Biochar Decelerates Soil Organic Nitrogen Cycling but Stimulates Soil Nitrification in a Temperate Arable Field Trial

Abstract

Biochar production and subsequent soil incorporation could provide carbon farming solutions to global climate change and escalating food demand. There is evidence that biochar amendment causes fundamental changes in soil nutrient cycles, often resulting in marked increases in crop production, particularly in acidic and in infertile soils with low soil organic matter contents, although comparable outcomes in temperate soils are variable. We offer insight into the mechanisms underlying these findings by focusing attention on the soil nitrogen (N) cycle, specifically on hitherto unmeasured processes of organic N cycling in arable soils. We here investigated the impacts of biochar addition on soil organic and inorganic N pools and on gross transformation rates of both pools in a biochar field trial on arable land (Chernozem) in Traismauer, Lower Austria. We found that biochar increased total soil organic carbon but decreased the extractable organic C pool and soil nitrate. While gross rates of organic N transformation processes were reduced by 50–80%, gross N mineralization of organic N was not affected. In contrast, biochar promoted soil ammonia-oxidizer populations (bacterial and archaeal nitrifiers) and accelerated gross nitrification rates more than two-fold. Our findings indicate a de-coupling of the soil organic and inorganic N cycles, with a build-up of organic N, and deceleration of inorganic N release from this pool. The results therefore suggest that addition of inorganic fertilizer-N in combination with biochar could compensate for the reduction in organic N mineralization, with plants and microbes drawing on fertilizer-N for growth, in turn fuelling the belowground build-up of organic N. We conclude that combined addition of biochar with fertilizer-N may increase soil organic N in turn enhancing soil carbon sequestration and thereby could play a fundamental role in future soil management strategies.

Biochar Impacts Soil Microbial Community Composition and Nitrogen Cycling in an Acidic Soil Planted with Rape

“…As nitrification is an acidifying process, 42 alkaline biochar may create much more favorable conditions for nitrifiers thus increasing nitrification rates due to its liming effect. 43,44 The decreased N 2 O emission and increased nitrification rates demonstrate that the relative contribution of nitrification to N 2 O emissions is much less than that of denitrification (including nitrifier denitrification) in this soil. This result shows that biochar inhibition on nitrification is unlikely to be the mechanism of N 2 O reduction in the soil.…”

Biochar affects soil organic matter cycling and microbial functions but does not alter microbial community structure in a paddy soil

“…Specifically, the microbial biomass was up to 43-125% higher in BC-rich soils than in BC-poor adjacent soils during 532 days of incubation (Liang et al, 2010). On the contrary, BC amendment did not affect the DOC and dissolved organic N (DON) in one field study (Jones et al, 2012), whereas it decreased the DOC concentration (Prommer et al, 2014) in another field study. These contradicting positive and negative effects of BC application on SOM fractions may be attributed to the specific processes governing C and N cycling under specific management practices.…”

“…The addition of BC to soil can increase the SOM level (Lehmann et al, 2006), affect C cycling (Bolan et al, 2012;Farrell et al, 2015;Liang et al, 2010), accelerate nitrogen (N) dynamics (Nelissen et al, 2012) or in some cases, even reduce organic N turnover (Prommer et al, 2014). The changes in the total SOM due to management practices are gradual because SOM is a heterogeneous mixture that contains numerous compounds varying degradability and turnover rates (Stevenson, 1994).…”

“…These contradicting positive and negative effects of BC application on SOM fractions may be attributed to the specific processes governing C and N cycling under specific management practices. These processes vary with climate, crop rotation, fertilization and soil biology characteristics and consequently result in inconsistent SOM dynamics and transformation (Demisie et al, 2014;Jones et al, 2012;Lin et al, 2012;Liang et al, 2010;Prommer et al, 2014).…”

The Response of Artificial Aging to Sorption Properties of Biochar for Potentially Toxic Heavy Metals

“…The C/N ratios of biochars were 200.75 for BC A and 122.74 for BC B. LEHMANN and JOSEPH (2009) identified the C/N ratio lower than 20 as a ratio of good soil amendment. Although it is still unclear whether the C/N ratio criterion is directly applicable to biochars which do not decompose at the same rate as other organic amendments, applications of biochars with higher C/N ratios may lead to lower N uptake and a delay in N turnover in soil (PROMMER et al, 2014). Comparison of physicochemical properties of BC A and BC B showed the main differences in ash content, CEC and SA values.…”