| Desert and oasis ecosystem are the main ecosystems in arid area. Studying the characteristics of decaying process, decaying remainders and soil humic acids can accumulate the first hand data for studying the accumulation and decomposition of soil organic matter, the situation of soil fertility, substance cycling and energy flowing in desert-oasis ecosystem, and has the great significance on desert ecosystem restraint and oasis ecosystem extension. Using corn straw and soybean straw, the characteristics of the decaying process and the remainders, the difference of soil fertility status and soil humic acids character in different using ways are studied by normal analysis combined with energy analysis, thermal analysis (DTA, TG, DIG) and infrared spectrum analysis (FTIR). The main conclusions were as follows:(1) The residues decayed quickly at 0-3 months, slowly at 3-6 months, and kept constant at 6-13 months basically. The decaying rate of corn straw adding N was higher than that of soybean straw, and the decaying rate in oasis ecosystem was higher than in desert ecosystem.According to the changes of the amounts of decaying remainders and the decomposition rate of organic C, the decaying process could be divided into 3 stage: the fast decomposition stage → the slow decomposition stage → the stage tending to be stable.The C/N ratios of corn residues and soybean residues still kept at 26-29, 29-36 at the end of experiment respectively, and were much higher than that of soil humus. It showed that the humification didn't complete after 13 months' decaying at the end of experiment.(2) The results obtained by using oxygen-bomb calorimeter showed that the changes of the caloric value (Qv) of corn residues presented as "saddle -shape", and the soybean residues presented as "bow-shape" basically. According to the Qv changes of two kinds of residues, the decaying process could be divided into 3 stage: the fluctuating and rolling stage →the stage tending to be stable→ the fluctuant reducing stage. The 3 stages divided by Qv, the changes of remainders amount and organic carbon decomposition rate were different on the beginning to ending time and the sequences .It showed that the changes of remainder amounts only reflected the weight loss of residues, but the Qv changes reflected the changes of component and character of residues.(3) The results of thermal analysis showed that the DTA, TG and DTG curve of remainders had the similar shapes in different decaying periods. 400-432℃ exothermic peak in DTA curve of remainders and 460-490 ℃ weight loss peak in DTG curve appeared at the decaying process in oasis ecosystem, but didn't appear in desert ecosystem.The weight loss rate of DTA 300℃ peak was correlative to Qv outstandingly; the weight loss rate of DTA 450℃ peak was not correlative to Qv. It showed that Qv was mainly decided by the amounts of pyrolysis parts at lower exothermic peak (300℃).The h300/h450 ratio at DTA curve and w320/w500 ratio at DTG curve have the similar tendency of changes. Both can be used as the index to describe the decaying process. According to their changes, the decaying process can be divided into 4 stages: the drastic change stage→ the fluctuant reducing stage→the stage tending to be stable → the fluctuating and rolling stage.(4) The results of FTIR showed that the FTIR spectrum of decaying remainders at all periods was near to that of original samples, and was far to that of soil humus. It indicated that the decaying remainders were at the stage of residues, and the humification didn't complete after 13 months' decaying in both two kinds of ecosystems.(5) Compared with virgin land, the soil organic matter, total N, total P, total K, slowly released K and available N of alfalfa land increased at different degree. Compared with alfalfa land, the soil organic matter, total K, slowly released K and available K all decreased, but total N, total P, available N and available P increased.The results of DTA, DTG and FTIR analysis all showed that the aliphat...
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