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  • Author or Editor: Ed Gilman x
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Columns (4 × 15 cm) of a pine bark medium amended with the equivalent of 4.2 kg per cubic meter of dolomitic limestone and either 0, 2.4, 4.7, 7.1 or 9.5 mg of urea-formaldehyde (38% N) per cubic centimeter of medium were leached daily with 16 ml of deionized water (pH 5.5). Leachate total N, NO3 --N and NH4 +-N concentrations were determined on day 1, 3, 5, 7, 14, 28, 49, 91, 133, 203, 273 and 343. Leachate total N ranged from 600 ppm on day 1 for the 9.5 mg treatment to 4 ppm on day 273 for the 2.4 mg treatment. Leachate NH4 +-N concentrations ranged from 38 ppm c4 day 3 for the 9.5 mg treatment to less than 1 ppm on day 7 for the 2.4 mg treatment and were less than total N concentrations at each sampling time. Leachate NO3 --N was not detectable during the experimental period. Eleven, 16, 20 and 25% of the applied N leached from the columns amended with 2.4, 4.7, 7.1 or 9.5 mg of urea-formaldehyde per cubic centimeter of pine bark, respectively, during the 371 day experiment.

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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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