Printed Potentiometric\nAmmonium Sensors for Agriculture\nApplications

Ammonium (NH<sub>4</sub><sup>+</sup>) concentration is\ncritical\nto both nutrient availability and nitrogen (N) loss in soil ecosystems\nbut can be highly variable across spatial and temporal scales. For\nthis reason, effectively informing agricultural practices such as\nfertilizer management and understanding of mechanisms of soil N loss\nrequire sensor technologies to monitor ammonium concentrations in\nreal time. Our work investigates the performance of fully printed\nammonium ion-selective sensors used in diverse soil environments.\nAmmonium sensors consisting of a printed ammonium ion-selective electrode\nand a printed Ag/AgCl reference were fabricated and characterized\nin aqueous solutions and three different soil types (sand, peat, and\nclay) under the range of ion concentrations likely to be present in\nsoil (0.01–100 mM). The response of ammonium sensors was further\nevaluated under variable gravimetric moisture content in the soil\nto reflect their reliability under field conditions. Ammonium sensors\ndemonstrated a sensitivity of 53.6 ± 5.1 mV/decade when tested\nin aqueous solution, and a sensitivity of 55.7 ± 11 mV/dec, 57.5\n± 4.1 mV/dec, and 43.7 ± 4 mV/dec was measured in sand,\nclay, and peat soils, respectively.