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Mehlich III >NaOH 0.1 M > Olsen > Morgan > AB-DTPA > Bray II.Extractants had different long-term and short-term potential to extract algal available P. The Cowell extractable P concentrations of sediments varied from 1.44 to 88.0 mg kg-1.This extractant was correlated significantly with algal growth and selected as the best P single extraction method among allextractants. The high correlation between 0.1 M NaOH and algae growth indicates the sensitivity of P bioavailability to redox conditions in river system. Algae (SenedesmusObliquus) was able to use P from different sediment components because its growth was correlated with Cowell, Mehlich III, NaOH 0.1M, Olsen and Morgan.
Conclusion: Legacy P (sediment P) evaluation by chemical extractants gives new insight into P bioavailability in river sediments of the Urmia Lake. The results of this work showed that Cowell extractant could be used to estimate algal available P in studied river sediments. Similarity between Olsen-P and Mehlich-P in estimating bioavailable P suggests that Mehlich III-P can be substituted for Olsen-P in studied sediments.For sustainable P management, monitoring P status by single chemical extraction methods is necessary. Phosphorous fertilizer application around the Lake Urmia basin lands should be conducted based onthe P soil test to avoid any aquatic pollution. Care must be taken in lower reach river sediments because of fragile ecosystems such as wetlands and lagoons. Further investigations are also needed to evaluate legacy P bioavailability by temporal and spatial variability.]]>
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CFeOX-Fe>AFeOX-Fe>Car-Fe> OM-Fe > Exch.-Fe
Applications of Fe had significant effect on dry matter, concentration, and uptake of Fe, Zn, Cu and Mn, extractable forms via extracting DTPA, EDTA, organic and exchangeable forms in soybean compared to control. Among chemical forms of iron, organic form with the amount of available iron plant (extraction by DTPA) had significant positive correlation. Also, many of the physical and chemical properties of calcareous soils studied, were significantly correlated with some chemical forms and amount of iron uptake by plant. DTPA extractable iron had negative correlation with pH ( R2= 0.514*) and EDTA extractable iron had positive correlation with organic matter (R2= 0.428*).
Conclusions
Application of Fe EDDHA, was leaded to significant increase organic and plant available (DTPA) forms of iron and due to significant regression equation (r=0.435*) between two chemical forms of iron (organic and DTPA extracted), it can be inferred that, the bulk of available iron plant was in form of organically bound. One reason for the positive reaction to the use of Fe EDDHA, subjected to a significant increase absorbable forms of iron in the studied soils.
Keywords: Chemical and Physical properties of soil, DTPA, EDTA, Iron, Sequential extraction]]>
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