Labile and Non-Labile Fractions of Phosphorus and Its Transformations in Soil under Eucalyptus Plantations, Brazil

Abstract

Phosphorus (P) is the main limiting nutritional factor in the cultivation of Eucalyptus in Brazil. Despite this, little is known about the P fractions and dynamics in Eucalyptus soils in tropical regions. The aims of this study were (1) to evaluate the distribution of labile and non-labile fractions of P in soil in 10 sites of Eucalyptus in the state of São Paulo, Brazil and (2) to determine the interactions among the P fractions and to identify which fractions act as sinks or sources for the available P fraction. The P fractions were separated using the Hedley sequential extraction method, and the P transformation processes were evaluated via structural equation modeling. The labile P (resin-Pi + Pi and Po in NaHCO 3 ) varied between 6% and 16%, the moderately labile P (Pi + Po in NaOH) varied between 28% and 40%, the occluded P (Pi + Po in Sonicate + NaOH) varied between 6% and 19%, the P associated with Ca (HCl-Pi) varied between 0.4% and 3% and the residual-P varied between 35% and 47%. The hypothetical structural model of soil P cycle was composed of four P pools (latent variables): the organic pool, occluded pool, inorganic pool, and available pool. The structural model was adequate to identify functional pools of P in soil, and to identify transformation processes of P based on the source-sink relationships. The available P pool was highly dependent on inorganic and occluded pools and the organic pool acted predominantly as a sink of P on available and inorganic pools. The results reinforce the high level of recalcitrance of the organic pool and the fact that Eucalyptus plants must access pools of limited-availability P to meet their nutritional demands.

Effect of Timber Harvest Intensities and Fertilizer Application on Stocks of Soil C, N, P, and S

“…Second, more studies should be implemented to better understand the contributions of organic and inorganic (mainly to P) fractions of low lability on the supply of nutrients to trees. Our results and others [29,41] suggest that Eucalyptus trees can access P fractions not identified by traditional soil analysis methods. Regarding N concentrations, even with high harvest outputs (more than 500 kg·ha −1 in each crop rotation) no response to N application by fertilization was found in terms of wood productivity in Brazilian conditions [28].…”

“…This discrepancy suggests that the Eucalyptus trees take up soil P hidden in fractions not extracted by the traditional resin method of analysis. Eucalyptus species can uptake organic and inorganic P fractions by phosphatase and exudation of low molecular mass acids [41]. More studies are necessary to clarify the complete origin of P absorbed by trees.…”

“…This study shows that in tropical conditions the use of forest residues for bioenergy purposes should be carefully considered, taking into account the unique conditions of each site. On steep sites and/or those with low buffer capacity, all forest residues should be retained on the soil in order to avoid soil erosion [43] and depletion of soil nutrient pools [14,16,29,30,33,41]. In sites with favorable conditions for residue removal, preference should be given to the coarse residues due to their high caloric power and reduced nutrient concentration.…”

Soil Chemical Attributes, Biometric Characteristics, and Concentrations of N and P in Leaves and Litter Affected by Fertilization and the Number of Sprouts per the Eucalyptus L’Hér. Strain in the Brazilian Cerrado

“…For the pH, the decreasing linear function was adjusted according to the increment of the fertilizer rates noted above. (5) 0.45 (6) 0.87 (7) 13.83 2.55 (8) 0.18 (9) For the chemical attributes of the soil at a depth of 0.40-1.00 m, 44 months after choosing the Eucalyptus sprouts listed in Table 4, we verified a higher S-SO 4 content in the one sprout per strain condition. This same finding was noted for the Mn content.…”

Applying Different Sample Treatment Strategies for Evaluating Phosphorus Distribution in Orange Juice

“…Several authors 22,23 have used the P fractionation technique proposed by Hedley et al, 24 which uses extractors from smaller to larger extraction forces, which remove P inorganic (Pi) and organic (Po) from the most available to the most stable forms. With the modifications proposed by Condron et al, 25 the extractors used in the fractionation are, sequentially, anion exchange resin, NaHCO 3 0.5 mol L -1 at pH 8.5, NaOH 0.1 mol L -1 and H 2 SO 4 + H 2 O 2 + MgCl 2 .…”