Influences Of Quality And Spatial Distributions Of Organic Amendments On Soil Community

Organic amendments can significantly improve soil fertility and increase soil biota in terms of numbers and activities,and spatial distribution of organic amendments could significantly aggravate the resource heterogeneity,and influence soil microbial community structure and function.However,the effects of organic material composition,quality and spatial distribution on the soil,especially on the microsite soil,still need more studies.Considering the organic material quality and the spatial distribution,it is very helpful to understand more comprehensively the effect of organic material decomposition on soil biological community.The effects of organic material quality and spatial distribution on soil biological community were studied by three independent cultivation experiments.First,we performed a 2 × 3 factorial experiment with four replicates to investigate how quality and heterogeneity of the organic affect soil biota.The treatments consisted of two quality of the organic?clover or rice straw?and three levels of organic matters aggregation?1-layer,4-layer or completely mixed?.In laboratory incubations,dynamics of soil dissolved organic carbon?DOC?,dissolved organic nitrogen?DON?,microbial biomass carbon?MBC?and nitrogen?MBN?,soil microfauna?protozoa and nematodes?were monitored in soils,following 14,35 and 70 days of incubation.The main results were as follows:During the incubation period,CO₂ emission rate in the soil amended with clover significantly?p<0.05?higher than rice straw in soil,and organic aggregation delayed the peak CO₂ emission rate by 5-7 days compared to uniformly distributed in the soil amended with clover.Compared with rice straw,clover in soil?one layer?significantly?p<0.05?increased the contents of DOC and DON.In addition,bacterial biomass was greater in the mixed system,and fungal biomass decreased continuously with the incubation time in the soil amended with clover regardless of heterogeneity.While the dynamic of fungal biomass,which was higher in 4-layer and mixed treatments than in 1-layer treatment,was relate to the heterogeneity of rice straw.With incubation time,soil nematode abundance in clover and rice straw treatments showed a significant increase,especially on heterogeneous distribution?1-layer?.Moreover,heterogeneous distribution of organic matter in the soil?1-layer and 4-layer?displayed a strong stimulating effect on bacteria-dominated soil microbial food web.In contrast,uniformly distribution?mixed?of organic stimulated fungivorous and omnivorous nematode,increasing the structural complexity of the nematode community.Secondly,in order to further understanding the micro-fauna in response to microsite soil with organic material,this study investigated the response of DOC,DON,MBC,MBN and soil microfauna?nematodes and protozoan?to different quality of the organic?clover or rice straw?in one layer in the center of the soil column?1-layer?.Soil samples were taken after 14,35,and 70 days in the microcosms,soil cores were separated into 2 layers with distance to the organic material,one was Soil A,which was within 1 cm from the organic material,and the another was Soil D away from 1 cm.The main results were as follows:Compared with straw?high C:N ratio?,the contents of DOC,DON and NO3--N were higher in Soil A with clover.During the incubation period,the content of MBC under the same small-scale were increased at the beginning and then decreased at the end.The content of MBN in Soil A with rice straw was higher than Soil D.With incubation time,the number of amoeba in small-scale was increasing,while the number of flagellates showed the opposite trend.In 14 d,the number of nematode in Soil A with clover significantly higher than Soil D.With incubation time,the number of nematode in Soil D with clover was significantly higher than Soil A.There were no significant differences in different small-scale regardless of the incubation time with rice straw.In contrast to clover,rice straw with higher C:N ratio stimulated fungivorous,herbivores and omnivorous nematode,increasing their proportions,diversity,maturity and structural complexity,which indicated that organic substances with high C:N ratio promoted the structure of fungi-dominated microbial food web.In the two above experiment,soil nematodes were intensely response to organic material quality and spatial distribution.So the following experiment was designed three-factorial with different quality of the organic?clover or rice straw?,heterogeneity?1-layer or completely mixed?and soil nematodes?with or without?.Dynamics of DOC,DON,MBC and MBN,soil microfauna?protozoa and nematodes?were monitored,following 14 and 52 days of incubation time.The main results were as follows:CO₂ emission was more significantly affected by the quality of organic matter than heterogeneity and nematodes.The CO₂ emission rate and CO₂ cumulated emission in the soil amended with clover significantly?p<0.05?higher than rice straw.There was no apparent difference regardless of the heterogeneity of the organic and with or without nematodes.The contents of DOC,DON,MBC,and MBN increased in the soil amended with clover,and were significantly higher than rice straw amended.Within clover treatments,the contents of DON in the 1-layer treatment higher than mix treatment.With nematodes treatment,the number of soil nematode showed a strong and significant increase during the incubation period,especially on heterogeneous distribution?1-layer?with 52 d.In contrast,rice straw contributed more significantly to the development of nematodes and amoebae abundance than clover.Moreover,rice straw with higher C:N ratio stimulated fungivorous nematodes,which further indicated that organic substances with high C:N ratio promoted the structure of fungi-dominated microbial food web.In summary,different quality and heterogeneity of organic amendments into the soil could improve soil fertility as well as change the structural complexity of soil biological community.The selection of the organic quality can regulate soil carbon,nitrogen efficiency and soil biological food web structure;also can contribute to biological coordination of soil carbon,nitrogen transformation processes and the contradictions of plant uptake.