Effects Of Biogas Slurry And Biochar On Soil Labile Organic Carbon And Nitrogen In A Poplar Plantation In A Coastal Area Of Northern Jiangsu, China

Biogas slurry contains necessary and rich nutrients for the growth of plants, and is used as a high-quality organic liquid fertilizer and can improve the physical and chemical properties of soil. Also, biochar can improve the soil properties, for instance, p H, CEC, organic carbon, etc. Moreover, biochar can release the nutrients slowly and decrease the leaching loss of that in biogas slurry and soil. Despite of the large area, plantation in China is commonly faced with soil degradation. Therefore, it’s important to study the application of biogas slurry and biochar to plantation. To understand the effects of biogas slurry and biochar on soil labile organic carbon and nitrogen of poplar plantation in a coastal area, we designed four addition treatments of biogas slurry i.e. CK(0 m3·hm-2), L(125 m3·hm-2), M(250 m3·hm-2), H(375 m3·hm-2), and four treatments of biochar i.e. B0(0 t·hm-2), B1(40 t·hm-2), B2(80 t·hm-2), B3(120 t·hm-2) at Dongtai forest farm in Jiangsu province. The experiment was carried out by randomized blocks desigh. The main results are as follows:(1) The dissolved organic carbon(DOC), dissolved organic nitrogen(DON) and soil microbial biomass nitrogen(MBN) increased by applying biogas slurry at all treatment levels. The biogas slurry decreased the soil microbial biomass carbon(MBC) and MBC/MBN as well. Moreover, biogas slurry significantly decreased soil p H and increased the concentration of NO3--N. There was a significant negative correlation between p H and NO3--N, indicating that the change of p H might be caused by the increase of available nitrogen. Meanwhile, it also increased the concentration of NH4+-N and available phosphorus, decreased soil C/N, and had no significant effects on soil total phosphorus. The correlation analysis showed that the concentration of soil labile organic carbon/nitrogen was closely related to soil p H, NO3--N, available phosphorus and C/N. Soil p H and NO3--N, NH4+-N were closely related as well.(2) Biochar increased soil labile organic carbon and DON, however, it decreased MBN. Besides, with high p H and ash in it, biochar increased soil p H. Soil NO3--N, NH4+-N, available phosphorus and C/N increased with the application of biochar. The interactic effects between biogas slurry and biochar were significant on soil labile organic carbon and nitrogen, p H, NO3--N and available phosphorus, and except for the index of available phosphorus, biogas slurry played a more important role, as compared with biochar.(3) Soil labile organic carbon and nitrogen showed significant seasonal variation and distributed unlikely as the following, the content of DOC in March > September > June > December, while the seasonal changes of DON were converse, that of MBC or MBN in June > March, September > December. Biogas slurry didn’t change the trendency of seasonal variations of soil labile organic carbon and nitrogen. However, repeated measurement analysis of variance showed that biogas slurry had significant influence on soil labile organic carbon and nitrogen, whereas biochar had no significant effect on DOC and DON but on MBC and MBN. Besides, there were significant interaction effects between biogas slurry, biochar and MBC, MBN but DOC, DON, indicating that biogas slurry may affect the seasonal variations of soil labile organic carbon and nitrogen, while biochar may influence that of soil microbial biomass and have no significant effect on soil dissolved organic matter.