Abstract
Phosphate fertilizers used in planted forests mainly come from scarce and non-renewable sources, and there is a need for new sources of phosphorus (P). An alternative is the use of sewage sludge (SS), rich in organic matter, nitrogen and P. The objectives were to evaluate the soil P availability and its effect on wood production in 22-months old Eucalyptus urograndis plantation treated with SS. A field experiment was set up in a randomized complete block design, four replicates, with the following treatments: control without fertilization; mineral fertilization (MF); 14.5 Mg ha-1 of SS + 22 kg ha-1 of P (S1P1); 29 Mg ha-1 of SS (S2); 29 Mg ha-1 of SS + 17.5 kg ha-1 of P (S2P2); and 43.5 Mg ha-1 of SS (S3), dry base. Of total P in SS, 65% was in organic form, and 42% was in labile + moderately labile forms. S2P2 and S3 positively altered the pattern of soil P distribution, with more P in the labile and moderately labile fractions than non-labile fraction, along 0-20 cm depths, than MF and control. There were higher microbial and available P as a function of SS dose. Wood volume and biomass were highly related to soil P availability as a function of SS dose. Within the SS treatments, S2P2 resulted in higher gains of volume and biomass of wood. The SS application at recommend rate, supplemented with 66% of recommended P fertilizer dose in Eucalyptus plantations, can reduce the use of P fertilizer by 33%, N fertilizer by 100% and maintain comparable soil P availability and wood production.
Highlights
Municipal wastewater treatment plants (WWTPs) have sharply increased worldwide, especially in the industrialized countries as regulated by specific laws (Nascimento et al, 2020)
SS application (i) increased concentration of available P from 7 to 43 mg kg−1, in soil surface Ap horizons (0–20 cm; Figure 4), while (ii) reducing by 33 and 100% the use of mineral P and N fertilizer, respectively (Table 6). These results demonstrated that the use of sewage sludge in commercial Eucalyptus plantations can improve soil P availability and wood yield by combining sludge and mineral P fertilizer doses, as compared to conventional NPK fertilization
The sewage sludge contained different pools of labile and nonlabile P that can be used to support the short- to long-term soil P availability to plants and to build up a legacy P in soil, when applied at the N criterion dose
Summary
Municipal wastewater treatment plants (WWTPs) have sharply increased worldwide, especially in the industrialized countries as regulated by specific laws (Nascimento et al, 2020). Depending on its origin and quality, SS may contain a huge amount of organic matter and essential elements for plants (Bettiol and Ghini, 2011), replacing or integrating mineral fertilizers of non-renewable origin widely used for crop cultivation (Alleoni et al, 2012; Ferraz et al, 2016; Abreu-Junior et al, 2017). This means that the use of non-renewable limited resources, such as phosphate fertilizers, can be significantly reduced by the SS agricultural use (Franco et al, 2010; Abreu-Junior et al, 2017), with a circular-economy perspective
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