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ARS Home » Research » Publications at this Location » Publication #83067
Title: MULTI-SENSOR ISFET SYSTEM FOR SOIL ANALYSIS

Author
item BIRRELL, STUART - UNIV OF ILLINOIS
item HUMMEL, JOHN

Submitted to: European Conference on Precision Agriculture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/5/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Concern about the intensive application of nitrogen fertilizers, and their potentially adverse effects on the environment, has provided inputs for development of improved fertilizer management. Different soil nitrate levels, and different soil types with differing crop producing capabilities within a field, suggest that application levels might be adjusted across the field, supplying just the supplemental amount of nutrient needs to produce the crop. The cost and time required for the intensive sampling needed, using conventional sampling and analysis techniques, makes implementation of a variable-rate nitrogen fertilizer management system based on soil nitrate tests impractical. On-the-go real-time nitrate sensors might be used to locate areas of fields where additions of nitrogen fertilizer will be beneficial, and other areas where soil nitrate levels are such that additions of nitrogen fertilizer may have no economic benefit and could result in environmental degradation. A sensor has been developed that can rapidly measure soil nitrate levels in soil extracts. When coupled with a high-speed soil sample collection and extraction system (yet to be developed), soil nitrate levels could be used to control the nitrogen fertilizer application rates in corn production. Use of the technology could benefit agricultural producers economically, and reduce the adverse effect of commercial fertilizers on the environment.

Technical Abstract: The use of ion-selective field-effect transistors (ISFETs) and flow injection analysis (FIA) was investigated for use as a system for real-time soil nitrate sensing. Conventional ion-selective electrodes were used to evaluate 8 different membranes (ligand/plasticizer combinations) with respect to their sensitivity to nitrate, lower detection limits, and selectivity against interferences from other ions. A complete ISFET/FIA system was designed to minimize sampling period and to maximize sampling frequency. The effects of sample flowrate, and sample injection and washout times, on the capability of the system to predict nitrate concentration were analyzed. The capability of the system to predict nitrate concentration of soil solutions that had been manually extracted from samples representing a range of soil types was evaluated. An automated soil extraction prototype was combined with the ISFET/FIA system and evaluated for real-time soil nitrate extraction and analysis. The membrane tests resulted in four ligand/plasticizer membrane combinations being selected and used in the multi-sensor ISFET/FIA system. The system was successful in measuring soil nitrates in manually extracted soil solutions (r2>0.9). The system was capable of analyzing samples within 1.25 s, demonstrating the soundness of the concept for real-time soil nitrate analysis. Considerable improvement is needed in the automated soil extraction system before successful, continuous operation can be demonstrated.