OrganicFarmer_AprMayFinal_e

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Continued from Page 19 on another soil test. Those who believe they always do are all too often making some very serious mistakes. For example, farmers and growers who request soil tests from our company are advised that calcium should occupy 60- 70 percent of the soil’s cation exchange capacity. There are other labs who use the same guidelines, but still others who advise 65-75 percent for calcium (Ca) saturation on their soil analysis. The target we shoot for on medium to heavy soils is ideally 68 percent. But that same soil sent to three other labs will not measure 68 percent. One will report it as 64 percent. Another reports it as 74 percent. And still another shows 80 percent. Yet all four labs are considered as within the tolerance range for measuring and reporting calcium levels on that soil. The lesson here is to learn and follow directions from the laboratory you are using based on their numbers, not a test from some other lab whose numbers could vary considerably and thus lead to wrong conclusions. Sometimes only Ca, Mg (magnesium) and K (potassium) are given as 100 percent of the total soil nutrient saturation from a soil testing lab, while on tests received from some other labs, sodium and other bases also contribute to that 100 percent total. Consequently, a farmer could have a field day and tell everyone he had to reach 80 percent calcium in his fields before attaining his top yields. If the intent is then to take a soil to 80 percent as that farmer found to be beneficial, be sure to send it to the same lab for analysis before deciding to spend what it takes to achieve that percentage. If a soil test from a different lab shows 68 percent calcium saturation when the lab that farmer uses shows it as 80 percent, then it can be a costly mistake to buy and apply the calcium required to reach 80 percent on the test that is showing 68 percent. Potassium Potassium is another example of how number differences on test reports can be misleading. To be most effective for growing crops on the test we use, potassium should be a minimum of 2 percent and a maximum of 7.5 percent to avoid problems caused by having too little or too much. For example, from the test we use, farmers are advised not to drive potassium above 7.5 percent because that will tie up boron availability and above this level also increases weed pressure in the field. Farmers and growers can see this happening to their crops and in their fields. Yet when the same soil is tested by another very reputable soil laboratory, they report that soil as having 8.5 percent potassium. For those who think 7.5 percent on one test means the same on tests from other labs, this now becomes a bone of contention, bringing claims that soil test numbers are just not reliable. If farmers using the test that recognizes the same results at 8.5 percent as the other test at 7.5 percent, then the numbers on the tests are certainly reliable, it is just the ability of the user to interpret those results that must be learned. But such differences as described in the paragraph above can cause complications when striving to educate farmers and growers about the value of using soil tests. Another problem with high potassium is that when combined with the sodium percentage, and both added together total 10 percent or higher, this will cause manganese uptake to be blocked from the plant, even on soils that show to have excellent manganese levels. But this is not true on the soils that show potassium as 8.5 percent, because then the soils have to be at least 11.00 percent before that happens, and that is assuming that sodium would be Continued on Page 22 Soils that test high in magnesium still grow crops that are deficient in magnesium. Photo courtesy of Neal Kinsey, Kinsey Ag Service. 20 Organic Farmer April/May 2019
California Organic Fertilizers, Inc. We are available to help you develop an agronomy based fertility plan including Nitrogen Budgeting, food safety planning and/or crop quality improvement. We are Certified Crop Advisors and are very skilled in organic crop nutrition. If you are experiencing low yields, poor crop quality, soil health issues, excessive nitrogen usage or costs, or plant disease problems, give us a call. We can help. COFI offers free consultations, custom nutrient planning and in-field evaluations for all crops from alfalfa to zucchini. 10585 Industry Ave., Hanford, Ca 93230 ♦ 800.269-5690 ♦ www.organicag.com ♦ info@organicag.com April/May 2019 www.organicfarmermag.com 21
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