Long-term impacts of soil compaction and cultivation on soil carbon and nitrogen pools, foliar δ13C and δ15N as well as tree growth in a hoop pine plantation of subtropical Australia

Purpose The aim of this study was to examine the long-term impacts of mechanical compaction and cultivation on soil C and N pools, delta C-13 and delta N-15 of soil and foliage as well as tree growth. Materials and methods In a hoop pine plantation of subtropical Australia, the diameter at breast height over bark (DBHoB) and tree height; delta C-13 and delta N-15 of soil and foliage; and soil C and N pools were determined after 17 years following forwarder compaction (control, light and heavy) and cultivation (control and disc plough) treatments. Results and discussion Light compaction was associated with the significantly higher soil total carbon (TC) and total nitrogen (TN) in the 20-30 cm soil and higher TN in the 30-60 cm soil (p < 0.01). Cultivation was linked to the significantly higher soil TC in the 0-10 cm soil, and TC, TN and hot water-extractable total nitrogen (HWETN) in the 10-20 cm soil (p < 0.01). Higher delta N-15 in the 0-10 cm soil and in the foliage in the heavily compacted plots was due to previous soil denitrification, while light compaction and cultivation were associated with the lower foliar delta C-13 due to decreased foliar N concentration and reduced photosynthesis rate with increasing foliar biomass under higher N supply. Conclusion The delta C-13 and delta N-15 of foliage and soil were useful indicators of the C and N processes in plant-soil system in response of management impacts in the plantation. Light compaction and cultivation generally had beneficial impacts on soil C and N pools over long term, whereas there was no difference in the impacts of different compaction and cultivation treatments on tree growth.