Know Your Soil Getting the Dirt on Your Dirt FWAA Dr. Steve Petrie Director of Agronomic Services
Crop productivity Genetics Soil Temperature Environ ment Crop Yield Moisture Manage ment
Take the time to know your soil Getting to know your soil is like meeting a new neighbor Where are they from? What brought them to town? Where do they work? What are their hobbies? All neighbors have different personalities
Soil Personality Texture ph Soil Personality Organic matter CEC
Soil Texture Description of the amount of sand, silt, and clay in the soil Sand > 0.05 mm Silt 0.05 0.002 mm Clay < 0.002 mm Sand is gritty Silt is slippery Clay is sticky Loam has equal feel of gritty, slippery, and sticky
Soil Texture Description of the amount of sand, silt, and clay in the soil Sand > 0.05 mm Silt 0.05 0.002 mm Clay < 0.002 mm Sand is gritty Silt is slippery Clay is sticky Loam has equal feel of gritty, slippery, and sticky
Soil Texture Most important physical characteristic of the soil Knowing soil texture alone will give you information about Fertility status CEC Water holding capacity Water movement Productivity
Soil texture and soil fertility Sand has no effect on soil fertility Silt has little effect on soil fertility Clay holds the key to soil fertility Surface area is the reason More surface area = more reaction
Particle size and surface area Soil is predominantly silica, quartz, and related minerals Silica and quartz density = 2.8 gm/cm 3 (H 2 O = 1) Start with a silica cube that is 1 cm square Surface area = 1 x 1 x 6 = 6 cm 2 /2.8 gm Let s divide the cube into 8 smaller cubes (0.5 cm in each dimension) Surface area = 0.5 x 0.5 x 6 x 8 = 12 cm 2 /2.8 gm Let s divide the cube into 64 cubes (0.25 cm in each dimension) Surface area = 0.25 x 0.25 x 6 x 64 = 24 cm 2 /2.8 gm
Clay particle size and surface area Largest clay particle = 0.002 mm = 0.0002 cm Surface area = 0.0002 x 0.0002 x 6 x 125,000,000,000 = 30,000 cm 2 /2.8 gm 4,651 sq. in. 32 sq. ft. 1 sheet of plywood Is this for real? Yes, plywood is a good analogy for clay because clay forms in sheets that are wide and thin
Photomicrographs of clay platelets
Soil texture and water availability
Soil texture and water availability Complex relationship between water holding capacity and water availability to crops Some water is held too tightly to be taken up by plants
Soil texture and water availability Complex relationship between water holding capacity and water availability to crops Some water is held too tightly to be taken up by plants Silty loam soils have the greatest capacity to store plant available water.
Soil texture and water holding capacity Soil Texture In. of water/ ft. of soil Sand 0.5-1.0 Loamy sand 1.10-1.20 Sandy loam 1.25-1.40 Fine sandy loam 1.50-2.00 Silty loam 2.00-2.50 Silty clay loam 1.80-2.00 Silty clay 1.50-1.70 Clay 1.20-1.50
Soil texture and water movement Soil texture Water movement inches/hour Sand 1.4-142 Silty sands 0.7-4.3 Silt, sandy clay 0.14-0.0014 Clay 0.0014 0.0000014
Effect of texture on key soil properties
Soil ph Sort of like going to the doc. The nurse always takes your temperature and BP. Baseline values that are broadly useful as the doc diagnoses your ailment. Soil ph is a measure of the acidity or alkalinity of a soil It is a measure of the activity of H + ions in the soil solution The ph scale is logarithmic 1 unit = 10x change Changing from ph 7 to ph 8 A 10 fold increase in alkalinity Changing from ph 6.5 to ph 4.5 A 100 fold increase in acidity
Soil ph and nutrient availability or toxicity P K Ca Fe Mn Zn Cu Mo Al Soil ph 5 6 7 8 9 Al is not an essential nutrient Key Essential nutrients Green = optimal availability Yellow = reduced availability Pink = greatly reduced availability Red = toxicity likely Toxic elements (Aluminum) Yellow = potentially toxic Red = toxicity
N Fertilizer Management and Soil Acidity All ammonium-based fertilizers are acid-forming in the soil Ammonium nitrate Urea UAN solution (Solution 32, etc.) Ammonium sulfate Band applications concentrate the acidity More ammonium = more acidity
Acidity from NH 4 and S fertilizers Nitrification of ammonium fertilizers results in increased soil acidity NH 4 + +2O 2 NO 3 - + 2H + + H 2 O Microbial oxidation of elemental S results in increased soil acidity CO 2 + S 0 + ½O 2 + 2H 2 O > CH 2 O + SO 4 2- + 2H + S-SO 4 fertilizers do not increase soil acidity CaSO 4 gypsum K 2 SO 4 potassium sulfate K-Mag 21
Ammonium acidifies the soil Plant uptake of ammonium Soil solution ph NH 4 + H + Root interior
Ammonium acidifies the soil Plant uptake of ammonium Soil solution ph NH 4 + H + Root interior Plant uptake of nitrate Soil solution ph NO 3 - OH - Root interior
Composition of typical N fertilizers N Fertilizer NO 3 -N NH 4 -N Urea Lime Equivalent ------------- % --------- Lbs lime/lb N Calcium nitrate 92 8 0-1.3 CAN-17 68 32 0 0.6 Ammonium nitrate 50 50 0 1.8 UAN 32 solution 25 25 50 1.8 Ammonium sulfate 0 100 0 5.3 More ammonium = more acidity
Nitrogen Fertilizer Effects on Soil ph 7 6.5 End of 20-year study in the midwestern US. Same total amount of N was applied as each source. Different crops were grown and N rate varied appropriately. 6 5.5 5 Check Anhydrous ammonia Ammonium nitrate Urea UAN solution From Darusman et al. SSSAJ 55:1097
Cost of Acidification from N fertilizers Fertilizer Lime demand Lime cost/lb N* Lbs lime/lb of N $/lb of N Calcium nitrate -1.3** 0.05 Urea or Am. Nit. 1.8 0.06 UAN 32 solution 1.8 0.06 Amm. sulfate 5.3 0.17 * Based on lime cost of $65 per ton applied. ** Calcium nitrate has a calculated liming value of 143 lbs of lime per 100 lbs of N. 1/16/2018 27
Cation Exchange Capacity Soil clay particles and organic matter have negative charge The quantity of negative charge varies with soil texture, clay type, organic matter content, and ph CEC is closely tied to soil fertility and nutrient availability in soil CEC keeps cations from leaching
Cations Positively charged ions Sodium Na + Ammonium NH 4 + Potassium K + Magnesium Mg 2+ Calcium Ca 2+ The metal micronutrients are also cations Copper Cu 2+ Iron Fe 3+ or Fe 2+ Manganese Mn 2+ Zinc Zn 2+ 29
Soil texture and CEC Soil texture and OM Typical CEC Meq/100 grams Sandy, light colored 3-5 Sandy, dark colored 5-15 Loam, light colored 10-20 Loam, dark colored 15-25 Clay loam, silty clay loam 30-40 Organic soils 50-100
CEC and base saturation Base saturation is used as an indicator of soil fertility Increasing base saturation indicates greater fertility Base saturation is also an indicator of soil ph
CEC and base saturation Base saturation is used as an indicator of soil fertility Increasing base saturation indicates greater fertility Base saturation is also an indicator of soil ph ph Base Saturation 4.5 0 5.3 25 6.2 50 7.1 75 7.5 90 8.0 100
Soil organic matter Largest single soil factor that affects soil productivity and sustainability Holds nutrients Supplies nutrients Affects water holding capacity and water use efficiency Promotes good aggregation Moderates extremes of soil texture
Soil Organic Matter is Complex Soil organic matter Humus All organic compounds in the soil, except undecayed plant residues and soil organisms
Soil Organic Matter is Complex Soil organic matter Humus Soil biomass All organic compounds in the soil, except undecayed plant residues and soil organisms Living microbes
Soil Organic Matter is Complex Soil organic matter Humus Soil biomass All organic compounds in the soil, except undecayed plant residues and soil organisms Living microbes Humic substances High molecular weight, brown to black compounds
Soil Organic Matter is Complex Soil organic matter Humus Soil biomass All organic compounds in the soil, except undecayed plant residues and soil organisms Living microbes Humic substances Humic acid High molecular weight, brown to black compounds Dark colored materials in soil that are insoluble in acid
Soil Organic Matter is Complex Soil organic matter Humus Soil biomass All organic compounds in the soil, except undecayed plant residues and soil organisms Living microbes Humic substances Humic acid Fulvic acid High molecular weight, brown to black compounds Dark colored materials in soil that are insoluble in acid Colored material left in solution after humic acid is removed
Soil variability is natural
Soil variability is human-caused Land leveling for irrigation Irrigation-induced erosion Field consolidation Tillage Differential fertilizer application
Natural Soil Variability ph and SOM vary within a field 0-12 inch sample depth Sample ph Soil OM # -- % -- 1 2 3 4
Natural Soil Variability ph and SOM vary within a field 0-12 inch sample depth Sample ph Soil OM # -- % -- 1 4.86 3.3 2 3 4
Natural Soil Variability ph and SOM vary within a field 0-12 inch sample depth Sample ph Soil OM # -- % -- 1 4.86 3.3 2 4.24 2.6 3 4
Natural Soil Variability ph and SOM vary within a field 0-12 inch sample depth Sample ph Soil OM # -- % -- 1 4.86 3.3 2 4.24 2.6 3 4.89 2.4 4
Natural Soil Variability ph and SOM vary within a field 0-12 inch sample depth Sample ph Soil OM # -- % -- 1 4.86 3.3 2 4.24 2.6 3 4.89 2.4 4 4.81 2.8
How far apart were the samples? 1,000 feet 500 feet 100 feet 50 feet???
How far apart were the samples?
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 2-4 4-8 8-12
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 2-4 4-8 8-12
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 2-4 4.9 4.7 4-8 8-12
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 2-4 4.9 4.7 4-8 4.9 5.3 8-12
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 2-4 4.9 4.7 4-8 4.9 5.3 8-12 5.6 5.8
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 2-4 4.9 4.7 4-8 4.9 5.3 8-12 5.6 5.8
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 2-4 4.9 4.7 4-8 4.9 5.3 8-12 5.6 5.8
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 2-4 4.9 4.9 4.7 4.9 4-8 4.9 5.3 8-12 5.6 5.8
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 29 49 2-4 4.9 4.7 4-8 4.9 5.3 8-12 5.6 5.8
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 29 49 2-4 4.9 4.7 28 23 4-8 4.9 5.3 8-12 5.6 5.8
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 29 49 2-4 4.9 4.7 28 23 4-8 4.9 5.3 24 12 8-12 5.6 5.8
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 29 49 2-4 4.9 4.7 28 23 4-8 4.9 5.3 24 12 8-12 5.6 5.8 13 8
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 29 49 2-4 4.9 4.7 28 23 4-8 4.9 5.3 24 12 8-12 5.6 5.8 13 8
Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm 0-2 4.9 4.4 29 49 2-4 4.9 4.7 28 23 26 24 4-8 4.9 5.3 24 12 8-12 5.6 5.8 13 8
Thank you Questions?