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Title: Soil-crop dynamic depth response determined from TDR of a corn silage field compared to EMI measurements

item Woodbury, Bryan
item Eigenberg, Roger
item Nienaber, John
item Spiehs, Mindy

Submitted to: Journal of Environmental & Engineering Geophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2010
Publication Date: 9/1/2010
Citation: Woodbury, B.L., Eigenberg, R.A., Nienaber, J.A., Spiehs, M.J. 2010. Soil-crop dynamic depth response determined from TDR of a corn silage field compared to EMI measurements. Journal of Environmental & Engineering Geophysics. 15:185-196.

Interpretive Summary: Measuring seasonal changes in nutrient content of the soil can help to minimize environmental contamination of manure use. Proper management means balancing the nutrient uptake by the plants with the amount of nutrients available from the applied manure. A method has been developed that can measure plant nutrient removal from soil for an entire field without disturbing the growing crop. However, it can not specify whether the removal is near the surface or deeper. Also, moisture is known to influence its measurement. A second method was used to identify where in the soil nutrients were being removed and monitor the amount of moisture in the soil. By putting the information measured by the two methods together, it was shown that most of the nutrients from the manure were located near the surface. The methods also showed that water had limited impact on the measurements.

Technical Abstract: Electromagnetic induction (EMI) mapping techniques have been used to monitor seasonal soil-crop electrical conductivity (EC) dynamics. These mapping techniques can be affected by many confounding seasonal changes in the soil profile, such as water content or salt leaching. Time domain reflectometry (TDR) has been used to measure localized bulk soil EC and may provide insight to the depth of the dynamic which is driving the EMI response. The objective of this study was to use TDR for clarifying near- surface (i.e. < 0.15 m) and deep (i.e. 0.9 m) soil-crop EC dynamics of an animal waste amended soil as measured by EMI. Seasonal soil-crop EC dynamics measured by TDR and EMI were significantly (p < 0.05) correlated for all surface EC**TDR** treatments and EMI horizontal dipole orientation from field A. Significant correlations were detected between surface EC**TDR** values and EMI horizontal dipole orientation from field B for all treatments except commercial fertilizer without cover (NK NCv). There were no significant correlations between surface or deep volumetric water content ('v) and either EMI dipole orientation for any treatment. The results from this study indicate seasonal soil-crop EC dynamics measured by EMI are driven by surface ionic changes.