Temperature sensitivity of soil organic matter decomposition varies with biochar application and soil type

Biochar application has the potential to improve soil fertility and increase soil carbon stock, especially in tropical regions. Information on the temperature sensitivity of carbon dioxide(CO2) evolution from biochar-amended soils at very high temperatures, as observed for tropical surface soils, is limited but urgently needed for the development of region-specific biochar management targeted to optimize biochar effects on soil functions. Here, we investigated the temperature sensitivity of soil respiration to the addition of different rates of Miscanthus biochar(0, 6.25, 12.5, and 25 Mg ha-1) in two types of soils with contrasting textures. Biochar-amended soil treatments and their controls were incubated at constant temperatures of 20, 30, and 40℃. Overall, our results show that: i) considering data from all treatments and temperatures, the addition of biochar decreased soil CO2 emissions when compared to untreated soils;ii) CO2 emissions from biochar-amended soils had a higher temperature sensitivity than those from biochar-free soils;iii) the temperature sensitivity of soil respiration in sandy soils was higher than that in clay soils;and iv) for clay soils, relative increases in soil CO2 emissions from biochar-amended soils were higher when the temperature increased from 30 to 40℃, while for sandy soils, the highest temperature responses of soil respiration were observed when increasing the temperature from 20 to 30℃. Together, these findings suggest a significantly reduced potential to increase soil organic carbon stocks when Miscanthus biochar is applied to tropical soils at high surface temperatures, which could be counteracted by the soil-and weather-specific timing of biochar application.

Biochar and sugar cane filter cake interaction on physical and hydrological soil properties under tropical field conditions

Biochar is known for its effects on carbon sequestration and soil fertility.However,there is a lack of information about its effects on soil physical and hydraulic properties for tropical soils.We assessed the effects of biochar(BC)plus sugar cane filter cake(FC)rate,and time of interaction on soil physical and hydraulic properties under humid tropical conditions.For this purpose,a field experiment was installed at a loamy sandy soil with five treatments and four replicates:control(only soil),25 Mg ha^(−1) sugar cane filter cake,and 25 Mg ha^(−1) sugar cane filter cake plus 6.25,12.5,and 25 Mg ha^(−1) Miscanthus biochar,respectively,two soil depths(0-10 and 10-20 cm)and two times of interaction(9 and 18 months).Physical prop-erties(aggregate stability,bulk density,total porosity,pores size distribution)and hydraulic properties(soil water holding capacity,hydraulic conductivity,plant-available water holding capacity)were measured after nine and eighteen months.The bulk density decreased slightly,and the porosity increased after nine months,for the biochar plus sugar cane filter cake(both 25 Mg ha^(−1)).After 18 months,biochar plus filter cake interaction increase micropores,aggregate stability,and plant-available water content.Saturated hydraulic conductivity was not influenced by sugar cane filter cake.However,biochar significantly reduced saturated hydraulic conductivity when combined with sugar cane filter cake after 18 months.We concluded that sugar cane filter cake in combination with biochar modified the pore size distribution,slightly increased plant-available water holding capacity,and significantly decreased saturated hydraulic conductivity.