SLOW-RELEASE FERTILIZATION REDUCES NITRATE LEACHING IN BAREROOT PRODUCTION OF PINUS STROBUS SEEDLINGS

Abstract

The nitrate (NO3 - ) leaching potential from bareroot tree nurseries is great, yet no researchers have investigated the effect of slow release fertilization on NO3 - leachate concen- trations. The effects of slow release fertilizer on nitrate-nitrogen (NO3-N) leachate concentra- tions, seedling morphology and nutrient content, soil nitrogen (N), and cation leachate concen- trations were studied in the bareroot production of Pinus strobus (L.) (eastern white pine) seedlings in southwestern Wisconsin. Three fertilizer treatments were used: slow release 1 (SRF1, 19N:6P2O5:1K2O); slow release 2 (SRF2, 12N:0P2O5:42K2O); and a conventional fertil- izer (Conv, 15.5N:0P2O5:0K2O). A total of 180 and 52 kg N/ha (161 and 47 lb/ac) were applied in the Conv and SRF treatments, respectively. Over a 2-year period, soil leachate concentrations were collected weekly (May to December) from porous cup samplers installed at a depth of 1 m (3.3 ft) below the surface; soil was collected every 2 weeks, and plant tissue was collected once at the end of each growing season (late August). There were no differences in seedling morphology (height, diameter, dry mass) during the first or second growing season. Seedling nutrient concentrations were the same for all treatments at the end of first growing season, but Conv-treated seedlings contained greater concentrations of N (33 g/kg N for Conv compared to 30 g/kg for SRF) by the end of the second growing season. Nitrate-N leachate concentrations were greater for the Conv treatment compared to both SRF treatments during the first and second growing seasons. However, treatment did not affect cation leachate concentrations. Similarly, there was little difference in soil N among treatments. Overall, SRF reduced NO3-N leachate concentrations in bareroot nursery tree production without sacrificing seedling quality.