Effects Of Straw And Biochar On Soil Aggregate Stability And Carbon And Nitrogen Sequestration In Greenhouse Vegetable Fields

Greenhouse vegetable field is a planting environment with high input of water and fertilizer,and this results in high crop yield.The soil quality in greenhouses declines severely because of the high levels of fertilizer use,continuous crop cultivation and incorrect tillage management.In order to improve the soil quality and make full use of agricultural waste materials,straw and biochar were applied into greenhouse soils to study the effects of different application amounts of the two organic materials on the aggregate stability and carbon and nitrogen sequestration in the greenhouse vegetable fields.The study was carried out at Jingliuhuan agriculture ecological park,Changping District,Beijing.The straw was applied at the rates of 0 t/hm²?S0?,0.8 t/hm²?S1?,and 2.4 t/hm²?S2?,and the biochar was applied at the rates of 0 t/hm²?B0?,30 t/hm²?B1?,60 t/hm²?B2?and 120 t/hm²?B3?,respectively,Thus,there were twelve treatments of combined straw and biochar application.Soil samples at 0-15 cm and 15-30 cm depth were collected,and the aggregate stability,carbon and nitrogen contents and soil enzyme activitywere determined.The effects of straw and biochar on soil carbon and nitrogen sequestration were discussed by analyzing the distribution characteristics of carbon and nitrogen between aggregate classes.The results showed that:?1?Application of straw and biochar significantly increased SOC content in the bulk soil.The SOC content was positively correlated with the amount of biochar applied.There was no significant effect of straw and biochar treatment on the TN content.At a high biochar level?B2,B3?,S2 treatment had the largest SOC increment?P<0.05?,which increased by 23%-73%as compared to the SO treatment.At a high straw?S2?level,B2 and B3 treatments had the largest SOC increment in the 0-15 cm soil layer?P<0.05?,which were 104%-109%higher than that of B0.The application of straw increased the EOC content.The S2 treatment at B2 level showed a significant increase in the EOC content?P<0.05?,with an increasement by 32%than the SO treatment.Biochar treatment had no significant effect on EOC content.?2?The activity of ?-glucosidase was increased under straw treatment at 0-15 cm depth.However,the input of biochar significantly reduced the activity of ?-glucosidase in the 0-15 cm soil layer?P<0.05?.With the increasing dose of the straw,the effect of biochar on the enzyme activity gradually decreased.?3?At different straw application levels,the content of 2-0.25 mm aggregate class showed a"v-shaped" trend with the increasing dose of biochar,and the content of 0.25-0.05 mm aggregate class showed a opposite pattern,In the 0-30 cm soil layer,the contents of macro-aggregates?2-0.25 mm?were significantly increased by high biochar dose treatments?B2?B3?,while the contents of micro-aggregates?0.25-0.05 mm?were significantly increased by low biochar dose treatment?BI?.With the increasing application of straw,the influence of biochar on aggregates was gradually reduced.?4?The results of MWD,GMD,PAD and R_0.25 showed that the improvement of aggregate stability by straw was mainly observed under B3 level,and the improvement of aggregate stability by biochar was mainly observed under S1 level.Therefore,the most favorable treatment on aggregate stability was S1B3?straw 0.8t/hm²,biochar 120t/hm²?.?5?The contents of SOC and TN in the 2-0.25 mm aggregate class were increased by high biochar dose application,and the contents of SOC and TN in the silt+clay fractions decreased with the increasing biochar application.With the increasing biochar application,the EOC contents in aggregates and silt+clay fractions gradually decreased.Furthermore,the effect of biochar on EOC content increased with the increasing straw application.The results of the two-year field experiment showed that application of straw and biochar significantly increased SOC content,but had no effect on TN and EOC contents.Application of straw significantly improved the activity of ?-glucosidase,while the application of biochar decreased the activity of ?-glucosidase.The high level of biochar application significantly improved aggregate stability.Application of biochar significantly increased SOC and TN contents in the macro-aggregates,and decreased the EOC contents in the macro-and micro-aggregates.We concluded that both application of straw andbiochar could improve aggregate stability,SOC content and ?-glucosidase activity in greenhouse vegetable soils.high levels of biochar is beneficial to the formation of macro-aggregates,while low levels of biochar is beneficial to the formation of micro-aggregates.This suggested that application of straw with biochar could be helpful to improving soil structure and soil C sequestration in the greenhouse vegetable fields.