Project and Research Management: Integrating Systems, Data, and People in Multidisciplinary Work (Vol. 5)

This technical report summarizes the experiential and technical knowledge in project and research management from the Sustainable Corn Coordinated Agricultural Project team. The management infrastructure, processes, outcomes, lessons learned, and insights presented in this report will be particularly relevant to directors and managers of other large teams

Estimation of change in soil water nitrate-nitrogen concentration using impedance spectra

A fast and reliable method for in situ monitoring of soil nitrate-nitrogen (NO3-N) concentration is vital for evaluation of N management practices focused on reduction of NO3-N losses to ground and surface waters from agricultural systems. Using dielectric measurements at multiple frequencies can help to estimate several physical and chemical soil properties simultaneously. Hence the goal of this study is to examine the feasibility to estimate changes in pore water NO3-N concentration together with volumetric water content (VWC) from the dielectric measurements obtained at multiple frequencies below several MHz where conductive behavior of soil dominates. An initial experiment with two off-the-shelf capacitance probes showed that at a relatively high frequency response of the probe was primarily correlated with VWC, while measurements at a lower frequency made by the second probe also incorporated the effect induced by changes in pore water ionic concentration. These results confirmed that using measurements at multiple frequencies can provide information about several soil properties, including NO3-N concentration. Consequently two follow-up laboratory experiments used impedance spectroscopy to estimate changes in NO3-N concentration in pure solutions and soil water, respectively, using a multivariate chemometric analysis, particularly partial least squares (PLS) regression. The results showed that change in NO3-N concentration could be estimated with sufficient accuracy when its concentration was greater than concentration of other anions (chloride in our case). In addition, estimation of NO3-N in soil water improved significantly with increasing VWC. A good agreement was found between actual and estimated NO3-N concentration when the PLS model was built using permittivity data obtained at VWC ≥ 0.20 m3 m-3. R2 and the root mean square error (RMSE) of NO3-N estimation for the best model (VWC ≥ 0.20 m3 m-3 and concentration of chloride -1) were 0.84 and 28 mg L-1, respectively. In general, the study demonstrated that PLS regression method coupled with the dielectric measurements obtained at multiple frequencies below several MHz can be used to indirectly estimate VWC and NO3-N concentration, but after the proper calibration equally covering the expected variations in VWC and NO3-N. For in situ application other environmental variables such as temperature should also be incorporated into the calibration process.</p

Response of Capacitance Probes to Soil Solution Nitrate Concentration

Dielectric properties of soil are highly correlated with volumetric water content (VWC) of the medium, but at a relatively low frequency soil salinity has an important effect on permittivity measurements. A laboratory experiment was conducted to understand the potential of monitoring nitrate and chloride ions in soil solutions using capacitance-type soil probes EC-5 and EC-10 operating at frequencies of 70 and 5 MHz, respectively. Dielectric response of soil samples wetted with nitrate and chloride solutions of different concentration were compared at each frequency within the volumetric water content ranging from 0.1 to 0.3 m3/m3. Linear regression models were fitted through data to correlate the actual VWC, concentration of solutions, soil temperature and sensor output. At 70 MHz frequency the sensor response was primarily explained by moisture content for both solutions. Dielectric response of the EC-10 probe to change in ionic concentration was different for each wetting solution. Change in chlorine concentration demonstrated no evidence of having effect on the sensor response, while nitrate solution illustrated that the EC-10 probe is sensitive to the change in nitrate-N concentration within the water content and salinity range tested (from 0.05 to 0.51 dS/m). None of the fitted models demonstrated the statistically significant effect of temperature on dielectric measurements due to the little variation of the temperature (+/- 1.5°C) during the experiment.This is an ASABE Meeting Presentation, Paper No. 097211.</p

Project and Research Management: Integrating Systems, Data, and People in Multidisciplinary Work (Vol. 5)

This technical report summarizes the experiential and technical knowledge in project and research management from the Sustainable Corn Coordinated Agricultural Project team. The management infrastructure, processes, outcomes, lessons learned, and insights presented in this report will be particularly relevant to directors and managers of other large teams.</p

Estimating Soil Solution Nitrate Concentration from Dielectric Spectra Using Partial Least Squares Analysis

Fast and reliable methods for in situ monitoring of soil NO3–N concentration could help guide efforts to reduce NO3–N losses to ground and surface waters from agricultural systems. While several studies have been done to indirectly estimate NO3–N concentrations from time domain spectra, no research has been conducted using a frequency domain technique. Hence, the goal of this laboratory study was to estimate NO3–N concentrations from frequency-response data obtained in a frequency range of 5 Hz to 13 MHz. Dielectric spectra of soil samples wetted to five different volumetric water contents (VWC) with 24 solutions containing different concentrations of KNO3 and KCl were analyzed using a partial least squares (PLS) regression method. Global models could not estimate NO3–N concentrations with sufficient accuracy. Models based on the imaginary part of the permittivity were better than those based on the real part. The PLS model estimates were improved when low VWC data and high Cl− concentration were eliminated, reducing the RMSE for NO3–N from 57 to 28 mg L−1. The best results were obtained when the PLS models were constructed at fixed VWC levels using the data without high Cl− concentration. The performance of these models improved with increasing VWC level, reaching the lowest RMSE of 18 mg L−1 at VWC of 0.30 m3 m−3.This article is from Soil Science Society of America Journal 76, no. 5 (2012): 1536–1547, doi:10.2136/sssaj2011.0391.</p