Assessment of five extractants for their ability to predict iron uptake and response of sorghum grown in calcareous soils

Forty-two calcareous soils representing most of the soil groups of Saudi Ar abia were used for assessing the ability of some soil extractants to predic t the response of Sorghum (Sorghum bicolor L. Moench BTX378) to iron fertil izer added as Fe-EDDHA chelate (ferric ethylenediamine di-o-hydroxyphenyl a cetate). Iron (Fe) was extracted from untreated and treated soils by utiliz ing five different extractants, namely, NH4HCO3-DTPA (AB-DTPA), DTPA, EDTA, 1.0 M NH(4)OAC, and 1.0 M NH(4)OAC containing 0.02% hydroquinone (H.Q). Am ount of extractable Fe followed the order: NH(4)OAC + 0.02% H.Q > NH(4)OAC > EDTA > DTPA > ABDTPA. Iron extracted by EDTA, DTPA, and AB-DTPA was signi ficantly correlated with amorphous-Fe, poorly crystalline-Fe, pH, organic m atter, and clay. However, NH(4)OAC+0.02% H.Q and/or NH(4)OAC solutions gave significant correlations with free iron oxides, total-Fe, and total CaCO3. The dry matter yield, Fe concentration and Fe-uptake of sorghum were affec ted by soil application of Fe at rates of 10 and/or 20 mg Fe kg(-1), added in a chelated form. The lower and higher levels of Fe application increased the mean dry matter of yield by 34% and 60%, respectively. Iron uptake by sorghum consistently was related to the Fe extracted by AB-DTPA, DTPA and E DTA solutions. However, the highest correlation was attained in the case of AB-DTPA. Assessment of Fr critical levels in soils, detected by AB-DTPA th rough separating plots, the graphical method, the Gate and Nelson 3-classic al, and the Chi-square method gave quite similar results. The Fe critical l evel as estimated by using AB-DTPA was 3.4 to 4.8 mg kg(-1).