Comparison of fertilizer nitrogen,nitrogen immobilization, carbon dioxide efflux,and leaching in peat-lite,pine,and pine tree substrates

Abstract

Additional index words. container substrate, loblolly pine, nitrogen tie-up, nitrogen drawdown , Pinus taeda, pine chips, potting media, wood fiber substrate . The objective of this study was to compare substrate solution nitrogen (N) , N immobilization, and nutrient leaching in a pine tree substrate (PTS), peatlite (PL), and aged pine bark (PB) over time under greenhouse conditions. Pine tree was produced from loblolly pine logs (Pinus taeda L.) that were chipped and milled to a desired particle size. Substrates used in this study were PTS ground a 2.38-mm hammer mill screen, PL, and aged PB. A short-term (28-d) N study was conducted on substrates fertilized with 150 or 300 mg-L-1 NO3- . Substrates were incubated for 4 days after fertilizing and NO3-N levels were determined and at the end of the incubation. A second medium-term study (10-week) also conducted to evaluate the amount of N immobilized in each substrate when with 100, 200, 300, or 400 mgL-1 N. In addition to determining the amounts of N,bstrate carbon dioxide (CO2) efflux (μmol CO2/m-2s -1) was also as an assessment of microbial activity, which can be an indication of N . A leaching study on all three substrates was also conducted to determine amount of nitrate nitrogen (NO3-N), phosphorus, and potassium leached over 14 under greenhouse conditions. Nitrogen immobilization was highest in PTS by PB and PL in both the short- and medium-term studies. Nitrogen increased as fertilizer rate increased from 100 mg-L-1 N to 200 mg-L-1 N in PL and from 100 mg-L-1 N to 300 mg-L -1 N for PB and PTS followed by a reduction no further increase in immobilization when fertilizer rates increased beyond these . Nitrogen immobilization was generally highest in all substrates 2 weeks after , after which immobilization tended to decrease over the course of several weeks less of a decrease for PTS compared with PL and PB. Substrate CO2 efflux levels highest in PTS followed by PB and PL at each measurement in both the short- and term studies. Patterns of substrate O2 efflux levels (estimate of microbial /activity) at both fertilizer rates and over time were positively correlated to N occurrence during the studies. Nitrate leaching over 14 weeks was lower PTS than in PB or PL through 14 weeks. This work provides evidence of increased activity and N immobilization in PTS compared with PB and PL. Increased N in PTS explains the lower nutrient (primarily N) levels observed in PTS crop production and justifies the additional fertilizer required for comparable growth to PL and PB. This work also provides evidence of less NO3-N leaching in compared with PL or PB during greenhouse crop production despite the higher fertilizer rates required for optimal plant growth in PTS.