Application Of 137Cs And 7Be To Assess The Effectiveness Of Soil Conservation Technologies In The Central Highlands Of Vietnam

The combined use of 137Cs and 7Be for assessment of medium- and short-term soil erosion rates for sloping lands with and without soil conservation technologies in the Central Highlands of Vietnam has been carried out. For the 2.5 ha mulberry field with the slope gradient of about 15%, where green manure hedgerows have been utilized as a soil conservation measure for 22 years, about 54.6% of the area suffered from erosion with erosion rates varying from 0.6 to 70 t ha-1 y-1 (the average: 31 t ha-1 y-1), and deposition occurred for 45.4% of the area with the deposition rates ranging between 0.2 and 74 t ha-1 y-1 (the average: 36 t ha-1 y-1). The medium-term erosion rate at this field was 1.2 ± 0.6 t ha-1 y-1, and short-term erosion rate was 1.5 ± 0.24 t ha-1 y-1. Soil erosion was almost controlled by the shrubby hedgerows and the net erosion rate was reduced from 28 t ha-1 y-1 to 1.2 t ha-1 y-1. 137Cs and 7Be were also used for assessment of soil erosion rates for two 0.5 ha coffee plots with the slope gradient of about 25%. For the plot without soil conservation, soil erosion occurred for all sampling points with medium-term erosion rates ranging between 1.2 t ha-1 y-1 and 35 t ha-1 y-1 (the average erosion rate was 22.7 ± 1.2 t ha-1 y-1). The short term soil erosion rate estimated by 7Be technique in the year 2005 was 32.7 ± 6.1 t ha-1 y-1 for this plot. For the plot with the last five year presence of Vetiver strips, about 93% of the area suffered from medium term erosion with erosion rates varying from 3 t ha-1 y-1 to 33 t ha-1 y-1 (the mean is 22.2 t ha-1 y-1), and medium term deposition occurred for only 7% of the area with the deposition rates ranging between 1.3 and 1.4 t ha-1 y-1, resulting in the net erosion rate of 20.4 ± 0.6 t ha-1 y-1. The short term soil erosion rate at this plot estimated by 7Be technique in the year 2005 was 2.3 t ha-1 y-1. By using Vetiver strips as a soil conservation technology, soil erosion was almost controlled and the net erosion rate was reduced from 32.7 t ha-1 y-1 to 2.3 t ha-1 y-1. (author)