Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2000
Publication Date: N/A
Citation: Interpretive Summary: Variable rate fertilizer application has the potential to improve fertilizer use efficiency, increase crop economic returns, and reduce environmental impacts by adjusting rates of fertilizers to specific conditions within small areas of a field. This study was designed to assemble a variable rate applicator capable of simultaneously varying rates sof two liquid fertilizers and evaluate its performance and field application accuracy. A control system was adapted to a side dressing applicator for variable rate applications of two different liquid fertilizers: N32 and 11-37-0. Laboratory testing indicated that the control system had good performance and fast response. The variable rate applicator accurately applied predetermined uniform and variable rates across three grain sorghum fields during the 1997 and 1998 growing seasons. This research is readily applicable to the development of variable rate liquid application equipment for precision farming.
Technical Abstract: Variable rate fertilization aims to improve fertilizer use efficiency and reduce leaching by varying fertilizer rates according to the needs of each area within a field. This article describes a variable rate applicator capable of simultaneously varying rates of two liquid fertilizers and reports on its static and dynamic performance and field application accuracy. A control system was adapted to a side dressing applicator for variable rate applications of two different liquid fertilizers: N32 and 11-37-0. Static calibration indicated that the controller had very good linearity. Dynamic response testing showed that the control system had a rise time of about half a second and could stabilize at desired rate within 1 to 2 s. Field experiments were carried out at three grain sorghum fields in the 1997 and 1998 growing seasons. Three fertilizer treatments, two uniform and one variable rate, were assigned in 18 experimental plots across the three fields. The variable rate applicator performed well during field applications for both years. Mean application rate errors for N32 and 11-37-0 were, respectively, 2.5% and 5.2% in 1997 and 2.8% and 5.8% in 1998. These results showed that the variable rate applicator had very good dynamic response and high application accuracy. The methodologies and testing results presented in this article have practical implications for the development and testing of variable rate equipment in precision agriculture.