Band application of slurry in orchards using a prototype spreader with an automatic rate controller

A prototype slurry spreader for band application in orchards was designed, constructed, and tested. The spreader comprised several components: 1) 5 m3 tank, 2) distribution device of trailing hoses to reduce ammonia emissions during application, 3) automatic rate controller to apply nitrogen per crop requirements, and 4) low-pressure, wide-section tyres to mitigate soil compaction and sward damage. The slurry tanker design fitted between tree row spacings accounting for tree shape differences. The spreading system consists of two groups of six trailing hoses; each hose group distributes slurry into two 1.0 m wide bands alongside the machine and 0.5 m from tree rows. Operator input of slurry total nitrogen content, determined by onboard hydrometer in the field, and target application rate in the control unit ensured that nitrogen was applied at a constant rate based on metering pump rotational speed as a function of machine forward speed. The rate control system was tested at different application doses and with rapid changes in machine forward speed (range of 3–9 km h−1). The machine responded promptly (<2 s) to forward speed changes, and the spreader evenly distributed slurry in both application bands (Dave < 2.5% on the treated surface). Band application of slurry by the trailing hose device reduced ammonia emissions by 63% compared to the common broadcast application system by splash plate.