Transformation And Distribution Of Exogenous Nitrogen In Three Typical Soils And Crop Responses

It is important for improving soil nitrogen （N） supplying capacity, crop yield and protectingenvironment to explore the effects and mechanism of different exogenous N on soil N and crop yield. Inthis study, greenhouse pot experiments were designed to investigate the effect of urea N, pig manure Nor combined application （manure N for30%chemical N） on soil N pool in black soil, fluvo-aquic soiland paddy soil of subtropical china; urea and manure was labeled by¹⁵N respectively，to study thetransformation in those three soils, dynamic process in paddy soil and the availability for maize, wheatand rice. The main results were as follows:1. Exogenous N increased the content of total N, it was significantly increased by5.2%～24.8%and3.5%～13.7%in OM*treatment (application of¹⁵N labeled pig manure totally) and OM*+CFtreatment (application of¹⁵N-labeled pig manure with common urea), respectively（p<0.05）.2. The contents of ammonium N （AN） and nitrate N （NN） were significantly increased by19.7%and32.9%in OM*treatment respectively （p<0.05） in black soil, and by59.0%and120times in OM*treatment respectively （p<0.05） in flavor-aquic soil, and by81.0%and53.0%in OM*+CF treatmentrespectively （p<0.05） in paddy soil.3. Compared to the non-fertilizer （CK） treatment, the application of N fertilizer increased thecontents of different fractions of organic N in soil, especially in OM*treatment, the contents of aminoacid N （AAN）, hydrolysable unidentified N （HUN） and non-hydrolysable N （NHN） were significantlyincreased by15.0%,24.7%and23.7%respectively （p<0.05） in black soil, and hydrolysable N （HN） andhydrolysable amminonum N （HAN） by25.3%and39.3%respectively （p<0.05） in flavor-aquic soil, andNHN by16.7%in paddy soil.4. The proportion of organic forms accounted for total N was in dynamic balance, it was in theorder of AAN （29.9%～31.2%）>NHN （22.9%～25.4%）>HAN （21.6%～24.8%）>HUN （16.2%～19.3%）>amino sugar N （ASN）（3.8%～4.7%） in black soil; NHN （30.6%～32.6%）>AAN （28.9%～31.9%）>HAN （18.5%～21.2%）>HUN （12.0%～14.0%）>ASN （4.3%～5.6%） in fluvo-aquic soil;AAN （26.5%～30.4%）>NHN （24.4%～28.2%）>HUN （18.3%～23.1%）>HAN （16.5%～20.1%）>ASN （4.5%～5.2%） in paddy soil.5. AN and NN mainly derived from exogenous N at harvest. Organic fertilizer N in OM*treatmenthad greater contribution to AN and NN than chemical ferlitizer N in CF*treatment (application of¹⁵Nlabeled urea only) in black soil and paddy soil,53.6%and66.2%of AN and NN respectively, derivedfrom organic fertilizer N in black soil, and53.1%and26.6%from organic fertilizer N in paddy soil; incontrast, chemical ferlitizer N in CF*treatment had greater contribution to AN and NN than Organicfertilizer N in OM*treatment in flavo-aquic soil,26.4%and27.4%of AN and NN derived fromchemical fertilizer N respectively.6. The contribution of exogenous N to the nitrogen contents in different fractions varied withfertilizer forms. The content of AAN, HAN and ASN in black soil, HAN and NHN in fluvo-aquic soil, HUN and NHN in paddy soil was significantly influenced by the application of the chemical fertilizerrespectively,2.6%～7.8%of them derived from chemical fertilizer N; and the content of HAN and ASNin black soil, HUN and NHN in fluvo-aquic soil, AAN, ASN and HUN in paddy soil by the applicationof the organic fertilizer significantly,4.5%～10.7%of them derived from organic fertilizer N; and thecontent of HAN and ASN in black soil, HAN, ASN and HUN in fluvo-aquic soil, AAN, HAN and ASNin paddy soil by the application of the organic fertilizer combined with chemical fertilizer significantly,1.6%～4.6%of them derived from organic fertilizer.7. Exogenous N increased the contents of AN and NN throughout the whole growth stage of rice.82.6%and38.6%of AN and NN derived from organic fertilizer N in OM*treatment at jointing stagerespectively;30.8%and27.6%from chemical fertilizer N in CF*treatment at jointing stage respectively;38.9%of AN from organic fertilizer N at jointing stage and17.4%of NN from organic fertilizer N attillering stage respectively in OM*+CF treatment.8. Different exogenous N had different transformation process to soil organic N. According to theorder of tillering stage, jointing stage, filling stage and maturing stage, chemical fertilizer N in CF*treatment mainly transformed to HAN, AAN, NHN and NHN, the proportion of residual N was45.5%、34.5%、30.9%and41.3%, respectively; organic fertilizer N in OM*treatment to HAN, HAN, HUNand AAN, the proportion of residual N was67.8%、36.8%、34.1%and32.0%, respectively; organicfertilizer N in OM*+CF treatment to HUN, HAN, NHN and AAN, the proportion of residual N was54.2%、38.6%、34.6%and42.4%, respectively.9. Exogenous N had different regulation on improving the biomass and grain yield of differentcrops, and the substitution of manue N for30%of chemical N was equivalent or superior to fullchemical or organic fertilizer N for the crop yield. The utilization ratio of N and the contribution to theyield of organic fertilizer N in combined application mode increased34.1%～130%and2.4%～28.4%respectively.In summary, there were different effects on soil N pool and different transform rule betweenorganic and inorganic fertilizer. The present results indicated that the chemical fertilizer combined withorganic fertilizer is a practical approach for promoting the transformation and distribution of organicfertilizer N to available N such as AAN, HAN, HUN, AN and NN, improving organic fertilizerutilization rate for crop and contribution to yield, increasing the availability of organic fertilizer,reducing environmental risk and maintaining the sustainability of soil.