Manure-based biochar decreases heterotrophic respiration and increases gross nitrification rates in rhizosphere soil

Abstract

This study hypothesized that pyrolyzed manure pellet (biochar) reduces heterotrophic respiration and N2O emissions from wheat (Triticum aestivum L.) rhizosphere soil by affecting net and gross nitrogen (N) transformation rates and the effects differ between rhizosphere and bulk soils. The biochar significantly decreased heterotrophic respiration but not N2O emissions, while unpyrolyzed manure pellets (feedstock) increased both of them, in both the rhizosphere and bulk soils. The biochar increased gross nitrification rate by 32.9% in the rhizosphere but decreased it by 19.4% in the bulk soil while the feedstock increased gross N transformation (mineralization and nitrification) rates in both soil zones. The biochar decreased the % recovery of 15NH4+ in the NH4+-N pool in the rhizosphere but increased it in the bulk soil, as a result of biochar's contrasting effects on gross nitrification rates in the respective soil zones. It can be concluded that biochar had similar effects on heterotrophic respiration and N2O emissions but had contrasting effects on gross nitrification rates between rhizosphere and bulk soils, supporting part of the hypothesis and highlighting the importance of studying gross N transformation processes in understanding rhizosphere-biochar interactions.