The benefits and risks of using river sediment for Vietnamese agriculture: a case study of the Nhieu Loc canal in Ho Chi Minh City.

This study was conducted to assess the potential of river sediment for amendment of agricultural land with respect to heavy metal mobilization. The mobility and concentration of bioavailable heavy metal containing in the sediment were evaluated with the use of DTPA (diethylenetriamine pentaacetic acid) extraction techniques. Sum of metals in exchangeable and carbonate fractions obtained from sequential extraction scheme was used to evaluate the potential plant available. Four land blocks of size (1 m x 5.8 m) were prepared for cabbage field experiment and applied with different loading rates of sediment (approximately 28 and 42 ton/ha or equivalent to 100 kgN/ha and 150 kgN/ha). In parallel test, land blocks treated with fertilizer at similar nitrogen loading rates were also conducted for comparisons. Pure soil plot was used as a control system. Results show that both plant available and total heavy metal concentration were found higher in those plots treated with higher loading rates of sediment (42 ton/ha). The concentrations of heavy metals (Cu,Zn,Pb) in soil were decreased with time after crop harvesting and the residues remain in the soil were well below those of the UK, USA and Germany standards. Simple linear regression was used to show the correlation between the DTPA extractable metals and the plant metals fractions (root and shoot) resulting from fertilizer and sediment applications in the amended soils. In most cases, plant available metal concentrations showed positively correlated with plant metal uptake concentrations (R2 = 0.01-0.95, n = 3). Concentration of metals in the cabbage tissue detected: Zn at 131.53+/-10.43 mg kg(-1) DM, Cu at 20.84+/-1.62 mg kg(-1) DM, Pb at 0.09+/-0.01 mg kg(-1) DM, Cd at 0.21+/-0.09 mg kg(-1) DM and Ni at 0.44+/-0.05 mg kg(-1) DM. None of these metals concentration exceeded the tolerable limits of plant. One-way analysis of variance (ANOVA) was applied to find out the effect of different soil amendments on cabbage yield in term of fresh and dry weights. The sequence of crop yields in this field studies for amended soils is chemical fertilizer > sediment > control soil.