Bioenergy sub-products as fertilizers: C, N and P soil dynamics after biochar and digestate application.

GARAY MAXIMILIANO; ORDEN LUCIANO; IOCOLI, GASTON; GOMEZ MARISA

Rio de Janeiro

Congreso; 21st World Congress of Soil Science; 2018

Brazilian Soil Science Society - International Union of Soil Science

Amendments incorporated to soil of arid and semi-arid environments are quickly mineralized, with little incorporation into the stabilized soil organic matter. Anaerobic digestates contain a high proportion of available nutrients but a vestigial C content, while Biochar provides C whit great stability. The objective of this research was to evaluate the advantages of the combined use of biochar and digestate for soil fertilization through the C, N and P mineralization in a microcosms assay. Biochar was obtain by slow-pyrolysis of Aspidosperma quebracho-blanco, while anaerobic digestate of pig slurry was collected from a pig farm (SW Buenos Aires, Argentina). The parameters C, N and H (CHN 440 Analyzer), TKN, NH4 +-N and NO3 - -N (semi-micro Kjheldal) were determined. The H/C atomic ratio and C/N mass ratio were calculated. Two sets of microcosms were prepared with 100 g of sandy-loam Entic Hapludoll soil. The treatments were: unamended soil; biochar (B); pig digestate (PD), and the combination of both (B+PD) (with three replicates), levelled according to the TKN content (6.5 g 100 g-1 soil). One set of microcosms was sampled repeatedly to follow C mineralization, while for the other set a destructive sampling was used to evaluate N and P dynamics periodically during 119 days. The CO2 released was captured in a NaOH solution and was determined by back titration with HCl. The parameters NH4+-N, NO3- -N, water soluble P (Ps) and extractable P (Pe) were determined. Data were subjected to ANOVA followed by Fisher LSD for mean comparison. The B presented a lower H/C that the PD (0.51 and 1.66 respectively), indicating a lower degree of saturation (greater aromaticity), and a greater C/N (53.82 and 1.97) as consequence of high inorganic-N content of PD. B showed a short-lived primer effect at the beginning of incubation, possibly as a result of the presence of short-chain organic acids resulting from low pyrolysis temperature. As consequence of the higher proportion of recalcitrant C this period is short-lived. B presented increased CO2 accumulated, DC presented a decreasing trend (p>0.05), but it was lower than B and B+PD (p