Effect of Humic Acid Application Method on Bioavailability of Iron in Canola

In order to investigate the effect of acid humic application method including soil application, spraying and fertigation on iron (Fe) supplying in rapeseed, an expriment was caried out consisting of 10 treatments and 4 replications. Treatments included humic acid soil application in three levels (1, 2 and 4 g kg-1 soil), spraying at three levels (0.1, 0.2 and 0.4%) and with fertigation at three levels (1000, 2000 and 4000 mg L-1) and control treatment (without humic acid). The results showed that the highest total iron and active iron concentration in stalk were 85 and 44.9 mg kg-1, respectively, in the treatment of 2000 mg L-1 of humic acid with fertigation, and the lowest value, respectively, with an average of 54.62 and 20.40 mg kg-1 for control treatment. Also, the order of significance for extractable- Fe from the pot soil by various extractants was as follows: rapid ammonium oxalate > hydroxylamine hydrochloride>AC-EDTA> DTPA> AB-DTPA >EDTA. The results obtained in the present study showed that extracted iron was significantly correlated with chlorophyll content by most of the extractants. Among extractants, only extracted Fe with DTPA correlated positively and significantly with total Fe (r=0.69*) and active Fe (r=0.79*) while, total iron of leaf had weak and non-signifcant correlation (r= 0.35) with DTPA. Based on the results of this study, active iron measurement can be a suitable method for predicting iron deficiency in canola plants.