Effects of Biochar on Soil Microbial Communities and Nitrogen Cycling in Two California Nutrient Management Systems.

Substantial biochar research has elucidated that biochar amendment to soils can influence microbially mediated nutrient cycling. Increases in microbial abundance and plant-available nutrients have been reported after biochar application, particularly in more nutrient-poor, acidic soils in tropical regions. There is less known about how biochar affects microbial and nutrient dynamics in more higher fertility soils of temperate regions, such as those in California. A field experiment was established in May 2012 at the Russell Ranch Sustainable Agriculture Facility in Davis, CA. Russell Ranch’s design provides a unique opportunity to analyze and compare cropping and management systems in the long-term and at an applicable farming scale. The experiment is in a RCBD with 2x2 factorial treatments of fertilizer type—either mineral fertilizer or composted poultry litter—and biochar amendment of either 0 or 10 t ha^-1, equivalent to approximately 0.5% (w:w). The biochar used in this study is produced locally from walnut shells through gasification at 900°C and was applied once to a depth of 15cm when the experiment was established. The plots have been planted in a tomato-corn rotation. Soil sample cores from 0-30cm were collected over several time points in summers 2013 and 2014 during corn and tomato growing seasons, respectively. Phospholipid fatty acid analysis (PLFA) was used to evaluate changes to soil microbial community composition as a result of biochar application. In addition, quantitative PCR (qPCR) was used to analyze how biochar affects the abundance of bacterial and archaeal 16s rRNA genes and nitrogen (N) cycling genes amoA, nirK, nirS, and nosZ. In conjunction with this assessment of nitrifier and denitrifier microbial communities, the effects of the biochar-fertilizer treatments on N transformation dynamics was examined. Exchangeable nitrate and ammonium-N concentrations were analyzed on all soil samples, and potentially mineralizable N (PMN) was assessed by measuring ammonium production over the course of an anaerobic incubation. Total carbon (C) and N, pH, dissolved organic C, and exchangeable cations (Ca, K, Mg, Na) were also measured on soil samples, and crop yield and quality were assessed at the end of each growing season.