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Marilyn Chambers - President

Email: Marilyn@TRI-COrganics.com

Telephone: (909) 590-1790

P.O. BOX 1367
Chino, CA 91708-1367

November 7, 2000 In response to questions regarding the use of humates in sodium-rich soils: If your soil and irrigation water are high in sodium, then you need to treat as soon as possible with gypsum and humates. Gypsum + leaching with excess water will cure the problem (unless your irrigation water is very high in sodium). The problem is that the sodium is destroying your soil structure, making it hard to leach. In addition, sodium is adsorbed to the CEC sites in your soil.

Here's how you can alleviate the problem, in general. I can also work with you on a recommendation specific to your soil type & soil + water test reports.

Reduce the sodium level

The Sodium needs to be brought down to less than 10% of your soil’s cation exchange capacity, or to a Sodium Adsorption Ratio (SAR) of less than 8. For every meq Na per 100g sodium (from the soil test report) you will need to add 3/4 ton of gypsum per acre.
This is your first priority!

Leaching

The next thing you need to do is to leach with enough water to move the sodium out of the root zone. How much is that? For medium textured soils, that's about 2 inches of extra water per foot; or about 6 inches of water after the soil is at field capacity (very moist) to get the sodium down about 3 feet. If the water you are using has high sodium, you will have to add more. If you have a fine textured soil you will need to add additional water because of the increased water holding capacity of the soil, and because finer soils can wick up sodium laden water from deeper depths to the soil surface.

When gypsum is added, the calcium, which binds much more strongly to CEC sites than sodium, will replace or knock off the sodium from the exchange sites and into solution where it now can be leached. In addition, the calcium will flocculate the soil, opening up some pores so that the sodium will leach downward more easily with the excess irrigation water. The leaching, if done with enough water, will move the sodium down and out of the root zone or capillary zone of the soil.

When gypsum is added, the calcium, which binds much more strongly to CEC sites than sodium, will replace or knock off the sodium from the exchange sites and into solution where it now can be leached. In addition, the calcium will flocculate the soil, opening up some pores so that the sodium will leach downward more easily with the excess irrigation water. The leaching, if done with enough water, will move the sodium down and out of the root zone or capillary zone of the soil.

Humates speed the process

You should also add 150 - 400 lbs humate per acre the first year, and more if the sodium levels are very high and if you can afford to do both. Adding humates will help to speed the remediation process. How do humates help? Even without leaching, humates will help the plants tolerate salt stress. With leaching, humates will help remove excess salt and sodium.

Humates facilitate leaching

Humates increase the strength of soil aggregates, or soil structure, by a phenomenon called cation bridging, which opens pores, making it easier to leach the sodium after the gypsum is added. The calcium and the humate molecules themselves will flocculate the clay, opening pores for water (which now has free sodium dissolved in it) to pass through. The water then can transport sodium and other salt anions (like chloride, sulfate & bicarbonate) down through the soil.

Humates will also provide some acidity to help exchange off the sodium, and help to reduce the high pH caused by the sodium. The calcium in the free lime will replace the sodium on the clays and organic matter. If free lime is not present, the hydrogen acidity will do the same thing.

Humates increase salt tolerance

The humic and fulvic acids in humates are taken up directly by plants. In addition to increases in plant growth rate, root development, nutrient availability and uptake, humates increase tolerance to salt and drought stress by enabling plants to develop increased control over their stomates, which helps them regulate water use more precisely. In addition, humates help plants to synthesize heat-shock proteins. Under salt or water stress, the plant cannot use enough water to cool itself, so tissue temperatures can get very high (one way to tell if a lawn needs watering during the heat of the day is to walk across it barefoot. If it is hot, then the grass is not transpiring enough water to cool itself). Heat shock proteins help the plasma membrane of the plant cells stay intact under the heat stress.

Sodium in irrigation water

If your irrigation water has excess sodium, then some leaching must be done each year after the treatment to prevent sodium from building back up in your soil. Yearly additions of humates will help keep the soil open and porous.

Summary

It is important to understand that the function of humates is an important enhancement in this process due to the functions listed above. However, humates alone will not "cure" the sodium problem, unless added in massive quantities (about 3 tons per acre for each meq. of sodium reported in the soil test). You must add gypsum and leach!

MICHAEL C. KARR, Ph.D. - Certified Professional Soil Scientist

EDUCATION & CERTIFICATION

Taught and passed National & State (NY) Certified Crop Advisor Exam - Feb. 1995

Certified Professional Soil Scientist - 1993, Amer. Reg. of Cert. Prof. in Agronomy, Crops and Soils.

Ph.D. Soil Fertility - August 1988, Purdue University, W. Lafayette IN.

M.S. Soil Chemistry - 1985, Purdue University, West Lafayette IN.

B.S. Soil Science, Magna Cum Laude - 1982, Calif. St. Polytechnic Univ., Pomona, CA.

B.A. Behavioral Sciences, Cum Laude - 1978, Calif. St. Polytechnic Univ., Pomona, CA.