7/25/2011 7:07 AM
Flushing is the key. Not just extra water, you need to run enough water until it flows through your drain tile. Depending on your soil struture and organic matter it could be as much as 120 minutes per head or more. Run heads until water starts running off the surface than let it soak for 20 minutes. Repeat the process until water flows out of your drain tile. Typically unless you have push up greens it takes 60 to 90 minutes per head.
You really haven't given enough information to determine what product to use along with your flush. You mentioned black layer; if you have excess sulfur in soil reserve, and excess SO4 in your soil solution the acid and Gypsum will cause more of a problem than the sodium.
Many sources of irrigation water contain dissolved sulfates, which are acid based and can cause low pH soils. The magnitude of the effect depends on the concentration of the sulfates in the water, and the amount of the water applied. If you are using the acid to reduce the soil pH or to buffer bicarbonates, you need to realize that you may be replacing one evil with another. Small amounts of acid used occasionally can be a good tool, but is there any research that shows when enough is enough? If there is I'd like to read it.
I'm always less concerned with high bicarbonates soils than I am high sulfate soils, simply because of soil structure. Although research shows excess sulfur and SO4 have very little affect on plant growth, the waterlogged soils caused by the excess does.
Calcium is associated with high bicarbonate soils, and because of its base density and double positive charge it's held tightly to the soil colloid. Calcium also flocculates the soil because, one of its positive charges can attach to one soil particle while the other attaches to a second; producing air space between the two.
Sulfur on the other hand, does not attach to the soil colloid, because it is negatively charged. High sulfates are typically associated with poorly structured and waterlogged soils. When elemental sulfur comes in contact with H2O it strips oxygen off of the water molecule. Sulfur also seeks out free oxygen in the soil because sulfates need 4 oxygen molecules to form the compound (SO4). If the soil is not sufficiently flocculated (oxygen rich) it will collapse, squeezing out the air pores replacing them with water pores. Unfortunately it doesn't end there; the two free hydrogen's released from the water lowers pH or attaches to the SO4 molecule to create H2SO4 (sulfuric acid). Isn't sulfuric acid what your paying a lot of money to buffer with? Why not just use elemental sulfur it's cheeper. When soils are waterlogged and acidic, beneficial aerobic bacteria are replaced by anaerobic bacteria (purple and green sulfur cyanobacteria). Purple and green sulfur bacterial have very few benefits for high plants, they do produce a little sugar. In fact the black crusty algae that forms in the thin turf areas on greens (mostly in the winter), is cyanobacteria. Are you sure that's what you want to grow?
If sulfur is a problem for you, use organic acids (humic, fulvic, human), penitrating wetting agents, and calcium carbonate to flush the sodium out. Depending on how bad your problem is and your rain patterns will determin how frequently you need to flush. Give me a call 239-707-9974 and I'll give you an email where you can send me a copy of your soil and water sample, and I can give you a more presice answer. Sodium is really fairly easy to manage if you use the products that are specific to your conditions.