Impacts of poplar harvesting residue additions on soil nutrients and CO 2 emission

Abstract

Objective Impacts of the addition of poplar harvesting residues on soil nutrients and CO2 emission were investigated in controlled conditions to provide a reference for its potential utilization. Method The indoor incubation experiment was carried out by selecting logging residues of twigs, barks, and leaves from a poplar plantation and the rice straw as research materials. Based on the litter amount in the unit area of the poplar plantation, the fresh soil equivalent to 100 g of dry soil weight and biomass materials equivalent to 2% of dry soil weight were mixed evenly. Then the mixed soils were loaded into a homemade polyethylene plastic box, and incubated in a constant temperature incubator at 25℃ for 180 days in darkness. During the culture period, the soil moisture content was controlled to 60% of the field moisture capacity. Dynamic variations in microbial biomass carbon (MBC) and nitrogen (MBN), inorganic nitrogen (NH4 +-N and NO3 −-N), available phosphorus (AP) and available potassium (AK) as well as CO2 in the soil were measured. Result (1) The addition of all four residue biomass significantly affected microbial biomass and nutrient availability in the soil (P＜0.05). Compared with the control, the soil MBC contents treated by the residue biomass of poplar twigs, barks, leaves and straw increased by 50%, 31%, 80% and 109% respectively, while the soil MBN contents increased by 54%, 40%, 72% and 203%, respectively. The contents of NH4 +-N in the soil treated with bark and twigs residues were higher than those in the control and rice straw treatments, whereas the NO3 −-N content in the soil was in the order of control>rice straw>leaf residue>bark residue>twig residue treatments. The highest AP content was observed in the soil treated with twigs, while the AK content in the soil treated with rice straw was higher than that treated with other biomass residues. (2) After adding biomass residues into the soil, the daily release rate of CO2 from the soil showed a tendency with being relatively fast in the initial period, gradually slowing down in the middle stage, and tending to be stable in the later stage of the incubation. After 180 days of indoor incubation, the cumulative CO2 emission from the soil treated with rice straw was significantly higher than that of the other treatments (P＜0.05), followed by the soil treated with poplar leaves. (3) Correlation analysis showed that microbial biomass, nutrient contents and CO2 daily release rate in the soil were obviously correlated to the properties of biomass residues. Of them, a significantly positive correlation of soil microbial biomass to the contents of total nitrogen, total phosphorus and total potassium but a significantly negative correlation to the total carbon content and C/N ratio in the biomass residues were detected (P＜0.05). Meanwhile, the CO2 daily emission rate was positively correlated to the contents of MBC, MBN, NH4 +-N, AP and AK in the soil (P＜0.05), whereas a significantly negative correlation of the CO2 daily emission rate to the contents of NO3 −-N was observed (P＜0.01). Conclusion From the views of soil nutrients and environmental effects, application of poplar harvesting residues not only can increase the contents of soil available nutrients, but also relatively reduce carbon emissions compared with the rice straw. [Ch, 3 fig. 3 tab. 47 ref.]