Effects Of Tillage Period On Soil Organic Carbon Pool And Aggregate Stability Of Sub-alpine Meadow

It is great effects of reclamation on soil organic carbon pool and soil aggregate stability, but, we cannot know how soil property change clearly with the increase of reclamation years after reclamation. We selected six different sub-alpine meadow reclamation soil: uncultivated, cultivated for 5 years, cultivated for 13 years, cultivated for 20 years, cultivated for 33 years, cultivated over 70 years. We analysis the effects of different reclamation years on soil organic carbon,nitrogen,carbohydrate,humus,mineralization-carbon and soil aggregate stability. The aims were to investigate changes of soil organic carbon and soil aggregate stability under different years of reclamation. The main conclusions of the study are summarized as follows:1. Sub-alpine meadow is predominated by silty loam. There is no obvious difference of the soil pH (0-15cm) between the uncultivated site and the after reclamation sites. The changes of silt and sand content are not significant too, but there is an upward trend of the clay content in the sample of cultivated for 33 years (mainly from cultivated for 20 years to cultivated for 33 years), which may be related to farming disturbance which could refine the soil particles; after cultivated 33 years, the clay content start to decline, which may be related to wind erosion. The CaCO3 content at 0~15cm depth layer present increasing trend, but there is no significant.2. There is significant decrease of soil organic carbon content at 0-15cm depth after cultivated 5 years in the sub-alpine meadow; there is decrease during the samples of cultivated 5 years to 33 years too, but no significant. Compared to the sample of uncultivated, total organic carbon content of the sample of cultivated over 70 years decreased by 34 percent. There is no significant difference of the particulate organic carbon during the samples of cultivated 5 years to over 70 years, but lower than that of the sample of uncultivated significantly. The mineral-associated organic carbon presented significantly declining trend only in the sample of cultivated over 70 years. Total nitrogen presented significantly declining trend, there is significant difference between the samples of after cultivated 5 years and uncultivated, no significant between the samples during cultivated 13~20 years, significantly declining during the samples of cultivated 33 years to over 70 years. The particulate organic nitrogen and the mineral-associated organic nitrogen have the same tend with the particulate organic carbon and the mineral-associated organic carbon separately.3. The soil carbohydrate carbon at 0-15cm depth decrease with the reclamation year increase after reclamation in the sub-alpine meadow. It decrease 29% significantly after cultivated 5 years, which is 4.3~4.2g/kg during the samples of cultivated 5~33 years, and no significant. There is significant decrease in the soil carbohydrate carbon of the sample of cultivated over 70 years than that of the samples of cultivated for 33 years. The soil humus carbon significant decrease after cultivated 5 years, but there is increase from cultivated 33 years, and the soil humus carbon decrease in the sample of cultivated over 70 years, decreased by 36 % compared to the uncultivated land. Mineralization in soil carbon content also decreased significantly in samples of after cultivated 5 years, decreased by 35 % compared to the uncultivated land. There is no significant difference of the mineralization in soil carbon content of the samples of cultivated 5~70 years.4. The total soil phosphorus content increases continuously with the reclamation year increase after reclamation in the sub-alpine meadow. But there is no significant during the samples of cultivated 5~20 years and significantly decreasing during the samples of cultivated 20~70 years. The fluctuation of available phosphorus is great, and which increase with the reclamation year increase, but decreased after 13 years and then went up again.5. Soil structure stability significantly decreased in the sub-alpine meadow, mainly in the sample of cultivated for 5 years. There is no significant difference in the soil structure stability under different years of reclamation. The aggregate stability rate decreased 66~84% during cultivated 5~33 years, and decreased 86% of the sample of cultivated over 70 years.