Effects of Management and Vegetation Types on Soil Nutrient Distribution of Grasslands from Eastern Qinghai Tibet Plateau
|Keywords||Eastern Qinghai Tibet Plateau Soil nutrient Grazingmanagement|
In this study, the distribution of nutrients in soils of the eastern Qinghai Tibet Plateau was investigated under different grassland types, grazing intensities, fertilizer application rates, slope direction and surface characteristics and altitudes. The results showed that within the7types of grasslands examined, soil organic carbon generally decreased with the soil depth and the total amount of soil organic carbon at0-15cm amongst different grassland types decreased in the following order: interforest grassland> alpine shrub meadow> alpine meadow> swamp meadow> saline-alkaline meadow> sub-alpine meadow> desertified steppe (P<0.05). The dynamic of soil total nitrogen in soil depths was similar to that of soil organic carbon, and the cumulative amount of soil total nitrogen at0-15cm depth in the investigated types, from highest to lowest, was:swamp meadow> interforest grassland> alpine shrub meadow> testalpine meadow> swamp meadow> saline-alkaline meadow> desertified steppe> sub-alpine meadow (P<0.05). Soil total phosphorus showed no obvious pattern in the desertified steppe and interforest grassland types, and the cumulative amount of soil total phosphorus at0-15cm depth in the7types was decreased in the following order: alpine shrub meadow> swamp meadow> alpine meadow> saline-alkaline meadow> sub-alpine meadow> desertified steppe> interforest grassland (P<0.05). Soil nutrient distribution varies when soil depth increases in different grassland types.Within swamp meadows under different grazing managements, the total carbon order in spring was:full year without grazing> full year grazing>seasonal grazing; while in summer and fall the order changed to full year forbidden grazing>seasonal grazing>full year grazing. In terms of full year grazing and seasonal grazing, soil total carbon peaked at fall, whereas for full year grazing the highest value was observed in spring, although this was not statistically significant. In spring, total nitrogen under a full year without grazing was higher than the other two grazing intensities (P<0.05); all the three grazing intensities had no obvious difference in summer and this was also observed in fall, with the total nitrogen order being:seasonal grazing>full year forbidden grazing>full year grazing. Total phosphorus under different grazing managements and different seasons did not present any statistical significant differences, however phosphorus content under seasonal grazing in fall was greater than the other two managements. Soil total carbon and nitrogen in grazing fields decreased gradually with the ascendance of soil depth, while full year and seasonal grazing fields showed no patterns. Soil total phosphorous decreased gradually with the soil in all grazing treatments except for full year grazing. At the depth of30-45cm and75-90cm under full year grazing, soil total phosphorous contents were higher and reached to0.48g/kg and0.44g/kg respectively. Additionally, there was a slow increase between full year and seasonal grazing in soil available phosphorous when depth increased.Within alpine meadows under different grazing intensities in various years, total carbon under medium grazing between2009and2010was on average higher than mild grazing and intense grazing. Significant differences in2010(P<0.05) were observed and reached3.78%and4.41%respectively. In2011, total carbon under mild grazing was significantly higher than that of the other two treatments (P<0.05) and values showed an unstable annual trend in different grazing levels. Intense grazing resulted in decreasing carbon stocks over3years, with3.26%,2.89%and2.76%respectively. There were no significant patterns of soil total nitrogen under different grazing intensities. Between2009and2010, total nitrogen in medium grazing was higher than mild and intense. There was a significant difference in2010with total nitrogen were0.37%and0.38%respectively (P<0.05),.In2009, total phosphorous under medium and intense grazing was significantly higher than mild grazing (P<0.05), while the order in2010, with a significant difference (P<0.05), was medium grazing>mild grazing>intense grazing. In contrast to2010,2011showed an order of mild grazing>medium grazing>intense grazing and mild and medium grazing were significantly higher than intense grazing (P<0.05). Under various grazing intensities, although there were unstable changes across the years, total phosphorous showed a significant difference (P<0.05).Under different fertilizer concentrations in alpine meadows, total carbon and nitrogen fertilizer no did not show obvious patterns with the increase of fertilizer application whereas soil total phosphorus in different periods of plant phenology changed regularly with the increase of fertilizer application. The order was: T0<T30<T60<T90<T120, with significant differences observed (P<0.05). During the period of seedling establishment, with the increase of the fertilizer, T30, T60, T90and T120were respectively higher than control by0.25g/kg,0.45g/kg,0.60g/kg and0.72g/kg; while during growth period increased by0.22g/kg,0.47g/kg,0.62g/kg and0.74g/kg; as for the fructicative period was0.13g/kg,0.29g/kg,0.37g/kg and0.39g/kg. Except for T120. total phosphorus of other fertilized lands in the fructicative period was higher than seedling establishment period and growth period. Additionally. TO and T30witnessed a significantly statistical difference (P<0.05).In a large scale and extensive range, total nitrogen content order was:sunny slope> beach land> shady slopes> shady slope and sunny slope.Organic carbon order was:shady slope and sunny slope>sunny slope>shady slope and sunny slope> beach land. Total phosphorus in different slope directions were similar, there was no significant difference. Surface shape also affected the distribution of soil nutrition; it varied from the top to the bottom of sloped land. If differences of vegetation type and grazing intensity were not taken into account, soil organic matter, total nitrogen and total phosphorus showed a ascending tendency with the increase of altitude.