| With the steep plowland by contrast, the biomass spatial distribution and its relationship with the soil anti-erodibility of fine root <2mm in diameter between two herbages' types (grass grown in natural conditions and ryegrass) of triploid populus tomentosa Carr woodland in Tianquan county, Sichuan province were studied. By using coring methods in the paper, the results were as follows:1. In the populus tomentosa Carr woodland under two types: In the ryegrass woodland, the average total biomass of tree root 0~1mm in diameter was 0.359 t.hm~-2 , the upper layer was 0.179 t.hm~-2 , live fine roots' accounted for 82.9%; Middle layer was0.118 t.hm~-2, live fine roots' accounted for 81.41 %; the ratio of biomass in upper layer, middle layer and down layer is 50 : 33 : 17. In the nature grass woodland, the average total biomass of tree root 0~1mm in diameter was 0.1891t.hm~-2, the upper layer was 0.101 t.hm~-2, live fine roots' accounted for 87.4%; Middle layer was 0.054t.hm~-2 , live fine roots' accounted for 77.69%, down layer was0.034 t.hm~-2, live fine roots' accounted for 71.25%; the ratio of biomass in upper layer, middle layer and down layer was 53 : 29 : 18. In these two types, the both total fine root of upper layer and middle layer accounted for over 80%, and in ryegrass, the total biomass of 0~ 1mm fine root was about 2 times as much as those in the nature grass. And the ratio of live root and died root was about 4 :1.In the ryegrass woodland, the average total biomass of fine root 1 ~2mm in diameter was 0.254 t.hm~-2, The ratio of biomass in upper layer, middle layer and down layer was 40 : 41 : 19. In the natural grass woodland, the average total biomass of fine root 1~2mm in diameter amounted to 0.276 t.hm~-2, The ratio of biomass in upper layer, middle layer and down layer was 42 : 34 : 24. In these two types, the both total fine root of upper layer and middle layer accounted for 80%, but the total biomass is similar. The ratio of live root and died root was also about 4 :1.In the ryegrass woodland, the average total biomass of tree root 0~2mm in diameter was 0.7335 thm"2, the grass roots' was 0.121 thm"2, made up 16.5% of the total biomass; In upper layer, the biomass amounted to 0.3832 t-hm"2, accounted for 52.2%; the middle layer and down layer were 32.9% and 14.9% respectively. In the natural grass woodland, the average total biomass of tree root 0~2mm in diameter amounted to 0.998 t-hm", the grass roots' was 0.533 t-hm"2 and made up 53.4% of the total biomass. In upper layer, the biomass amounted to 0.5879 t-hm"2, accounted for 58.9% ,the middle layer and down layer were 23.5% and 17.5% respectively 02. From the vertical distribution and monthly changes of biomass of root 0~2mm in diameter under two types: The upper layer biomass showed mild double-peak trend, with peak in May and September; the maximum in ryegrass and natural grass forest were 0.5142 t-hm'2 and 0.8066 t-hm"2 respectively. The total biomass of tree root of 0~lmm and l~2mm in diameter in ryegrass forest were more than those in the natural grass forest. However, the grass root biomass in the natural grass forest was far more than that in the ryegrass forest; therefore, the total root amount of 0~2mm in the natural grass forest was more than that in the ryegrass forest. The biomass in the middle layer under two types both showed single-peak trend. The biomass in the ryegrass forest increased steadily and reached the highest in June, but the biomass in the natural grass forest increased little before June, and reached the highest in July. The down layer root biomass under two types changed smoothly, with little fluctuation.3. After 4 years in the land of converting from cropland to forest, between the woodland and steep plowland, the total content of water stable aggregate had little variation.The content of water stable aggregate in step plowland changed unorderly. But both two types showed that the content of bigger water stable aggregate in upper layer was more than that in the middle and down layer. The total content of water stable aggregate had little difference between the forest and step plowland. However, the bigger water stable aggregate in the upper and middle layer in the forest was obviously more than that in step plowland. In general, the content in the natural grass forest was more than that in the ryegrass forest.In the same depth, the organic matter content of the upper, middle and down layer inthe step plowland were more than those in the forest. The organic matter content of the upper and middle layer in the natural forest were less than those in the ryegrass forest. However, in the down layer the natural grass root input more organic matter to the soil than that in the ryegrass forest, which demonstrated that it was a relatively slow process increasing soil organic matter content through root.Disperse coefficient and disperse rate were taken as the index to soil anti- erodibility. To some extent, they could reflect the disperse and concretion capacity of the soil, but the bigger particle diameter water stable aggregate was more suitable to denote the anti-erodibility of the soil.4. With regard to increasing the content of bigger water stable aggregate(>5mm, 5~3mm) and the totals' and reducing the content of small water stable aggregate in the soil, the effect of 0~2mm root was notable on the whole, and the significant coefficients were 0.752, 0.572, 0.786 and -0.563 respectively. 0~lmm root also played an important role, and the function of grass root is very significant. The root could increase the bigger water stable aggregate and decrease the small water stable aggregate content in the soil. In this way, fine roots increased the soil anti-erodibility.In conclusion, the converting farmland to forest (grass) was a comparatively suitable popularization method for increasing the soil anti-erodibility. |
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