Development of Components of a Real-Time SoilMacronutrient Sensor

摘要

Soil macronutrients, especially nitrate nitrogen, can vary both spatially and temporally.A real-time sensor that automatically collects and analyzes soil samples could provide data tooptimize variable-rate fertilizer application. This paper discusses progress on the developmentof three major components of a real-time soil macronutrient sensor based on ion-selective fieldeffect transistor technology. The technology dictates that a sample of soil be collected so thatan extracting solution can be used to obtain a liquid sample containing the soil macronutrientions. This paper discusses research on 1) design of an electro-pneumatic device for rapid soilsample collection, 2) laboratory investigations of membranes and extracting solutions that mightpermit a single extraction to support real-time analysis of soil nitrate and potassium, and 3)techniques for rapid extraction of macronutrient ions from the soil sample. In the soil samplerdesign research, a range of soil types was included in the laboratory study. Soil bin testing of asoil sampling shank using the electro-pneumatic method showed that air pressure, pulseduration, soil moisture content, and travel speed had highly significant effects on the mass ofthe sample collected. The extraction studies showed that TDDA-based nitrate membranes werecapable of detecting low concentrations in soils to about 10-5 mole NO3- /L. The valinomycinbasedpotassium membranes showed satisfactory selectivity performance in measuringpotassium in the presence of interfering cations such as Na+, Mg2+, Ca2+, Al3+, and Li+ as