Quantifying soil carbon, nitrogen, and phosphorus after subsurface drainage installation

summary

Two publications based on findings and results from this work were submitted for publication in 2022. These publications are summarized below.

1. Sherbine, K., A. Frankl, F. Fernandez, L. Pease & A. Cates (2023). Haney Soil Health Test changes with season, not subsurface drainage. Agricultural & Environmental Letters, 8, e20098. https://doi.org/10.1002/ael2.20098
   • This study used the Haney Soil Health Test (HSHT) to monitor changes in soil health following subsurface drainage installation, evaluate seasonal variability in soil nutrient pools, and calculate a potential N fertility credit.
   • Subsurface drainage did not significantly affect the three soil biological indicators used in the HSHT (potentially mineralizable carbon, water-extractable organic carbon, water- extractible organic nitrogen). These indices changed seasonally and annually, but not by drainage treatment. This suggests that variability in environmental factors such as rainfall and temperature have a stronger influence on soil biology than subsurface hydrology.
   • Calculated N credits were highly variable (ranging from 1 to 187 kg N ha-1) but were also unaffected by the presence or absence of subsurface drainage.
     Soil biological indicators did not change abruptly following subsurface drainage installation. Further long-term tracking of these metrics will help to quantify whether these indicators change gradually over time.
2. Frankl, A.*, K. Sherbine*, J. Strock, F. Fernandez, A. Cates, and L. Pease (In Press). Comparing the short- and long-term impacts of subsurface drainage installation on soil physical and biological properties. Journal of Soil and Water Conservation (Submitted: 10/30/22; Accepted: 07/17/23).
   • This study quantified changes to soil properties over time in six subsurface-drained fields in Northwest Minnesota. These fields were grouped into two timescales: three fields were drained prior to 2006, and three fields were drained in 2016 or later.
   • We evaluated three soil physical properties: saturated hydraulic conductivity (Kfs), bulk density, and aggregate stability, and three soil health metrics: water-extractable organic carbon (WEOC) and nitrogen (WEON), and potentially mineralizable carbon (PMC).
   • The fields with older drainage systems had greater Kfs, WEON (all depths), WEOC (15 to 30 cm), and PMC (15 to 30 cm). There were no differences in bulk density, aggregate stability, WEOC (0 to 15 cm), and PMC (0 to 15 cm). We suspect that the increased Kfs resulted from development of preferential flow pathways in fields with older drainage systems. These preferential flow paths could also be areas with increased microbial diversity and activity, indicated by the higher biological indicators in the fields with older drainage systems.
   • Our findings suggest that nutrient losses, soil physical properties, and soil health metrics evolve over time. This knowledge will improve the information provided to growers and help them more effectively manage their soil’s health and reduce nutrient losses into waterways.