Determination of Soil Iron Critical Level for Corn plant in East Azerbaijan Province

Knowledge about the iron (Fe) critical level and plant response to application of Fe can effectively help to proper use of this element. Corn is used in human nutrition, poultry and livestock in pharmaceticals, starch, and alcohol and oil production. Because of the calcareous soils, low organic matter content, low solubility of iron in alkaline pH, carbonate and bicarbonate ions present in irrigation water, and phosphorus over fertilization, Fe deficiency is common in most fields and gardens.The aim of this study was investigation effect of Fe-EDDHA on corn growth indices and determination of Fe critical level in some calcareous soils of East Azerbaijan province using DTPA and ABDTPA by conventional methods.
In this research, Fe critical level for corn (Zea mays L.) was determined in 21 soils from corn fields of East Azerbaijan province during 2014-2015. Corn plant was cultivated in two level of Fe (zero and 10 mg Fe kg-1 as Fe-EDDHA) as a factorial experiment in a randomized complete blocks design with three replications in pots containing 4 kg air-dried soil. After 60 days, the plant growth parameters were measured. Fe available of studied soils were extracted by DTPA and ABDTPA methods and measured by atomic absorption spectroscopy (AAS).
The results showed that soil type had a significant effect on the growth indices of corn and the effect of applied Fe levels was significant in some of growth indices while the fertilizer and soil interaction was not significant. Critical level of soil Fe for corn with DTPA-Fe, based on 90% relative yield, was determined 10.08, 5, 11.4 and 7.44 mg Fe kg-1 soil by using plant response column order procedure, graphical Cate–Nelson, Cate–Nelson analysis of variance and Mitscherlich-Bray, respectively and for AB-DTPA method was 6.19, 4.4, 9.8 and 4.53 (mg Fe kg-1 soil) respectively. As well as to achieve a 90% relative concentration of active Fe in shoot by using graphical Cate–Nelson and DTPA and AB-DTPA methods, critical soil Fe level were 6.8 and 4.8 mg Fe kg-1 soil, respectively. Mitscherlich-Bray equation coefficients, C1 and C2, for DTPA-Fe were 0.1344 and 0.0356 kg soil mg-1Fe, respectively and for AB-DTPA-Fe were 0.2207 and 0.0556 kg soil mg-1Fe.
In this study, statistical Kate- Nelson's method due to very low coefficient of determination was unsuccessful. Also, due to the low level of applied Fe fertilizer, C2 factor of Mitscherlich--Bray equation was mostly negative. Iron critical levels by averaging and using DTPA and AB-DTPA methods for corn in these areas, respectively, 33/7 and 98/4 mg kg is suggested.