1 Soil Solution Sampling Ralph Oborn Precisionist

2 Precision Agriculture Grower challenges New technologiesNew technologies Spatial and temporal variabilitiesSpatial and temporal variabilities Increase labor costsIncrease labor costs Lower profitsLower profits Yield and Quality bonusYield and Quality bonus Environmental concernsEnvironmental concerns

3 Precision Agriculture Goal: Just the right amount at Just the right place at Just the right time

4Information As growers have better informationAs growers have better information Can make better decisionsCan make better decisions –Agronomically –Economically –Environmentally

5Soils Healthy soil is about 50% solids, 25% water, 25% air Bone Dry Soil has no moisture. Pores are empty. (Only in laboratory at 100° C) Wilt Point Plant cannot remove any more water. Pores are slightly filled with water film held by surface tension Field Capacity Soil can hold no more water. Any additional water flows with gravity. Saturation All soil pores are totally filled. Water puddles on surface and flows to next lower level Available water Most crops do best when soil moisture is between 50% and 100% of available water. 0% 50% 100%

6 Soil: Vadose Zone Between surface and water tableBetween surface and water table Air, Water, Solids, OM etcAir, Water, Solids, OM etc Non homogeneous!!Non homogeneous!! 3D spatial variability3D spatial variability ChemicalsChemicals Pores Big and smallPores Big and small

7Pores MacroporesMacropores LargerLarger Freeways for flowFreeways for flow FastFast Relatively little interchange with solidsRelatively little interchange with solids Pores Smaller City streets for flow Slow Tortuosity Large amount of interaction

8 Soil Solution QuantityQuantity Movement (flux)Movement (flux) ConstituentsConstituents –Dissolved –Ions –Colloids Amount taken up by roots is very complex That which is not used becomes problematic Potential to leach into ground and surface water

9 Soil Solution Saturated flowSaturated flow –Macro pore –Capillary flow Unsaturated flowUnsaturated flow –Capillary flow Tightly heldTightly held –Interstitial

10 Idealized Soil Water Flow Life would be easy

11 Reality Soil Water Flow Variable Quantity Convergence Divergence Variable Flux Rate Variable Concentration Obstructions

12 Need for Measurements AgronomicAgronomic –Make sure crop is adequately supplied EconomicEconomic –Avoid waste EnvironmentalEnvironmental –Avoid loose contaminants If it’s going to be used, it’s a nutrient If not it's a contaminant

13 Areas of Concern Coarse sandy soilsCoarse sandy soils NitratesNitrates Available to crops (my interest)Available to crops (my interest) Available to leach (environmental concern)Available to leach (environmental concern)

14 Needed: “ Holy Grail of Samplers ” QuantityQuantity Flux (movement)Flux (movement) ConstituentsConstituents Star Trek Tricorder

15 Needed: Samplers Integrated area –Large to be representative –Low cost –Ease of maintenance Repeatable Nondestructive Continuous Multiple levels Accurate

16 Current Art Moisture quantityMoisture quantity TraditionTradition Look and feelLook and feel GravimetricGravimetric TensionometerTensionometer Neutron probeNeutron probe ET matchET match TDRTDR CapacitanceCapacitance Solution sampling Core extraction Pan lysimeters Porous cup Wick

17 Moisture Quantity TraditionTradition Look and feelLook and feel GravimetricGravimetric TensionometerTensionometer Neutron ProbeNeutron Probe ET MatchET Match TDRTDR CapacitanceCapacitance –Continuous, current, multiple depth, large volume

18 Capacitance Probe Irrigation Penetration Free Drainage Daily Crop Usage Scheduling Control Leaching Depth of root zone Sentek EnviroScan Calibrate to quantity, Get an idea of flux, no solution data

19 Solution Sampling Core extractionCore extraction Pan lysimetersPan lysimeters Porous cupPorous cup WickWick What part of soil solution are you measuring? Free water Large pore Small pore Interstitial in clay Placement of all samplers is extremely critical

20 Reality Soil Water Flow

21 Soil Core – Solution Extraction Remove Soil CoreRemove Soil Core Extract soil solutionExtract soil solution AnalyzeAnalyze Fixed volume (good) Destructive Non repeatable Difficult to extract What portion are you extracting? Quantity - maybe Flux – no Solution - maybe

22 Pan Lysimeters Needs good soil contactNeeds good soil contact Drips - only gets saturated flow (macro pore)Drips - only gets saturated flow (macro pore) Divergence of unsaturated flow around samplerDivergence of unsaturated flow around sampler Saturated flow can be more diluteSaturated flow can be more dilute Create capillary fringeCreate capillary fringe Unsure of sampling volumeUnsure of sampling volume

23 Porous Cup Ceramic interfaceCeramic interface Similar to soilSimilar to soil –Hydraulically Vacuum applied to extract solutionVacuum applied to extract solution –Continuous –Intermittent Saturated and unsaturated flowSaturated and unsaturated flow Gradient of suctionGradient of suction 1904 “Artificial Root”

24 Porous Cup Diversions Can divert streamflowsCan divert streamflows Uncertain sampling volumeUncertain sampling volume Ineffective for clayIneffective for clay

25 Porous Cup Diversions Intermittent sampling may not match intermittent flowIntermittent sampling may not match intermittent flow May miss flux frontMay miss flux front May miss solution frontMay miss solution front

26 Porous Cup Diversions Too much suction removes nearby, tightly held, high concentration waterToo much suction removes nearby, tightly held, high concentration water Wilt pointWilt point

27 In a Nutshell “One cannot be sure from what macroscopic volume of soil the sample was extracted nor from which pores it was drained” England

28 Porous Cup Conclusions Quantity - noQuantity - no Flux – noFlux – no Solution - maybeSolution - maybe

29 Wick Sampler Hanging water columnHanging water column Wick designed to match soil suctionWick designed to match soil suction Continuous samplingContinuous sampling No distortion of streamlinesNo distortion of streamlines Only samples available waterOnly samples available water Relatively easy to install, maintain, use, sampleRelatively easy to install, maintain, use, sample No continuous powerNo continuous power Brown 1986

30 Wick

31Wicks Wicks must be preparedWicks must be prepared Heat to 400°CHeat to 400°C Splay and secure on collector plateSplay and secure on collector plate Must be held tightly to soilMust be held tightly to soil Measure collected volumeMeasure collected volume Capture solution for analysisCapture solution for analysis Doesn’t sorb or slow down collectionDoesn’t sorb or slow down collection Large integrated sampling areaLarge integrated sampling area

32 Wick Sizing Number of Wicks = K sat soil x Plate Area K sat wick x Wick Area K Sat Soil ~ 2.54 cm/hr K sat Wick ~ 36 cm/hr Wick area ~ 1.2 cm 2

33 Wick Research Flux ratesFlux rates Sorption propertiesSorption properties Installation methodsInstallation methods Sampling methodsSampling methods

34 Wick Conclusion Quantity – YesQuantity – Yes Flux – YesFlux – Yes Constitutes _ YesConstitutes _ Yes Becoming “just” a toolBecoming “just” a tool

35Conclusion “A large cross section together with a low extraction rate … can yield a sample large enough for chemical analysis”

36 For More Information Knutson, J. H. and J. S. Selker Fiberglass wick sampler effects on measurements of solute transport in the vadose zone. Soil Science Society of America Journal 60: Knutson, J. H. and J. S. Selker Fiberglass wick sampler effects on measurements of solute transport in the vadose zone. Soil Science Society of America Journal 60: Zhu, Y, R. H. Fox, and J. D. Toth Leachate Collection Efficiency of Zero-tension Pan and Passive Capillary Fiberglass Wick Lysimeters. Soil Science Society of America Journal 66:37-43.Zhu, Y, R. H. Fox, and J. D. Toth Leachate Collection Efficiency of Zero-tension Pan and Passive Capillary Fiberglass Wick Lysimeters. Soil Science Society of America Journal 66: Rimmer, Alon, Tammo S. Steenhuis, and John S. Selker One Dimensional Model to Evaluate the Performance of Wick Samplers in Soils. Soil Science Society of America Journal 59:88-92.Rimmer, Alon, Tammo S. Steenhuis, and John S. Selker One Dimensional Model to Evaluate the Performance of Wick Samplers in Soils. Soil Science Society of America Journal 59: Goyne, Keith W., Rick L. Day, and Jon Chorover Artifacts caused by collection of soil Solution with Passive Capillary Samplers. Soil Science Society of America Journal 64: Goyne, Keith W., Rick L. Day, and Jon Chorover Artifacts caused by collection of soil Solution with Passive Capillary Samplers. Soil Science Society of America Journal 64: Brandi-Dohrn, Florian, Richard P. Dick, Mario Hess, John S. Selker Suction Cup Sampler Bias in Leaching Characterization of and Undisturbed Field Soil. Water Resources Research. 32: Brandi-Dohrn, Florian, Richard P. Dick, Mario Hess, John S. Selker Suction Cup Sampler Bias in Leaching Characterization of and Undisturbed Field Soil. Water Resources Research. 32: Barbee, G. C., and K. W. Brown Comparison Between Suction and Free Drainage Soil Solution Samplers. Soil Science. 141: Barbee, G. C., and K. W. Brown Comparison Between Suction and Free Drainage Soil Solution Samplers. Soil Science. 141: Wood, Warren W A Technique Using Porous Cups for Water Sampling at Any Depth in the Unsaturated Zone. Water Resources Research. 9(2): Wood, Warren W A Technique Using Porous Cups for Water Sampling at Any Depth in the Unsaturated Zone. Water Resources Research. 9(2): England, C. B., Comments on ‘A Technique Using Porous Cups for Water Sampling at Any Depth in the Unsaturated Zone’ by Warren Wood Water Resources Research. 10(5):1049.England, C. B., Comments on ‘A Technique Using Porous Cups for Water Sampling at Any Depth in the Unsaturated Zone’ by Warren Wood Water Resources Research. 10(5):1049. Boll, J., J. S. Selker, B. M. Nijssen, T. S. Steenhuis, J. Van Winkle. and E. Jolles. Water Quality Sampling Under Preferential Flow Conditions. In p R. G. Allen et al. (ed.) Lysimeters for Evapotranspiration and Environmental Measurements. Procedings ASCE International Symposium. Lysimetry, Honolulu, Hawaii July ASCE, New York.Boll, J., J. S. Selker, B. M. Nijssen, T. S. Steenhuis, J. Van Winkle. and E. Jolles. Water Quality Sampling Under Preferential Flow Conditions. In p R. G. Allen et al. (ed.) Lysimeters for Evapotranspiration and Environmental Measurements. Procedings ASCE International Symposium. Lysimetry, Honolulu, Hawaii July ASCE, New York. Poletika, N. N., Roth, K., and W. A. Jury Interpretation of solute transport data obtained with fiberglass wick soil solution samplers. Soil Science Society of America Journal 56: Poletika, N. N., Roth, K., and W. A. Jury Interpretation of solute transport data obtained with fiberglass wick soil solution samplers. Soil Science Society of America Journal 56: Boll, J., T. S. Steenhuis, and J. S. Selker, Fiberglass Wicks for Sampling of Water and Solutes in the Vadose Zone. Soil Science Society of America Journal 56: Boll, J., T. S. Steenhuis, and J. S. Selker, Fiberglass Wicks for Sampling of Water and Solutes in the Vadose Zone. Soil Science Society of America Journal 56: Knutson, John H., and John S. Selker Unsaturated Hydraulic Conductivities of Fiberglass Wicks and Designing Capillary Wick Pore-Water Samplers Soil Science Society of America Journal. 58: Knutson, John H., and John S. Selker Unsaturated Hydraulic Conductivities of Fiberglass Wicks and Designing Capillary Wick Pore-Water Samplers Soil Science Society of America Journal. 58: