Value of Maintaining Optimum Soil pH Peanut Notes No. 17 2020

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Maintaining pH between 5.8 and 6.2 across fields is important. This minimizes aluminum toxicity on coastal plain soils in North Carolina. Soil pH in this range can also decrease the risk of zinc toxicity if levels are around 250 (N.C. Department of Agriculture & Consumer Services index) or slightly higher (zinc is in a less available form for pant uptake when pH is higher.)  Virginia market-type peanut often respond to gypsum when pH is in the optimum range (yield and market grades) but not when soil pH is lower. Peanuts also respond to inoculant for nitrogen fixation when pH is in the optimum range. These are all good reasons to make sure peanuts are grown in fields with pH levels greater than 5.8. The return on lime investment to bring pH from 5.5 to 5.8 was 11:1 in research plots when all lime cost was charged to peanuts. If prorated over 3 crops, the return would be 33:1. Keep in mind that when fields are sampled, the potential variation in pH across the field should be considered. If the average pH is 5.8, there are likely areas in the field where the pH is perhaps 5.6 or 6.2. There are few drawbacks to a higher pH. Manganese deficiency is likely (but can be corrected with one manganese spray) and Sclerotinia can be a greater problem (but you likely would need to make an application if the pathogen is present – higher pH may increase the disease in a moderate way but likely not in a catastrophic way.)  The percent of the field with low pH will determine the overall negative impact on yield. This is an unknown in most cases because many more samples would need to be collected to make a better estimate. Consider liming to get a pH of 6.0 or higher to make sure the lower pH areas of the field are corrected to the optimum level.