The gypsum requirement equation for sodic soils: What s the app about? Tom DeSutter 2018 Soil and Soil/Water Workshop

Transcription

1 The gypsum requirement equation for sodic soils: What s the app about? Tom DeSutter 2018 Soil and Soil/Water Workshop

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3 32 Wyndmere CIG Field Soil SARe or % = % Water (1/3 bar) Reference He et al, EC (ds/m; mmhos/cm)

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5 Sodium is much happier to be hydrated than coordinated Calcium is much happier to be coordinated than hydrated

6 When Ca is present it does not matter if EC is high or not

7 When repulsion becomes greater than attraction dispersion will occur This happens when is on exchange sites and when EC is low

8 Recent NDSU research has found that swelling and/or dispersion can occur when the % is greater than 5 when the EC 1:1 is less than 1.0 mmhos/cm.

9 Photo by Tom DeSutter

10 2X + CaSO 4 CaX SO 4 No Ca amendments Ca Ca Ca Ca tile -Very reduced, or no water movement -Become hard-set when dry -Poor trafficability when wet With Ca amendments Ca Ca Ca Ca Ca Ca Ca Ca Ca Ca Ca Ca Ca Ca Ca Ca tile -Increased water movement -Soil aggregates become established -Improved trafficability Figure by Thomas DeSutter and Maria Breker

11 Sources of Calcium Gypsum (CaSO 4. 2H 2 O) Mined Most likely pelletized About $200/ton Synthetic Byproduct from coal combustion Powder form Now available, less than $15/ton Both are very pure and are good sources of S too

12 Sources of Calcium Sugar beet spent lime Lots of beneficial uses for ag Very low solubility, so not ideal for sodic soils Organic compounds within it are very degradable and can improve microbial respiration Calcium nitrate High solubility Often used in reclamation of brine spills

13 So, how much gypsum should one apply? Need to know, or assume, some basic soil parameters Soil density Actual cation exchange capacity (CEC) What level of you are starting with? What level of doing you want end with? What is the thickness of soil that needs treating? How pure is your gypsum?

14 GR = 0. 86(F)(D)(ρ b )(CEC)(ESPi - ESPf)(100/%purity) GR = gypsum requirement (Mg/ha) F = Ca- exchange efficiency; 1.1 for ESP of 15, 1.3 for ESP of 5 D = depth of soil to treat (m) b = soil bulk density (Mg/m 3 ), typically ranges from 1.1 to 1.6 CEC = soils actual cation exchange capacity (mmol c /kg) ESPi = soils initial exchangeable sodium percentage (%) ESPf = soils final exchangeable sodium percentage (%) Purity = the actual purity of the gypsum that you are using (%) 0.86 is derived from the mass of CaSO 4 *2H 2 O required to replace one +

15 Let s talk about CEC Summation When soils have soluble salts, exchanger and salt cations are summed This is then termed as extractable cations - is added to the exchange sites and then removed by, then quantified This is termed as exchangeable cations

16 Soil s exchange sites Air-dry soil: cations (in red) and anions predominantly in the crystal form. A sulfatedominated system is used for simplicity. A MgSO 4 2 SO 4 CaSO 4 Ca MgSO 4 2 SO 4 MgSO 4 2 SO 4 2 SO 4 MgSO 4 CaSO 4 2 SO 4 2 SO 4 Mg 2 SO 4 T. DeSutter NDSU Dept. of Soil Science Soil s exchange sites Exchanger phase cations (green) and solution phase cations (red) are moved to solution using ammonium acetate. Cations in red and green are then quantified. B SO 4 Ca NH Ca 4 SO 4 NH SO 4 4 NH Mg 4 Mg NH Ca Mg 4 SO 4 NH SO 4 4 SO SO 4 4 SO 4 NH 4 SO 4 NH SO 4 4 Mg SO 4 NH 4 Mg NH4 SO 4 SO 4 Summation method: CEC = sum of the red and green cations This would be termed extractable cations Cations adsorbed to the soil s exchange sites (exchanger phase) in green. Ammonium adsorbed to the soil s exchange sites (exchanger phase).

17 Soil s exchange sites Soil s exchange sites Soil s exchange sites - exchange: CEC = sum of A This would be termed exchangeable cations MgSO 4 2 SO 4 CaSO Ca 4 MgSO4 2 SO 4 MgSO 4 2 SO 4 2 SO 4 MgSO 4 CaSO 4 2 SO 4 2 SO 4 Mg 2 SO 4 B C NH4 T. DeSutter NDSU Dept. of Soil Science Cations adsorbed to the soil s exchange sites (exchanger phase) in green. Ammonium is added to be adsorbed to the soil s exchange sites. Other cations are discarded. Potassium adsorbed to the soil s exchange sites (exchanger phase). Ammonium is then quantified and CEC determined.

18 GR = 0. 86(F)(D)(ρ b )(CEC)(SARi - SARf)(100/%purity) Where SAR is the sodium adsorption ratio. When ESP<50 then ESP SAR. So, what about %?

19 Soil s exchange sites Air-dry soil: cations (in red) and anions predominantly in the crystal form. A sulfatedominated system is used for simplicity. A MgSO 4 2 SO 4 CaSO 4 Ca MgSO 4 2 SO 4 MgSO 4 2 SO 4 2 SO 4 MgSO 4 CaSO 4 2 SO 4 2 SO 4 Mg 2 SO 4 T. DeSutter NDSU Dept. of Soil Science Soil s exchange sites Exchanger phase cations (green) and solution phase cations (red) are moved to solution using ammonium acetate. Cations in red and green are then quantified. B SO 4 Ca NH Ca 4 SO 4 NH SO 4 4 NH Mg 4 Mg NH Ca Mg 4 SO 4 NH SO 4 4 SO SO 4 4 SO 4 NH 4 SO 4 NH SO 4 4 Mg SO 4 NH 4 Mg NH4 SO 4 SO 4 + % = sum of all red and green cations Cations adsorbed to the soil s exchange sites (exchanger phase) in green. Ammonium adsorbed to the soil s exchange sites (exchanger phase).

20 GR = 0. 86(F)(D)(ρ b )(CEC)(%i - %f)(100/%purity) SAR = 1.04%- 0.35; r 2 = 0.92 So, just replace SAR or ESP with %.

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27 Example 1. A 0-6 (0.15 m) soil sample was sent to the lab to determine why 30 acres does not produce the same yields as the rest of the field. The %i was 15 and EC1:1 was 1.0. What is the GR needed to help improve its productivity? Gypsum source is pelletized and has a purity of 95%. Assume a bulk density (ρb) of 1.47 Mg/m 3 Target a final %f of 5 Using NH4- exchange the CEC was determined to be 150 mmol c /kg Processing, processing, processing 3.9 Mg/ha or 1.7 tons/acre So, at $200/ton for 30 acres the cost will be $10,200.

28 Example 2. A 0-12 (0.3 m) soil sample was sent to the lab to determine why 10 acres does not produce the same yields as the rest of the field. The %i was 24 and EC1:1 was 2 mmhos/cm. What is the GR needed to help improve its productivity? Gypsum source is flue gas and has a purity of 88%. Assume a bulk density (ρb) of 1.47 Mg/m 3 Target a final %f of 5 Using NH4- exchange the CEC was determined to be 200 mmol c /kg Processing, processing, processing 21.3 Mg/ha or 9.5 tons/acre So, at $15/ton for 10 acres the cost will be $1,425.

29 Example 3. Post brine spill, a 0-12 (0.3 m) soil sample was sent to the lab to determine why 10 acres does not produce the same yields as the rest of the field. The %i was 70 and EC1:1 was 30 mmhos/cm. What is the GR needed to help improve its productivity? Gypsum source is flue gas and has a purity of 88%. Assume a bulk density (ρb) of 1.47 Mg/m 3 Target a final %f of 5 Using NH4- exchange the CEC was determined to be 180 mmol c /kg Processing, processing, processing 65.6 Mg/ha or 29.2 tons/acre So, at $15/ton for 10 acres the cost will be $4,380.

30 How does CEC influence GR? Use the following: Soil depth = 0.3 m Bulk density = 1.47 Mg/m3 Purity = 100 %i = 10 %f = 5 For a CEC of 100 mmol c /kg the GR is? For a CEC of 200 mmol c /kg the GR is? For a CEC of 400 mmol c /kg the GR is? For a CEC of 800 mmol c /kg the GR is? 1.1 tons/acre 2.2 tons/acre 4.4 tons/acre 8.8 tons/acre

31 Summary Swelling and dispersion will occur when the is high and the EC is low If the and EC are both high, track with soil sampling Don t expect short-term miracles Soil sampling is a must Assess the economics, not just the irritation Split applications are just fine

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