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  • Author or Editor: Jerry Kidder x
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Nitrogen fertilizer rates are often expressed as lb N/A. However, without explanation of the actual area fertilized, exact rates cannot be duplicated because the rate may be given in terms of an acre equivalent. For example, 100 lb N/A for turf implies that 100 lb of N was applied on 43,560 sq ft or real estate acre (R.E.A.). The same rate applied to row crops where the actual area fertilized consists of bands that total 0.05 of a R.E.A., means that 20 times the amount of fertilizer was applied per sq ft even though the rate was reported as 100 lb of N/A and 100 lb of N were actually applied. Fertilization of trees in a field nursery is similar in concept, but what does a rate of 100 lb of N/A mean? If the area fertilized around the trees was 0.05 of a R.E.A., it is not clear whether 0.002 lb N/sq ft or 0.04 lb N/sq ft was applied. If 0.002 lb N/sq ft was applied, then 5 lb of N would have been applied on 0.05 of a R.E.A., thus the rate was given as 100 lb N/A equivalent. To avoid confusion, area fertilized per plant or tree, amount per unit area, number of applications per year and number of plants per R.E.A. are needed to actually calculate the amount of N applied per year per R.E.A.

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The Mehlich-l (double-acid) soil test extractant is used widely on sandy soils in the southeastern United States. Research with eight major vegetables in Florida showed that the Mehlich-1 solution for phosphorus was correlated with crop yield and quality responses. Soils with a Mehlich-1 index for phosphorus greater than 30 mg·kg-1 required no phosphorus fertilization. Crop responses were not highly correlated with Mehlich-1 potassium index and it was difficult to predict crop response to potassium fertilization. The lack of predictive capability of the Mehlich-1 extractant for potassium raises questions over soil testing for potassium on sandy soils in Florida where potassium is mobile.

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