What is ph Soil ph Sources of soil acidity Managing soil ph Lime sources and use

Transcription

1 What is ph Soil ph Sources of soil acidity Managing soil ph Lime sources and use

2 ph is the negative logarithm of the hydrogen ion concentration - log [H + ] What is the log of 100? What is the log of

3 ph = - log [H + ] [H + ] = M (moles/liter) - log 10-4 or (-4) ph = 4 Which is larger: 10-4 or 10-6 What is the ph of these two values? Which is more acidic? How many more H + at ph 4, versus ph 6? ph scale: 0 14 < 7 acidic, >7 basic, 7 neutral

4 Two pools of H + in soils Active acidity H + in soil solution Measured b y standard soil tests A very small part of the total soil acidity A few ounces of lime will neutralize Reserve or exchange acidity H + on the cation exchange sites Measured by the buffer ph Takes tons of lime to neutralize Coffee pot example

5 Low base forming cation content of parent material (low Ca and Mg) Acids from organic matter decomposition Acid deposition (acid rain) Leaching of base forming cations Crop uptake of base forming cations Breakdown of N fertilizer, manure, and other ammonium containing materials NH O 2 ---> NO 3- + H 2 O + 2 H + Hydrolysis of water by free Al (low ph only) H + from root exudates

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9 ph is the single most important soil fertility factor Soil ph must be adjusted for the most acid sensitive crop in the rotation Controls the availability of most plant nutrients Enhance nitrogen fixation by legumes Affects the activity of soil microorganisms Reduces Al and Mn toxicity

10 Phosphorus: At low ph forms insoluble complexes with Fe, Al, Mn At high ph forms insoluble precipitates with Ca Optimize P availability by maintaining soil ph between 6 and 7 Manganese and Zn Mn toxic to plants at low ph where compounds are soluble Zn and Mn may become deficient at high ph Mn deficiency, ph 7.8

11 Crop Optimum ph Corn 6.0 Alfalfa 6.8 Red Clover 6.3 Soybean 6.3 Oat 5.8 Wheat 6.0 Blueberry 5.6 Pea 6.0 Snapbean 6.8 Source: UWEX Pub. A2809

12 Lime: Any material which when added to the soil will increase the soil ph Aglime: Ground limestone most common Calcitic - imported Dolomitic domestic Domestic source is less expensive Dolomitic limestone is slightly less soluble Over 3 year period reaction is similar Source: UWEX Pub. A3671

13 Burned lime (CaO) Made by heating limestone driving off CO2 Reacts very fast Costs more Caustic Difficult to store Hydrated lime (CaOH) Made by adding water to CaO Similar issues compared to CaO, but less severe Marl CaCO3 deposits in alkaline freshwater swamps Variable and impure

14 Sea shells Collection issues Must be ground before use Wood ash From fireplaces, wood stoves, boilers, etc. Supply other nutrients (potash) A reason some gardens have very high ph values, use caution when disposing Refuse lime Papermill lime sludge Water treatment residuals Certain biosolids

15 Neutralizing Index (NI) Purity relative to CaCO3 (CaCO3 equivalent) Most aglime Wis. sources are similar Dolomitic limestone actually has a higher CaCO3 equivalent Fineness Finer ground materials react faster because of greater surface area < 8 mesh = not reactive 8 20 mesh = 20 % reacts in 3 years mesh = 60 % reacts in 3 years >60 mesh = 100 % reacts in 3 years Lime recommendations are based on full reaction in a three year period

16 No silver bullet compare NI and prices Wis. Lime law sets NI in groups of 10 Wis. soil test report gives rec. for and Source: UWEX Pub. A3671

17 Soil test report recommends 4 tons/a of lime You have easy access to and lime Forgot that nice chart existed. t/a = 4 t/a x 65 = 5.8 t/a 45 t/a = 4 t/a x 65 = 3.1 t/a 85

18 40 $10/ton vs. 80 $18/t = 5.8 t/a vs = 3.1 t/a 5.8 t/a x $10/t = $58/a 3.1 t/a x $18/t = $55.80/a Other lime purchase considerations.. - Does the quote include application - Rates greater than 4 5 t/a should be split, re-test and apply if needed

19 Spread evenly Proper calibration and overlap Wind issues More difficult on recently tilled ground Mix into the plowlayer For quickest reaction lime should be well incorporated Adjust rate for plow depth Timing Avoid compaction and crop damage Application timing for most lime sensitive crop Winter application??

20 Depth (in) 0 to 2 0 to 2 2 to 4 2 to 4 4 to 6 4 to 6 6 to 8 6 to ph Initial 5 mo. after application 2.5 ton/a rate ph 17 mo. after application Source: Wolkowski, unpublished

21 CaCO3 (calcitic) or CaCO3:MgCO3 (dolomitic) are slowly soluble salts. Dissociate into Ca 2+ and CO3 2- Step 1. The Ca 2+ exchanges for H + on the CEC, displacing them into the soil solution Step 2. 2 H + combine with a CO3 2- to form H 2 CO 3 Step 3. H 2 CO 3 H 2 O + CO 2

22 Gypsum: CaSO4 Potassium carbonate: K2CO3

23 Not practical on a field scale Hi ph gardens, blueberry bushes, azaleas Use elemental S S + 3/2 O2 + H2O 2 H2SO4 (sulfuric acid) Process is mediated by bacteria Takes up to 1 year to complete Limit application rate to 20 lb/1000 sq. ft. Source: UWEX Pub. A2809