Know Your Soil Getting the Dirt on Your Dirt FWAA. Dr. Steve Petrie Director of Agronomic Services

Transcription

1 Know Your Soil Getting the Dirt on Your Dirt FWAA Dr. Steve Petrie Director of Agronomic Services

2 Crop productivity Genetics Soil Temperature Environ ment Crop Yield Moisture Manage ment

3 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

4 Soil Personality Texture ph Soil Personality Organic matter CEC

5 Soil Texture Description of the amount of sand, silt, and clay in the soil Sand > 0.05 mm Silt mm Clay < mm Sand is gritty Silt is slippery Clay is sticky Loam has equal feel of gritty, slippery, and sticky

6 Soil Texture Description of the amount of sand, silt, and clay in the soil Sand > 0.05 mm Silt mm Clay < mm Sand is gritty Silt is slippery Clay is sticky Loam has equal feel of gritty, slippery, and sticky

7 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

8 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

9 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

10 Clay particle size and surface area Largest clay particle = mm = cm Surface area = x 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

11 Photomicrographs of clay platelets

12 Soil texture and water availability

13 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

14 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.

15 Soil texture and water holding capacity Soil Texture In. of water/ ft. of soil Sand Loamy sand Sandy loam Fine sandy loam Silty loam Silty clay loam Silty clay Clay

16 Soil texture and water movement Soil texture Water movement inches/hour Sand Silty sands Silt, sandy clay Clay

17 Effect of texture on key soil properties

18 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

19 Soil ph and nutrient availability or toxicity P K Ca Fe Mn Zn Cu Mo Al Soil ph 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

20 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

21 Acidity from NH 4 and S fertilizers Nitrification of ammonium fertilizers results in increased soil acidity NH O 2 NO H + + 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 H + S-SO 4 fertilizers do not increase soil acidity CaSO 4 gypsum K 2 SO 4 potassium sulfate K-Mag 21

22 Ammonium acidifies the soil Plant uptake of ammonium Soil solution ph NH 4 + H + Root interior

23 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

24 Composition of typical N fertilizers N Fertilizer NO 3 -N NH 4 -N Urea Lime Equivalent % Lbs lime/lb N Calcium nitrate CAN Ammonium nitrate UAN 32 solution Ammonium sulfate More ammonium = more acidity

25 Nitrogen Fertilizer Effects on Soil ph 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 Check Anhydrous ammonia Ammonium nitrate Urea UAN solution From Darusman et al. SSSAJ 55:1097

26 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 UAN 32 solution Amm. sulfate * 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/

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

28 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

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 Loam, dark colored Clay loam, silty clay loam Organic soils

30 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

31 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

32 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

33 Soil Organic Matter is Complex Soil organic matter Humus All organic compounds in the soil, except undecayed plant residues and soil organisms

34 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

35 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

36 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

37 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

38 Soil variability is natural

39 Soil variability is human-caused Land leveling for irrigation Irrigation-induced erosion Field consolidation Tillage Differential fertilizer application

40 Natural Soil Variability ph and SOM vary within a field 0-12 inch sample depth Sample ph Soil OM # -- %

41 Natural Soil Variability ph and SOM vary within a field 0-12 inch sample depth Sample ph Soil OM # -- %

42 Natural Soil Variability ph and SOM vary within a field 0-12 inch sample depth Sample ph Soil OM # -- %

43 Natural Soil Variability ph and SOM vary within a field 0-12 inch sample depth Sample ph Soil OM # -- %

44 Natural Soil Variability ph and SOM vary within a field 0-12 inch sample depth Sample ph Soil OM # -- %

45 How far apart were the samples? 1,000 feet 500 feet 100 feet 50 feet???

46 How far apart were the samples?

47 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

48 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

49 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

50 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

51 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

52 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

53 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

54 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

55 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

56 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

57 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

58 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

59 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

60 Soil ph and P Vary by Tillage and Depth Depth ph Soil test P Tilled No-till Tilled No-till ppm

61 Thank you Questions?