Abstract
Forty-two calcareous soils representing most of the soil groups of Saudi Arabia were used for assessing the ability of some soil extractants to predict the response of Sorghum (Sorghum bicolor L. Moench BTX378) to iron fertilizer added as Fe-EDDHA chelate (ferric ethylenediamine di-o-hydroxyphenyl acetate). Iron (Fe) was extracted from untreated and treated soils by utilizing five different extractants, namely, NH
4
HCO
3
-DTPA(AB-DTPA), DTPA, EDTA, 1.0 M NH
4
OAC, and 1.0 M NH
4
OAC containing 0.02% hydroquinone (H.Q). Amount of extractable Fe followed the order: NH
4
OAC + 0.02% H.Q >NH
4
OAC>EDTA > DTPA > AB-DTPA. Iron extracted by EDTA, DTPA, and AB-DTPA was significantly correlated with amorphous-Fe, poorly crystalline-Fe, pH, organic matter, 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 CaCO
3
. The dry matter yield, Fe concentration and Fe-uptake of sorghum were affected 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 EDTA solutions. However, the highest correlation was attained in the case of AB-DTPA. Assessment of Fe critical levels in soils, detected by AB-DTPA through separating plots, the graphical method, the Cate and Nelson 3-classical, and the Chi-square method gave quite similar results. The Fe critical level as estimated by using AB-DTPA was 3.4 to 4.8 mg kg
−1
.