Effect of Iron Seed Dressing and Form of Nitrogen-Supply on Growth and Micronutrient Concentration in Shoots of Sorghum Grown in a Calcareous Sand Culture

ABSTRACT

Seeds of sorghum [Sorghum bicolor (L.) Moench cv ‘Wrangler’] dressed with three increasing concentrations of an iron ethylenediamine-di-O-hydroxphenylacetic acid (FeEDDHA) product up to 480 mg Fe kg^{− 1} seed as a sole source of iron supply as well as a treatment without any dressing were grown for 19 days after germination in sand culture buffered to pH 8 by calcium carbonate. Nitrogen was supplied either as ammonium (NH₄)-N or nitrate (NO₃)-N, the former being supplemented with nitrapyrin (N Serve) to prevent nitrification. Chlorosis of the younger leaves was evident in all treatments except at the two higher levels of NH₄-supplied plants. Dry matter yields of the shoots were raised only relatively slightly by the increasing levels of Fe supply and at each level the NH₄ form was superior to that of NO₃ -N. At the end of the growth period the pH of the sand around the roots had fallen by about 0.5 of a unit for NH₄–fed plants and increased by about 0.2 of a unit for NO₃-fed plants. At each level of Fe supply, NH₄ nutrition approximately doubled the micronutrient [Fe, zinc (Zn), copper (Cu), manganese (Mn)] shoot concentrations and uptakes as compared with NO₃-nutrition. For the NO₃ –fed plants, increasing rates of Fe seed dressing had little effect on shoot Fe concentrations or uptakes, the concentration values determined (about 40 μ g g^{− 1} dry wt.) being below the range of critical deficiency concentration. Similarly concentrations of Mn were also in the deficiency range in the seed dressed NO₃-fed plants (11–12 μ g g^{− 1} dry wt) so that in the NO₃ treatments chlorosis may have resulted from a lack of Mn as well as Fe. Dressing sorghum seeds with Fe chelates in conjunction with NH₄ fertilization supplemented with an inhibitor to prevent nitrification would appear to be a worthwhile approach to ensure an initial source of Fe to the young developing plant in the avoidance of iron-induced chlorosis in the growth of sorghum on high pH calcareous soils.

Keywords:

• iron
• chelates
• sorghum

ACKNOWLEDGMENTS

We are most grateful to Dr. G Adams for the help and financial support of Phosyn Yara in allowing us the use of their glasshouse facilities and to David Bilsborough for his excellent technical work in the experiment.