Development and tests of a variable rate system for the distribution of livestock slurry with pressurized tankers

Effluent management has become increasingly important among livestock farming activities, particularly relating to the environmental impacts that could result from inadequate effluent management especially at the farm level. Due to this issue, the European Commission, with Directive 91/676/EC, aimed at protecting the environment while ensuring that farmers could achieve proper production levels. Due to this directive, nitrate vulnerable zones have been set with strict regulations regarding the timing and rates of nitrogen application in these zones. In the vulnerable zones, a specific threshold limits the application rate to 170 kg/ha per year for nitrogen whilst, in the remaining areas, the threshold is 340 kg/ha. The present study aimed to develop a variable-rate (VRT) system capable of automatically controlling the nitrogen distribution rate in the open field specifically designed for pressurized slurry tanker (the most diffused spreading technology used in Italy. For field-testing purposes, this system was mounted on a double-axis 10 m3 slurry tanker equipped with a crawling nozzle distribution unit. Field experiments were conducted at two typical forward speeds (2 and 3 km/h) and three different nitrogen application rates (170, 250, and 340 kg/ha). Based on the experimental results, the system was generally capable of limiting the differences between the nominal and measured application rates to less than 7% and the transverse field distribution resulted uniform throughout the working width of the machine and at all tested operating conditions, with maximum deviations of about 15% (limit value imposed by UNI EN 13406:2002 standard).