RESUMO
Total concentrations of Cu, Pb, As, Cr, Ni and Zn were determined for 53 soil samples using portable X-ray fluorescence (PXRF) system in in-situ and ex-situ (Lab.) conditions. PXRF metal concentrations were statistically compared with analytical results from traditional AAS/AFS analysis. The ability of PXRF instrument to produce comparable analytical results to the reference method was assessed by linear regression. To investgate the effects of soil moisture on PXRF, the in-situ moisture content of all soil samples was quantified and the metal concentrations of selected samples with known moisture contents were measured too. The results showed that the detection limits of PXRF for Cu, Pb, As, Cr, Ni and Zn were 10.6, 8.1, 5.7, 22.5, 21.6 and 10.4 mg kg(-1) respectively. A good degree of linearity was found for Pb, Cr, Ni and Zn in in-situ condition. While in ex-situ condition, quantitative level data were achieved across the entire range of samples tested for Cu, Pb, Cr, Ni and Zn. X-ray fluorescence spectrometry was shown to be an effective tool for quantification and rapid assessment of heavy metals in soils. Soil moisture content did affected the performance of PXRF, the mean percent difference for soil samples in-situ with moisture content less than 15% and higher than 25% was -17% and -31% respectively. In ex-situ condition, as the soil moisture content increased from air dried level to 30%, the mean percent difference decreased from 10% to -24%. The dilution effect of moisture in soils may cause discrepancies with conventional analytical results and induce worse data quality, and it should be controlled within 0-25% in in-situ condition.
RESUMO
An 8-year field experiment was conducted in the Taihu Lake region of eastern China to investigate the effects of incorporation of straw and manure on the yield and phosphorus (P) accumulation in the paddy soil, and to evaluate the potential risk of P loss from soil to environment. The experiment had four fertilization treatments, i. e., chemical fertilizers alone (NPK), chemical fertilizers plus rice/wheat straw (NPK + S), chemical fertilizers plus 7.5 t x (hm2 x a)(-1) wet pig manure (NPK + M7.5), and chemical fertilizers plus 15.0 t x (hm2 x a)(-1) wet pig manure (NPK + M15). Among the four treatments, no significant differences were observed in the yield of rice or wheat. Long-term application of chemical fertilizers plus pig manure significantly increased the soil total P, the degree of P saturation (DPS), and the concentration of extractable P forms, including Olsen-P, Mehlich 3 extractable P, CaCl2 extractable P, and water extractable P, which became a potential source of eutrophication in Taihu Lake. In contrast to chemical fertilizers plus pig manure, there were no significant differences in the concentrations of extractable P forms between the NPK + S and NPK treatments. We concludes that chemical fertilizers [P 45 kg x (hm2 x a)(-1)] plus rice/wheat straw should be recommended in the paddy soil in the Taihu Lake region under the rice-wheat rotation system.