In order to study the changes in the composition of humic substance and elemental composition of humic acid in the rhizosphere soil of different crops

a two-year field experiment in Jilin Agriculture University experimental field was carried out. Three crops (corn

soybean and cabbage) were selected in the experiment with chemical fertilizer

leaves combined with chemical fertilizer

and poultry manure combined with chemical fertilizer. The water-soluble substance (WSS)

humic acid (HA)

fulvic acid (FA)

and humic material (HM) were extracted by the modified method of humic substance composition. The organic carbon contents of soil humic components were measured by the method of K2Cr2O7 thermal oxidation

the optical properties of HA and FA were measured by a spectrophotometer

and the structural changes of humic acid were indicated from the ratio of E4/E6 and elemental composition. The results showed that the contents of total organic carbon and humic components followed the order of cabbage＞corn＞soybean. Compared with the CK

the application of organic materials significantly increased the organic carbon contents of TOC

WSS

HA in rhizosphere soil of different crops by 5% to 8%

34% to 55%

8% to 20%

respectively. Organic materials had no significant effect on carbon contents of FA. Compared with leaves and poultry manure

the application of maize straw significantly increased total organic carbon

application of different types of organic materials did not show a remarkable difference in organic carbon contents of WSS

the order of carbon contents of humic material were: maize straw＞leaves＞poultry manure＞CK. The effect of organic materials on the PQ values (the radio of HA/(HA+FA)) varied with different crops. The maize straw and poultry manure treatments had similar effects on PQ values in the rhizosphere soil of corn and soybean

and the poultry manure significantly increased PQ values in rhizosphere soil of cabbage. The application of organic materials resulted in a significant increase of the E4/E6 value in fulvic acid

while a little bit decreased E4/E6 of humic acid. Organic materials enhanced condensation degree

complicated the structure of HA

and increased the contents of nitrogen-containing groups of HA

with the effect of maize straw being the most significant. In general

organic materials showed better fertilization effect on soil than chemical fertilizer. The effect of poultry manure on the rhizosphere soil of cabbage was the most significant

maize straw and poultry manure treatments had similar effects on the rhizosphere soil of corn and soybean.