Optimized fertilization using online soil nitrate data

Abstract. Managing fertilizer application according to actual soil nutrient availability is a key strategy for achieving sustainable agriculture and a healthy environment. A new soil nitrate monitoring system that was installed in cultivated field enabled, for the first time, controlling the nitrate concentration across the soil profile. The monitoring system was installed in a full-scale agricultural greenhouse setup that was used for growing a bell pepper crop. Continuous measurements of soil nitrate concentrations were performed across the soil profile of two plots: (a) an experimental plot, in which the fertigation regime was frequently adjusted, according to the dynamic variations in soil nitrate concentration and (b) a control plot, in which the fertigation was managed according to a predetermined fertigation schedule that is standard practice for the area. The results enabled an hourly resolution in tracking the dynamic soil nitrate concentration variations, in response to daily fertigation and crop demand. Nitrate concentrations, in and below the root zone, under the control plot, reached very high levels of ~800 ppm throughout the entire season. Obviously, this concentration reflects excessive fertigation, which is far beyond the plant demand, entailing severe groundwater pollution potential. On the other hand, frequent adjustments of the fertigation regime, which were carried out under the experimental plot, enabled control of the soil nitrate concentration around the desired concentration threshold. This enabled a dramatic reduction of 38 % in fertilizer application, while maintaining maximum crop yield and quality. Throughout this experiment, decision-making on the fertigation adjustments was done manually based on visual inspections of the soil’s reactions to changes in the fertigation regime. Nevertheless, it is obvious that an algorithm that continuously processes the soil nitrate concentration across the soil profile and provides direct fertigation commands could act as a "fertistat" that sets the soil nutrients at a desired optimal level. Consequently, it is concluded that fertigation that is based on continuous monitoring of the soil nitrate concentration may ensure nutrient application that accounts for plant demand, improves agricultural profitability, reduces nitrate down-leaching, and eliminates water resource pollution.