Florida Land Judging

Land Judgers,

I've received several requests for a guide that helps in determining seasonal high water tables, drainage, and that sort of thing. Let me put it bluntly: such information has never been formally assembled anywhere by any person or agency. We are going to do this very soon.

Water tables, drainage, wetness, etc. is not a cut and dry thing. It varies from sight to sight, soil to soil, and even the concept of a water table is nebulous. It can mean different things depending on the application. In Land Judging we treat it like a straight-forward, simple concept because like everything else in the contest, it’s important for land use recommendations and has to be graded. In reality, where soil water is and for how long, well that is a complex subject. It's not rocket science... it's harder than that.

So as a contestant, you are asked to determine the depth to seasonal high water table and plug that into the other parts of the rules and generate recommendations. That’s fine, but your water table call is your attempt to match what experienced soil scientists call, and that my friends is incredibly challenging.

I will attempt to distill the thought process of a soil professional into a blog style post right here. That's about the best I can do a the moment so here goes:

Step 1) Determine your landscape position. Are you at the top of a hill or on a mostly flat landscape position? If so, expect there to be some build up of a water table. If there is subsurface clay, then definitely expect that. Are you on the steep slope of a hill? You should probably not expect subsurface water to accumulate. It would rather run laterally downhill. There are exceptions, of course, like seepage slopes, but in general steep slopes result in pretty good subsurface drainage. Are you at the bottom of a hill? Expect upslope subsurface water to drain into this soil. Also expect some amount of surface runoff to puddle and perc downward. All this will likely cause a build up of a water table unless there is a sink hole or some other reason for subsurface to quickly leave the soil. Again, we're just generating an expectation at this stage. Now it's time to dig a hole or walk into a pit and look at the soil morphology (that's the patterns of color and texture in the soil, it tells you a lot).

Step 2) Now that you have your expectations, look for clues in the soil morphology. Start at the top of the soil and move your eyes down. Is there a thick, dark topsoil? If so, that’s an indication of moisture and wetter land. Some forest soils have very thin topsoils, so this isn’t always the case. Keep moving your eyes down. Are you seeing dull white/grey colors? If so, that’s further evidence of wetness. What’s happening is that iron has been largely removed from the soil. Is the soil brightly colored? If so, that zone is probably drier so keep moving your eyes downward. When you think you are staring at a really wet zone of the soil, everything below that should continue to look wet. Move your eyes back up to the point where it starts to transition from dry to wet looking. Now stare more carefully and look for the exact indicators of saturation: redox concentations and/or stripping are the indicators in sandy horizons. Redox depletions are the indicators in loamy/clayey horizons.

Pro Tip: well developed Spodosols almost always have a seasonal high water table above the spodic, but closer to the spodic than to the topsoil. You will NOT see redox concentrations above a well developed spodic. You will only see stripping and it's tough to see. If the spodic is not well developed (lighter in color and w/ a fuzzy upper boundary) then the seasonal high water table is either in the spodic or more than likely below the spodic. Look for stripping and/or redox concentrations to tell you where the water table is.

If you are not seeing anything in the sandy horizons, then look at the loamy/clayey horizons. Is the top of the loamy/clayey horizon mostly dull grey? If so, this is really wet and you probably missed the indicators of the water table that perches in the sand above they clay. Go back and double check your observations. If the clay is brighter in color, keep moving your eyes down until you see grey colors. The point at which you see grey colors as redox depletions that occupy 2% of the soil, that's where the seasonal high water table is in the clay.

Call the water table at the shallowest of sandy or clayey indicators and proceed to step 3.

Step 3). Evaluate whether your conclusions from step 1 and step 2 agree. Do they? Congratulations, you are getting good at this and I am honestly impressed. Good Job. Do they disagree? If step 2 was pretty conclusive for you, then you probably just misunderstood the landscape in step 1 and you just learned something. Nice. Pat yourself on the back for improving your understanding. Go with your call in step 2. If your evidence from step 2 was inconclusive or is just seriously violating all that you know to be true based on step 1, then pause. Ask yourself what's going on. Do you just not understand the landscpe? Are you instead struggling with interpreting the soil morphology? At this point, you are going to have to commit to something. I'd advise you to go with what the morphology told you in step 2. Odds are the soil isn't lying to you.

I apologize for the casual nature in which I wrote this. I’m tight on time and this is just meant help the many folks that are calling me in a panic right now. This long blog post is captured in this powerpoint

An expereicned soil scientist knows the land and expects things. The soil morphology helps fine tune the expectations and both ususally agree. Beleive it or not, the "rules" on how to do this are not formalized anywhere. There is no NRCS, UF/EDIS, etc publication you can download and get this from. The necessary information is buried in text books, soil survey reports, and passed along from scientist to scientist. I and some UF folks will change this soon.

Feel free to email me or call me with questions. I hoped this rambling helped some folks.

- Rex