Soil p H Paulo Pagliari Department of Soil

Soil p. H Paulo Pagliari Department of Soil, Water, and Climate University of Minnesota

• p. H = – log [H+] • p. H decreases as [H+] increases: 0. 0001 g H+ kg-1 soil will have p. H of 4; change [H+] to 0. 001 g H+ kg-1 soil p. H will go to 3 – ACIDIC • p. H increases as [H+] decreases: 0. 0000001 g H+ kg-1 soil will have p. H of 7; change [H+] to 0. 00000001 g H+ kg-1 soil p. H will go to 8 – ALKALINE

Buffer p. H Sikora Soil p. H water [H+] and [Al+3] on the CEC + OM [H+] and [Al+3] in the soil solution

H+ and Al 3+ in the soil and OM Clay particles • http: //www. google. com/imgres? q=soil+cation+exchange+capacity+minerals&um=1&hl=en&sa=N&biw=1323&bih=958&tbm=isch&tbnid=8 a 0 h. Uiha. Sm 2 zy. M: &imgrefurl=http: //h ubcap. clemson. edu/~blpprt/acid 1. html&docid=o. Ofnbaas 8 sk. S 7 M&imgurl=http: //hubcap. clemson. edu/~blpprt/acid_photos/Buffering 2. jpg&w=467&h=321&ei=z. Rqw. Tsqg. LMGLs. A LT 4 q. Dj. AQ&zoom=1 • http: //www. extension. umn. edu/distribution/horticulture/components/M 1193 fig 02. html

Soil p. H Effects on Soil Properties • Availability of most essential and nonessential elements • Activity of microorganisms • Ability of soil to hold cations • Herbicide performance

Soil p. H Effects on Soil Properties • Availability of most essential and non-essential elements • Activity of microorganisms – p. H 5. 5 - 6. 5 best nitrification and OM decomposition rates • Ability of soil to hold cations

Soil p. H Effects on Soil Properties • Availability of most essential and non-essential elements • Activity of microorganisms – p. H 5. 5 6. 5 enhance nitrification and OM decomposition • Ability of soil to hold cations – As p. H decreases, soil exchange sites get saturated with H+ and Al+3 • cations (K+, Ca+2, and Mg+2) come off exchange sites and may leach out of soil

Soil p. H Effects on Soil Properties

How Does the Soil Become Acid?

Causes of Soil Acidification • Acidic parent material • Leaching of basic cations + Crop removal of cations • Use of Nitrogen fertilizers • Other- Acid rain, industrial emissions, internal combustion engines, etc

Acid Forming Fertilizers • Nitrification • 2 NH 4 + 4 O 2 2 NO 3 + 2 H 2 O + 4 H+ • NH 4+ immobilization • NH 4 + R-OH R-NH 2 + H 2 O + H+

Effect of Nitrogen Fertilizer on Soil p. H Nitrogen Applied each year for 5 years (lbs/a) 0 40 80 120 160 200 Soil p. H* 6. 11 6. 10 6. 02 5. 98 5. 81 5. 68 Aglime needed to return soil p. H to 6. 1 (ton/a) 0. 00 0. 31 0. 65 0. 96 2. 03 2. 72 Nitrogen applied as ammonium nitrate, Walsh, L. M. 1965; * Soil was a Plano silt loam cropped to corn

Aglime Required to Neutralize Acid Forming N Fertilizers Nitrogen source Ammonium sulfate Diammonium phosphate Anhydrous ammonia Urea Solutions (28% - 41% N) Ammonium nitrate 1 Approximation Pounds of aglime needed per pound of Nitrogen 1 7. 5 5 5 4 4

Why do I Need Lime? One year old stand

One year old stand

Lime No lime

Effect of Soil p. H on Crop Yield Response

Liming Reaction in Soil • Calcium does not change soil p. H, rather changes %BS • The oxide, hydroxide, and carbonate present in the lime are the compounds responsible for changes in soil p. H Ca. CO 3 + 2 H+ Ca+2 + CO 2 + H 2 O [H+] decreased p. H increased

Al 3+ Reaction Against p. H Increase Ca. CO 3 + 2 H+ H 2 O + 1/3 Al 3+ Ca+2 + CO 2 + H 2 O 1/3 Al(OH)3 + H+

What Factors Determine the Lime Needs of a Soil • Soil p. H (Active acidity) – determined by soil test (p. H in water) • Buffer p. H (Residual acidity) – determined by soil test (p. H in Sikora) • Target p. H – determined by crop and crop rotation

Target p. H • • • Alfalfa – 6. 8 Red Clover – 6. 3 Soybean – 6. 3 Corn – 6. 0 Pasture – 6. 0 Oats – 5. 8

Target p. H • Rotation of Soybean, Corn, and Alfalfa – Soybean – 6. 3 – Corn – 6. 0 – Alfalfa – 6. 8 • Alfalfa is the most sensitive so the target p. H for the rotation is 6. 8

Is all Lime the Same?

What Determines the Quality of a Liming Material • Purity – measure of Ca. CO 3 equivalency • Fineness – a dry sieving process is used – exact sieves used vary by state

The Purity Factor (Ca. CO 3) Equivalent

What Determines the Quality of a Liming Material • Purity – measure of Ca. CO 3 equivalency • Fineness – a dry sieving process is used

Particle Size Distribution

Particle Size Distribution Effect on Soil p. H

Limestone Behavior in Soil Mixing is critical

Calculating the Neutralizing Index (NI) of a Liming Material

Calculating Lime Rate Soil p. H in water (Wp. H) = 5. 90 Soil p. H in Buffer Sikora (Bp. H) = 6. 79 LR for p. H of 6. 8 = 195 – 28. 4(Bp. H) + 0. 144(Wp. H) LR 6. 8 = 3. 0 ton/a

When Should I Apply Lime?

Any time you can

Choosing Between Liming Materials • Example – 5 tons of 50 -59 NI material at $ 13/ton results in a cost per acre of $ 65 – 2 tons of 80 -89 NI material at $ 16/ton results in a cost per acre of $ 32 – The cheaper product may not always be the best buy

Can the Soil p. H be Lowered ? § Some crops may have lower optimum p. H range § Soil p. H can be lowered by addition of acid-forming fertilizers Elemental Sulfur (S) 2 S + 3 O 2 + 2 H 2 O 2 SO 4 -2 + 4 H+ Aluminum Sulfate [Al 2(SO 4)3] Al 2(SO 4)3 + 6 H 2 O 2 Al(OH)3 + 3 SO 4 -2 + 6 H+ Ammonium Nitrate (NH 4)NO 3 NH 4 NO 3 + 2 O 2 2 NO 3 - + H 2 O + 2 H+

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