Add organic matter to buffer the pH. It is just fine at 6.6 otherwise.

Don't bother. If you re-ran the test with a different set of samples it would be slightly different.

organicdan

That's all it would take? I'll bet this reading is the clay's natural state.

I haven't added any organic matter to this 40 x 4-ft soil area, which is beyond my raised beds. I used the area to grow a few ears of corn and a strip of pole beans last year. I was planning to add compost this year to the 24 ft. tomato bed I plan for that area, though I probably won't do it for the remaining 16 feet, where I'll plant pole and bush beans. They're supposed do well in 6.6 pH.

But I guess it won't hurt anything to pay attention to the pH required for optimal vegetable growth. Some don't do well with a pH that high.

I did find this online advice: Lowering the soil pH to make it more acid If your soil needs to be more acidic, sulfur may be used to lower the pH if it is available. To reduce the soil pH by 1.0 point, mix in 1.2 oz of ground rock sulfur per square yard if the soil is sandy, or 3.6 oz per square yard for all other soils. The sulfur should be thoroughly mixed into the soil before planting. Sawdust, composted leaves, wood chips, cottonseed meal, leaf mold and especially peat moss, will lower the soil pH.

The corn and beans can handle a pH range of 5.5 - 6.8 with good nutrient cycling (healthy soil). The average pH range for most vegetables is specified as 6.0 - 6.5 in mixed plantings. Egg plant, okra and peppers have an upper limit of 6.0.

The nutrient availability at 6.6 will only mildly limit iron. My suggestion of organic matter will aid in buffering potential fluxuation of the pH while also contribute to nutrient cycling.

Unless you are growing a specific crop needing the lower pH, the adjustment is not required. It can be considered an unnecesary expense. In a mixed garden you are best to go with the average requirement.

Good luck.

Thanks, Dan.

The optimal pH for soils ranges from 6.2 to 6.8 because in that range the majority of essential nutrients are most available to most plants. As Dan indictes adding organic matter can help buffer, not totally necessary for you, your soils pH.

organicdan said, "Egg plant, okra and peppers have an upper limit of 6.0"

I have the usual alkaline desert dirt (usual pH in this soil is 7.5-8) and my chilis, okra and eggplant thrived in it with minimal amendment. I was sending huge baskets of them to the office with my house-mate.

I scattered some soil sulfur and ammonium sulfate on the dirt, covered everything with 4-6 inches of shredded palo verde trees and dug small holes to plant.

Plants aren't as delicate as you may think. the link below gives OPTIMAL pH, but you can grow veggies outside those ranges ... only the acid-loving things like blueberries are picky.

Here is a link that might be useful: Optimal pH for Veggies

I wouldn't bother to make any adjustments. I think you'll find most plants will perform very well under those conditions and the adjustment is so slight as to be insignificant.

Most plants will tolerate - perform as expected without problems - in a rather wide range of soil pH. And since your soils test out well within the preferred range for the majority of plants and the greatest nutrient availability, I doubt you will have any concerns. Even acid lovers don't need extremes. Blueberries grow like weeds here and produce bumper crops at our natural pH range of 6.3-6.8. As do peppers and eggplants - they are only limited by our lack of summer heat, which can hinder satsfactory ripening.

I would add organic matter, however - it increases fertility as well as adding to the soil texture and improving drainage. btw, gypsum has no affect on altering soil pH.

gardengal

Then what does gypsum DO since it's recommended to treat soil?

Gypsum (calcium sulfate) supplies extra calcium and sulfur to those crops that need it....all without altering the pH. For example, if you visit an agricultural supply store during soil prep time for cabbage (or any of those Cruciferous veggies), you'll see the gypsum fly out of the warehouse like crazy. The crop takes the sulfur up in large volumes and it will be replaced every year.

Most plants can benefit from calcium, if there isn't enough in the soil to meet their needs. Liming products increase the pH, but gypsum doesn't.

Gypsum can also be used in sodic soils, or in locations with a high saline water table, or salt water intrusion, or salt in the well water to 'remove' the sodium from availability status. I've sure had to use it on a number of occasions for one or more of those reasons. Coastal golf courses order it by the tractor trailer load.

Late here, but I also don't see why 6.6 needs to be brought down. Gypsum can improve structure in some clay soils, but OM might be better in the veggie garden.

Dan

Thanks for offering that explanation, rhizo :-)

Gypsum's benefit as a soil conditioner is greatly over-stated - most extension service bulletins will explain that well. Here's an excerpt from my own: "Gypsum (calcium sulfate) has been promoted as a soil amendment to improve soil structure. In the vast majority of cases it will not work. Gypsum only improves structure when the problem results from excess sodium in the soil, a rare condition in Washington."

And here's the word from a GA gardening pro which might be more relevant to your location:

Here is a link that might be useful: Gypsum....as a soil amendment.

Ditto Ggal on the sodic soils. And followed by leaching irrigation.

Gypsums benefit with soils is where you have a sodic soil. The Calcium Sulfate binds with the excess sodium in those soils so they are no longer a major problem. Beyond that, as Gardengals link explains, Gypsum is of little value as a soil amendment.

Gypsums benefit with soils is where you have a sodic soil.
That part is right.
The Calcium Sulfate binds with the excess sodium in those soils so they are no longer a major problem.
That part is.......less right. ;)

Gypsum provides calcium, which helps in two ways.
A bit of set up: Clay and organic matter carry a negative charge while both calcium and sodium carry a positive charge. The positive atoms (sodium and calcium) "stick" to the negative soil particles; kind of like magnets. Sodium has a positive charge of +1 and calcium has a positive charge of +2.
First benefit: The calcium that is provided by gypsum will displace (aka: take the place of) sodium on the exchange (surface of negatively charged particles). When sodium is floating around in the soil solution rather than being stuck (aka: "adsorbed") to soil particles, it is free to be flushed out of the active root zone with water.
Second benefit: Sodium, with its charge of +1 can only stick to one negatively charged soil particle (clay or o.m.) at a time. It will take up that little chunk of the soil surface and not bind to anything else. With enough sodium on their surfaces, the particles won't be able to stick together.

[Clay Particle]+Naooocolor> Na+[Clay Particle]---Sproing!--->

Calcium's +2 charge will allow it to stick to one particle and grab another at the same time.

"Click"--->[Clay Particle]+Ca+[Clay Particle]This helps the particles stick to gether (aka: "floculate"). It is that sticking together that allows the soil to form structure. The structure facilitates good air and water movement. Since water can now move through the soil, it is possible to leach sodium.

Sigh. Mr BigWords up there used 'flocculate' when I worked real hard to keep it out of my reply. Humph. Thanks for showing us up. ;o)

The CaSO4reacts more bettah and binds more tightly with ions to displace Na+ . Hopefully the sodium leaches out after the reactions take place.

But this takes place only in some clay soils and the Gypsum Industry's assertions that every homeowner should apply Magical Gypsum to make their flowers the envy of the neighborhood and Daddy's lawn praise-worthy is simply hokum. And practically nowhere in these reactions do H+ ions magically appear freely to bop around in the soil to react and lower pH.

Dan

So the posters here are a flocculation of wanna-be organic gardeners?

[FWIW, that word is also frequently used in city sewer system plans.]

Mr BigWords up there used 'flocculate' when I worked real hard to keep it out of my reply.

I spelled it wrong. That's gotta count for somethin'! :P

So the posters here are a flocculation of wanna-be organic gardeners?[FWIW, that word is also frequently used in city sewer system plans.]

I had an old GF who was never on time to anything and we used to say flocculate often when she walked in the door.

Thank you. I'll be here all week.

;o)

Dan

Gargwarb: didn't I say the same thing just before Kimmsr's post :-). Thanks for the details I was too lazy to include.

Michael

Composted pine needles, oak leaves, and peat moss will help lower ph slightly if used in large amounts in frequent intervals for several years. My SW Virginia red clay started at 6.9, after 3 1/2 years adding several hundred Lbs. of compost bi-annually it's now down to 6.7. I read that wood ash is full of potassium but it will raise Ph so I use very little.

DS
I had an old GF who was never on time to anything and we used to say flocculate often when she walked in the door.

Very clever! To those not familiar with it, there's something vaguely obscene and definitely funny about the sound of that word and whatever meanings of it people might guess at. Did she look sheepish?