土壤水分和氮添加对华北平原高产农田有机碳矿化的影响

Abstract

A highly productive soil from the North China Plain was used for a homoeothermic incubation study at 25 ℃ for105 d to identify the characteristics of soil organic C mineralization and investigate the impacts on that mineralization of soil moisture,and addition of inorganic and organic nitrogen. Four fertilizer input levels and four moisture gradient treatments were used in the experiment,including a control( S0),inorganic nitrogen( urea,S1),inorganic and organic nitrogen( 50% urea+50% chicken manure,S2) and organic nitrogen( chicken manure,S3). The N application rate of the S1,S2 and S3 treatments was 200 kg N /hm2,with 20% field capacity( M0),50% field capacity( M1),75% field capacity( M2) and 100% field capacity( M3) used with each soil treatment,giving a total of sixteen treatments with three replicates. The soil organic C mineralization rate of all treatments sharply declined at the first day of incubation,decreased by 57. 2% —75. 0% over the first 7 d,and appeared as secondary peaks at the 20 thday of incubation. Soil organic C mineralization ranged from 208. 8 to 1161 mg /kg and mainly happened in the first 50 days,especially in the first 30 days( accounting for 59.1%—69.9% of the total mineralized soil C). The net mineralization rate of all treatments ranged from0. 07% to 2. 01%. According to simulation using a double exponential model,the potential organic C mineralization flux and rate were 219. 1—1204 mg /kg and 1. 75% —9. 66%,respectively. The active and resistant pools were 53. 0—135. 1mg /kg and 156. 9—1069 mg /kg,respectively. Organic C mineralization of soil with fertilizer was significantly affected by the soil water content( P 0. 05). The higher the soil water content( from 25% to 100% of field capacity),the more organic C accumulated in the soil under the same fertilizer addition conditions. The relationship between organic C mineralization and soil water content was well fitted by a quadratic function equation( P 0. 05). When the soil water content increased from M0 to M3,the average organic C mineralization rate significantly increased to 18. 4 mg·kg-1·d-1,20. 9 mg·kg-1·d-1,22.3 mg·kg-1·d-1and 23. 5 mg·kg-1·d-1from 4. 47 mg·kg-1·d-1,4.64 mg·kg-1·d-1,4.61 mg·kg-1·d-1and 4. 88 mg·kg-1·d-1,respectively. However,the increasing rate gradually reduced to 30.0%—43.9% and-3.08%—12. 4% from 66. 9% —261%. The amount of C mineralized in the soils amended with fertilizer was significantly higher than that in the control treatment. The average mineralization rates of the S1,S2 and S3 treatments increased above that in the S0 treatment by 3. 86% —27. 9%,3. 28% —39. 5% and 9. 27% —31. 5%,respectively. However,there were no significant differences among the S1,S2 and S3 treatments at the same soil water content conditions. Thus there were no significant differences between the forms of added nitrogen,i. e. organic nitrogen( chicken manure) or inorganic nitrogen( urea). The amounts of soil organic C mineralization were linearly related to the microbial biomass carbon( P0.01) and mineral nitrogen( P0. 05),indicating that the contents of microbial biomass carbon and mineral nitrogen were the key factors affecting the mineralization of C. It can be concluded that soil organic C mineralization was significantly affected by soil moisture and nitrogen addition,and that there was a significant interaction with soil moisture and nitrogen addition( P0. 05).