Soil Sampling and Nutrient Additions for Crop Production Edwin Ritchey Extension Soil Specialist UK-REC

Soil Sampling Indicates the current nutrient status of soil A guide for nutrient additions Diagnose nutrient deficiencies or toxicities Saves money Cost is small compared to over/under fertilization 2 Photo, Josh McGrath

Random Soil Sampling Want a representative sample (AFS=2,000,000 lb) Uniform areas - based on drainage, cropping history, erosion, past management e.g. feeding areas (manure), fencerows, etc. Collect at least 10 cores, more for larger areas The more samples (cores) collected, the closer to the true field value obtained Every two years, or so… Fall or Spring? Depth?

MANURE SAMPLING & TESTING Recommendations are only as good as the sample they are based on 4

Determining Nutrients Present H H H H _ _ _ Na + Al 3+ Mg 2+ K+K+ Ca 2+ _ soil pH 5Mehlich 3 NH 4 + Base cations analyzed in leachate

How much fertilizer do I add? Soil Test (UK, Waters, A&L) Considerations for soil lab – Must be easily repeatable – Relatively quick – Must be “equivalent” to what is available to plant Correlation Calibration

Nutrient availability to plants Readily available Slowly available Soil solution

Image: Raising-chicken.org

01 Soil Test P (lbs/acre) Yield (% of maximum) Soil Test P (lbs/acre) Correlation: Is a soil test a good predictor of nutrient ……………………..availability?

01 Soil Test P (lbs/acre) Yield (% of maximum) Soil Test P (lbs/acre) Low Med High V.low Calibration: How much fertilizer is needed below threshold? Arrows represent the amount of fertilizer needed to achieve maximum yield

Response Curve

No Response to Fertilizer

UK Soil Test Levels Low testing soils, expect a yield response to added fertilizers and large amounts are added Medium testing soils, yield response is small to none, add fertilizer to maintenance levels High testing soils, no yield response expected, no fertilizer recommended

Time (years) Soil test P or K 9 lb/ac P 2 O 5 remaining in soil increases soil test 1 lb/ac 4 lb/ac K 2 O remaining in soil increases soil test 1 lb/ac Agronomic Threshold Sufficiency 2 Philosophies with a Low Soil Test

Time (years) Soil test P or K Agronomic Threshold Rapid Build-up

Time (years) Soil test P or K Agronomic Threshold maintenance sufficiency buildup 3 Philosophies with a High Soil Test

Differences in Soil Labs Many labs use Mehlich III extractions – UK, Waters, A&L, etc – Test for pH, Bu pH, K, P, Ca, Mg, Zn “Similar” nutrient results from all labs Differ some in philosophy (so do people) Sufficiency, Maintenance, Build-Up – Micronutrients, Soil Cation Balance

Soil Test Labs One soil sample mixed and submitted to – UK: P = 84 lbs/A, K = 234 lbs/A – Waters: P = 79 lbs lbs/A; K = 243 lbs/A – A&L: P = 47 ppm (94 lbs/A); K = 135 ppm (270 lbs/A) Recommendations for corn – UK: P 2 O 5 = 0 lbs/A; K 2 O = 40 lbs/A – Waters: P 2 O 5 = 85 lbs/A; K 2 O = 125 lbs/A – A&L: P 2 O 5 = 60 lbs/A; K 2 O = 80 lbs/A Differ some, more philosophy than test

High Med Low V.Low Soil Test Level 100% % 50-70% <50% Sufficiency Level Nutrients available from soil External nutrients required soil fertilizer fert. Relative Sources of Nutrients

University of Kentucky AGR-1

K deficiency - yellowing of leaf margins of older soybean leaves. WHY??? Photo: Greg Schwab

What is CEC and How Does CEC Influence Fertilizer Rates in KY?

Cation Exchange Capacity Ca ++ Plant Root H+H+H+H+ K+K+K+K+ H+H+H+H+ K+K+K+K H+H+H+H+ NH 4 + Ca ++ H+H+H+H+ H+H+H+H+ K+K+K+K+ K+K+K+K+ Mg ++ Ca ++ Mg ++ H+H+H+H+ H+H+H+H+ H+H+H+H+ K+K+K+K+ K+K+K+K+ H+H+H+H+ K+K+K+K+ Ca ++ NH 4 + Clay Soil Solution

Determining Nutrients Present H H H H _ _ _ Na + Al 3+ Mg 2+ K+K+ Ca 2+ _ soil pH 5Mehlich 3 NH 4 + Base cations analyzed in leachate

Calculated CEC Measured CEC Number of marbles are estimated Number of marbles are counted

557 Kentucky soils

Uncertainty in Calculated CEC For CEC less than 10 meq/100 g: ± 2 meq/100 g For CEC between 10 and 20 meq/100 g: ± 3 meq/100 g 7 meq/100 g 5 to 9 meq/100 g 15 meq/100 g 12 to 18 meq/100 g

What does CEC and cation saturation tell you? Soil texture (sandy vs clayey soil) % base saturation as another indicator of soil acidity Ability to Buffer Change

Indiana soils

Ag samples with soil pH <= 7 in All counties Year = 2011 Total number = 28, % >18 1 % <10 Frank Sikora, 2012

Ag samples with soil pH <= 7 in Breckinridge, Daviess, Hancock, Henderson, McLean, Ohio, Webster Year = 2011 Total number = % >18 1 % <10

Why Do We Lime? Proper pH is the foundation of a good soil fertility program – BIG BANG FOR YOUR BUCK Adjust soil pH (neutralize acidity) Soil pH influences: – Nutrient Availability – Root Growth – Herbicide Activity Soil pH can limit crop yield w/out noticing

Corn Alfalfa Alfalfa THE MASTER VARIABLE The effect of soil pH on the activity of soil micro- organisms, availability of plant nutrients, and occurrence of toxic elements

Effect of Soil pH on Soil Tests of Nutrients 1.Availability of many nutrients is changed by changing soil pH. 2.Maintaining proper pH will maximize nutrient availability and reduce fertilizer need. 3.Soil tests will rise faster and reduce slower if pH is properly maintained.

Sources of Soil Acidity 1.Kentucky soils have a naturally low pH due to high rainfall and the leaching of calcium from the soil. 2. Main source of acidity in modern farming is nitrogen - Most common nitrogen sources lower pH Urea, Anhydrous Ammonia, liquid nitrogen, and ammonium nitrate. NH O 2-  NO H 2 O + 2H + 3. In general, 3 lbs of ag lime are needed to neutralize acidity from one pound of nitrogen

Sources used to neutralize acidity Lime: Calcitic: CaCO 3 or dolomitic: CaMg(CO 3 ) 2 – CaCO 3 + 2H +  H 2 CO 3  H 2 O + CO 2 Quick lime: CaO Hydrated lime: Ca(OH) 2 Pelletize Lime: CaCO 3 Waste products: biosolids, paper waste, shells Gypsum: CaSO 4 – CaSO 4 + 2H H +  Ca 2+ + SO H 2 O + 2H +

Liming soil H H H H _ _ _ Na + Mg 2+ K+K+ Ca 2+ _ soil pH 5 CaCO 3 Ca 2+ CO 3 2- H 2 CO 3 H 2 O and CO 2 _ _

Liming soil H H H H _ _ _ Na + Mg 2+ K+K+ Ca 2+ _ soil pH 6 CaCO 3 Ca 2+ _ _

Summary Soil testing is the foundation – DON’T GUESS, SOIL TEST Labs differ little in results, more in recs CEC is important, but don’t worry about it Yield responses are typically not seen when soil fertility is adequate Mind the fundamentals pH management – basis of good fertility

Questions or Comments

Manganese Deficiency Symptoms Interveinal chlorosis Photo Greg Schwab

Soil pH Affect on Herbicide Activity 1.The effectiveness of several herbicides is influenced by soil pH. 2.Herbicides in Triazine family (Atrazine and Princep) are widely used with corn. 3.The effectiveness of weed control of Triazines is reduced below a pH of 6.0 and greatly reduced at 5.5 pH. 4.Extends persistence of many Sulfonylurea herbicides above pH 7 and may cause carry over problems.