Project leader Dr James Hills, from the University of Tasmania, said the research was the first of its kind in Australia and New Zealand.
«There’s one sensor per nozzle, the boom is six metres wide and each of the sensors and nozzles are half a metre apart,» he said.
«The distance between our nozzles and sensors have been set up so that we can spray at the normal rate of about 15-16 kilometres an hour in the pasture.»
The team of researchers trialled the project on four Tasmanian farms with intensively managed dairy pastures over the last three years.
They found that using the optical sensor or ‘Smart-N’ technology led to a reduction in fertiliser use by about a third.
Fertiliser is one of the biggest input costs for farmers, particularly dairy producers who want to boost pasture growth to increase their herd’s milk production.
Dr James Hills said the idea was that the spray unit did not apply liquid nitrogen on the pasture where there was already enough in the ground.
«Where there are urine patches (dark green grass patches) there’s ample amount of nitrogen, so what theses sensors do is identify the patches by identifying the amount of greenness.
«The darker green and denser the patch then the higher the reading from the sensor compared with the background areas that don’t have that amount of nitrogen.»
Essentially the optical sensors tell the nozzles to spray around the dark green, nitrogen-rich patches that need the fertiliser to get the desired pasture growth.
Farmers hope to see environmental and financial benefits
North-west Tasmanian dairy farmer Duncan McDonald, who participated in the trial, said the environmental benefits were important, but it had to help the bottom line too.
«From our point of view the next step is whether that can be done commercially at a competitive rate,» he said.
«Obviously if the cost goes up to outweigh the savings we’d get from using less nitrogen it doesn’t help financially, you still get the benefits in reduced nitrogen losses but it would be great to see a saving on both ends.»
Decreasing the amount of fertiliser applied by a third or about eight tonnes per year from an average Tasmanian dairy farm could mean a saving of about $6000 a year at current prices.
But the liquid fertiliser used in a boom sprayer is more expensive than granular fertiliser, so Dr Hills said the savings may not be that big for all farmers.
«Certainly in Tasmania there is a price differential between liquid and granular fertiliser, in some areas of Australia that’s not so much the case,» he said.
«In Western Australia they use a lot of liquid nitrogen so the differential is not so great.»
Dr Hills also said producers who have the facilities on-farm to store bulk liquid or dissolve granular fertiliser would see the cost savings.
The University of Tasmania project found that a reduction in fertiliser through using the optical sensor equates to a potential abatement of about 50 tonnes of CO 2 equivalent.
The researchers propose that of the greenhouse gases emitted from Tasmanian pasture-based dairy farms, 10 per cent are nitrous oxide from urine and dung. Fertilising pasture further increases the risk of what is called nitrogen loss as nitrous oxide, a potent greenhouse gas.
The project is funded through the previous federal Labor government’s Action on the Ground grants scheme, which targeted on farm trials of abatement technologies that were trying to reduce agricultural greenhouse gas emissions.
Source: ABC
