| This paper used the combination method of monitoring and time interchange to research the composition, characteristics, combining form of soil humus and the seasonal variations of soil humus in Eucalyptus plantation of different generations(The first, second and third rotation) from in Dongmen town, Guangxi with the shrub-grass lands as the control and to explore the relationship of the composition and combining form of soil humus with the main fertility factors of soil for providing the scientific basis and material for the sustainable management in Eucalyptus plantation. The main results were as follows:1. The carbon content of HA and FA in the soil of shrub-grass lands was higher than that in Eucalyptus plantation of different generations. And the differences were extremely significant (P<0.01), and the trends of them were decreasing with the increase of continuous cropping of Eucalyptus plantation. The HA/FA values tended to be the same in shrub-grass lands and Eucalyptus plantation of different generations. The tends of E4 was as follow:SL(means the shrub-grass lands)>SR (the first generation of FR in the sample plot)>TR (the second generation of FR in the sample plot)>FR (the first time planted eucalyptus in the sample plot).The E4/E6:FR> TR> SR> SL. Humification:SL> FR> SR> TR. The carbon content of HA and FA was decreasing with increasing soil depth in Eucalyptus plantation of different generations, and the differences were extremely significant (P<0.01). The maximum value of HA in SL and Eucalyptus plantation of different generations all appeared in summer, sometimes appeared in the other three seasons. The seasonal variations of carbon content of HA in FR and SR were not significant(P>0.05), but in the TR and SL in spring was significantly higher than those in winter, autumn but no significant differences in other seasons(P>0.05).2. The tends of loose combined form of soil humus, stable form of soil humus and Ⅰ/Ⅲ were as follow:SL>FR>SR>TR, the loose combined form of soil humus in SL was higher than those of other three Eucalyptus plantations with a significant difference (P<0.05), but no significant differences between the three Eucalyptus plantations. Different Eucalyptus plantations and SL tightly combined humus content had no significant difference (P>0.05). The activity of soil humus of different forest types:SL>FR>SR>TR. The loose combined form and stable combined soil humus, Ⅰ/Ⅲ were extremely significant negatively correlated with soil depth(P<0.01). The same as the tightly combined humus, but had no significant difference (P>0.05).3. The total nitrogen, available potassium share the tend of SL>FR>TR>SR and the total phosphorus of SL> TR>SR>FR and the pH, hydrolyze nitrogen of SL>FR>SR>TR. Available phosphorus in SL was the highest but was the lowest in the SR. The trend of natural water content was: FR>SL>SR>TR. The soil total nitrogen, hydrolytic nitrogen, available phosphorus content in Eucalyptus plantation was the highest in summer but the lowest in autumn and winter. The content of available potassium was the highest in summer or autumn, lowest in autumn or winter. C/N is the minimum value appeared in spring or summer, the maximum value appears in winter.4. The correlation between total nitrogen and the content of carbon in humic acid (HA+FA), HA, FA were all positive extremely significant(P<0.01), but the E4/E6 was negative correlation significant(P<0.05); The correlation between available potassium and the content of carbon in humic acid(HA+FA), HA, FA, E4 were positive significant(P<0.05) or positive extremely significant(P<0.01), but the E4/E6 was negative correlation significant(P<0.05). The correlation between hydrolytic nitrogen and the content of carbon in humic acid(HA+FA), HA, FA, were all positive extremely significant(P<0.01), but the E4/E6 was negative correlation significant(P<0.05). |
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