A GIS Methodology to Calculate In-Field Dispersion of Fertilizer from a Spinning-Disc Spreader

Abstract

A model was developed within a GIS environment using the transverse spread pattern and GPS driving track during spreading to map actual fertilizer application at any point in a paddock. The spreading vehicle required a GPS of sufficient accuracy in order to provide proof of placement and guidance assistance to the driver. The method was used to assess the effect of field size and shape on actual application rate and application variation. At a target application rate of 80 kg ha-1, measured application rates ranged from 51.8 to 106.7 kg ha-1 of urea (46% N) fertilizer over 102 paddocks on four farms. Average field variation calculated over all paddocks was 37.9%. Irregular-shaped paddocks were found to have higher application variation (40.8%) compared to regular-shaped paddocks (35.9%). Hot spot analysis was performed to identify areas receiving statistically significant high and low application rates (s < 2.0). Over all paddocks, 7.4% of the total area received significantly high application rates, while 10.2 % received significantly low application rates. This information, collected over a number of applications, could be incorporated into subsequent variable-rate application maps whereby rates could be adjusted on areas that have received incorrect quantities of fertilizer in previous applications. This system will improve sustainability for a farm by ensuring that nutrient management plans can be followed, as well as providing a means of traceability and proof of placement.