Effects Of Long-Term Fertilization On Nutrient Balance And Dynamic Changes Of Humus Components And Structure Of Black Soil Under Crop Rotation

The importance and complexity of soil organic matter?SOM?have been considered as a hot topic for domestic and foreign scholars.Soil humus?HS?as the main part of SOM plays an important role in soil nutrient cycling and carbon sequestration.Long-term overdose of fertilizers can adversely affect soil physical,chemical and biological diversity,which leads to the nutrients imbalance and soil degradation in farmland.Although a large number of long-term experiments have been carried out at home and abroad,there are few reports on the nutrient income and expense in different rotation seasons,the dynamic changes of the optical properties and molecular structures of HS components in Black Soil with different fertilization treatments.Based on the long-term?39 years?experiment of Black Soil with typical fertilization treatments,this paper analyzed the nutrient budget balance under different rotation seasons.And the methods of elemental composition analysis,thermal properties,infrared spectroscopy,¹³C nuclear magnetic resonance spectroscopy were used to analyze the optical characteristics and compositional structure of HS components of Black Soil in four typical fertilization treatments?organic manure combined with chemical nitrogen,phosphorus and potassium fertilizers,MNPK;organic manure,M;chemical nitrogen,phosphorus and potassium fertilizers,NPK;no fertilization,CK?in 1997,2002,2008 and 2012.The results as showed in follow would provide a theoretical basis for the mechanism of soil fertility in Black Soil.?1?Long-term fertilization and rotation season effected the crop yield and soil nutrient balance.The average crop yield after long-term fertilization decreased as the order of MNPK>NPK>M>CK.The effectiveness of fertilizer application on the crop yields was wheat>corn>soybean.The amounts of soil N and K₂O in all treatments were in deficit from1980 to 2014.And the amounts of P₂O₅ were in surplus under the MNPK and NPK treatments.The total nutrient deficit was the most in CK treatment,with a value of 581.2 kg hm^-2 and the total nutrient surplus was only found in MNPK treatment(40.0 kg hm^-2).?2?Long-term fertilization in Black Soil increased soil organic carbon?SOC?content and improved the quality of SOM.And the content of SOC increased with the fertilization years.Long-term fertilization increased the contents of extracted humus?HE?,humic acid?HA?,fulvic acid?FA?,humin?Hu?,and the?log K and E4/E6 values of soil HA and FA compared with CK treatment.The E4/E6 value of FA and?logK value of HA increased in MNPK and M treatments,while the values of?logK and the value of E4/E6 in HS components decreased with fertilization years in CK treatments.?3?Long-term application of organic manure simplified the structure of HS components in Black Soil.Compared with CK,MNPK and M treatments increased the ratios of H/C in soil HA and Hu by 1.0%and 1.1%and 2.7%and 6.2%,respectively,while NPK treatment decreased the ratio of H/C in soil HA and Hu by 2.1%and 1.1%.With the increase of fertilization years,the ratio of H/C of soil HA decreased in NPK treatment,while the ratio of H/C of soil HA and Hu increased in M and MNPK treatments.?4?Long-term application of organic manre increased the total reaction heat?endothermic and exothermic?of HA and Hu.The treatments of M and MNPK decreased total reaction heat of HA and the high temperature/medium temperature ratio of HA and Hu but increased total reaction heat of Hu with fertilization years,which indicated they enhanced the contents of labile SOM in HS components and reduced the aromatization degree.The decrease of labile SOM of HA and the increase in that of Hu with fertilization years showed the transformation of HS from soluble to recalcitrant components.?5?The application of organic manure combined with chemical fertilizers enhanced the contents of aliphatic C in HA and Hu components.The treatments of MNPK,M and NPK increased the ratios of IR absorption peak at 2920 cm^-11 to 1620 cm^-1?2920/1620?,at 2920cm^-11 to 1720 cm^-1?2920/1720?and 2920 cm^-11 to 2850 cm^-1?2920/2850?of HA compared with CK treatment.The ratio of 2920/1620,2920/1720 and 2920/2850 in MNPK and M treatments increased,while the ratio of 2920/2850 in NPK treatment decreased with years.The ratios of 2920/1620 and 2920/2850 in soil Hu were 6.1%and 34.2%higher in 2014 than that in 1997 under MNPK treatment.And these were not obviously affected by fertilization time in CK treatment.?6?The similar C skeleton was found in soil HA and Hu components,while their contents of C types were different in Black Soil.The ratios of aliphatic C/aromatic C and hydrophobic C/hydrophilic C of HA were increased in MNPK and M treatments,while those were decreased in NPK treatment compared with CK treatment.The ratio of each type of C in Hu was higher in fertilization treatments than that in CK treatment.The ratios of aliphatic C/aromatic C,alkyl C/alkoxy C and hydrophobic C/hydrophilic C in HA were increased with fertilization years in the fertilization treatments.The ratio of alkyl C/alkoxy C of soil Hu was increased in MNPK and M treatments,but decreased in NPK treatment.The application of organic manure enhanced the contents of aliphatic C in HA and Hu and the recalcitrant components in Hu,while the application of chemical fertilizers reduced the contents of aliphatic C in HA and stable components in Hu.In conclusion,the application of organic manure combined with chemical fertilizers benifits the balance of N,P and K nutrientsin soil,promotes the contents of soil humic substance,which improves crop yields.The structures of HA and Hu tends to be simplified after the long-term application of organic manure combined with chemical fertilizers,but be complicated after single application of chemical fertilizers.The reasonable application of organic manure combined with chemical fertilizers would ensure the balance of soil nutrients,the improvement of soil organic matter and soil fertility in Black Soil of Northeast China.