Study Of Wheat And Rice Straw Residues Incorporation On Chemistry Structure Of Soil Organic Matter And Contents Of Different Nitrogen Forms In Soil

Crop residue including cellulose,hemicellulose and lignin.It can significantly increased soil organic matter contents and improved soil capacity of carbon sinks in the degradation process.Soil organic matter(SOM)is a variety of different substances,such as higher plants,or the residues of animals and microorganisms which contain carbon and nitrogen compounds.It is the main form of the soil nitrogen,about 90% of total nitrogen in th soil.The soil nitrogen forms divided into organic nitrogen and inorganic nitrogen,the former including available nitrogen and mineral nitrogen.The crop can be directly absorbed by the available nitrogen which include the water-soluble ammonium nitrogen,the exchangeable ammonium nitrogen and nitrate nitrogen.However,the mineral ammonium nitrogen is difficult to use of crops.The main factors affecting soil fertility and crop yields are soil organic matter,nitrogen forms and the effectiveness of nitrogen.In this experiment,the objective of this work was to investigate influences of long-term crop residues returning and chemical fertilizer application on the different nitrogen contents and chemical composition of SOM and HA(mobile humic acid and calcium-binding humic acid)which were examined by Element analysis,Fourier transform infrared spectroscopy(FTIR)and 13 C multi cross polarizatin/magic angle spinning NMR spectroscopy(Multi-CP/MAS NMR)technique.The main results are as follows:1.Single straw residues incorporation increase the contents of soil organic matter,total nitrogen and organic nitrogen of the soil,while reduce the content of soil inorganic nitrogen.Crop residues returning and chemical fertilizer can significantly increase the contents of soil organic matter and nitrogen(total nitrogen,inorganic nitrogen and organic nitrogen).The soil total nitrogen,organic nitrogen and inorganic nitrogen contents in SF2 treatment(C/N ratio:18:1)were increased by 16.62%,16.49% and 22.58% higher than those in the CK,respectively.2.Straw returning increased soil organic matter as well as C% and N% in SOM,while decreased the ratio of C/N,H/C and O/C in SOM.Meanwhile,the NMR spectra showed that the alkyl C and the carbonyl C were increased,the O-alkyl C and aromatic C were reduced.It demonstrated that the amount of nitrogen compound,alcohols,phenols,lignin derivatiives group(aromatic carbon functional group)and carboxylic acids in SOM increased.Crop residues incorporation decreased the ratio of alkyl C to O-alkyl C,reducedthe degree of humification of soil organic matter.Straw residues returning and chemical fertilizer could significantly increased C% and N% in SOM,while decreased the relative proportion of aromatic C and the relative contents of NCH and COO/N-C=O groups.3.Compared with Calcium-binding humic acid(Ca HA),the mobile humic acid has less carbon functional groups and the lower C/N ratio.Compared with MHA,the Ca HA have more aromatic C,higher degree of condensation,larger molecular and the more content of carboxyl groups.While the MHA have stronger fatty,and higher activation.The changes in the chemical structure of humic acids(HA)can reflect the changes of SOM.Crop residues incorporation enhenced the the alkyl C and the carbonyl C were increased,the O-alkyl C and aromatic C were reduced.Meanwhile it increased aromatic C in HA,reduced the relative content of NCH and COO/N-C=O functional groups.4.Compared with CK treatment,single straw residues returning treatment can reduced the rice production by 10.6%.Crop residues incorporation and chemical fertilizer application increased by 12.6%,22.7%,19.1%,respectively.Single straw residues returning reduced the nitrogen contents of rice grain and straw,nitrogen absorption and rice yields.When the C/N ratio is 18:1,the rice yields is obviously increased and reached to the highest(P<0.05).