Evaluating the profitability of a soil sensor-based variable rate applicator for on-the-go phosphorus fertilization

Variable rate (VR) phosphorus (P) fertilization aims at improving fertilizer use efficiency and environmental impacts by varying fertilizer rates according to the needs of each zone within a field. This study evaluates the profitability of an on-the-go VR fertilization of phosphate (P2O5) in grain corn yield using visible (VIS) and near infrared (NIR) soil sensor-based VR applicator. This evaluation was considered in two different soil phosphorus levels (high & very high with minimum & no fertilization, respectively), which are the common phosphorus levels in Belgian agricultural fields. A previously developed VIS-NIR model was used to predict the extractable phosphorous (Pal). An experimental field divided into two zones according to soil P levels, namely, Zone 1 (high Pal level of 55 mg 100 g-1) with 2 plots and Zone 2 (very high level of Pal of 63 mg 100 g-1) with 3 plots. In these five plots VR of phosphate (P) was adapted using th e VR applicator. For each plot, the amount of uniform rate (UR) P need was also obtained using the traditional soil test phosphorus (STP). The overall P application in each plot using the VR approach was compared with the corresponding UR. Amount of P applied with VR fertilization depended upon the initial level of Pal. Compared with the STP recommendation for UR application, in Zone 1 with high level of P, VR provided a positive fertilizer return of 1.5 kg P per ha, (0.96 epsilon per ha), whereas in Zone 2 with very high level of P, VR led to a negative fertilizer return of 16.37 kg P per ha (10.52 epsilon per ha). Compared with the UR fertilization plots, 305 kg per ha corn net return was obtained in Zone 1, which introduced a revenue of 33.54 epsilon per ha. However, in Zone 2 there was a loss of 324.6 kg per ha introducing a cost of 35.73 epsilon per ha. The results showed that the on-the-go VR fertilization of P based on a VIS-NIR sensor is profitable in fields with high level of phosphorus. However, the profitability of this system should also be investigated in fields with medium, low and very low levels of P levels, which are not the case in most of the fields in Belgium.