For one thing, you're in a low rainfall region.

Normal rainfall here is 48-54 inches per year. Is that low?

This post was edited by TXEB on Sat, Jul 27, 13 at 22:09

Those numbers are much higher than what the National Weather Service lists for most of Texas except Corpus Christi and Houston. That is about twice what we get here in Michigan.

kimm - yep! I'm about 50 miles south of Houston. The NCDC Report No. 81 ("Monthly Station Normals of Temperature, Precipitation, ... 1971-2000", Report 81) shows our area annual normal to be 51.73 inches. Last year, second in a continuing drought we had a total of 38.45 inches at the NWS reporting station 2 miles north of my house. Last I checked, we get more than Seattle. We're NOT in a low rainfall region, just the opposite.

Pass this along for anyone who is interested in historical climate data for their area in the U.S. The monthly station normals for 1971-2000 may be obtained in pdf report form, by state, from the link posted below.

The newer report series covers 1981-2010 and may be viewed online via the site at the url:
http://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/climate-normals/1981-2010-normals-data

I just realized the '71-'00 includes the NWS reporting station 2 miles north of my house. That period report shows the annual normal precip amount to be 57.24", the '81-'10 data series shows 50.86". Guess that's life on the Gulf Coast, variable.

kimm - where I lived in MI shows 31.94" for the '81-'10 period.

Here is a link that might be useful: Monthly Station Normals - CLIM81

54 inches would be very high for North Dakota, but perhaps skimpy for some high temperature places. Still 54 isn't low I imagine.

Where I am, the limestone bedrock [Wabash Formation[ is 60 feet down to the top of it.

That is about the same precip we get here. But no naturally-occurring calcium carbonate, or if there was any it's buried deep under glacial till.

So even with all that rain there is no leaching from the soil, basically, right? Because of the self-sealing clay?

When saturated the clay does become essentially self sealing. But short of that there is some movement down with rainfall, but there is also movement up from capillary action in the clay as water distributes horizontally beneath the surface. Indeed the subsoil levels of calcium carbonate rise considerably, in some areas north of me to the point that the clay becomes very pale gray a few feet down.

edit - added afterthought ... I didn't mention this but this is essentially clay, and not much else. It has a lot of ion binding capacity.

This post was edited by TXEB on Sun, Jul 28, 13 at 20:22

That you live in east central Texas is of much greater use for many of us than the United States you have listed as well as that USDA Plant Hardiness Zone of 9a which tells us nothing more then which plants should survive a normal winter where you are. For some of us somewhat familiar with Texas that would tell us that the soil you have is clay and your weather tends to be a bit wetter then most other places and that most all of the rain runs off the soil instead of soaking in, which means that that clay would tend to be alkaline.

kimm - apparently you don't follow posts much. All of that has been repeated many, many times. Did you miss the first sentence of my original post in this thread? And it's SE Texas (50 miles south of Houston, 12 miles from the Gulf Cost), not east central TX (that would be the Piney Woods region).

Actually, a lot of rain soaks in, so long as we haven't reached near saturation levels. We get to primarily runoff when we get tropical systems that hit us with an inch or more per hour for 4-24 hours. Haven't had one of those in at least 5 years. Our terrain is very flat. About the steepest natural grade from where I am is if you head NW perpendicular from the coast. Over at least 75 miles that grade is

This post was edited by TXEB on Tue, Jul 30, 13 at 6:16

Tex, Do you have standing water very much? Also I am wondering if you are in Matagorda county? The pictures in the soil types sites around your area show mostly grazing with some cotton....and very flat terrain.

Also I wonder if you have a limestone bedrock close to the soil or just chunky layers of calcium deposits.

wayne - one county east, Brazoria, and I'm in the southern portion. But, Matagorda is very similar. Both are part of the TX Coastal Plain. Outside of urban developed areas, when we get toad stranglers or a tropical system, we'll get standing water on naturally contoured (i.e., very flat) land areas. But normally there is enough lapse between successive rainfalls that the clay soils soak it up faster than most would believe. If you get the soil saturated, it will expand enough to seal. That's one of the reasons rice has historically been a major crop for the region. Not sure if that will continue because of issues with water rights. No bedrock anywhere near the surface - the limestone here was incorporated via successive flooding/reversion during the late Cenozoic period that led to the final withdrawal of the Western Interior Seaway. The deposits are quite deep, but the limestone is well distributed due to the successive flood/reversion cycles that occurred over millions of years..

Results from the Aggie Soil lab ...

pH = 8.0
Calcium = 5,366 ppm

That's our native clay soil.

Apparently after 9 years of no P-containing feeds and mulch cutting I actually managed to get the P down to 10 ppm, so now I need to add P to get it back to ~ 50 ppm(amazing in my experience with our soils). Also surprising to me is I've managed to a accumulate 2.6% organic matter.

I would have thought in such a heavy soil it would be easy to achieve high SOM, even excess? 2.6 is not much, our poorer soils around here will have more than that after years in grass.

pat - heat (prolonged) + moisture (it's irrigated as needed) = low SOM.

I'm impressed with anything not amended or mulched over 2%. Some of that will, no doubt, came from grass roots/hairs, etc.

Potassium and calcium compete for the same holding/exchange sites on a soil...calcium competes much more effectively.

Over time rainfall/watering and weathering will drive more P out of the soil than Ca if there's a lot of Ca around even if there's an excess of P.

On Ca - I've talked several times about our soils with the Aggie soil docs and a very knowledgeable county agent who is the local soil guy. I've come to the conclusion that what we have is what we're going to have. It stems from high natural levels of carbonate, that gets higher as you go deeper. Several feet down the levels are 10,000 - 35,000 ppm. In a predominately clay soil that is well known for moving water upwards via capillary rise, there is no hope of leaching - it tends to equilibrate vertically, like a damp sponge sitting on top of a pool of a saturated calcium carbonate solution.

P has always kept me perplexed. Our soils have the reputation of accumulating P quite easily. I would think that with the abundance of Ca it would be largely paired with Ca, and because of the abundance and the very sparing solubility of Ca phosphate (Ksp of ~ 10-33), it would basically just sit there. I am pleased, but still perplexed on how it moves out of the upper levels under alkaline conditions.

This post was edited by TXEB on Tue, Aug 13, 13 at 20:58

If you are raising produce or farm crops on that soil, some phosphorus will be removed with the crop unless the P also moves upward by capillary action....providing the subsoil has spare P.

If Ca and K compete for the same sites, does adding calcium knock some K out of the exchange?

Generally, yes, Ca will knock K out of the exchange, but a lot depends on the amount of Ca and K. If there is a whole lot of Ca in relation to K, the amount of K becomes a bit moot even if it's high because Ca will generally out-compete for exchange sites. If there's just a similar amount or smaller amount of Ca than K then the K amount may remain rather stable in the soil or leech slower.

Ca competes much better than K for exchange sites. Think of soil as being a piece of metal and Ca/K being magnets of different strengths...with Ca being a stronger magnet that can not only cling better to an exchange site, but push out K into the soil solution (and away from holding/exchange sites) easier for a site that K already holds. This makes K leechable while the Ca sticks around.

Al > H > Ca > K > NO3 > Na...etc

That said, we're talking about a MEGA TON (not very scientific, but whatever) of exchange sites in your soil...and just because something competes better doesn't mean it competes with 100% brute force. Even the weakest of competitors will still be found on exchange sites...it just may not be as much as more prominent competitors depending on the amount found in the soil. In the South-East soils are full of extremely strong Al, but Ca/K added to soil doesn't exactly wash out of the soil like it's nothing.

As an aside...raising pH doesn't make the Al go away, it just makes it a form that's plant unavailable. The Al is still strongly in the soil and on exchange sites, but the way it's complexed in higher pH soils makes it a form of Al that plants won't uptake and therefore won't suffer from toxicity.

btw -- the K level was 204 ppm, and Mg was 480 ppm.

nc - if I try to think through the myriad of ionic equilibria involved, and focus just on Ca, wouldn't the Ca that ends up being associated or paired with exchangeable sites on say clay particle edges first have to exist as a soluble form in the soil solution, then associate with the clay particle, thus lowering the concentration in the soil solution, at least temporarily? What I'm trying to wrap my head around is the equilibrium balance of Ca between the scattered solid limestone in the clay with available Ca in solution, and that held on exchange sites. It leads me to believe that when tested with a Melich 3 solution, more Ca shows up in the test via limestone dissolution than exists as plant available, either as exchange site bound or as soluble in the soil solution.

After pondering the equilibria overnight, I tend towards the disappearance of P over time is most probably a result of P being "fixed" as a highly insoluble complex with Ca (headed toward apatite, or something similarly intractable). Since this is soil under turfgrass that only gets mulch mowed, the only routes I can see for a true loss of P are leaching vertically, or loss with soil runoff, nether of which is very likely for different reasons. It seems that in an alkaline soil with a lot of free lime that P leaching isn't going to much occur, but that re-speciation from soluble into very insoluble Ca-phosphate complexes does occur, although very slowly, and this is what leads to the analytical disappearance of P as it becomes truly sequestered.

The general way that exchangeable cations/anions sites get into the soil to do their thing is through water/moisture or weathering.

Depending on parent material of the soil minerals, you will always have some sort of exchangeable "nutrient" in your soil, whether it's Ca or Fe or etc...such as the high Ca parent material found in your soil.

Clays exchange charges on their edges/surfaces and occasionally between layers, but the clay/mineral itself is made up of unavailable cation/anion materials building the structure of the mineral soil, itself. It's not exchangeable because it's making up the actual structure of the soil and it's protected by it's structure.

Edges/surfaces are exposed so it's easier for charges to take/give...it's a very minor part of the overall bulk of the mineral, but it's crucial to the exchange/holding of charged nutrients. When weathering breaks these minerals up there's new/fresh edges/surfaces exposed.

Freezing/thawing, compaction, roots displacing soil, water/moisture, and a few other things can all weather minerals and create new areas for charges to hold/exchange "nutrients"...as well as release parent mineral materials into the soil solution.

And you didn't even mention that our tap water is usually over 8 on the PH scale :-) The limestone base affects everything.

Where I am it runs right at 8. But it is quite hard.

"Freezing/thawing, compaction, roots displacing soil, water/moisture, and a few other things can all weather minerals and create new areas for charges to hold/exchange "nutrients"...as well as release parent mineral materials into the soil solution"

One of the few other things potentially being the mechanical grinding of appropriate rocks. Or the retreating of an ice-age and subsequent blowing of fresh rock powder around the globe.

With ground water at or above ph8 you guys can probably make hominy without adding a basic agent.

"With ground water at or above ph8 you guys can probably make hominy without adding a basic agent."

Nah - a moderate strength solution of baking soda has a pH of ~ 8.3-8.5.

Texas seems to have mineral well and spring water...Sweetwater, Texas,,,,,,.Minerals Wells, Texas, and probably many more.

In central florida the groundwater makes passable hominy, doesn't get the skins off completely but softens them a lot.