| Straw is the carrier of material, energy and nutrient, there is limited information about how it influences dryland soil carbon source/sink after returning the carbonization straw, whether it will improve the soil carbon storage capacity, increase carbon sequestration and reduce carbon emissions or not in farmland. The effects and mechanism of straw-biochar on farmland carbon emissions, soil carbon dynamics and plant biomass carbon fixation sequestration rules and mechanisms are analyzed, that maybe provide scientific evidence for reasonably applying biochar to carbon budget and promote efficient utilization of straw resource in dryland.This study based on inputting different amounts of biochar from a field experiment, regarded spring maize as the object in Loess Plateau dryland, evaluated the effects of biochar on the transformation and balance of organic carbon in farmland ecosystem. The experiment included eight treatments: C0N0(without biochar, without nitrogen), C0N1(without biochar, nitrogen 225 kg N·hm-2), C0N1M(without biochar, nitrogen 225 kg N·hm-2, film mulching)、C1N1(biochar 10 t·hm-2, nitrogen 225 kg N·hm-2), C2N1(biochar 20 t·hm-2、nitrogen 225 kg N·hm-2)、C2N1M(biochar 30 t·hm-2, nitrogen 225 kg N·hm-2)、C3N1(biochar 30 t·hm-2, nitrogen 225 kg N·hm-2, film mulching), C5N1(biochar 50 t·hm-2, nitrogen 225 kg N·hm-2). The results showed as follows:1. The spring maize farmland showed the sink of CH4 and the source of CO2 in different treatments, and the CO2 emission flux appeared some variation of the peak value in two spring maize growing seasons. The CO2 emission flux and the cumulative total emissions was inordinately reduced with different biochar and nitrogen application, The effects of CH4 emission flux and cumulative total emission were vary from the amount of biochar and the test cycle.2. Soil temperature and water content was an important factor to influence CO2 and CH4 emissions of spring maize farmland. The average soil temperature and water content of 0 cm and 10 cm were increased after biochar addition which it did not significantly affect the relationship between soil temperature, water content and CO2, CH4 emission flux. There was a significant positive correlation between CO2 emission and temperature of 0 cm and 10 cm soil(P<0.05), while there were negative correlation between CO2 emission and the soil water content and between CH4 emission and the 0 cm and 10 cm soil temperature(P<0.05), while there was a significant positive correlation between CH4 emission and the soil water content(P<0.01). And the correlation of CO2, CH4 emission and soil temperature of 10 cm was higher than that in 0 cm.3. During the experiment period, the content of soil organic carbon in farmland were as follows: 0-20 cm soil layer > 20-40 cm soil layer > 40-60 cm soil layer, there was a significant difference among this three soil layers. Biochar addition could increase soil organic carbon content in 0-20 cm in dryland,that was the most significant in the treatment of 50 t·hm-2 biochar(225 kg N·hm-2) application. Film mulching significantly reduced the content of soil organic carbon in the 0-20 cm soil layer with biochar addition.4. Biochar and nitrogen application significantly increased the total biomass of different organs and plants of spring maize, which was not significant between different biochar treatments; film mulching significantly increased the total biomass of different organs and plants of spring maize under biochar addition.5. During different growth stages of spring maize nitrogen, biochar and film had no significantly effect on the organs organic carbon content, while the carbon sequestration of each organ was significantly increased. Compared with C0N0, the carbon sequestration increased significantly in 2014 and 2015 in the treatments of C0N1, C1N1, C2N1, C3N1 and C5N1(P<0.05); The carbon sequestration of C2N1, C3N1 and C5N1 treatments increased significantly compared with C1N1, while the difference of the shoot and regional carbon sequestration was not significant among C2N1, C3N1 and C5N1 treatments. Whether adding biochar or not, film mulching could significantly increase total carbon sequestration and regional carbon sequestration in spring maize plants. The amount of total and regional carbon sequestration were the highest in the treatment of C2N1 M, and the difference was significant with other treatments(P<0.05).All the above results have proved that, in the Loess Plateau dryland ecosystem, biochar addition will, to some extent, reduce CO2 fluxes and cumulative emissions in dryland of low nitrogen application during growing season of spring maize, increased soil organic carbon content, the biomass and carbon sequestration of spring maize, significantly influenced the conversion and carbon budget in farmland, has the effects of enhancing carbon sequestration and emission reduction in dryland. |
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