| As one of the four black soil regions around the world,northeast China plays an important role in China’s agricultural production,and it’s regarded as the cornerstone of China’s food security.However,the degradation of soil carbon and nitrogen contents caused by excessive reclamation have directly restricted the sustainable food production in recent years.Therefore,in order to maintain the healthy and sustainable development of black soil,it is urgent to explore effective nutrient management strategies on the basis of understanding the effective mechanism of fertilizer managements on carbon and nitrogen contents in black soil.This research was conducted in Harbin city,Heilongjiang Province,and explored the variation mechanism of black soil carbon and nitrogen content.We examined the variation of organic carbon and nitrogen as well as their natural abundance over a long period to explore the effect of long-term different fertilizer treatment on soil carbon and nitrogen storage and regeneration;a 15N pot experiment was conducted to investigate the distribution of nitrogen derived from different sources in the crop-soil system,and to clarify the mechanism of soil carbon and nitrogen accumulation in bulk and rhizospheric soil under different nutrient management;soil aggregate was separated with wet-sieve method and the content of carbon and nitrogen was determined to clarify soil carbon and nitrogen storage potential in soil particles and its physical protection mechanism;besides,this research further adopt life cycle assessment to assess fertilizer treatments on carbon footprint during the whole maize-life and comprehensive evaluation of the role of different fertilizer measures of carbon flow potential.Base on the results above,we summarized a suitable fertilizer practice for carbon and nitrogen stock in black soil.The main results are as follows:(1)Long-term no fertilizer application or inorganic fertilizer alone could aggravate soil carbon loss,while the combination of inorganic fertilizer and organic fertilizer could improve soil carbon storage in 0～20cm soil layer.The annual growth rates of soil carbon storage in under chemical N and P fertilizer plus manure(MNP),chemical N,P,and K fertilizer plus manure(MNPK)and double chemical N and P fertilizer plus manure(2MNP)treatments were 0.05,0.06 and 0.11 t/hm2,respectively.In 0-60cm soil profile,carbon and nitrogen contents decreased gradually with soil depth increasing,and its natural abundance was the highest in 20～40cm soil layer,and the MNPK and 2MNP treatments were the highest among fertilizer treatments.The natural abundance method showed that fertilization application increased the contribution rate of new carbon and the degradation rate of old carbon in 0-20cm soil layer,and the contribution rate of new carbon under MNP,MNPK and 2MNP treatments were the highest among all treatments,which reached 91.41%,91.27%and 93.08%,respectively,and the degradation rates of old carbon reached 0.06%,0.06%and 0.07%,respectively.(2)Pot experiment showed that the combination of inorganic fertilizer with organic material significantly increased the contents of soil organic carbon and total nitrogen by 2.90%～5.66%and 23.98%～252.64%in comparison with inorganic fertilizer treatment during the whole maize growth stage.Meanwhile,the contents of dissolve organic carbon(DOC),microbial biomass carbon(MBC)and particulate organic carbon(POC)were increased by 13.13%～20.42%,20.23%～110.22%and 6.50%～22.67%,respectively.The distribution of inorganic fertilizer N in dissolve organic nitrogen(DON),microbial biomass nitrogen(MBN),particulate organic nitrogen(PON)and mineral-bound nitrogen(MTN)were increased by 70.89%to 76.01%,152.03%to 226.50%,271.00%～814.00%and 190.00%to 217.00%,respectively.In addition,straw application restricted nitrogen flow to rhizosphere soil from bulk soil,which resulted in the content of total nitrogen in rhizospheric soil was significantly lower than bulk soil;meanwhile,rhizospheric soil enhance the decomposition of particulate organic matter,which contributed to the content of POC,mineral-bound carbon(MTC)and PON in rhizospheric soil was significantly lower than bulk soil.(3)Compared with inorganic fertilizer treatment,the combination of inorganic fertilizer with organic fertilizer significantly increased the turnover rate of large aggregates in 0～20cm soil layer,and MNP and 2MNP treatments significantly increased the turnover rate of large aggregates by 8.65%and 28.75%in comparison with NP treatment,which was conducive to the release of inter-aggregate silt and clay(inter-SC)and intra-aggregate silt and clay(intra-SC)containing in large aggregates.As a result,MNP increased free microaggregate(free-M)and free silt and clay(free-SC)by 13.59%and 7.41%,and 2MNP increased these fractions by 26.31%and 27.42%,respectively,compared with NP treatment.In addition,the aggregate turnover in 0～60cm soil profile decreased with the increase of soil depth,and it was decreased by 46.79%in 20～40cm soil depth than 0～10cm soil depth.MNP and 2MNP treatments mainly increased the accumulation of carbon and nitrogen in micro-aggregates and micro-aggregates containing in large aggregates,and the content of carbon increased by 10.74%and 23.48%,and the content of nitrogen increased by 5.89%and 25.93%,respectively,compared with NP treatment.There was a significant positive correlation between carbon accumulation in aggregates and organic carbon input in aggregates.(4)The research of carbon footprint of maize-soybean-wheat production system in black soil under different fertilization conditions showed that fertilization significantly increased the CO2 emissions in maize,soybean and wheat growing seasons,which reached 4 557.18,2 276.78 and 3 796.76 kg CO2/hm2 under 2MNP treatment,respectively.Nitrogen fertilizer input and nitrogen loss were the main contributor to carbon emission in each crop growing season,reaching 71.54%～83.46%,58.87%～66.35%and 71.54%～82.23%in maize,soybean and wheat seasons,respectively.In addition,maize had the highest carbon emission(0.63～1.68 kg/kg)and soybean had the lowest carbon emission(0.16～0.24 kg/kg)during the whole rotation period.The carbon footprints of maize and wheat seasons were significantly affected by different treatments,but there was no significant difference for soybean season.In the whole rotation period,CK and MNPK treatments had the lowest carbon footprint,which was only 1.54 and 1.70 kg/kg,respectively.The contribution rate of maize season was the highest(41.13%～59.95%),and that of soybean season was the lowest(7.27%～14.18%).In conclusion,the combination of inorganic fertilizer with organic fertilizer is an effective way to improve the soil carbon and nitrogen contents in the northeast black soil area.This measure mainly enhances the soil carbon and nitrogen fixation ability by increasing the distribution of carbon and nitrogen to the soil stabilization pools and the small aggregates.In addition,the combination of inorganic fertilizer with organic fertilizer can improve soil carbon and nitrogen storage while ensuring high and stable grain yield,and also effectively reduce the carbon emissions of the corn-soybean-wheat planting system,which is conducive to realizing the healthy,green and sustainable development of black soil in China. |
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