Effect of agricultural management on N 2 O emissions in the Brazilian sugarcane yield

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Soil Biology and Biochemistry, ISSN: 0038-0717, Vol: 109, Page: 205-213

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Felipe J.C. Fracetto; Giselle G.M. Fracetto; Simone C.B. Bertini; Carlos C. Cerri; Brigitte J. Feigl; Marcos Siqueira Neto
Elsevier BV
Immunology and Microbiology; Agricultural and Biological Sciences
article description
The expansion of sugarcane cultivation in Brazil for sugar and bioethanol production has led to increased N-fertilizer use. Today, sugarcane is harvested mechanically and resulting crop residues are retained as a mulch on the soil surface. We hypothesized that the combination of these activities (topdressing N-fertilization applied on the mulching) promotes soil conditions that modify the microbiota involved in the soil N cycle, and consequently raise N 2 O emissions. We investigated a commercial sugarcane crop to determine whether a topdressing of N-fertilizer (100 kg N ha −1 as ammonium nitrate) combined with sugarcane straw mulch (14 Mg ha −1 dry mass) change soil attributes (pH, total C and N, microbial biomass C and N, inorganic-N and WFPS%), and the copy numbers of genes ( nirS, nirK, norB and nosZ ) involved in soil N-transformation with consequent increases in N 2 O emissions. The 3 × 2 factorial treatments were: three soil surface treatments: i) bare soil (no-straw); ii) sugarcane straw and, iii) synthetic straw (polypropylene strips) and with or without an application of N-fertilizer. The mulch treatments (sugarcane or synthetic) produced the highest emissions, which occurred at two ‘N 2 O hot moments’ within 10 days after fertilization. Regarding fertilizer treatments, cumulative N 2 O emissions did not differ between the straw treatments (∼99 mg m −2 ) but were higher than those of the no-straw treatments (51 mg m −2 ). Similar behavior was found in the no-fertilizer treatments where the highest emissions were found in the straw treatments (∼30 mg m −2 ) and lowest in the no-straw treatments (6 mg m −2 ). The copy numbers of the nirS, nirK, norB and nosZ genes were equal in the straw treatments, but were significantly lower in the no-straw. While high copy numbers of the norB gene were associated with the ‘N 2 O hot moments,’ the same was not observed for the other genes. Redundancy analysis (RDA) indicated that N 2 O emissions were higher in relation to microbial biomass and WFPS% than they were in relation to the norB gene and inorganic-N. Our findings show that N-fertilization combined with sugarcane-straw mulching raised N 2 O emissions by promoting a chain of interactions between soil attributes and microorganisms involved in N-transformation.