| Biogas slurry is the liquid residue of organic matter such as livestock manure after anaerobic fermentation.Biogas slurry is rich in N,P,K and other plant nutrients,and also contains various amino acids,vitamins,protein and antibiotics,etc.Biogas slurry has high utilization value and is a high-quality and efficient green organic fertilizer.This paper takes poplar plantations in northern Jiangsu as the research object,and studies the effects of applying different concentrations of methane on the content of the main components of soil carbon,nitrogen and phosphorus,the biomass of understory ground cover,the amount of litter and the growth of poplar trees,with a view to supplying the theoretical basis and practical experience guidance for the rational application of methane to improve the productivity and sustainable development of poplar plantations in northern Jiangsu.The experiment adopts random block design.In 2012,three repeated blocks were set up,and each block was set with four levels（treatments）of biogas slurry application,namely,the application concentration of biogas slurry was 0,125,250 and 375 m3·hm-2,which were recorded as CK（control treatment without biogas slurry）,L（low concentration biogas slurry treatment）,M（medium concentration biogas slurry treatment）and H（high concentration biogas slurry treatment）respectively.The investigation contents include:the effects of the biogas slurry application at different concentrations on the C,N and P content of the soil,underforest herb biomass and its C and N contents,litter volume and its C and N contents,and poplar growth.At the same time,the changes of litter and poplar growth in 2018 and 2021 were compared and analyzed.The results show that:1.Biogas slurry application significantly increased surface soil（0～20 cm）organic carbon（SOC）,soil microbial biomass carbon（MBC）,soil dissolved organic carbon（DOC）,soil total nitrogen（TN）,soil microbial biomass nitrogen（MBN）,soil total phosphorus（TP）and soil available phosphorus（AP）,and significantly decreased the C/N and MBC/MBN in the topsoil;the application of biogas slurry also significantly increased the contents of DOC and TP in 20～40 cm soil layer;however,in deep soil（40～60 cm）,the application of biogas slurry has no significant effect on soil C,N and P indexes.At the same time,the application of biogas slurry significantly reduced the soil p H of each layer and significantly increased the water content of the top soil of 0～20 cm.2.In poplar plantation,applying biogas slurry with different concentrations can increase underforest herb biomass.Underforest herb biomass increased by 28%,18.1%and 13.2%under the L,M and H treatments,respectively,than under the CK treatment,but there was no significant variation between the treatments with different application concentrations.The underforest herb biomass in July（vigorous growth period）is higher than that in October and January.3.The biogas slurry application altered the C and N contents of the underforest herb.In the three months,there was no significant difference in the C content of underforest herb among the four treatments.In the seasonal variation of vegetation growth,the C content of underforest herb in January（non-growing season）was higher than that in July and October（growing season）.The N content of the underforest herb in the CK treatment was very significantly inferior to the other three treatments（P<0.01）,and the N content of underforest herb was lower in July（growing season）.Underforest herb C/N was higher under the CK treatment than the other three treatments,and there was no significantly difference in vegetation growth seasonal variation in underforest herb C/N between all three months.4.The application of biogas slurry increased the litter amount.For the amount of litter leaf,it increased by 77.7%,79.5%and 32.3%under the L,M and H treatments respectively in comparison to the CK treatment.For the quantity of litter branches,it increased by 31.4%,52.1%and 19.3%under the L,M and H treatments respectively in comparison to the CK treatment.The amount of litter debris increased under L,M and H treatments by 41.6%,7.9%and 16.3%respectively than the CK treatment,among which the monthly variation of litter was the most in July and the least in January and December.This is due to the fact that July is more affected by wind speed（typhoons）and therefore has the highest amount of the litter.5.The biogas slurry application altered the C and N content of the litter.The content of C in litter was significantly higher under the CK treatment in comparison to the L and H treatments（P<0.05）,and the content of litter C in October（growing season）was higher than that in other three months.The N content of litter under the L and H treatments was very significantly higher compared to the CK treatment（P<0.01）,and the N content of litter was the lowest in July（growing season）.The litter C/N was very significantly higher in the CK and M treatments than in the L and H treatments（P<0.01）,and the litter C/N was the highest in July（growing season）.6.Applying biogas slurry with different concentrations can promote the growth of poplar plantation.Poplar height growth under the H treatment was significantly higher than the other three treatments from 2018 to 2021（P<0.05）;under the CK treatment,the diameter growth at breast height of poplars was very significantly inferior to the M and H treatments（P<0.01）.The results of the measurement in 2021 showed that the height growth of poplar trees under the CK treatment was extremely significantly lower than that under the L,M and H treatments（P<0.01）,and compared with the CK treatment,the tree height increased by 4.3%,8.0%and 11.1%under the L,M and H treatments,respectively;the growth of poplar tree diameter at breast height was extremely significantly higher under the M treatment than that under the CK and L treatments（P<0.01）,the diameter at breast height increased by 5.0%,8.9%and 7.6%under the L,M and H treatments,respectively,compared with the CK treatment.In a word,our experiments show that the application of biogas slurry can significantly improve the nutrient content of soil C,N and P;proper concentration of biogas slurry can significantly increase litter yield,underforest herb biomass and poplar growth;at the same time,the biogas slurry application also increases the elemental C and N content of underforest herb and litter.The results indicate that biogas slurry can be used as a high-quality and quick-acting organic fertilizer,which has a certain effect on maintaining or improving soil fertility and stand productivity of poplar plantation,and the related process and mechanism need further study. |
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