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Impacts of timber harvest intensity and P fertilizer application on soil P fractions

Rocha, José Henrique T., Menegale, Marcella L.C., Rodrigues, Marcos, Gonçalves, Jose Leonardo de M., Pavinato, Paulo S., Foltran, Estela Couvre, Harrison, Robert, James, Jason N.
Forest ecology and management 2019 v.437 pp. 295-303
Eucalyptus, acid phosphatase, enzyme activity, excretion, fertilizer application, harvesting, inorganic phosphorus, molecular weight, phosphorus fertilizers, plantations, soil, soil organic carbon, stemwood, trees
Research has shown significant effects of timber harvest residue management on soil organic carbon (SOC), but less impact has been observed on the available P pool. The objectives of this study were: (1) to estimate the effects of different timber harvest intensities and P fertilization on soil labile P and P fate over time; and (2) to identify which soil P fractions supply P to Eucalyptus plantations cultivated in soils with low P availability. P fractions were assessed using Hedley’s sequential extraction methodology, which corresponds to differing degrees of soil P lability. Three timber harvest intensities (stemwood only, whole tree and whole tree plus litter) and two levels of P fertilization (0 and 44 kg ha−1 of P) were used. A total of 70% of total soil P was found in a non-labile form in the whole tree plus litter removal treatment, while in the whole tree treatment only 66% was found in this form. Removal of harvesting and litter residues resulted in a 40% reduction in the labile P fraction when compared to stemwood only harvested treatment even with fertilizer application. Acid phosphatase activity, which is crucial in mobilizing P for plant uptake, was 45% higher in soils that did not receive P fertilizer, but it did not resulted in higher concentration of labile P. Timber harvest intensity and P fertilizer application did not influence the soil total P concentration over 12 years of Eucalyptus cultivation. However, there was an increase in non-labile and inorganic P fractions and a reduction of labile and organic P fractions with increasing timber harvest intensity. The organic, moderately labile P fraction was the main source of P to the trees under low P availability conditions. Acid phosphatase and low molecular weight organic acid excretion seem to be important strategies of Eucalyptus species to improve P uptake.