Water is a valuable resource but for the Mitchell and Webster Group it is quite literally liquid gold. The Group was formed by the Mitchell and Webster families in 1972 and now runs two businesses; 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 land in the North Otago area.

Their McCarthy centre-pivot is 500m long, irrigating 85 hectares of rolling clay rich soils and is one of four which the Mitchell and Webster Group has invested in Electro-magnetic (EM) soil surveys by Agri Optics NZ Ltd and  Growsmart Precision VRI technology. With an impressive ROI of 140% (based on returns from the sale of excess irrigation shares no longer required), the precision agriculture technology on the McCarthy centre-pivot 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 23.5% from 34 litres per second to 26 litres per second. Savings have been the result of avoiding irrigation application over seven hectares of springs and ditches as well as varying application rates based on soil texture groups that were identified by EM soil surveys. 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 they are expected to be returning an extra $23,000 per annum due to reduced water usage and annual share costs. An increase in production is also expected.

Figure 1 – EM soil survey of the McCarthy Block showing the Growsmart Precision VRI and location of soil moisture sensors

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

They estimate that through the use of Growsmart Precision VRI there has been an average increase in production of 5%. This is due to irrigation application being able to be determined by soil types, reducing the variability in plant available water and increasing productive area by avoiding application to an area of unproductive springs and ditches. The result of avoiding this 7ha area allowed it to dry out and be partially bought back into production with only 2.5ha avoided in the second year of using Growsmart Precision variable rate irrigation.

The profit from increased production varies according to the crop being grown, however as an estimate based on an average wheat crop an annual return of $16,500 as a result of precision agriculture technology is realistic. 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 EM soil survey data and Growsmart Precision VRI system.

They have determined three factors which affect soil moisture on their property; soil type, slope and aspect. Soil moisture sensors have been placed across the irrigated area using their EM soil survey data which can be made to display interactions between these factors and therefore used to identify representative zones for monitoring. Through continued observation of these calibrated moisture sensors the Group will continue to refine their variable rate irrigation plans 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