Soil-erosion rate was negatively correlated with the concentration of available Si in soils. This finding may indicate that available Si or soil rich in Si was redistributed through soil erosion. Available Si content in river sediments was also studied and determined to be higher than those in sawah or other land-use types. Sawah means a leveled and bounded rice field with an inlet and an outlet for irrigation and drainage, respectively.

Results showed that the available Si levels in sawah soil were less than 300 mg SiO2 kg⁻¹ on average. This watershed is the main rice-production area in Sumatra, Indonesia. Herein, the distribution of available Si and its correlation with land-use type and soil-erosion status were investigated and discussed using the universal soil loss equation (USLE) in the Sumani watershed (SW). Silicon (Si) is an important element for rice plant, and its availability in soil is an important factor affecting sustainable rice production. The USLE model in Surfer was used to identify specific regions susceptible to soil erosion by water and was also applied to identify suitable sites to conduct soil conservation planning in Sumani Watershed. Traditional soil conservation practices were applied by farmer for a long time such as terrace in Sawah. Land use (C-factor), rainfall erosivity (R- factor), soil erodibility (K-factor), slope length and steepness (LS-factor) were dominant factors that affected soil erosion.

These results were verified by comparing one year’s sediment yield observation on the outlet of the watershed. Other land, soil eroded from upland were deposited in lowland. Upland area was designated as having a severe to extreme severe erosion hazard compared to lowland which was designated as having very less to moderate. Annual average soil loss for Sumani watershed was 76.70 Mg ha-1 y-1 in 2011. Sumani Watershed had erosion hazard in criteria as: severe to extreme severe (26.23%), moderate (24.59%) and very low to low (49.18%). Calculating soil loss and map of USLE factor were determined by Kriging method in Surfer 9. Landsat TM imagery and field survey were used to determine crop management (C-factor) and conservation practices (P-factor). Of Sumani Watershed was used to calculate slope length and Steepness (LS-factor). As many as101 sampling sites were used to investigate soil erodibility (K-factor) with physico-chemical laboratory analysis. Climatology data from three stations were used to calculate Rainfall erosivity (R) factor. West Sumatra, Indonesia using data soil survey and monitoring sediment yield in outlet watershed.

The Universal Soil Loss Equation (USLE) and Erosion Three Dimension (E3D) in Surfer were used to identify characteristic of dominant erosion factors in Sumani Watershed in Quantitative evaluation of soil erosion rate is an important basic to investigate and improve land use system, which has not been sufficiently conducted in Indonesia.

Cara membuat overlay peta di surfer 9