Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Other
Publication Acceptance Date: 7/13/2000
Publication Date: N/A
Interpretive Summary: Nutrient loads in tile outflows, and subsequently in surface streams and drinking water reservoirs, continue to indicate a need for improved matching of commercial fertilizer application rates with projected crop needs. 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 technology is being 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: Commercialization of a real-time nitrate sensing system would allow site- specific control of fertilizer application rates. Better control of fertilizer application could have a positive effect on crop production profitability while also reducing the amount of nitrate that leaches from farm fields and contaminates drinking water sources. In this research, an intact core extraction procedure was tested that might be used in the fiel for real-time prediction of soil nitrates. An extracting solution was pushed through a soil core held between two filters, and an ion selective field effect transistor/flow injection analysis (ISFET/FIA) system was used to sense soil nitrates in real time. Laboratory tests were conducted using four soil types, and two levels of nitrate concentration, soil moisture, core length, core diameter, and extraction solution flowrate. The extraction solution flow was sampled at the exit face of the core and routed to the ISFET/FIA system. The ISFET output voltage was sampled at 100 Hz. Results of the test indicate that nitrate extraction and washout occurred in the soil cores, and that peak slope, and cumulative area data descriptors of the nitrate extraction curve indicate prediction in a few seconds. The presentation will include discussion of the significance of the variables tested with regard to the development of a real-time nitrate sensor for field use.