Date of Award
Master of Science (MS)
Environmental Engineering and Science
Sustainable water resources management requires tools to help farmers identify variations in soil hydraulic characteristics so that precision irrigation schemes can be developed to optimize water use. In this study we use electromagnetic induction (EMI) to evaluate whether changes in the apparent electrical conductivity (σ_a) of agricultural fields can be related to hydrologic processes. Field work for this study was completed at three different sites - 1) in different agricultural fields located in a watershed near Salri, Madhya Pradesh, India, 2) over an agricultural field located near Clemson University, SC, and 3) at a flood plain wetland restoration site near Madison, Wisconsin.
The spatio-temporal study of σ_a for fields in India revealed that σ_a were related with the overall wetting and drying cycles at both seasonal and short term (daily) time scale. It was also found that there was a dependence of σ_a patterns associated with the location of the field within the watershed. The short term EMI mappings revealed that σ_a and changes in σ_a both showed a similar spatial pattern for one of the fields. However, in contrast another field showed emergence of different patterns for both the σ_a and changes in σ_a. Infiltrometer tests were performed to further investigate the field and a better relation, was observed with the measured hydraulic conductivity estimated using mini disk infiltrometer measurements and the changes in σ_a as against the absolute conductivity values.
The cluster analysis performed for the fields in India showed that clustering performed using spatial data was able to capture the two different soil textures qualitatively observed in the field. A Monte Carlo analysis showed that the two clusters always had significantly different means showing that they belong to different clusters statistically as well.
The purpose of the study performed in an agricultural field near Clemson University was to evaluate the relationships between σ_a and soil hydraulic properties. At this site, repeated σ_a measurements were made using Geonics EM-38 MK2 over two rain events. The range of σ_a changed over time as a result of wetting and drying of the field to some extent but the within field spatial patterns of σ_a were relatively consistent. The conductivity values correlated with the water content and finer particles obtained from the soil properties analysis with significant correlation values ranging from R = 0.36 - 0.78 for water content and R = 0.44-0.81 for % fines. The changes in σ_a, however, were not found to show any linear relationship with changes in water content, water retention curves or basic infiltration rate obtained using infiltration tests. The exact reason behind such behavior are unknown and other parameters like fluid conductivity and temperature might be take into account for future studies to investigate it further.
The last part of the study investigated application of EMI to capture the water content and soil variability at a restored wetland location near Madison, Wisconsin. The soil moisture was recorded at the field site using various soil moisture methods including a fiber optic distributed temperature sensor (DTS). The σ_a weakly correlated with the soil moisture however spatial patterns in σ_a and changes in σ_a illustrated the overall wetting and drying of the field. Persistent wet and dry zones were observed along the DTS transect and indicate variations in soil hydrology. The σ_a was able to qualitatively capture a similar trend.
From all the studies performed at different field site, it can be concluded that Electromagnetic Induction can capture the variation in water content, soil texture and could also be related to the spatial patterns present in these soil properties The transient electromagnetic induction surveys however were not very efficient in capturing the changes especially for Clemson field site using the analysis technique adopted in this study. The future work can involve exploring the reasons why this relationship between the change in conductivity and changes in soil properties were not being captured by taking into account the effect of fluid conductivity, porosity and temperature as well.
Gangrade, Sudershan, "EVALUATION OF USE OF EM38-MK2 AS A TOOL TO UNDERSTAND FIELD SCALE CHANGES IN SOIL PROPERTIES" (2012). All Theses. 1457.