A Technique to Determine Iron Efficiency in Plants

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Abstract
Soil tests should predict crop response to fertilization. In the case of Fe, plant factors seem to affect the use of Fe by the plant; thus, soil tests may not be reliable. Use of soil Fe by plants is genetically controlled by an adaptive mechanism which is activated in Fe‐efficient plants in response to Fe‐stress, but remains inactive if Fe is sufficient. Fe‐inefficient plants develop less Fe‐stress response than Fe‐efficient plants. Using this range of Fe‐stress response in plants as a basis, we developed a technique to screen plants for Fe efficiency.A limited supply of Fe and some control of pH in the growth medium were required in this technique. The pH was controlled by using nutrient solutions, N only as No3, and N as NH4 and NO3, and by varying the CaCO3 and P concentrations in the solutions. The optimum supply of Fe (0.2 mg Fe/liter) was determined by growing the plants at different Fe concentrations.Four Fe‐inefficient and four Fe‐efficient plant varieties, representing four plant species, were used as test plants. The plants were screened in mixed cultures and were rated in order of greatest Fe efficiency as follows:T3238FER tomato (Lycopersicon esculentum Mill.) ≥ Hawkeye soybean (Glycine max (L.) Merr.) > W59 Corn (Zea mays L.) > Pioneer 846 sorghum (Sorghum bicolor (L.) Moench) > PI‐54619‐5‐1 soybean > Wheatland sorghum > ys1/ys1 corn > T3238fer tomato.Green plants contained more and chlorotic plants contained < 43 µg Fe/g, but the degree of Fe‐chlorosis was the best index of Fe‐efficiency. A suggested sequence for screening plants for Fe‐efficiency is presented.

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