Soil Carbon And Nitogen, Quality Evaluation Under Different Land Use In Central Hilly Area Of Hunan Province

Different land use types have an important effect on characteristics of soil carbon and nitrogen, soil quality levels and global warming. Comparative analysis soil carbon and nitrogen contents, carbon and nitrogen storages of 7 kinds of typical land use (secondary woodland, economic forest-land, Chinese fir plantation, nursery garden, slope farm land, deforested-land and abandoned land) were made in central hilly area of Hunan province. Soil quality levels and deterioration extent were evaluated by the integrated soil quality index and soil deterioration index. The main results of the research are as follows:There existed highly significant difference (p<0.01) among soil organic carbon, total nitrogen, ammonium nitrogen, nitration nitrogen contents on 7 kinds land use types; while not significant difference (p>0.05) among soil hydrolyzed nitrogen content. The topsoil (0～15cm) organic carbon content (g/kg) on 7 kinds land use types were ranked as follows: economic forest-land (16.96)> secondary woodland (16.46)> Chinese fir plantation (14.96)> deforested-land (11.82)> abandoned land (11.77)> slope farm land (11.41)> nursery garden (10.11); total nitrogen content (g/kg): secondary woodland (1.45)> economic forest-land (1.27)> slope farm land (1.26)> deforested-land (1.02)> abandoned land (1.01)> Chinese fir plantation (1.00)> nursery garden (0.95); ammonium nitrogen content (mg/kg):economic forest-land (12.20)> secondary woodland (8.45)> slope farm land (8.04)> Chinese fir plantation (7.96)> abandoned land (7.88)> nursery garden (4.48)> deforested-land (3.95); nitration nitrogen content (mg/kg):slope farm land (14.12)> deforested-land (5.88)> Chinese fir plantation (3.59)> abandoned land (3.15)> economic forest-land (2.96)> secondary woodland (2.20)> nursery garden (2.14); hydrolyzed nitrogen content(mg/kg):secondary woodland (149.89)> abandoned land (132.53)> economic forest-land (123.83)> deforested-land (107.73)> Chinese fir plantation (107.66)> nursery garden (100.51)> slope farm land (96.78).The soil depth change of organic carbon content, total nitrogen content and hydrolyzed nitrogen content on 7 kinds land use types almost showed: 0～15cm soil layer>15～30cm soil layer>30～45cm soil layer>45～60 cm soil layer. But the spatial vertical variation of soil ammonium nitrogen content and nitration nitrogen content under different land uses was complex comparatively and had not obvious rules. There almost existed insignificant differrence (p>0.05) among every month of soil carbon and nitrogen contents under different land uses. Except several months, the seasonal dynamic of soil carbon and nitrogen contents on 3 type woodlands was similar, but that on nursery garden, slope farm land, deforested-land, abandoned land was difference. The seasonal dynamic of soil organic carbon, total nitrogen and hydrolyzed nitrogen contents on different soil layer was similar comparatively. Correlation analysis showed that there existed highly significant positive correlation (p<0.01) among soil organic carbon, total nitrogen and hydrolyzed nitrogen contents of 7 kinds of land use types.The trend of eat and flow about soil organic carbon and nitrogen storages under different land uses was similar on the whole. The soil carbon storage (t/hm2) on 7 kinds land use types were ranked as follows:secondary woodland (104.68)>economic forest-land (99.62)>Chinese fir plantation (87.55)>deforested-land (84.63)>abandoned land (61.38)>slope farm land (55.91)>nursery garden (49.59); soil nitrogen storage (t/hm2):slope farm land (7.92)>secondary woodland (7.69)>economic forest-land (7.48)> deforested-land (6.78)>Chinese fir plantation (6.73)>abandoned land (6.52)>nursery garden (5.60).The integrated soil quality index (%) on 7 kinds land use types were ranked as follows:'secondary woodland (95.35)> economic forest-land (73.83)> deforested-land (64.41)> Chinese fir plantation (62.61)> aban-doned land (56.30)> slope farm land (27.35)> nursery garden (4.84); the soil deterioration index (%):secondary woodland (0)> economic forest-land (-9.90)> deforested-land (-14.35)> Chinese fir plantation (-14.96)> abandoned land (-22.22)> slope farm land (-32.16)> nursery garden (-40.44). It is identical that the evaluation results were found using two quantitative methods. There existed highly significant positive correlation (R=0.99, p< 0.01) between the integrated soil quality index and the soil deterioration index.To sum up, it has very obvious effect that land use and man-made management act on soil quality and characteristics of soil carbon and nitrogen. The secondary woodland still preserved more the storage of soil carbon and nitrogen, better soil quality level. Due to extensive management and tree species, the economic forest-land preserved better soil carbon and nitrogen level. Deforested-land had obvious trend of soil carbon and nitrogen loss. Chinese fir plantation can not preserve the storage of soil carbon and nitrogen because of effects of human disturbance and worse site condition etc. Abandoned land has accumulated gradually nutrition elements when its soil renewed. Unreasonable cultivation and predatory management resulted in mass loss of soil carbon and nitrogen, decline of soil fertility on slope farm land and nursery garden.Hence, it has very important meaning that forest conservation can mitigate global warming. It can decrease CO2 concentration in atmosphere and increase carbon storage of terrestrial ecosystem by attaching importance to forestation, fostering forest plantation and adopting protective measure such as reducing deforestation, restoring vegetation etc. At the same time, adopting a long term of protecting farmland measure, for example no tillage, minimum tillage, rotation and agroforestry ecosystem etc., can lessen loss of organic carbon in field ecosystem and preserve even increase soil carbon storage. As a result of that, agriculture soil can become CO2 pool; soil quality can be maintained and improved in the long term; agriculture sustainable development can be kept.