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Nutrient Losses from a Forest Soil as Affected by Nitrapyrin Applied with Granular Urea¹

ABSTRACT

Nitrapyrin (2-Chloro-6-(trichloromethyl)pyridine) effects on nitrate production in a forest soil (Bladen fsl) of the Lower Coastal Plain of Florida were evaluated in a pot study. Nitrapyrin (as N-Serve® 24) was applied to the soil with two rates (25 and 100 ppm) of N as granular urea; for each N rate a range of nitrapyrin concentrations (0, 0.5, 1.0, 2.0, and 4.0% of the urea-N) was evaluated. Postfertilization leaching of N and of other nutrients and growth and nutrient uptake by seeded slash pine (Pinus elliottii var. elliottii Engelm.) were observed in unlimed (pH 5.2) and limed (pH 6.5) soil.

Nitrapyrin effects were most apparent in limed soil and at the higher N and nitrapyrin rates. In general nitrapyrin concentrations below 2.0% of the urea-N and below approximately 4.0 kg of nitrapyrin/ha were ineffective. Effectiveness increased up to the highest concentration (4.0%) and the highest rate (8.0 kg/ha). Leaching data indicate that the duration of the nitrapyrin inhibition of nitrification was from 5 to more than 10 weeks. Nitrapyrin to 8.0 kg/ha did not affect germination of slash pine seed.

Seedling N uptake and growth were reduced in proportion to nitrate-N leaching losses. Quantities of K, Ca, and Mg in leachates were also correlated with leached nitrate-N, but tissue analyses indicated that growth deficits associated with leaching were due primarily to N deficiency. In limed soil heavily fertilized with urea-N, results also suggest some benefits to pine seedling growth and N utilization associated with inhibition of nitrification apart from those attributable to reduced leaching losses of nitrate.

¹ Contribution from Soils and Fertilizer Research Branch, National Fertilizer Development Center, TVA, Muscle Shoals, AL 35660.

² Research Forester. Present address: Associate Dean, School of Forestry, Oregon State University, Corvallis, OR 97331.

Received for publication January 26, 1979. Accepted for publication May 21, 1979.