Effects of Long-term Application of Fertilizers on Rhizosphere Soil Organic Nitrogen Fraction in Barley-Double Cropping Rice Field
Rhizosphere soil organic nitrogen(SON)fraction play an important role in soil nutrients and crop nitrogen(N)nutrition.This study was based on a long-term(37 years)located fertilization experimental field,including four fertilization treatments:without fertilizer input as a control(CK),chemical fertilizer alone(CF),rice straw residue and chemical fertilizer(RF),and 30%organic manure and 70%chemical fertilizer(OM).At the maturity stage of late rice,the rhizosphere soil basic physiochemical properties,microbial biomass N(MBN)and SON fractions,including amino acid N,amino sugar N,ammonia N,hydrolysable unknown N,non-hydrolysable N in barley-double cropping rice field were determined.The results indicated that RF and OM significantly increased the contents of soil organic carbon(SOC),total N,ammonium N and nitrate N in rhizosphere soil compared to CK.Soil MBN content was significantly increased by 19.8%and 30.7%under RF and OM,respectively,compared to CK.Rhizosphere soil acid hydrolyzable N was the main component of soil total N,accounting for 59.61%-72.06%of total N.The content of acid hydrolyzable N in rhizosphere soil was in order of OM>RF>CF>CK.Soil amino sugar N,amino acid N and hydrolysable unknown N contents were found significantly highest under OM,increased by 139.3%,47.9%and 110.0%,respectively,compared to CK.Soil ammonia N content was significantly highest under RF,with an increase of 69.9%over CK.SOC,total N,ammonium N and nitrate N contents all showed a significantly positive correlation with soil amino acid N,amino sugar N,hydrolysable unknown N and MBN contents.Therefore,the application of rice straw or organic manure and chemical fertilizer is an effective practice for improving soil fertility,which can effectively increase the capacity of rhizosphere soil N supply in barley-double cropping rice field.
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