is best by our land”.

Case study source: Agri Optics -