Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Ca mg16slideshare


Published on

I developed these slides for the Soil Fertility class that I teach at Western Illinois University.

Published in: Education
  • Be the first to comment

Ca mg16slideshare

  1. 1. How important is CALCIUM?
  2. 2. Answers to reading Qs should be submitted using the IA before the start of class TODAY (11/4)
  3. 3. What is FGD gypsum, how does it differ from mined gypsum and why has agricultural use of FGD gypsum increased in recent years? Ron Chamberlains company Gypsoil is one of the biggest if not the biggest marketer of FGD gypsum to farmers. Spend a little time browsing the Gypsoil website and discuss some interesting info you found. Mike Starkey and Jack Maloney are continuous no-tillers who use cover crops and lots of other innovative practices in addition to gypsum. If you could ask either of them 1 question related specifically to their experience with gypsum, what would you ask? The title of the article is Gypsum may enhance soil-growing conditions rather than Gypsum enhances soil growing conditions. How convinced are you of the value of gypsum after reading the article? Do you think the article should have contained any additional information (e.g., more explanation of how gypsum impacts soil structure or nutrient availability). Discuss your perspective. Questions
  4. 4. MSIS presentations (2011-2014) provide a window into the science and practice of agricultural utilization of gypsum and are all available on-line.
  5. 5. This Ohio State U publication presents current science based- information about agricultural utilization of gypsum.
  6. 6. Calcium (Ca) has an atomic number of 20 and an atomic weight of 40.08 What does Ca share in common with other elements in group IlA?
  7. 7. Calcium (Ca) has an atomic number of 20 and an atomic weight of 40.08 Ca+2
  8. 8. Have you ever heard of the Chernobyl Disaster? A fire and explosion at the Chernobyl Power Plant released large quantities of radioactive particles into the atmosphere on April 26, 1986. A 30 km exclusion zone was established.
  9. 9. The plume from the burning reactor initially traveled in a northwest direction toward Sweden, Finland and eastern Europe, exposing the public to levels up to 100 times the normal background radiation. Contamination of grain and dairy products was a serious concern. Both Sr-90 and I-131 migrate to vital organs in the body where they are impossible to remove, serving as a constant source of radiation and as a potential cause of cancer. Radioactive fall-out from Chernobyl Sr can substitute for Ca with very unhealthy consequences
  10. 10. element atomic number % by weight oxygen 8 46.60 silicon 14 27.72 aluminum 13 8.13 iron 26 5.00 calcium 20 3.63 sodium 11 2.83 potassium 19 2.59 magnesium 12 2.09 titanium 22 0.44 hydrogen 1 0.14 phosphorus 15 0.12 manganese 25 0.10 fluorine 9 0.08 sulfur 16 0.05 chlorine 17 0.05 Calcium is the 5th most abundant element in the earth’s crust
  11. 11. Most young soils contain large amounts of calcium. Old, highly weathered soils contain much less calcium. Young Ca rich soil in IL Old Ca deficient soil in NC Soils formed from parent materials low in Ca (e.g., quartz sand) contain low levels of Ca
  12. 12. The highly weathered soils of Brazil’s Cerrado region naturally had such low Ca levels that cattle ranchers lost cattle due to brittle Ca deficient bones and large scale crop production was considered impossible.
  13. 13. The highly weathered soils of Brazil’s Cerrado region naturally had such low Ca levels that cattle ranchers lost cattle due to brittle Ca deficient bones and large scale crop production was considered impossible. > 150 million acres converted to ag since 1985, Brazil is now the #1 soybean exporter Large quantities of lime have been applied!! Brazilian soybean breeders have also developed well adapted soybeans varieties with high tolerance of Al toxicity
  14. 14. Ca+2 Ca+2 Forms of calcium in soil Ca-rich minerals CaSO4 * 2H2O CaAl2Si2O8 Calcium-organo-mineral complexes ExchangeableCa+2 Most of the Ca in soil Solution Ca+2 Plant available Ca All of these forms of Ca are part of biogeochemical cycles but the ones on the right side of the slide are most dynamic CaCO3 plagioclase gypsum calcium carbonate 2.0–2.5 g/l 0.015 g/l Very insoluble
  15. 15. For most soils, Ca+2 is the dominant exchangeable cation and cation in solution exchangeable cations Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 cations in solution Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 Soil water Ca concentrations in temperate region soils tend to range from ~30 to ~300 ppm. 15 ppm Ca is considered adequate for most crops Ca+2
  16. 16. How many lbs of Ca arrive at the roots of a corn crop that transpires 20” of water during a growing season if the average concentration in soil water is 15 ppm Ca? 1 acre-inch = 27,000 gallons 1 gallon = 8.3 lbs 27,000 gal/ac-in * 20 inches * 8.3 lbs/ gal = 4,482,000 lbs of H2O/ac 4,482,000 lbs * 15 ppm = 67 lbs of Ca Very few crops need more than 67 lb of Ca/ac
  17. 17. Multi-valent cations such as Ca+2 , Al+3 and Fe+3 are important binding agents at this scale. Impact of cations on flocculation of clay particles
  18. 18. In contrast, monovalent cations such as Na+ and K+ cause clay domains to disperse. Impact of cations on flocculation of clay particles What about Mg+2 ?
  19. 19. Does this difference matter?
  20. 20. Recent research indicates that high Mg levels can destabilize the structure of some soils
  21. 21. Plant uptake of Ca sometimes exceeds all other elements except for N and K Monocots generally contain less Ca (0.15-0.5% of dry plant tissue). Dicots generally contain more Ca (1-3% of dry plant tissue) Woody plants store large amounts of Ca and often have similar uptake of Ca and N. Ca movement within plants occurs mostly through the transpirational stream (water moving upward through the xylem) as opposed to in the phloem. Ca movement to growing tissues that are not transpiring (e.g.., fruits) is very restricted.
  22. 22. Crop Yield N P205 K20 Ca Mg S Lbs/acre Corn (grain) 150 bu 110 53 40 2 8 10 Corn (stover) 4.5 tons 100 37 145 26 20 14 Wheat (grain) 40 bu 50 25 15 1 6 3 Wheat (straw) 1.5 tons 20 5 35 6 3 5 Soybeans (beans) 50 bu 188 41 74 19 10 23 Soybeans (stover) 6,100 lb 89 16 74 30 9 12 Calcium content of grain and stover for corn, wheat and soybeans
  23. 23. Location N P2O5 K2O Ca Mg S lb/ton Alabama 52 12 50 19 4.5 3.3 N. Carolina 45 15 45 28 5.3 4.8 IPNI – N. Central 51 12 49 -na- 5.4 5.4 Alberta, Canada -na- 10-15 50-65 30 5-7 5-7 P. Northwest 50-70 8-16 48-72 28-35 5-8 4-6$department/deptdocs.nsf/all/agdex10073 Variation in nutrient levels in alfalfa So how much Ca is removed by a typical alfalfa crop? 100 to > 300 lbs/ac
  24. 24. Physiological importance of Ca Cell division and elongation Cell wall development Cell membrane function Cell protection against toxins Nitrate uptake and metabolism Activity of key enzymes Starch metabolism
  25. 25. Many fruits and vegetables have dramatic Ca deficiency symptoms such as Black Heart in celery and broccoli, Tipburn in lettuce and cabbage, White Heart or Hollow Heart in cucurbits, Blossom End Rot in tomatoes and peppers, and Pops in peanuts. Tree fruit with low calcium exhibit storage problems such as bitter-pit in apples, cork-spot in apples and pears, cracking in cherries, and other degradation of the fruit while in storage. Ca deficiency is usually associated with growing points (aka meristems) For example: buds, unfolding leaves, fruits and root tips Lack of moisture or non-uniform moisture availability is frequently associated with symptoms of calcium deficiency
  26. 26. Most commercial fruit producers in the Pacific NW spray their apple and pear trees with CaCl2 or Ca(NO3)2. Some varieties receive 3-4 treatments, others 6-7. The application of foliar Ca is cost effective and can dramatically improve fruit quality.
  27. 27. High Response Crops The following crops have been reported to be especially sensitive to Ca availability: apples, broccoli, brussel sprouts, cabbage, carrots, cauliflower, celery, cherries, citrus, conifers, cotton, curcurbits, melons, grapes, legumes, lettuce, peaches, peanuts, pears, peppers, potatoes, tobacco, and tomatoes
  28. 28. According to the U of I, Ca deficiency does not occur in Illinois when soil pH is greater than 5.5. “Calcium deficiency associated with acidic soils should be corrected using limestone. The laboratory procedure used for Ca is easy and reliable—probably more accurate than the K test— but since the deficiency does not exist, there is no reason to recommend the test”.
  29. 29. SOIL TEXTURE CALCIUM MAGNESIUM Sandy 400 60-75 Silt loam 800 150-200 Levels of soil test Ca and Mg (lbs/A) considered adequate for crop production Illinois Agronomy Handbook A state wide (598 fields in 52 IL counties) soil fertility survey conducted in 2007/2008 reported average Ca and Mg levels of 4,452 and 732 lbs/ac, respectively. 4500 >> 800 !!
  30. 30. According to Tiedjens, pH measurements do not give a true picture of the need for Ca additions
  31. 31. In this study, low Ca and Mg levels in plant tissue were not always associated with low pH levels and high Ca and Mg levels in plant tissue were not always associated with higher pH levels. Other factors which influence plant tissue levels of Ca and Mg include competitive cations, crop disease/injury and sub-soil pH.
  32. 32. Portion of nutrients taken up by corn that are typically supplied by 3 main mechanisms Nutrient Root interception Mass flow Diffusion % of uptake Nitrogen <1 80 19 Phosphorus 2 5 93 Potassium 2 18 80 Calcium 150 375 0 Magnesium 33 600 0 Sulfur 5 300 0 Why are some of these #s greater than 100%??? The amount of Ca and Mg brought to roots by mass flow aka the transpirational stream is often much greater than crop uptake
  33. 33. Why isn’t Ca uptake higher, when more is available? In contrast with most other nutrients, Ca is taken up almost exclusively by young root tips. K uptake is generally higher than Ca uptake even though solution concentrations of Ca are often 10 times greater than K concentrations.
  34. 34. Interactions with other nutrients Competitive cations: The relative amounts of other cations such as Na+ , K+ , Mg+2 , NH4 + , Fe+2 , and Al+3 impact plant uptake of Ca+2 . Large additions of Ca+2 displace other cations from exchange sites which may temporarily increase their availability to crops but also increase their tendency to leach. High K applications have been known to reduce the Ca uptake in apples, which have inefficient Ca uptake and translocation within the tree. Phosphorus: Free or un-combined Ca is normally present in alkaline soils. This Ca interacts with other nutrients. Free Ca reacts with P to form insoluble (or very slowly soluble) Ca-P compounds that are not readily available to plants. Boron: High soil or plant tissue levels of Ca can inhibit B uptake and utilization. Calcium sprays and soil applications have been effectively used to help detoxify B over-applications.
  35. 35. Impact of clay mineralogy on Ca availability Ca Saturation, % High CEC clay Low CEC clay High CEC clays generally need > 70% Ca saturation to provide adequate Ca availability Low CEC clays generally only need 40-50% Ca saturation Calciumavailability High Mg may be an issue.
  36. 36. Review of factors affecting Ca nutrition Total Ca supply Soil pH CEC % Ca saturation Relative abundance of other cations Clay mineralogy Moisture availability and uniformity of uptake New root growth
  37. 37. Many crop consultants promote Ca products! Many claims do not appear to be supported by research but Ca supplementation programs merit consideration, especially when growing “high response” crops
  38. 38. A wide range of calcium products are available on the market.
  39. 39. Tissue testing can help identify situations when Ca supplementation is likely to be of value.
  40. 40. Liming Material Approx. % Ca Calcitic Limestone 32 Dolomitic Limestone 22 Hydrated Limestone 46 Precipitated Lime 60 Blast Furnace Slag 29 Ca fertilizers Approx. % Ca. Gypsum 22 CaCI2 36 Ca(NO3)2 19 Ca-Chelates 3-5 Calcium amendments When evaluating Ca products, carefully consider a) PRICE b) APPLICATION METHOD and c) WHETHER A LIMING MATERIAL IS APPROPRIATE.
  41. 41. Magnesium (Mg) has an atomic number of 12 and an atomic weight of 24.3 What does Mg share in common with other elements in group IlA?
  42. 42. Magnesium (Mg) has an atomic number of 12 and an atomic weight of 24.3 Mg+2
  43. 43. According to the U of I, Mg deficiency occasionally occurs in IL for both corn and soybean but is limited to sandy, low organic matter soils. Southern Illinois University research has shown no response to applied Mg even when the Mg test from the surface soil was below recommended levels. They observed that Mg levels below the surface 7-inch level were adequate and apparently met the needs for optimum crop production even when surface levels were considered deficient.
  44. 44. Magnesium deficient corn
  45. 45. Magnesium deficient tomato leaves
  46. 46. ?
  47. 47. Are you on sandy soils? Looks like a Mg deficiency to me… some Epsom salts through the drip should clear it up. I would do both run 1# ES per acre foliar to jump start and apply 5# per acre in drip as needed. Don't go too high because you can flush your nitrate out of the plants.
  48. 48. Physiological role of Mg in plants Central element of the chlorophyll molecule Enzyme activator and a constituent of many enzymes Sugar synthesis Starch translocation Plant oil and fat formation Nutrient uptake control Increase Fe utilization Aids N fixation in legume nodules
  49. 49. The basic structure of a chlorophyll molecule is a porphyrin ring, coordinated to a central atom. This is very similar in structure to the heme group found in hemoglobin, except that in heme the central atom is iron, whereas in chlorophyll it is magnesium.
  50. 50. High Response Crops The following crops have been found to be especially sensitive to availability of Mg: alfalfa, blueberry, beet, broccoli, cabbage, cauliflower, celery, clover, conifers, cotton, cucumber, eggplant, lettuce, onion, pepper, potatoes, pumpkin, spinach, squash, tobacco, tomato and watermelon
  51. 51. High K concentration in soil solution interferes with Mg uptake by ryegrass
  52. 52. For the turf manager, one of Mg’s most important functions is its involvement in the transport of soluble carbohydrates from leaves to sites of utilization in roots, rhizomes and growing points. One common observation associated with Mg deficiency is a sharp decline in the root: shoot ratio (weight of roots/weight of shoots). When magnesium is inadequate, the root: shoot ratio will often decline to less than half that of a magnesium sufficient plant. This means that when turf grasses are experiencing inadequate magnesium, they will produce less root mass and roots do not grow as deeply.
  53. 53. SOIL TEXTURE CALCIUM MAGNESIUM Sandy 400 60-75 Silt loam 800 150-200 Levels of soil test Ca and Mg (lbs/A) considered adequate for crop production Illinois Agronomy Handbook A state wide (598 fields in 52 IL counties) soil fertility survey conducted in 2007/2008 reported average Ca and Mg levels of 4,452 and 732 lbs/ac, respectively. 732 > 200 !!
  54. 54. Spectrum Analytic Inc (a plant and soil testing lab in OH) analyzed thousands of plant tissue samples in 2010. The results indicate that many crops would benefit from more magnesium. In looking at the data, keep in mind that this is a biased survey. Plant samples are more often than not submitted to find out why a crop is underperforming.
  55. 55. Sources of Mg Dolomitic limestone is a mixture of CaCO3 and MgCO3 and is the lowest cost source of Mg but should only be applied when lime is needed. The Mg content of dolomitic limestone varies from 8-10%. To be most effective as a source of Mg, dolimitic lime should be broadcast and incorporated. Neutral salt sources of Mg Sul-po-mag has a Mg content of 11%. The sulfur (S) and K2O concentrations are ~22%. Epsom salts = MgSO4·7H2O = 9.9% Mg MgCl2, Mg(NO3)2 and Mg chelates can be used as solutions and foliar sprays
  56. 56. Good overview of Mg concepts$webindex/9657B817A2FFCA5E85257723004A0967/$file/BC22010-Page-26-28.pdf
  57. 57. Cation Balancing?? Proposed by Firman Bear, William Albrecht and others prior to the determination of critical levels
  58. 58. Claims associated w/ “balanced” Ca:Mg ratios • Improves soil structure • Reduces weed populations • Stimulates populations of earthworms and beneficial microorganisms • Improves forage quality • Excess soil Mg “ties up” and promotes leaching of other plant nutrients • Better “balance” of soil nutrients • Improved plant and animal health • “Cows milk easier”
  59. 59. U of WI Conclusions • Alfalfa yield related to exchangeable K and soil pH, not Ca:Mg ratio • Neither Ca or Mg additions affected weeds • Earthworms related to organic matter, not Ca:Mg ratio • Alfalfa quality related to pH and stand, not Ca:Mg ratio • No justification to use calcitic over dolomitic lime or adding extra Ca
  60. 60. NCR 103 Committee NC Regional Publication 533 Soil Cation Ratios for Crop Production – Ca and Mg levels can be balanced but too low – Field research does not support “optimal” Ca:Mg ratio concept Concludes: “A sufficient supply of nutrient cations is the most important consideration in making economic fertilizer recommendations” Sufficient supply is an especially important concern in low CEC soils
  61. 61. Bear, F.E., and S.J. Toth. 1948. Influence of calcium on availability of other soil cations. Soil Sci. 65:67-74. Eckert, D.J., and E.O. McLean. 1981. Basic cation saturation ratios as a basis for fertilizing and liming agronomic crops: 1. Growth chamber studies. Agron. J. 73:795-799. Eckert, D.J. 1987. Soil test interpretations: Basic cation saturation ratios and sufficiency levels. In J.R. Brown (ed.) Soil Testing: Sampling, Correlation, Calibration, and Interpretation. Special Publication No. 21. Soil Science Society of America. Madison, WI. Graham, E.R. 1959. An explanation of theory and methods of soil testing. Missouri Agric. Ext. Stn. Bull. 734. Hunter, A.S. 1949. Yield and composition of alfalfa as affected by various calcium -magnesium ratios in the soil. Soil Sci. 67:53-62. Liebhardt, W.C. 1981. The basic cation saturation concept and lime and potassium recommendations on Delaware’s Coastal Plain soils. Soil Sci. Soc. Am. J. 45:544-549. McLean, E.O., R.C. Hartwig, D.J. Eckert, and G.B. Triplett. 1983. Basic cation saturation ratios as a basis for fertilizing and liming agronomic crops. II. Field studies. Agron. J. 75:635-639. Simson, C.R., R.B. Corey, and M.E. Sumner. 1979. Effect of varying Ca:Mg ratios on yield and composition of corn and alfalfa. Commun. Soil Sci. and Plant Anal. 10:153-162. Many studies have evaluated the base saturation ratio concept – I am not aware of any that concluded specific cation ratios are optimal across diverse soils
  62. 62. Why no crop response to “Ca:Mg ratio” ? • Ca and Mg levels in the soil solution are normally high compared to plant uptake • Plant uptake of K is 2-4 times that of Ca and Mg despite much lower levels of K in the soil solution • Roots preferentially take up K and exclude Ca and Mg • Soils studied may not have been sensitive to high Mg
  63. 63. K:Mg ratio may be more important than Ca:Mg ratio A number of studies (e.g., Rahmatullah and Baker (1981) and Stout and Baker (1981) have reported an inverse relationship between K:Mg ratio and Mg uptake by corn seedlings Wilkinson et al. (1987) reported that applications of high rates of K to cool season grass pastures, whether from manure or inorganic fertilizers, increased the incidence of grass tetany. .
  64. 64. Does gypsum improve soil structure ?? It has long been known that gypsum can be used to remediate soils that have poor structure due to high Na levels
  65. 65. Recent article in Journal of Soil and Water Conservation (peer reviewed scientific journal) Does science support the use of gypsum in the Midwest?
  66. 66. (Norton, 2009) Soils receiving gypsum had less run-off and less loss of sediment and soluble P
  67. 67. Using Gypsum to Affect Soil Erosion Processes and Water Quality. Dale Norton A driving force in soil erosion is the low electrolyte content of rain water. Various electrolyte sources have proven useful in serving as electrolyte sources such as phosphogypsum, lime and various salts, however, each has other potential problems. We performed a number of studies on low cost gypsum from scrubbing air from coal fired power plants for pollution control (FGD gypsum) and found the neutral salt produced is an excellent electrolyte source which is slowly soluble in rainwater and has few if any potential environmental problems. It has proven very useful in keeping soil clays flocculated and maintaining greater infiltration rates, therefore, reducing runoff and erosion.
  68. 68. Water that is too clean causes corrosion in metal pipes
  69. 69. This research presents evidence that it is beneficial to manage soils for high Ca:Mg ratios *IF* they are prone to sealing.
  70. 70. Jack Maloney, IN farmerKeith Schlapkohl, IA Farmer Routine applications of gypsum are used by some successful farmer innovators in the Midwest region. Mike Starkey, IN Farmer
  71. 71. STOCKTON, IA — Keith Schlapkohl concedes he doesn't know everything about farming. That hasn't stopped him from trying new things on his Scott County farm. "It seems for every one question I get answered, 10 more are raised," he says. Schlapkohl has been trying different ideas dealing with improving nitrogen efficiency and using gypsum on his Eastern Iowa fields. During this time, his yields have averaged close to 300 bushels per acre for corn.
  72. 72. Excerpt from the Iowa Farmer Today article: “Schlapkohl believes gypsum increases production by improving water infiltration. "Its chemical tillage," says Schlapkohl about gypsum. By using gypsum, he has been able to lower the magnesium levels in his soils. Higher magnesium levels tighten up the soil, he explains. Using gypsum also has increased the amount of oxygen in the soil and increased N efficiency, Schlapkohl notes. (he has harvested >300 bu of corn/acre with less than 100 lbs/a of fertilizer N) He uses a calcium-sulfate product from Cedar Rapids that has a higher ratio — 3:1 — of calcium to sulfur, compared with other sources that have a 1:1 ratio. Schlapkohl says there is more available calcium and less heavy metals in this product compared with regular gypsum. This substance is not as powdery as typical gypsum. He has a business that spreads the gypsum product over the winter. Because he also farms, Schlapkohl likes to spread the product between harvest and planting and stay close to home.”
  73. 73. Mike Starkey says his background in accounting helped him to prioritize information gathering functions at the farm, including a heavy use of on-farm trials to evaluate the impact of various inputs. “We are not afraid to change things when we find something that works better,” Mike Starkey says. The Starkey family has been a no-till operation since 2000 after trying it briefly in the early '90s. Once he and his family learned how to properly set up no-till planting equipment, place nitrogen efficiently and monitor calcium and magnesium levels in soils, the operation was successful in using no-till. Starkey echoes Maloney’s comments about water infiltration improvements after using Gypsoil. “It is amazing how water does not stand anymore. When it rains hard, water is just gone now.”
  74. 74. Once a Pollutant, ` Scrubber Sludge ' Finds a Market By John J. Fialka The Wall Street Journal, Page B1, 10/05/1998 Some electric utilities are spinning gold out of the gunk they once spewed in the air. To comply with the 1970 Clean Air Act, power companies have been "scrubbing" the smoke coming out of their stacks to remove sulfur and fly ash, then dumping the wastes into landfills. Now, they are finding farmers and construction companies will buy the stuff. Near Oak Ridge, Tenn., a unit of Caraustar Industries Inc. is building a factory to make wallboard out of sulfur residue produced at the mammoth Tennessee Valley Authority power plant next door. About 180 miles east, near Clarksville, Babb Cellular Concrete Co. is building a plant to make a special lightweight concrete out of fly ash from another TVA plant. Farmers, too, are buying sulfur residue -- called " scrubber sludge " -- because it improves soil and increases their crop yields. Ken A. Curtis. who farms and runs a fertilizer business in Prairie City, Ill., sells between 20,000 tons and 30,000 tons a year at $6 a ton. "Wherever you put that stuff," he says, "it just greens up.
  75. 75. Figure 1. Varying degrees of clay dispersion in soils. The higher amounts of dispersal (4 and 5) indicate a soil's suitability for gypsum application. No.0 displays slaking (breaking off of soil particles), compared to 1 to 5 which show clay dispersion
  76. 76. What about the jar test? A tablespoon of any soluble salt (including table salt) will flocculate clay in a quart jar! Without the addition of a flocculating agent, it is normal for fine clay to stay in suspension after soil is shaken vigorously with water.
  77. 77. 24 hrs after salt was added to flask on the right High electrolyte concentration promoted flocculation of clay Class Demo 11/4
  78. 78. Excellent review of research on the value of gypsum in humid regions
  79. 79. Soils which respond positively to gypsum have greater ability to adsorb both Ca+2 and SO4 -2 than soils which are not responsive. This could be developed into a routine soil test. Green data points represent soils that responded positively to gypsum