Abstract
Biochar incorporation as a soil amendment has been shown to enhance soil quality. However, there has been conflicting reports on its short term effects on C and N mineralization and microbial biomass. An incubation experiment was conducted to determine the effects of three different levels (0.5, 1 and 2%) of biochar on carbon mineralization, soil organic carbon, nitrogen mineralization, microbial biomass and total nitrogen from mollisols of two different organic matter (high organic matter soil and low organic matter soil) levels. The experiment consisted of four treatments (Soil, Soil + 0.5% biochar, Soil + 1% biochar and Soil + 2% biochar) and each was replicated three times. Overall, soil respiration rate was reduced by biochar additions over a 100-day period. Two percent biochar application rate showed greatest CO2-C reduction. Soil respiration in high organic matter soil was higher than low organic matter soil. NO3--N level was reduced by biochar addition in both high and low organic matter soils. Control (Soil) of the high organic matter soil showed the highest NO3--N (33.79 mg kg-1) and NH4+-N (7.23 mg kg-1) values at 70 days. The total nitrogen was increased by biochar additions; 1 and 2% application rates showed the highest total nitrogen values. Biochar additions also increased soil microbial biomass carbon and soil microbial biomass nitrogen of both soils. Key words: Biochar, C mineralization, N mineralization, microbial biomass.
Highlights
Biochar is the product of the thermal degradation of organic materials in the absence of air and is distinguished from charcoal by its use as soil amendment (Lehmann et al, 2011)
The respiration rate of 0.5% biochar was higher at the beginning than the control until 20 days incubation (15 mg CO2-C g-1d-1) for high organic matter soil (Figure 1a) and 15 days incubation (15.4 mg CO2-C g-1d-1) for the low organic matter soil (Figure 1b)
It was observed that the higher the rate of biochar applied, the lower the amount of CO2-C released, which is an indication that there is decreased decomposition following biochar application to soils
Summary
Biochar is the product of the thermal degradation of organic materials in the absence of air (pyrolysis) and is distinguished from charcoal by its use as soil amendment (Lehmann et al, 2011). It is considered as a carbon-rich organic matter with long residence time up to hundreds of years (Kuzyakov et al, 2009; Lehmann et al, 2015). The effect of biochar is said to be strongly connected to the soil properties and the climate but the correlations with crop yield are not completely clear (Cornelissen et al, 2018). The differing results observed in previous studies may have been due to variations in the proportion of labile C in biochars (Luo et al, 2011), the presence or absence of plant-derived labile organic matter input in soil (Keith et al, 2011), and the degree of biochar ageing in soil (Zimmerman et al, 2011; Cross and Sohi, 2011; Liang et al, 2010)
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