Abstract
The sugar and bioethanol industry generate large amounts of filter cake and vinasse, residues that are applied to sugarcane fields as conditioners and organic fertilizers. However, these may be significant sources of greenhouse gases emissions to the atmosphere. This study assessed the impact of sugarcane straw biochar on the emissions of CO2, CH4and N2O promoted by filter cake and vinasse applied to soil, and its effects on the chemical properties and bacterial communities of a Typic Hapludox and a Quartzipsamment. A laboratory incubation was conducted for 100 days with both soils under five treatments: vinasse and filter cake amendment (FV), plus biochar at 10 (FV + B10), 20 (FV + B20) and 50 (FV + B50) Mg·ha-1, and a control. Soil pH, available P and exchangeable base contents increased with biochar added to sandy soil. Mineral N decreased with biochar addition to both soils. The FV treatment increased CO2 emissions by 5-fold and 2.4-fold in sandy and clayey soils, respectively, compared to the control. Moreover, FV +B10 increased CO2 emissions by 4% and 6.4% in sandy and clayey soils, respectively, compared to FV. Cumulative N2O emissions in FV were 537% and 125% higher in sandy and clayey soils, respectively, compared to the control. Nevertheless, increasing biochar amendment rates reduced N2O emissions from 24% to 34% in sandy soil, and from 14% to 56% in clayey soil. CH4 emissions were negligible. The effects of filter, vinasse and biochar amendments on soil amelioration were closely related to its buffering capacity. Temporal changes on bacterial community structure were more pronounced in the sandy soil compared to clayey, and indicated that N2O emission mitigation in clayey soil was directly related to biotic mechanisms, while abiotic mechanisms caused by biochar played a more important role in mitigating N2O emissions in sandy soil.
Highlights
The intensification of green cane harvesting has led to a greater deposition of leaves and tips on soil surface, ranging between 10 and 20 Mg∙ha−1 of dry matter, and the amount of sugarcane crop residues generated in Brazil is estimated in 175 million Mg∙yr−1 [1]
This study assessed the impact of sugarcane straw biochar on the emissions of CO2, CH4and N2O promoted by filter cake and vinasse applied to soil, and its effects on the chemical properties and bacterial communities of a Typic Hapludox and a Quartzipsamment
It was hypothesized that: i) The effects of biochar amendments on soil amelioration is closely related to soil buffering capacity; ii) biochar suppresses greenhouse gases (GHG) emissions from filter cake and vinasse applied to soils as a function of its application rate; and iii) soil-biochar interactions cause temporal changes in bacterial communities both directly and indirectly, affecting niche-microbe interactions related to N2O emission mitigation
Summary
The intensification of green cane harvesting has led to a greater deposition of leaves and tips on soil surface, ranging between 10 and 20 Mg∙ha−1 of dry matter, and the amount of sugarcane crop residues generated in Brazil is estimated in 175 million Mg∙yr−1 [1]. Against the claiming demand to use this biomass for bioenergy generation, the Brazilian sugarcane sector has considered the partial removal of the post-harvest residues from soil surface without harming sustainability and yields [2]. Vinasse is an acidic (pH ≈ 4.5) nutrient-dense effluent that is produced at a rate of approximately 13 L for every liter of ethanol. Filter cake is a nutrient-rich solid residue from the filtration of sugarcane juice, produced in an average of 8 kg per ton of processed sugarcane [4]. Despite vinasse and filter cake benefits to conservation agriculture [3], these residues may be significant sources of greenhouse gases (GHG), mainly nitrous oxide (N2O) and methane (CH4) [5] [6] [7]
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