Nitrification in a pine bark medium

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Virginia Polytechnic Institute and State University


The influence of nitrification on the “soil” solution of container media has not been documented. The investigation of this influence is justified since the ionic form of N in a soil solution has a significant influence on plant tissue nutrient content and growth. Three genera of woody plants were grown in one-liter containers filled with pine bark, treated with and without a nitrification inhibitor and fertilized with 210 ml of a 100 ppm NH₄-N solution. Without the inhibitor and over time, “soil” solution NH₄-N concentrations and pH decreased and NO₃-N concentrations increased. “Soil” solution and tissue cation concentrations were generally greater without the inhibitor.

In a second experiment, pine bark in one-liter containers was treated with either 0, 3 or 6 kg lime m⁻³. “Soil” solution data and NO₃-N accumulation rate (NAR) data showed an earlier nitrification of NH₄-N at the 6 kg lime compared to the 3 kg lime treatment whereas NO₃-N was not found at the 0 kg lime treatment.

In a 3rd experiment, pine bark in one-liter containers was treated with 210 ml of either 25, 100 or 200 ppm NH₄-N. Over time “soil” solution NO₃-N concentrations were greatest and pH values were lowest at the 200 ppm N treatment. The NAR of the 25 ppm N treatment was less than the 100 and 200 ppm N treatment which were not different. The lack of correspondence between the “soil” solution NO₃-N data and the NAR data for the 100 and 200 ppm N treatments was explained on the basis of NH₄-N supply.

In a 4th experiment, pine bark in one-liter containers were subjected to either 10°, 20°, 30° or 40° C for 24 days. “Soil” solution NH₄-N concentrations decreased over time at 10°, 20° and 30°. “Soil” solution NH₄-N and NO₃-N concentrations at 40° were considerably higher and lower, respectively, than at other temperatures. Over time the general order of NAR was: 20° = 30° > 10° > 40°. Results of these experiments indicate that nitrification is an important consideration in the nutrition of container-grown plants.