Carbon stability and soil N2O emissions: Pyrolyzed or unpyrolyzed manure?

Pyrolysis is a useful alternative to current waste management practices. Manure biochars can be used as C-rich soil amendments, reducing the risk of greenhouse gas (GHG) emissions derived from unpyrolyzed manure decomposition. In this study, two manure biochars and their feedstock were used as soil treatments to evaluate the impact of pyrolysis on CO2 and N2O emissions, C stability, and global warming potential (GWP) for one year under field conditions. The experiment included five treatments: unamended soil (control), pig manure (PM), pig manure biochar (PMB), dairy manure (DM), and dairy manure biochar (DMB). The amendments were applied at a 1% w/w, adding approximately 0.5 kg C m−2. All amendments increased soil CO2 emissions; however, C mineralization was lower in pyrolyzed manures than in their corresponding feedstocks. CO2–C emissions were 8.35%, and 63% of the C from biochar and manure treatments, respectively. Biochars reduced soil N2O emissions, producing a negative N2O emission factor (N2O Ef), whereas manure treatments induced N2O fluxes for 105 days, with an N2O Ef of 0.27% after one year. Soil C stock variations were 16.4 and 6.58 t CO2-eq avoided ha−1 in treatments of biochars and manures, respectively. The mitigation potential of unpyrolyzed manure was affected by the high CO2 and N2O fluxes, whereas the biochar treatments reduced the GWP due to the changes in soil C stock with a low impact on soil emissions. Manure was more stable after pyrolysis, indicating that manure biochars are more favorable as soil amendments for environmental purposes. This could reduce the C footprint of pig and dairy farms, promoting the enhancement of soil C stocks.Fil: Ginebra Aguilar, Milagros. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Muñoz, Cristina. Universidad de Concepción; ChileFil: Zagal, Erick. Universidad de Concepción; Chil

First national-wide survey of trace elements in Cuban urban agriculture

International audienceAbstractOver the last three decades, urban agriculture has been improving food security in Cuba by providing fresh vegetables within and on the outskirts of cities and villages. However, organic fertilizers and substrates that are used in urban agriculture systems can be contaminated by trace elements and accordingly pose risks to human health. This study was carried out to measure the concentrations of cadmium, lead, arsenic, selenium, mercury, nickel, and chromium in composts and substrates used in Cuba’s urban agriculture, as well as in vegetables grown in this cropping system to assess risks to human health. Extraction of trace elements from samples was performed with a mixture of nitric and hydrochloric acid in a microwave oven. Cadmium, lead, nickel, and chromium were determined via optical emission spectrometry, and mercury, selenium, and arsenic were measured using an atomic absorption spectrophotometer coupled with a hydride generation system. We demonstrated that the concentrations of trace elements in organic fertilizers, with the exception of compost from municipal solid waste, were within permissible values and do not pose risks to human health. The compost produced from municipal solid waste and the substrates prepared with this material presented cadmium and lead concentrations above maximum permissible concentrations. This work represents the first national-wide survey of trace elements in Cuban urban agriculture. As a result of this investigation, the use of municipal-solid-waste compost for food production was forbidden in Cuba