Kevin J. Sibley

Field-scale validation of an automated soil nitrate extraction and measurement system

One of the many gaps that needs to be solved by precision agriculture technologies is the availability of an economic, automated, on-the-go mapping system that can be used to obtain intensive and accurate ‘real-time’ data on the levels of nitrate nitrogen (NO3–N) in the soil. A soil nitrate mapping system (SNMS) has been developed to provide a way to collect such data. This study was done to provide extensive field-scale validation testing of the system’s nitrate extraction and measurement sub-unit (NEMS) in two crop (wheat and carrot) production systems. Field conditions included conventional tillage (CT) versus no tillage (NT), inorganic versus organic fertilizer application, four soil groups and three points in time throughout the season. Detailed data analysis showed that: (i) the level of agreement, as measured by root mean squared error (RMSE), mean absolute error (MAE) and coefficient of efficiency (CE), between NEMS soil NO3–N and standard laboratory soil NO3–N measurements was excellent; (ii) at the field-scale, there was little practical difference when using either integer or real number data processing; (iii) regression equations can be used to enable field measurements of soil NO3–N using the NEMS to be obtained with laboratory accuracy; (iv) future designs of the SNMS’s control system can continue to use cheaper integer chip technology for processing the nitrate ion-selective electrode (NO3−–ISE) readings; and (v) future designs of the SNMS would not need a soil moisture sensor, ultimately saving on manufacturing costs of a more simple system.

Laboratory evaluation of the ion selective electrode for use in an automated soil nitrate monitoring system

Abstract Environmental pollution partly caused by excessive use of nitrogen fertilizer is focusing the attention of the agricultural industry towards prescription farming. It has been suggested that fertilizer application rates should be varied in response to the in situ nutrient concentrations of the soil. The time consuming nature of present methods of soil nitrate testing limits their suitability for in situ use. The nitrate ion‐selective electrode was tested in the lab for its suitability for use in an automated soil nitrate monitoring system. Tests were conducted to evaluate the parameters of soikextractant ratio, extract clarity, and electrode response time. Results indicate that with proper calibration, the electrode is suitable for in situ measurement of soil nitrate concentration and reliable readings may be obtained in less than four seconds.

In-field measurement of soil nitrate using an ion-selective electrode

Standard laboratory methods for measurement of soil nitrate (NO3–N) use various procedures and instruments to analyze soil samples taken from the field and transported to the laboratory. Concerns with these procedures range from delays in measurement time, the high cost of soil sampling and analysis, high labour requirements, and the need to aggregate samples. With recent advances in using the ion-selective electrode, as presented in this chapter, soil NO3–N can now be measured directly, rapidly, accurately, at low cost, at a fine scale, and in real-time right in the field. This chapter describes the methodologies and procedures for how this can be done and provides experimental data and results from data analyses that validate measurements of soil NO3–N obtained with a prototype soil nitrate mapping system (SNMS) developed at the Nova Scotia Agricultural College, Truro, Nova Scotia, Canada. These advances in the in-field use of the nitrate ion-selective electrode (NO3 –ISE) provide the ability for (i) assessing soil nitrate variation, (ii) linking soil nitrate variation to crop growth, (iii) developing site-specific crop management practices, and (iv) environmental monitoring of soil nitrate. This chapter will begin with a discussion of the concerns with nitrate in the soil and environment, precision agriculture and site-specific crop management, variation in soil nitrate and its links to crop growth and yield, and issues with assessing soil nitrate variation in a field. Next will be a discussion of ion-selective electrode theory and application for measuring soil nitrate, followed by a presentation and discussion of early experiments conducted for determining electrode operating parameters to enable the electrode to be used in a soil slurry. The development and testing of the mechanical system used for soil nitrate extraction and measurement along with a description of the control sub-unit, measurement methodology, and operation of the nitrate extraction and measurement subunit (NEMS) for using the NO3 –ISE in the field will be presented. And the results of experiments used to validate in-field measurements of soil NO3–N obtained with the ionselective electrode will be presented and discussed. There will be a discussion of what is 1