Effect of nutrient availability and competition control on end of rotation C, N, and P accumulation and retention in loblolly pine forests in north-central Florida

Effect of nutrient availability and competition control on end of rotation C, N, and P accumulation and retention in loblolly pine forests in north-central Florida

Background/Question/Methods Managed pine forests in the southeastern United States are critical to the regional economy and the uptake of CO2. Fertilization and competition control is widely used to increase the production of these forests. The  question of this study is how does competition control and fertilization affect C, N, and P dynamics in intensely managed loblolly pine forests? We examined the end of rotation effects of fertilization and weed control on C, N, and P dynamics for a managed loblolly pine (Pinus taeda L.) forest in north-central Florida. We determined the effect of fertilization with different nitrogen and phosphorus fertilizers (diammonium phosphate (FDAP; 250 kg N ha-1, 90 kg P ha-1)); triple superphosphate (FTSP; 200 kg N ha-1, 90 kg P ha-1)), weed control (W) and the combined application of these treatments  on C accumulation, and N and P accumulation and retention. Plants tissues and forest floor were collected at the end of 25 year rotation and soils were sampled at depth intervals of 0-10, 10-20, 20-50 and 50-100cm. Samples were analyzed for total C, N and P and extractable NH4+, NO3- and PO43-. Results/Conclusions FDAPW and FTSPW significantly increased total aboveground biomass by 22% and 20%, respectively, above the control. These combined treatments also had greater accumulation of C than the fertilization alone in soils and vegetation. FTSP and FTSPW had greater N accumulation than FDAP and FDAPW in soils and forest floor.  FDAP and FDAPW increased P accumulation in soils and vegetation compared with FTSP and FTSPW. For soils, C,N and P decreased from 0-10 cm to 20-50 cm, but there was a relative increase in the 50-100 cm depth, likely due to the presence of a spodic horizon.  The type of fertilizer was not significant for any treatment. Soil extractions of NH4+ and NO3- (KCl) and PO43- (Mehlich III) indicated few significant differences among treatments except for PO43-, which was significantly greater in the FDAPW than the FTSPW treatments in the 20-50 cm soil layer. . Analysis of data of effects of intensive silvicultural treatments on N and P retention is ongoing.