Effects Of γ-HCH Application On Soil Carbon And Nitrogen Components Under Plastic Film Mulching

Plastic film is widely used in agricultural activities because of its characteristics of increasing temperature and moisture,and long-term plastic film mulching will change the properties of soil.Due to their persistence and huge usage,the detection rate and concentrations of organochlorine pesticides are relatively high all around the world.And because of its good insecticidal property,γ-HCH has once had the highest yield and consumption in the world.In order to explore the effects of mulching,different concentrations ofγ-HCH and their interaction on carbon and nitrogen cycle in the soil-plant microecosystem,pot experiment was carried out with ryegrass and alfalfa.The main results are summarized as follows:1)By analyzing the effect of plastic film mulching on soil carbon and nitrogen components,we found that:the soil temperature and humidity showed that PM was higher than NM,and the difference of soil humidity was very significant（p<0.01）.Soil microbiomass carbon（MBC）contents in rhizosphere soil were lower than NM under50 and 500 ng·g^-1γ-HCH（p>0.05）;the contents of soil microbiomass nitrogen（MBN）in rhizosphere soil under no exposure and 500 ng·g^-1γ-HCH were significantly higher than those in NM（p<0.01）,and under 50 ng·g^-1γ-HCH,PM was markedly lower than NM（p<0.01）.The enzyme activity of NAG in alfalfa soil was memorably affected by mulching,and the enzyme activity of NAG in PM was higher than that in NM（p<0.01）;however,mulching had less obvious effect on the enzyme activities ofβG,βx and CBH in ryegrass soil（p>0.05）.Under the action of soil microorganisms and soil enzymes,soil organic matter is transformed and decomposed,which affects the carbon and nitrogen components and greenhouse gas emissions.The contents of ammonium nitrogen（NH₄-N）,total nitrogen（TN）and organic carbon（SOC）in PM were higher than those in NM,but the differences were not significant（p>0.05）,except TN,the trends of change decreased firstly and then stabilized with the plant growth.Plastic film mulching increased soil CO₂ and N₂O emissions（p<0.01）,increased CH₄ absorption（p>0.05）,there was a significant positive correlation between soil CO₂ emission flux and soil moisture（p<0.01）,and there was a significant positive correlation between soil CO₂ emission flux and soil temperature and MBC content（p<0.05）;there was a significant positive correlation between N₂O emission flux and soil temperature and humidity（p<0.01）,and there was a significant positive correlation between N₂O emission flux and TN content（p<0.05）.The changes of soil carbon and nitrogen components also affected crop fresh weight,the underground and root biomass of PM was very significant higher than NM（p<0.01）,except for alfalfa underground biomass（p>0.05）.2)By analyzing the effect ofγ-HCH on soil carbon and nitrogen components,we found that:firstly,γ-HCH might affect the microbial community structure and soil enzyme activity.The effect ofγ-HCH on MBN and MBC in rhizosphere soil was not significant（p>0.05）,showing the order:the content of 50 ng·g^-1γ-HCH was the highest,and the lowest under no exposure treatment.The enzyme activity of NAG in alfalfa soil was significantly affected by different concentrations ofγ-HCH(p<0.01,The content was the highest under no exposure treatment,and the lowest in 500 ng·g^-1γ-HCH treatment),but different concentrations ofγ-HCH had no obvious effect on the activities ofβG,βX and CBH（p>0.05）.Soil microorganism and enzyme activity played an important role in soil carbon and nitrogen transformation.The contents of NO₃-N and TN in soil showed the content of 50 ng·g^-1γ-HCH was the highest,and the lowest under no exposure treatment,the NO₃-N contents in alfalfa soil under no exposure and 50 ng·g^-1γ-HCH were higher than those of ryegrass soil（p<0.05）.The contents of SOC were significantly affected by different concentrations ofγ-HCH(p<0.05,The content was the highest under no exposure treatment,and the lowest in 50 ng·g^-1γ-HCH treatment).The CO₂ and N₂O emissions and CH₄ absorption fluxes of the soil are approximately showed under 500 ng·g^-1γ-HCH treatment,it was the highest,and 50 ng·g^-1γ-HCH treatment was the lowest,there was significant difference in N₂O emission of soil（p<0.05）.By analyzing the effects of plastic film mulching andγ-HCH interaction on soil carbon and nitrogen components,we found that:there was no interaction among mulching and different concentrations ofγ-HCH on soil temperature,moisture,p H,carbon and nitrogen content,soil enzyme activity,plant biomass and greenhouse gas emissions（p>0.05）.