Precision Farming Paying Back

Water is a valuable resource but for the Mitchell and Webster Group it is quite literally liquid gold.

The Group was formed by two families, the Mitchell and Webster families, in 1972 and owns two business, Topflite Ltd specialising in small animal feed and Mitchell and Webster Ltd selling grains such as sunflower, barley and wheat. The farming enterprise consists of 1400 hectares of cropping land in the North Otago area. The McCarthy pivot is a 500 meter long pivot irrigating 85 hectares of the area’s rolling, clay rich soils and is one of four for which the Mitchell and Webster Group has invested in Growsmart Precision VRI technology (Lindsay International) and Electro-magnetic (EM) maps (by Agri-Optics NZ Ltd). With an impressive ROI of 140% the system is proving its worth in gold.

Through the implementation of precision agriculture technology on the McCarthy block the Mitchell and Webster Group has been able to reduce their water usage from 34 litres per second to 26 litres per second. These savings have been the result of avoiding irrigation application over 7 hectares of springs and ditches as well as varying application rates based on soil texture groups identified by EM mapping. With high costs for irrigation shares as well as additional water usage charges, reduced flow requirements meant the Group no longer needed $77,000 worth of irrigation shares. In addition, per annum, they are expected to be returning an extra $39,500 due to reduced water and annual share costs as well as increased production.

“We have a long term goal of achieving maximum water use efficiency and maximising yield while minimising environmental impacts.” The Group believes that so far their investments in precision agriculture technology have helped them achieve these goals with further gains to be made in the future.

Fast Facts:
Peter Mitchell, Nick Webster & Jock Webster
McCarthy Farm
Type: Cropping
Location: Alma

– 85 hectares of irrigated wheat and sunflowers
– Capital return from selling excess shares of $77,000. Annual savings on water cost of $23,000 and profit from increased production of $16,500 per annum.
– Precision agriculture technology investment of $55,100
– Initial ROI of 140%
– Establish void zones for 7 hectares of springs and ditches
– Soil type, slope, aspect all influence soil moisture.

AgriOptics Precision Farming Image 2














Figure 1 – EM map of the McCarthy block showing the VRI pivot and location of soil moisture sensors

They estimate that through the use of VRI there has been an average increase in production of 5%. This has been through effective application based on soil types, reducing the variability in plant available water, and through increasing productive area, avoiding irrigation application to 7 hectares of unproductive springs and ditches and decreasing this area to 2.5 hectares. Profit from increased production contributes $18,000 to the annual amount that they return as a result of precision agriculture technology. This amount is assuming a wheat crop of 82.5 hectares with an increased yield from 10 T/ha to 10.5 T/ha and a value of $400/T.

Co-owner Peter Mitchell expresses the need to invest in order to see continued improvements on the farm “You don’t go forward if you don’t invest”. Constantly looking to the future the Group has invested in soil moisture monitoring equipment and their next step will be to carry out soil testing to help them realise the full potential of their VRI system and EM maps. They have determined three factors which affect soil moisture on his property: soil type, slope and aspect. Soil moisture sensors have been placed across the pivot area using their EM maps, which can be made to display interactions between these factors, and therefore identify representative zones for monitoring. Through continued observation of these calibrated moisture sensors the Group will continue to refine the VRI plan for the area improving water use efficiency, soil structure and nutrient management.

Two families passionate about both their occupation and land, the Mitchells and Websters are showing that both economic and environmental benefits can be achieved with capital investment and a desire to learn.

Case study source: Agri Optics -