P-024
Evaluations of sediment loss and nutrient condition in various land use
types in the low mountainous area of Northern Vietnam.
Tokyo University of Agriculture and Technology○ Pham ANH THI QUYNH
Takashi GOMI
Takahisa FURUICHI

Vietnam Forestry University

Phung Van KHOA

1. INTRODUCTION
Soil erosion and associated changes in soil production is one of the leading environmental
concerns around the world. Water supply and storage reservoirs, freshwater and coastal environments,
agriculture and urban productivity can be negatively impacted by soil erosion. Approximately 10million ha of cropland are lost due to soil erosion (Pimentel, 2006). Declining of soil production is also
occurred related to soil erosion and nutrient loss. Soil erosion can also relate to local socio-economic
activity because local economic and human activity can control vegetation types, species, and groundsurface conditions. Thus, vegetation overstory and understory covers related to land use types are
considered the most important factors for the soil erosions followed by precipitation patterns andtopography (Thornes, 1990). Integration of soil erosion processes at given land use types can also
affect soil nutrient conditions. Hence, the relationships between the soil erosion and soil nutrient loss
in various land use types from forested areas to agricultural land have not been examined. The
objectives of this study were (1) investigated soil erosion conditions in various land use types, (2)identified the characteristics of soil nutrient and carbon accumulations; and (3) examined therelationships between soil erosion and nutrient conditions with respect to land use types.
2. STUDY AREA AND METHODThis study was conducted in Xuanmai town in thenorthwest of Hanoi capital, Vietnam (latitude
20°54’00’’North and longitude 105°35’00’’East; Fig.
1). Mean annual precipitation and temperature aroundstudy area was 2268.4mm and 22.7oC, respectively.
For examining soil erosion and soil production, we
selected representative 10 land use types including
forest and agricultural land around Xuanmai town.
Spatial distribution of these 10 land use types wasexamined using the latest Landsat image (taken in2007). For each land use types, we selected threeplots (1m x 1m) for investigating vegetation biomass,
Fig. 1. Outline of study site
litter cover, soil erosion, overstory vegetation
condition, and soil physical and chemical properties. We also measured high of soil pedestal forpresentation soil erosion feature (Sidle et al., 2000). For soil physical and chemical properties, wemeasured soil hardness, soil bulk density, water contents, soil water repellency, soil C/N ration, soilorganic content. For soil surface condition, we sampled all litter and vegetation in 1 x 1 m plot. Since
litter and ground cover condition may be associated with solar radiation input (light condition) toground surface, we also measured canopy openness using fish eye lens.
3. RESULTS AND DISCUSSION
Dominant overstory vegetation in this area was Acacia mangium, Pinus massoniana, Acacia sp,- 374 -Eucalyptus and some of native forest.
Agriculture crops were cassava andlemon grass. Shrub land was also
occurred in abandoned land afterplantation. Dry biomass in mature
forest (except pine forest) andagriculture land were higher than inlandscape plantation and bare land.
Highest dry mass was occurred shrub
land use type (373.4 g m-2). Mean litter
Fig. 2. Relationship of soil erosion and understory
dry mass of 1020.5 g m-2 at shrubs land
-2vegetation/litterwas significantly higher than 259.6 g m ,266.0 g m-2 and 0 g m-2 at native trees, cassava and bare land, respectively (Fig. 2)
Significant differences about bulk density among land use types were observed. Bulk densities
were higher in lemon grass (1.3 g cm-3), landscape plantation (1.2 g cm-3) and cassava (1.2 g cm-3).
Bulk density tended to be higher in Eucalyptus forest. The soils revealed a very high percentage of silt
and clay fractions, over 70% of total, and a low sand fraction. Sand contents were higher in Lemon
grass and bare land, as compared to soils from Acacia forest, native tree, shrub and cassava. Thus,
lemon grass and bare land can be affected by more soil erosion than the other land use types.
The height of soil pedestals due to soil erosion varied from 0 to 3 cm. Mean soil pedestals highwas 1.0 cm among all land use types. Highest soil pedestal was occurred at bare land and pine forest(3.3 cm and 3.0cm). We did not observed soil erosional features in native trees forest, young Acacia
forest, Eucalyptus forest, shrub and Lemon grass
Soil organic carbon (SOC) and total nitrogen (TN) contents in surface layers differedsignificantly across land use types (Table 1). The result showed that land use affected contents of soilorganic carbon, total nitrogen. Ranged of SOC and TN was 0.79 to 5.17% and 0.07 to 0.29%,
respectively. The mean C: N ratios ranged from 10.61 and 19.08 with 16.23 in mean with 2.22 ofstandard deviation. Although vegetation biomass significantly related to soil erosion feature, suchphysical processes may not directly affect the availability of soil total C and N in our study sites.
Because litter is quickly decomposed in the tropical environment, soil carbon and nutrient are rapidly
produced than the soil erosion and transport processes in our study sites.
Table 1. Chemical properties of soil

ReferencesPimentel D. 2006. Soil erosion: a food and environmental threat, Environment Development andSustainability 8: 119-137
Thornes J.B. 1990. The interaction of erosional and vegetational dynamics in land degradation: spatialoutcomes. In: J.B. Thornes, Editor, Vegetation and Erosion. Processes and Environments, Wiley,
Chichester (1990), pp. 41–53.
Sidle RC, Tsuboyama Y, Noguchi S, Hosoda I, Fujieda M, Shimizu T. 2000. Streamflow generation insteep headwaters: A linked hydro-geomorphic paradigm. Hydrological Processes 14: 369–385- 375 -