UREA FERTILIZATION EFFECTS ON NUTRIENT-UPTAKE AND GROWTH OF PLATANUS-OCCIDENTALIS DURING PLANTATION ESTABLISHMENT

The benefit of fertilizer application during establishment of a tree p lantation depends on effective nutrient uptake and the utilization of the nutrients in growth. Five urea treatments (0, 50, 75, 150, and 450 kg N/ha) were applied in a completely randomized plot design to a fie ld planted with American sycamore (Platanus occidentalis L.) seedlings to evaluate growth responses and nitrogen use efficiency during the f irst season of plantation establishment. The site was in the Oak Ridge Reservation in eastern Tennessee on a highly weathered soil. Harvests were conducted on 3 occasions during a 22 week experimental period, a nd dry weights of stems, leaves, and large and small roots were measur ed. Chemical analyses were conducted on plant tissues from the 0, 75, and 450 kg N/ha treatments. Plant dry weight increased with urea appli cation and growth analysis showed that this was mainly associated with increase in leaf area and to a minor extent with increase in net assi milation rate. Root weight increased significantly with urea applicati on. The specific absorption rate of roots for several nutrients was gr eater at higher urea levels for the first 2 harvest periods, but this pattern reversed during the 3rd growth period. Surprisingly, manganese uptake and the specific absorption rate for manganese were enhanced w ith higher urea application. The acidifying effect of urea nitrificati on is a likely explanation for the increased Mn availability, and nitr ate leaching and/or nitrogen immobilization contributed to low uptake of urea-N by the seedlings. The proportion of the applied nitrogen inc orporated into the seedlings was 1.5 and 0.6% for the 75 and 450 kg N/ ha urea treatments, respectively. Broadcast fertilizer application is not an effective way of supplying nutrients to seedlings during planta tion establishment.