Manure pellet, woodchip and their biochars differently affect wheat yield and carbon dioxide emission from bulk and rhizosphere soils.

Abstract

Application of biochars produced by pyrolyzing organic residues to cropland has been proposed to be an effective approach to better use of organic residues, decrease soil greenhouse gas emission and increase soil fertility. However, the effect of biochar application on processes occurring in the bulk soil vs that in the rhizosphere is poorly understood. This study investigated the effects of manure pellet and woodchip biochars, as compared to that of unpyrolyzed (raw) manure pellet and woodchip, on plant grain yield, and soil respiration in the bulk and rhizosphere soils in a greenhouse experiment using the rhizobox technique. The raw manure pellet and woodchip and their biochars were applied to the soil at the rate of 57\u202ft\u202fha-1 and spring wheat (Triticum aestivum L. var. GP168) was grown in the rhizosphere compartment of the rhizobox. Soil amendment with raw manure pellet and its biochar significantly increased plant grain yield by 36.3 and 16.1%, as compared to the control (without amendment), while raw woodchip and its biochar applications significantly decreased plant grain yield. Manure pellet and woodchip biochars significantly reduced soil respiration from the rhizosphere by 24.6 and 29.7%, respectively, relative to the control, but not that from the bulk soil (P\u202f>\u202f0.05). Relativized cumulative CO2 emission was significantly reduced by both manure pellet and woodchip biochars from rhizosphere and bulk soils. Dissolved organic carbon and nitrogen were increased (P\u202f<\u202f0.01) in all soil amendment treatments in both bulk and rhizosphere soils, but microbial biomass carbon and nitrogen in the rhizosphere soil were reduced by manure pellet biochar application. We conclude that biochars produced from organic residues have differential impacts on processes in bulk and rhizosphere soils, and thus measurements based on bulk soil alone may result in erroneous conclusions about the effect of biochars on soil CO2 emission.