“Getting the soil pH correct gives you a good platform for agronomy,” he said. “It’s the first issue to cross off the list, which then allows you to look at drainage and fine-tuning other nutrients.”
His company uses the VerisTM soil pH detector to map soil pH. With “20,000 hectares of experience” the company is a firm believer in the advantages of the technology.
The device is mounted on the back of a quad bike and takes soil water pH measurements at a depth of around 7.5cm. The device takes five to 10 seconds to settle on and log a pH reading at which time GPS co-ordinates of the reading’s location are also sent to the data logger.
The probe is regularly calibrated against pH buffer solutions of 4 and 7.
“High soil moisture in the top 10cm layer is critical for getting accurate readings, firstly to ensure good soil contact with the probe and secondly to allow the probe to penetrate the soil easily,” Torpy said.
“Wash nozzles and ensure that the probe is cleaned between each sample.”
The information from the data logger is then uploaded to a global information systems (GIS) software program which creates a visual map of the high, medium and low pH zones.
“The pH detectors are designed to show where pH trends occur across paddocks or farms. We then use strategic soil sampling across those zones to calculate the required lime rates.”
In broadacre country, measurements are taken in a 1ha grid; on more intensive farms the sampling is reduced to either a 0.4 or 0.2ha grid, aiming to capture 35 to 40 samples a paddock.
During the pH zone soil sampling and testing process, soil samples are also taken from the exact location of several pH detector readings.
Raw data from the data logger is used to establish a pH contour map.
This allows the correlation between pH water in the lab and the pH reading from the soil pH detector to be established. Torpy said he was then able to confirm with his clients the accuracy of the pH mapping system.
In the broadacre cropping zones of Australia, soil pH can vary hugely across single paddocks, making one lime rate ineffective and inefficient for correcting soil pH over the entire area.
Variable rate lime application has not only been shown to improve crop uniformity, it also allows considerable cost savings by identifying the zones that need no or low rate lime applications. Identifying areas that require no lime also saves on the cost of spreading.
Torpy presented the pH mapping costs at around A$10/ha and economic analysis showed that a “10% lime saving is required to render pH mapping cost-effective”.
“In the experience of precisionagriculture.com.au, most cases showed much greater savings of 20-60%.”
In broadacre terms this can represent tens to hundreds of thousands of dollars.
“In addition to the savings there are the production benefits gained by creating a good platform for agronomy and producing better crop yields,” Torpy said.
He estimates that variable rate lime application has been justified on 90% of the paddocks mapped by the company, with the greatest cost savings typically seen on areas of land in a “lime maintenance” phase.
“The aim of the process is to establish a consistent pH level across an entire paddock or farm. It is important to note that soil pH can vary significantly in smaller paddocks as well as the more extensive ones.”
Torpy said the future of pH mapping technology was likely to involve the associated benefit of identifying significant variations in soil phosphorus and buffering index.
“Introducing variable rate P application will not only benefit soil and crop production but also catchment health by reducing phosphorus run-off.”
DID YOU KNOW?
In New Zealand a Primary Growth Partnership (PGP) is under way involving Ravensdown, AgResearch and Massey University’s Precision Agriculture Group to develop the technology to allow precision fertiliser application on hill-country farms via aircraft.
The initiative is making use of a hyperspectural camera mounted on a plane to remotely sense soil fertility over hill-country areas.
The camera works by measuring reflections at many different wavelengths and this information, along with pasture and soil samples, is analysed to establish soil fertility status.
With the guidance of a GPS and automatic hopper doors it is then possible for aircraft to target fertiliser applications and adjust application rates accordingly.
The PGP is in the contracting phase.
