Short-term response of soil respiration and soil enzymatic activities to biochar application in semiarid agricultural soils under a climate change scenario

The application of biochar is presumed to be a climate change mitigation strategy in agriculture. However, we still need to better understand the effects of biochar application on soil properties, particularly on soil microbial activity. This is because soil microorganisms play a key role in ecosystems functioning, as they have a central role in soil metabolic activity given that they are responsible for soil organic matter decomposition and nutrient cycling. Conversely, little is known about how climate change will affect the soil microbial activity. In a rainfed field experiment, we studied the effect of forecasted warming and rainfall reduction on soil respiration and soil enzymatic activities after 3 years of consecutive application of biochar at a rate of 20 t/ha on a barley-camelina-fallow rotation in a semiarid region in Central Spain. Soil respiration was not affected by the application of biochar or/and warming and rainfall reduction treatments in comparison to the control treatment (no amendment). However, biochar amended soils had lower temperature sensitivity of soil C mineralization in the first two years when soils were cultivated but higher temperature sensitivity of soil C mineralization in the third year during fallow treatment. Enzymes involved in the C and N cycles (dehydrogenase, \u3b2-glucosidase and urease) significantly increased their activity under warming and rainfall reduction treatments, albeit biochar application tended to decrease the enzymatic activity under those treatments

Soil respiration and soil organic matter pools in soils amended for 7 years with biochar combined with mineral and organic fertilizers

Biochar application is now considered to be one of the most promising agricultural practices to mitigate climate change. However, to fully assess the benefits of biochar, we still need to better understand its effects on soil properties, and particularly on native soil organic matter (SOM) dynamics. In this work, we investigated soil respiration and changes in SOM pools (mineral-free, intraaggregate, and mineral-associated SOM) as affected by the application of 20 t / ha per year of biochar alone or combined with mineral fertilizer, municipal solid waste compost, or sewage sludge. The experiment was run for 7 years in a semiarid agricultural soil. We found that biochar had no effect on soil respiration with respect to mineral fertilization and no amendment (control), and tended to decrease CO2 emissions from soils amended with municipal solid waste compost and sewage sludge. Biochar accumulated mainly in the mineral-free SOM fraction and its addition, especially in combination with municipal solid waste compost, promoted the amount of SOM occluded with aggregates and associated to mineral surfaces