Effects of soil compaction, forest leaf litter and nitrogen fertilizer on two oak species and microbial activity

A greenhouse study examined the effects of soil compaction and forest leaf litter on the growth and nitrogen (N) uptake and recovery of red oak (Quercus rubra L.) and scarlet oak (Quercus coccinea Muencch) seedlings and selected microbial activity over a 6-month period. The experiment had a randomized complete block design with three replications. Ammonium N-15-sulfate at 33 mg N-15 kg(-1) was used to quantify seedling N uptake and recovery. After 6 months, seedlings were harvested and analyzed for dry matter production, total N, N-15 uptake and N derived from N-15 labeled fertilizer (Ndff). Soil enzyme activity and soil microbial biomass C and N were measured as indicators of microbial activity. Soil compaction significantly decreased seedling height, dry matter production, and N-15 recovery of both oak species. Significantly greater N losses were observed in compacted pots compared with the non-compacted pots. Less N-15 was immobilized in the soil microbial biomass in the compacted pots than under non-compacted conditions, probably due to greater overall N-15 losses in the compacted conditions. Soil compaction significantly affected microbial activity by reducing acid phosphatase. Severe soil compaction decreased young tree growth and reduced N fertilizer uptake. (C) 2003 Elsevier Science B.V. All rights reserved.