Improving the Field CV of Aerial Topdressing; Through Computer Controlled Prescription Delivery

摘要

Fertilizer is applied on New Zealand hill country properties mostly as single superphosphate and urea using agricultural fixed wing aircraft. The delivery is by gravity feed through a gate-box controlled manually or hydraulically by the pilot.Work undertaken to establish how accurate a pilot is in delivering the correct rate has calculated the coefficient of variation (CV), which is the standard deviation of the spread over the mean to be 78%. In addition the spread is non random as areas which are cheaper to apply, through their proximity to the airstrip, tend to receive higher application rates than those furthest from the airstrip.The accuracy of the spread was significantly improved by fitting a computer controlled hydraulic operated gate-box control unit linked to the aircraft differential corrected global positioning system (DGPS) achieving a CV of 42%.The aircraft was pattern tested to Spreadmark~R standard to establish a swath or bout width to fly which would achieve a CV of 25% over collectors applying single superphosphate (SSP) in a single pass at 3 rates to be applied. The DGPS guided aircraft was then flown in a 338.4ha block to achieve three targeted rates, 125kgha~(-1), 250kgha~(-1) and 750kgha~(-1) using the pilot operated gate-box. Subsequently, the computer controlled gate-box linked to the DGPS was installed and an 887ha block where two rate were applied, 250kgha~(-1) and 750kgha~(-1). Spread rate was measured from 180, 0.5m2 collectors placed in three blocks in each application zone.