SOIL

• Physical elements {TILTH} – e.g. sand, silt, clay, organic material and aggregates (see SOIL {1})

• Living elements (other than plants)

– e.g. nematodes, earthworms, fungi, protozoa, bacteria, insects, spiders, mites… (see SOIL {2})

•Chemical elements –pH and its effect on nutrients

(primary, secondary and micro- nutrients); water; oxygen

SOIL

pH

A controversial topic!!??

pH – a controversial topic

pH – a controversial topic

Author has gardened in Oregon, Canada, California and now lives in Australia – the article was adapted from a book published by MOTHER EARTH NEWS titled, “Book for Wiser Living”.

Research based information

• The previous two slides were not from a source that bases its findings on research.• When looking for accurate

information online, be sure the source ends with .edu or .gov.

• Soil pH is one of the most important soil measurements. It plays a huge role in the availability of nutrients to plant roots, nutrient run-off, leaching and microbial efficiency

Significance of pH

pH 6.5 pH 3.8 & 5

Low pH (5 and below) and low Ca result in damage to root membranes. http://hubcap.clemson.edu

Root development of tomato plants in self-watering containers

Root development in self-watering containers

pH 6.25-gallon (healthy,

white roots)

pH 3.8 in 30 gallon tub (lack of healthy white roots)

What is pH?• p= proportion / H = of H+ ions• Relative concentration of H+ in water–H20 H+ + OH-

–H+ and OH- must always be equal in a neutral solution–Water has properties of both a weak acid

and a weak base.

Significance of pH• Chemical controls (insecticides, fungicides,

miticides)

• Nutrient availability• Root system development• Microbial activity

Significance of pH• Chemical controls (insecticides, fungicides

and miticides)

–Ideal pH range between 5.5 to 6–Acceptable range is 4 – 7

Insecticides and basic pH of water

• The effectiveness of some classes of insecticides is greatly reduced when the pH of the water used for dilution is at or over a pH of 8.

• In these instances, a high temperature also reduces the effectiveness. (Alkaline hydrolysis)

Insecticides and basic pH of water

• Most susceptible are: ORGANOPHOSPHATES (malathion)

-(and DIMETHOATE, a mitecide), • CARBAMATE (Sevin), and some

PYRETHROIDS. • Fungicides are not sensitive to pH.

≈pH precautions not usually on the label≈

Biologicals and pH•A pH over 8 will reduce the

effectiveness of BT (Bacillus thuringiensis)

• Never mix COPPER SULFATE, COPPER OXIDE or BORDEAUX MIXTURE with acidic water…they may produce a phytotoxic effect.

Insecticides/Fungicides and pH

Half life of chemical at different pH values

chemical pH 7 pH 8 pH 9

Carbaryl (Sevin) 24 days 3 days 1 day

Chlorothalonil(Bifenthrin)

Stable below 7 38 days

Malathion 3 days 19 hours 2 hours

Treat ‘em all alike• Rather than try to memorize which

insecticides and miticides are sensitive to pH, threat them all with the same precautions until you are certain that they will be unaffected.

• Using the wrong pH can render the chemical ineffective.

pH of water to dilute insecticide

• pH range of 3.5 – 6.0– Spray– Short term storage of 12 to 24 hours

• pH range of 6.1 – 7.0– Spray– Do not leave in leave in sprayer over 2 hours

• pH above 7 or below 3– Do not use to mix insecticide

St. Tammany Water pHLocation Well Water pH MGFolsom 4.4 ArtFolsom 4.7 Jerry

Lacombe 7.4 Judy

Municipal Supply pH

Madisonville 7.3 Pam P.Mandeville 7.8 Kappy

Folsom 7.9 ArtMandeville 8.8 Julie

Municipal water supplies

Why are they all alkaline

(above a pH of 7)(Because an acidic pH will dissolve

copper pipes over time)

• Optimum pH for most crops is 5.5 – 7 http://soils.missouri.edu

• As soil pH decreases, availability of nutrients are reduced

• As pH drops below 5.5, population of microbes is reduced

• As pH drops below 5.5 solubility of Al and Mn increases along with their toxicity

• As pH drops below 5.5, the effect of Al toxicity and greatly reduced availability of Ca contributes to poor root development and plant growth

Keep pH 6 – 7.2– Ideal for plants (But, some prefer a more acid soil like

blueberries and azaleas while others like it a little more alkaline.) (http://ext.colostate.edu)(http://www.soils.umn.edu)

–Optimum pH for most nutrients is 6 – 7

–Most bacteria like pH between 6 – 7.5

– Fungi and actinomyces OK with a pH of 5.5 – 8 (Actinomyces are anaerobic bacteria with fungal like filaments.)

– Earthworms do best with pH >6.5

Practical significance of pH

• N+/-

• P+

• K+

• S-

• Ca+

• Mg+

• Fe+

• Mn+ • Cu+

• Zn+

• B+

• Mo-

• Al+

Primary nutrients

Secondary nutrients

Micronutrients {Ni+ and Cl-

are sometimes included}

http://plantsinaction.science.uq.edu.au