Capability of ground fertiliser placement when spread from a fixed wing aircraft

Aerial topdressing using differential rate application technology improves fertiliser spreading on hill country farms. However, the system’s ability to place fertiliser accurately and precisely within an area needs to be determined. Accuracy was determined by comparing measured and intended application rates. Precision was indicated by the coefficient of variation (CV), which is the standard deviation of the measured application rate over the mean of this rate. Two trials were carried out, where aircraft deposited fertiliser at two application rates and fertiliser was captured using cone-shaped collectors. The average measured application rate for both trials was less than the intended rate. The CV ranged from 35 to 57%, and was lower than CV’s from pilot-operated hopper systems (78%). A one-way analysis of variance test found the difference between measured application rate in the high and low application zone was statistically significant. The results indicate work is required to improve the accuracy and precision of the differential rate system, however, the system shows promise. Keywords: differential rate application technology, aerial spreading, fertiliser placemen