Effect Of Management On Grassland Soil Organic Carbon

Grassland is an important part of terrestrial ecosystem and plays an key role in carbon cycle. In this paper, based on the collection of literatures concerning China and foreign countries and experimental data on the impact of different management measures on soil organic stock change, impact of different management measures on soil organic carbon change was studied. Meanwhile, a integration of SOC under different management of China was made with Meta analysis software, as well as the different effect of each management measure on soil organic carbon in different soil depth. And the impact of the experimental duration and the average annual precipitation on soil organic carbon was analized. It was helpful to provide a basis to evaluate grassland ecosystem carbon sink and resource in China and reached the following conclusions:1) Meta analysis method was used to estimate the yearly changing amount of soil carbon under the regulations on the main types of grasslands in China. Concretely, the yearly reducing amount of soil organic carbon is the highest under the overgrazing regulations, which reaches -2.34tC·hm^-2·a^-1>heavy grazing(-1.52tC·hm^-2·a^-1)>light grazing(-0.54tC·hm^-2·a^-1)>medium grazing (-0.49tC·hm^-2·a^-1), while the yearly increasing amount of soil organic carbon was the highest under the resowing management, which reaches 0.90tC·hm^-2·a^-1 followed by enclosure management (0.48 tC·hm^-2·a^-1) and forbidden grazing(0.19 tC·hm^-2·a^-1).2)The annual soil organic carbon change under different management shows that: the difference of SOC change was not significant in temperate grassland and alpine meadow grassland under various managements. However, the difference of SOC change among the light grazing with forbidden grazing, moderate grazing and heavy grazing was not significant in alpine meadow steppe, temperate steppe and temperate desert steppe grasslands, but the SOC stocks under over grazing management has been significantly higher than that of light grazing and forbidden grazing (p <0.05).3) Collecting the foreign literatures, variation ranges of SOC change for 12 kinds of management measures on the grassland were as follows: improving grassland cropping systems 0.05 0.8 tC·hm^-2·a^-1, conversion grassland into cropland -0.14^-1.7tC·hm^-2·a^-1, change from short duration to permanent grasslands 0.3⁰.4tC·hm^-2·a^-1, intensification of organic soils with permanent grassland -0.9¹.1tC·hm^-2·a^-1, improving grazing system 0.03⁰.7 tC·hm^-2·a^-1, firing -0.04^-0.07 tC·hm^-2·a^-1, reducing the degradation of grassland (including reclaiming forest or grassland from farmland, forbidding burning, improving the nutrition of vegetation on grassland)0.02⁰.5tC·hm^-2·a^-1, heavy grazing (including moderate grazing and forbidding grazing) -0.03^-2.04 tC·hm^-2·a^-1, moderate grazing 0.1¹.37tC·hm^-2·a^-1, fertilization 0.02⁰.52 t C·hm^-2·a^-1, forbidden grazing -0.14⁰.59tC·hm^-2·a^-1, increasing the duration of grassland 0.1⁰.5 tC·hm^-2·a^-1.4) In this paper, all data was collected for Meta analysis .The impact of different management ,experimental duration and annual precipitation on SOC change in different soil depth was studied. The loss of SOC under the conversion from grassland to cropland was obvious in the 200⁵00mm-average annual rainfall areas, but the amount of SOC decreased seriously in the soil depth of 0²0cm under moderate, heavy and over grazing intensity. Under light grazing, SOC increased gradually during 10³0years. But the loss of SOC in 20⁴0years under heavy and over grazing was larger during 0²0years. Judging from the annual precipitation, SOC change of 500¹000mm rainfall areas increased by 4.1% than the <500mm region under light grazing, while under the moderate and heavy grazing the loss of SOC decreased with the increasing rainfall amount. It was an opposite result for the overgrazing management. Meanwhile, the impact on SOC change under forbidden grazing was most significant in 100³00mm rainfall areas. It was significant that the increase rate of SOC was larger(10³0cm) than that (<10cm)under enclosed management and the value of SOC change during the <10years was about 2.6 times than that in 10²0years.