Effect Of Long-Term Fertilization On Transformation And Bioavailability Of Zinc In Black Soil

Zn is an essential nutrient element for plant growth. Appropriate application of Zn fertilizer is important for improving crop yield and its quality, as well as protecting natural environment. With the year of soil reclamation increasing, Zn fertilizers are applied in some black soil regions in Northeast of China. Understanding of transformation and availability of Zn in soils is of great significance for reasonable fertilization and environmental assessment.Long-term fertilized black soil samples were collected from Hailun National Research Station of Agroecology, including control (CK), chmical fertilization (NPK), chemical fertilizer plus organic manure (NPKM), and chemical fertilizer plus organic manure plus Zinc fertilizer (NPKM+Zn) treatments. We analysed various Zn fractions and their availability in soils. Zn content and availability were also analysed in the three typical black soils collected from Gongzhuling in Jilin province, Hailun and Nenjiang in Heilongjiang province. The results show as follows:(1) Long-term fertilization affected total Zn, available Zn and Zn fractions at different degrees. Long-term chemical fertilization consumed up Zn in black soils. Total Zn, available Zn and different Zn fractions increased in treatments of NPKM and NPKM+Zn. Contents of total and available Zn were in the order of NPKM+Zn>NPKM>CK >NPK. Compared to CK, long-term chemical fertilization decreased Zn fractions, however, the fertilization modes of NPKM and NPKM+Zn increased Zn fractions at different degrees. Long-term chemical fertilization decreased percentages of exchangeable Zn (Ex-Zn), manganic oxide chelated Zn (MnO-Zn), organic matter chelated Zn (OM-Zn) and amorphous ferrous oxide chelated Zn (AFeO-Zn) in total Zn. The results suggested that the fertilization modes of NPKM and NPKM+Zn could enhance Zn availability.(2)Zn fertilization increased wheat biomass and Zn content in wheat plant, but it decreased use efficiency of Zn fertilizer. Wheat biomass and its Zn content with or without Zn fertilization were in the order of NPKM+Zn>NPKM >NPK>CK.The fertilization modes of NPKM and NPKM+Zn enhanced wheat growth and Zn bioavailibality. Use efficiency of Zn fertilizer was less than 3% in the four fertilization treatments.(3)Total Zn contents ranged from 68.10 to71.54 mg kg-1 in typical black soils. The total Zn contents in black soils were in the order of Hailun>Nenjiang>Gongzhuling. Available Zn content in the three typical black soils ranged from 1.41 to 2.16 mg kg-1, in the order of Nenjiang > Hailun > Gongzhuling. Zn fractions were in the order of RES-Zn >CFeO-Zn >AFeO-Zn >MnO-Zn >OM-Zn >Ex-Zn, and RES-Zn accounted for more than 50%. Most of Zn in soils existed as mineral Zn. Pot experiments showed that Zn fertilization increased soybean biomass, seed yield and Zn content in plant. There was significant correlationship between Ex-Zn, MnO-Zn and OM-Zn to soybean biomass and seed yield. Use efficiency of Zn fertilizer was less than 1% for the three typical black soils.