Effects of weed control and fertilization on soil carbon and nutrient pools in an exotic pine plantation of subtropical Australia
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Soil carbon (C) and nutrient pools under different plantation weed control and fertilizer management treatments were assessed in a 7-year-old, F1 hybrid (Pinus elliottii var. elliottii × Pinus caribaea var. hondurensis) plantation in southeast Queensland, Australia. This research aimed to investigate how early establishment silvicultural treatments would affect weed biomass, soil C, nitrogen (N) and other nutrient pools; and soil C (δ13C) and N isotope composition (δ15N) to help explain the key soil processes regulating the soil C and nutrient pools and dynamics.
Materials and methods
Soils were sampled in June 2006 in both the planting row and in the inter-planting row at three depths (0–5, 5–10, and 10–20 cm). Soil parameters including total and labile C and N pools; soil δ13C and δ15N; total phosphorus (P); extractable potassium (K); moisture content and weed biomass were investigated.
Results and discussion
The luxury weed control treatments significantly reduced weed biomass and its organic residues returned to the soil in the first 7 years of plantation development. This resulted in significant variations at some depths and positions in soil δ13C, δ15N, extractable K, hot water extractable organic C (HWEOC), hot water extractable total N (HWETN), potentially mineralizable N (PMN), and soil moisture content (MC). Luxury weed control in the absence of luxury fertilization also significantly decreased extractable K. There was a significant interaction between soil depth and sampling position for soil total C, total N, HWEOC, and HWETN. Weed biomass correlated positively with soil total N, δ13C, PMN, MC, HWEOC, and HWETN.
Luxury weed control treatments significantly reduced weed biomass leading to a reduction of soil organic matter. Soil δ13C and δ15, together with the other soil labile C and N pools, were sensitive and useful indicators of soil C dynamics and N cycling processes in the exotic pine plantation of subtropical Australia.
KeywordsC and N pools Exotic pine plantation Silviculture Soil organic matter
Respect and gratitude go to colleagues in the Centre for Forestry and Horticulture at Griffith University for their assistance with the field work, guidance and persistence; and to Mr. Scott Byrne and Mr. and Mrs. Diocares of Griffith University technical staff for technical assistance with aspects of analysis for this research. We also acknowledge operating costs, access to GYM350 and technical support from Forestry Plantations Queensland (in particular Dr. Ken Bubb, Mr. Paul Keay, Dr. Marks Nester, Mr. Ian Last), and from the numerous staff who were responsible for the development and maintenance of the GYM350 site. Paula Ibell was supported by a research scholarship grant through the Australian Research Council and an extension scholarship from the Centre for Forestry and Horticulture Research, Griffith University.
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