Effect of biochar on soil respiration in the maize growing season after 5 years of consecutive application

The effect of biochar on soil respiration (Rs) over one maize-growing season was studied after 5 years of consecutive application in an intensive cropland in the North China Plain. The experiment was carried out in randomly arranged plots with four treatments being evaluated. Three replications were conducted per treatment: a control plot without biochar addition (CK), biochar incorporated at 4.5 t ha–1 year–1 (BC4.5), biochar incorporated at 9.0 t ha–1 year–1 (BC9.0), and incorporated wheat straw (SR). The Rs was determined throughout the growing season of maize in 2012. Soil temperature and moisture were measured simultaneously at 5 cm depth. The results showed that the seasonal and diurnal variations of Rs in the four different treatments were approximately equal, and there was a positive correlation between Rs and soil temperature. The Rs values of treatments BC4.5 and BC9.0 were significantly lower than of SR but not CK. Significant correlations between Rs and soil temperature and soil moisture were observed. Soil temperature had a stronger effect on Rs than did soil moisture, and Rs was more sensitive to soil temperature in the biochar treatments than in the SR and CK treatments. The application of biochar and straw increased the soil active organic carbon content, but an obvious relationship between Rs and the soil active organic carbon content was not found.