Characteristics Of Carbon & Nitrogen Evolution And Aggregates Mineralization Under Long-term Different Management Measures In Kastanozems

Soil carbon and nitrogen is an important index of soil fertility and plays an important role in soil nutrient release and global carbon and nitrogen cycle.Soil carbon and nitrogen content was affected by management measures.Different cropping systems and fertilization are common management measures.However,previous studies on planting system were mostly based on short-term experiments.There were few studies on the changes and mechanisms of carbon and nitrogen in soil and aggregates under different long-term planting systems and fertilization measures.In addition,there are few reports of soil inorganic carbon change in soil aggregates under different management measures.There were few long-term studies on different rotation order of the same crop.In addition,few studies on the change mechanism of carbon and nitrogen content in soil aggregates Based on the 0-20 cm historical soil samples of chestnut soil under different planting systems（12 years）and different fertilization（16 years）in Wuchuan dry farming experimental station,this thesis discussed the evolution characteristics of soil carbon and nitrogen.Moverover,soil samples in 2019 were collected by wet sieving and physical grouping method,respectively,to explore the carbon and nitrogen contents and mineralization characteristics in soil and its fractions.This thesis discussed the carbon and nitrogen contents and the mineralization characteristics of chestnut soil,and provides a new way to select an appropriate cropping system and fertilization mode for soil carbon nitrogen sequestration.The main results and conclusions are as follows.1.Long-term continuous cropping of grass（V-V）,intercropping of grain and grass（V/P）and one year of grass and one year of grain（V-P）significantly increased the carbon and nitrogen content in soil and different particle size,among which long-term continuous cropping of grass had the best effect.But there was no significant change among the treatments.Compared with long-term potato continuous cropping（P-P）,the contents of total carbon（SC）and total nitrogen（TN）in V-V soil were significantly increased by 18.1%and 22.2%,respectively,and the contents of SC,soil organic carbon（SOC）and TN in V/P soil were significantly increased by 10.4%,25.5%and 15.6%,respectively.The content of SC and TN in V-V increased by 8.7%and 15.6%,respectively.Compared to P-P,the contents of SC and TN of V/P and V-V treatments in0.25 mm particle size significantly increased by 13.5%～17.1%and 37.5%～47.2%,respectively.The contents of SC and SOC in V-V treatment in 0.053-0.25mm particle size significantly increased by 23.0%and 19.2%,respectively.Redundancy（RDA）analysis showed that NO₃^-,AP and SMBN were the main driving factors of SC,SOC,SIC and TN contents,while p H and AP were the the main driving factors in>0.25 mm particle size are the main factors,and AK and SMBC were the main factors driving in0.053-0.25 mm particle size.2.Long-term application of manure fertilization significantly increased carbon and nitrogen content in the soil and aggregates.The aggregate stability also increased under manure fertilization.Chemical fertilizer combined with manure（NPKM）had a better effect on SOC,SC and TN contents,while fertilization manure alone（M）had a better effect on inorganic carbon（SIC）content.Compared with control（CK）,the contents of SC,SOC,SIC and TN in soil with M and NPKM were significantly increased by 67.98%～68.76%,46.27%～60.74%and 145.4%～275.4%,54.4%～59.9%,respectively.Compared to CK,The SC contents of coarse free particulate fraction（cf POM）,fine free particulate fraction（ff POM）,mineral-associated fraction inner microaggregate（i MOM）and mineral-associated fraction outer microaggregate（o MOM）by M and NPKM were significantly increased by 109.2%～120.8%and 33.54%～50.84%,162.8%～157.3%and 37.78%～40.47%,respectively.The SOC content of these fractions increased significantly by 97.5%～124.5%,36.07%～38.55%,137.7%～119.5%and 30.50%～39.68%,respectively.TN content of these fractions increased significantly by 115.1%～136.6%,35.55%～62.95%,154.2%～144.0%and 26.04%～35.12%,respectively.The SIC content of cf POM,i MOM and o MOM increased by 72.86%～140.89%,145.8%～158.8%and 68.49%～145.28%,respectively.The mean equivalent diameter（MWD）and geometric mean diameter（GMD）of soil aggregates under NPKM were significantly increased by 10.51%and 19.66%than CK,respectively.Soil SOC and p H values were the main driving factors affecting the distribution of aggregates.RDA analysis showed that Mg²⁺,p H and AP were the main driving factors of soil TN,SC,SOC and SIC contents.3.Long-term application of manure fertilization significantly increased SOC accumulative mineralization amount and potential mineralized carbon pool（Ca）of soil and its aggregates,and changed the mineralization rate constant（ka）of soil and its aggregates.After 120 days of incubation,compared with CK,the cumulative carbon mineralization of Bulk soil,cf POM,ff POM and o MOM under M and NPKM were significantly increased 3.0～4.1 times,87.4%-94.1%,29.4%-56.4%,64.9%～62.2%,respectively.The cumulative carbon mineralization of physically protected fraction（i POM）and i MOM were significantly increased by 72.5%and 15.35%,respectively.The M and NPKM increased the cumulative carbon mineralization contribution of cf POM and ff POM,but decreased it of i MOM and o MOM.The Ca values of Bulk soil,ff POM,i POM and i MOM under NPKM treatment were the highest,which were 1.32,4.05,0.79and 1.40 g kg^-1,respectively.The Ca values of cf POM and o MOM components in M treatment were the highest,which were 0.91 and 1.50 g kg^-1,respectively.In addition,M and NPKM increased the mineralization rate constants（ka）of Bulk soil,cf POM and ff POM,and i POM,but decreased the ka values of Bulk soil,i MOM and o MOM components.4.Long-term application of manure fertilization significantly increased the cumulative nitrogen mineralization amount and nitrogen mineralization potential（N₀）,and changed the mineralization rate constant（k）of soil and its aggregates.After 32weeks of incubation,compared with CK,the cumulative nitrogen mineralization content of cf POM,i POM and i MOM under M and NPKM were significantly increased by78.46%～87.12%,278.47%～326.10%and 40.41%～105.51%,respectively.The cumulative nitrogen mineralization content in o MOM fraction under M treatment was significantly increased by 28.82%.After 32 weeks of incubation,M and NPKM increased the cumulative carbon mineralization contribution rate of cf POM,ff POM,i POM and i MOM,and decreased the cumulative nitrogen mineralization contribution rate of o MOM.N₀ value of Bulk soil component in NPKM treatment was the highest(43.60 g kg^-1),while that of ff POM and o MOM components was the lowest(367.4 mg kg^-1)and49.5 mg kg^-1,respectively.The N₀ values of cf POM and i POM were 40.90 mg kg^-1 and111.80 mg kg^-1,respectively.Compared with CK,M and NPKM increased the k value of i POM,but decreased the k value of Bulk soil,ff POM and o MOM.In conclusion,long-term continuous cropping of grass,intercropping of grain and grass,and one year of grass and one year of grain significantly improved soil carbon and nitrogen contents in bulk soil,and>0.25 mm,0.053-0.25 mm particle size,among which long-term grass continuous cropping had the best effect.However,there was no significant change among the treatments.Long-term application of chemical fertilizer combined with manure could better improve the contents of SC,SOC and TN,while fertilization manure alone could better improve the content of SIC.Based on the effect of soil carbon and nitrogen sequestration,long-term grass continuous cropping,application with chemical fertilizer combined with manure had the best effect on SC and TN fixation.