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When it comes to farm variability it would seem that Simon Johnson’s property is as variable as it gets. His 450 ha dairy farm, situated towards the seaward end of Rangitata Island, features an old riverbed as well as areas of sand and pockets of silt soils.
Through the use of Electro-magnetic (EM) soil surveying by Agri Optics NZ Ltd and Growsmart Precision VRI technology Simon has been able to largely overcome some of the major constraints on his farm, including limited water resources, high soil variability and a limited area for his effluent application; allowing him to continually improve his whole farm management. Use of precision agriculture technology has allowed Simon to spread his water further, meeting pasture requirements and saving him an outright $500,000 by not having to buy irrigation shares or build a water storage pond.
Simon’s decision to adopt precision agriculture technology was made when he determined that he would need an extra 5% or 30 L/s of water to meet his pasture demands. Already operating at his water consent’s limits, Simon’s options were to buy into an irrigation scheme and build a storage pond or improve his water use efficiency.
“Building a pond only ticked one box; sorting the water supply. It didn’t help with effluent application and why build a pond with all this extra capacity when I only needed 5% more water? The extra capacity would have been wasted money.”
Using EM soil surveys and Growsmart Precision VRI Simon was able to eliminate the $500,000 cost of building a storage pond and the additional cost of buying into the local irrigation scheme. By contrast he invested $116,500 on his precision agriculture technology EM soil surveys and Growsmart Precision VRI, resulting in a significant outright saving. The precision agriculture technology allowed him to save 5% of his irrigation water by avoiding application over laneways, swamps, water-races and by varying the application depth applied over the irrigated area based on soil type variation. Simon was able to apply less water to his heavy silt soils, those able to retain higher amounts of water within the plant available range, and use some of this water to maintain plant available water levels on his light, stony soils which would otherwise dry out quickly as water passes through the soil profile.
Figure 1 – EM soil survey of the Rangitata Dairies showing the location of the two Growsmart Precision VRI and three soil moisture sensors
On many properties farm profit as a result of variable rate irrigation water savings can be quantified in terms of the additional area that could become irrigated, therefore increasing grass growth and milk production. For Simon Johnson the benefits of his precision agriculture system were more extensive than water savings alone. Simon describes another four areas of improvement:
1. Effluent management
“An effluent spreader and pivot in the same paddock was a big concern because of potential collisions. My original consent was for a small confined area, but with the Growsmart Precision VRI I was able to demonstrate that I can spread effluent over the river bed part of the farm with small rates often.” Consequently he was approved to expand his effluent application area, benefiting pasture growth as well as eliminating the potential for accidents from having both pivot and travelling irrigator operating in the same paddock.
2. Improving production on wet areas
The EM soil survey can be made to highlight topography features such as depressions and raised areas and a wetness index can also be generated. “We’ve turned off the water altogether over some wet areas or cut it right down. Some of them have dried right up and bounced back and some I’ve had to go in with the digger and break the pan up and aerate them before we can get it back into a good productive state again.”
3. Reduced track maintenance costs
Simon believes that by turning off irrigation over tracks, troughs, gate ways and pivot tracks his track maintenance costs of $25,000 per year have already been halved. Reducing wet areas and improving the state of tracks has also meant a decrease in lame cows for the farm.
4. Reduced nitrate leaching
The farm currently has a nitrogen baseline of 28 kg N/ha and the use of variable rate irrigation technology means that the farm is in a strong position to gain consent meeting ECAN (regional council) requirements for farmers that come in 2017.
Figure 2 – Soil moisture from Probe 1 on soils with a higher silt content
Another aspect of precision agriculture technology that Simon has recently begun to investigate are AquaCheck soil moisture probes from Agri Optics NZ Ltd. Soil moisture graphs enable Simon to monitor his soil moisture and adjust his irrigation accordingly. Figure 2 shows a graph of one of Simon’s soil moisture probe readings. The sensor is within a soil zone with a high silt content as can be seen the soil moisture is remaining relatively stable within the optimum levels.