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    Improving granular fertiliser aerial application for hill country farming : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Agricultural Engineering at Massey University, Palmerston North, New Zealand
    (Massey University, 2017) Chok, Sue
    Soil fertility and pasture productivity varies significantly over hill country farms. Therefore conventional aerial fertiliser application of a single application rate is inefficient. Automation of the aircraft hopper door increases control of fertiliser application. This includes the ability to achieve variable rate application, where multiple application rates can be applied over the farm. Ravensdown Limited has installed variable rate application technology (VRAT) on their Pacific Aerospace Cresco (PAC) 600 aircraft to improve the aerial application of granular fertiliser to hill country farms. The objective of this study was to measure and improve the performance of the VRAT system. Various aspects of the system’s performance were examined; including hopper flow dynamics, control of the hopper door, estimation of a fertiliser particle’s landing position from a known release point, collection of field data, and prediction of wind effects on the ground fertiliser distribution. Performance trials, bench testing and static hopper flow tests were used to improve the VRAT system. Three performance trials were carried out. Each had a different sampling configuration: grid, nested grid and line. Sampling configuration varied because the objective of each trial differed, and there were advantages and disadvantages to each configuration. Accuracy, precision, level of off-target application, and capability of the VRAT system to vary application rate was measured. The trials observed accurate application rates, and improved precision when compared to pilot operated hopper doors. Off-target application occurred because the buffer was insufficiently sized, and did not consider the forward motion of particles, wind effects, and the mechanical/hydraulic limitations of the VRAT system. Bench testing, modelling and field trials can be used to improve the sizing of buffers under varying field conditions. Statistical tests showed the VRAT system was capable of applying different application rates to application zones. While some parts of aerial topdressing can be controlled, there are other factors that cannot be controlled and are a source of variation. Several factors are discussed. Particle bounce out of the collectors was observed after the second performance trial. This issue under-estimated the field application rate in the first two performance trials. Additional trials were completed to improve the capture efficiency by 38% for superphosphate, and provided correction factors for DAP and urea. Wind contributes to variability in aerial applications, and automation of the hopper door is unlikely to significantly mitigate its effects. Ravensdown Limited wished to develop a wind displacement calculator tool. The calculator uses a single particle granular fertiliser ballistics model to predict the displacement of the transverse spread pattern and swath width by wind. To achieve this, the ballistics model was validated for superphosphate, urea, di-ammonium phosphate (DAP), and a 70% superphosphate/30% Flexi-N blend. The model was validated from two data sets for each fertiliser type. From the first data set, the propeller wash component was excluded because fertiliser particles leave the hopper door in a mass flow. Therefore in the initial time steps, the particles are not singular and the propeller wash does not significantly influence their motion. There was good agreement between the field and modelled transverse spread patterns. Additionally, the Kolmogorov-Smirnov test statistically showed that the two distributions were similar. The development of the wind displacement calculator tool and production of wind displacement look up tables is described. From a limited number of inputs, the calculator predicts the displacement of the peak mass in a transverse spread pattern. To decrease modelling time, wind displacement look up tables were created from the tool for superphosphate, urea and DAP. In conclusion, the VRAT system will improve fertiliser application to hill country. However, aerial topdressing is highly variable and some factors cannot be controlled. Ballistics modelling can be used to minimise these factors and improve understanding of the variability. The model and wind displacement calculator should be used with care, as they are based on assumptions, which may not be completely representative of field conditions.
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    Variable rate application technology in the New Zealand aerial topdressing industry : a thesis presented in partial fulfilment of the requirements of the degree of Doctor of Philosophy in Agricultural Engineering at Massey University, New Zealand
    (Massey University, 2007) Murray, Robert Ian
    Greater use of technology to assist aerial application of fertiliser will be of benefit to the topdressing industry and farmers. Benefits arise through automating the fertiliser flow control system; reducing off target fertiliser application, and managing fertiliser inputs based on the potential outputs of the farmland; thus increasing the profitability of hill country farming systems. A case for technology assisted application is developed by investigating the field performance of conventional and enhanced flow control systems and the effect of variable rate application on hill country pasture production. A single particle model that predicts flight trajectory from the particle force balance based on the aircraft groundspeed, axial and tangential propeller wash, wind characteristics and particle properties including sphericity was developed. Model predictions were compared to predictions from AGDISP 8.15. Results and trends were similar. The single particle ballistics model described above was extended to predict the lateral distribution of fertiliser after release from an aircraft. To achieve this, two parameters are important, the transverse flow profile of material leaving the hopper gatebox and the sphericity of the particles. Techniques for measuring these parameters are described and experimental results are presented for superphosphate. These data were used in the model to predict the lateral distribution pattern from a Gippsland Aeronautics 200C for a known discharge mass, which was compared to a measured pattern from the same aircraft for the same discharge mass. Good agreement between the shapes of the two distributions was found. The transverse distribution model provides a practical tool for optimising the design of spreaders, or optimum particle characteristics for a given spreader. It has the ability to predict the distribution profile of any particle size distribution from each, or all, of the spreader ducts. Culmination of the single particle and transverse distribution models led to the development of a deposition footprint model that was capable of predicting field application within a 25 ha trial site. The deposition footprint model was embedded inside a geographical information system and comparisons were made between the actual and predicted deposition across a series of transect lines. Good agreement was found. Following this, a comparison of the predicted field performance between an automated and manual control system were made. Economic benefits for a single application of superphosphate were identified through using automated control, where 10% less fertiliser was applied outside of the application zone when compared to the manually operated system. This equated to a net benefit of NZD $2800 for a 1500 ha hill country farming system. The value of improving the performance of a topdressing aircraft, on an industry level, was also examined. Cost/benefit analysis between a manual and automated system revealed a benefit of NZD $111,700 yr-1 for a single topdressing aircraft using the automated system. The economic impact of Variable Rate Application Technology (VRAT) is examined, using Limestone Downs as an example. The spatially explicit decision tree modelling technique was used to predict the annual pasture production over the entire Limestone Downs property. The resulting decision tree classes tended to follow the farm's digital elevation model. A series of six different fertiliser application scenarios were developed for comparison to a base line scenario using conventional aerial application techniques. VRAT outperformed the fixed rate applications in terms of pasture production and fertiliser utilisation. Full variable rate application and a model optimised prescription map, produced the highest annual pasture yield. Variable rate techniques were predicted to increase annual production and the spatial variability of that production. An economic analysis of the six production scenarios was undertaken. Farm cash surplus was calculated for each scenario and clearly revealed the benefits of using variable rate application technology. VRAT was found to be the most efficient and highest returning application method per hectare. Additional costs and increased charge-out rates were likely to occur under VRAT; nevertheless, the analysis indicated that significant financial incentives were available to the farmer. A sensitivity analysis revealed that even with a 20% increase in charge-out rate associated with VRAT, the farm's annual cash position varied by only $4500 (0.4%), suggesting the cost of implementing such a system is not prohibitive and would allow aircraft operators to add value to their services.