Macropore Characterization to Enable the Selection of Practices that Minimize Soluble Phosphorus Loss

Soluble nutrients are believed to be contributing to the recent high-profile impacts in the Great Lakes including excessive cyanobacteria growth (Ohio 2010; Baker et al. 2014).   Retaining nutrients, and especially phosphorus in the Great Lakes region, on crop land is also important to the producer as it is non-renewable, scarce, expensive, exhibits high price variability, and can cause adverse environmental impacts when discharged into fresh water systems.

This research program was designed to quantitatively investigate preferential flow pathways caused by macropores by conducting field analyses using the mobile macropore characterization unit. Such pathways enable soluble nutrients, such as phosphorous, to rapidly migrate through soil, into tile drains, and then to surface water (Geohring et al. 2001; Heathwaite and Dils 2000). Results, along with site characteristics such as farm-management practices, topography, soil texture, depth to water table, depth and spacing of subsurface drains, if applicable, topography, and proximity to surface water, enable the qualitative selection of the best management practice to retain nutrients. This approach recognizes that all farm fields are unique and best practices to maximize nutrient uptake and minimize its transport off site are not equally applicable

What did we do?

Forrer et al., 2000, developed a visual technique to assess liquid flow through microporous soil. The technique entails adding dye to small plots of saturated soil and excavating trenches in each area. This method was expanded by photographing the soil profiles, processing the image to convert pixels with dye to white and soil without dye to black, and quantifying each with depth using MATLAB (Figure 1). The result is an estimate of the amount and extent of the macropores.

Figure 1. Assessment of Soil Macropores
Figure 1. Assessment of Soil Macropores


This technique was packaged into the mobile macropore characterization unit to allow for efficient measurements (Figures 2 and 3).

Figure 2. Mobile Macropore Characterization Unit
Figure 2. Mobile Macropore Characterization Unit


Figure 3. Dye and Water Distribution Unit using Sprinklers
Figure 3. Dye and Water Distribution Unit using Sprinklers

What we have learned?

Five sites across Michigan with varied management practices and soil structure were tested using the newly developed protocol as shown in Figure 4.  

Figure 4. Representative Images from Five Sites using Dye Tracer Study
Figure 4. Representative Images from Five Sites using Dye Tracer Study

What are the next steps?

The mobile micropore characterization unit will be used extensively at an ongoing edge-of-field monitoring research site in Michigan to develop correlations between soluble pollutants in the tile drain water and quantitative macropore characterization. Thereafter, the unit will be used by extension educators for field-specific measurements to help producers decide on the most appropriate best management practices.     


Steven I. Safferman1, Jason S. Smith2, Thiramet Sothiyapai3, Ehsan Ghane4

1 Associate Professor; Michigan State University, Biosystems and Agricultural Engineering; Corresponding Author:

2 Teaching Specialist, Michigan State University, Engineering CoRe

3 Undergraduate Research Assistant, Michigan State University, Biosystems and Agricultural Engineering

4 Assistant Professor and Extension Specialist, Michigan State University, Biosystems and Agricultural Engineering

Additional Information

Baker, D. B., R. Confesor, D. E. Ewing, L. T. Johnson, J. W. Kramer, and B. J. Merryfield. 2014. “Phosphorus Loading to Lake Erie from the Maumee, Sandusky and Cuyahoga Rivers: The Importance of Bioavailability.” Journal of Great Lakes Research 40 (3): 502–17.

Forrer, I., A. Papritz, R. Kasteel, H. Flühler, and D. Luca. 2000. “Quantifying Dye Tracers in Soil Profiles by Image Processing.” European Journal of Soil Science 51 (2): 313–22.

Geohring, Larry D, Oloro V Mchugh, M Todd Walter, Tammo S Steenhuis, M Saleem Akhtar, and Michael F Walter. 2001. “Phosphorus Transport Into Subsurface Drains By Macropores After Manure Applications :” Soil Science 166 (12): 896–909.

Heathwaite, A. L., and R. M. Dils. 2000. “Characterising Phosphorus Loss in Surface and Subsurface Hydrological Pathways.” Science of the Total Environment 251–252: 523–38.

Ohio, E P A. 2010. “Ohio Lake Erie Phosphorus Task Force Final Report.” Ohio EPA OH Task Force.


This project was funded by the Michigan Soybean Promotion Committee, Corn Marketing Program of Michigan, and Michigan Wheat Program. The author wish to acknowledge contributions from Brendon Kelly, Lyndon Kelly, Steve Miller, and the MSU Soil and Plant Nutrient Laboratory.



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