SOIL SENSING AT HIGH SPATIAL RESOLUTION—BROADENING THE OPTIONS AVAILABLE TO THE SUGAR INDUSTRY

GROWING INTEREST IN Precision Agriculture in the sugar industry has been matched by an increasing use of electromagnetic soil sensing for characterising soil variation within cane blocks. Possible alternative technologies for such soil sensing include the VERIS 3100, which measures soil electrical resistivity (ER), and EM38, which uses electromagnetic induction (EMI) to estimate the apparent electrical conductivity (ECa) of the soil. To date, VERIS has been the most commonly used soil sensor in the sugar industry. However, since conductivity is the inverse of resistivity, EM38 and VERIS ought to provide the same information in regard to spatial variation in the key soil properties which affect electrical conductivity. Our interest here, was in demonstrating that this is indeed the case. A 27 ha block in the Burdekin was surveyed on-the-go with an EM38 sensor mounted on a polypropylene sled towed by a utility in July 2011. Approximately one month later, the site was resurveyed using a VERIS 3100, also towed by a utility. For all practical purposes, the maps derived from these surveys were the same, thus demonstrating that, as expected, both soil sensors are suitable for assessment of spatial variation in soil electrical conductivity. In a complimentary study conducted during 2009 in a 6.8 ha block in the Bundaberg district using EM38, patterns of spatial variation in ECa were seen to be unaffected by the presence (July, immediately post harvest) or absence (November, following cultivation) of trash. These results in no way suggest any diminution of the utility of ER sensors for assessing soil spatial variation in cane blocks; indeed, we support their on-going use. However, not only do these results demonstrate that EMI sensors do just as good a job as ER sensors, they also open up the prospect that much larger areas may be surveyable than just those with bare fallow, since their ability to detect soil variation appears unaffected by the presence of dry trash. The results therefore raise opportunities for increased adoption within the sugar industry of soil survey at high spatial resolution.