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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #110112


item Hummel, John

Submitted to: Illinois Fertilizer Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/2/2000
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 impetus for development of improved fertilizer management. Different soil nutrient 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 makes implementation of a variable-rate fertilizer management system based on soil nutrient tests impractical for some nutrients and spatial variabilities. 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 additions of nitrogen fertilizer may result in environmental degradation. A sensor technique that can rapidly measure soil nutrient levels in soil extracts is being explored to identify the important variables that would affect a high-speed soil sample collection and extraction system. Soil type, soil core length and diameter, and extraction fluid flowrate are variables that significantly affect the soil nutrient extraction process. Several descriptors were evaluated, and nitrate-N prediction may be possible in an elapsed time of 0.25 s to 2.0 s. A sensor and control system to control the nitrogen fertilizer application rates may also provide data for producing maps for controlling application of other nutrients at later times. Use of the technology could benefit agricultural producers economically, and reduce the adverse effect of commercial fertilizers on the environment.

Technical Abstract: The objective was to develop and test a real-time soil nutrient analysis system, based on ion-selective field-effect transistors (ISFETs). The development of a real-time soil nutrient sensor could allow the automated collection of soil nutrient data on a fine resolution to accurately characterize within-field variability for site-specific fertilizer application. A system was designed to evaluate the effect of soil type and texture, soil moisture content, soil sample volume, sample preparation, and rate of extraction solution injection into the sample on extraction efficiency and extraction time. Test soils were selected to provide a broad range of both textural properties and organic matter content. A multi-ISFET chip was prepared for the experiment by applying membranes composed of a ligand, tetradodecylammonium nitrate (TDDA), and a plasticizer, 2-nitrophenyl octyl ether (NPOE), and high molecular weight polyvinyl chloride (PVC) to the gate areas of all four ISFETs. The tests showed that nitrate extract collected from an intact soil core is indicative of the nitrate concentration in the soil core. The method of extraction and sample injection into the ISFET/FIA system were satisfactory, although conclusions are limited somewhat by large variations in laboratory nitrate-N analyses. Nitrate-N level, soil type, core length, core diameter, and extraction pump flowrate were variables whose effects were highly significant. Several data descriptors appeared to be accurate estimators of the nitrate-N concentration in the soil core, with some opportunity to predict nitrate-N concentration in less than 2 s.