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Abstract SUMMARY In a trial to elucidate some aspects of the iron chlorosis phenomenon, the effects due to application of iron, calcium carbonate and phosphate were investigated. Three separate greenhouse experiments using a sand culture technique, with sorghum bicolor as an indicator plant, were conducted. The involved treatments can be listed as follows: ~xperimen!-!: Iron applicL~tion as FeS04 or Fe-EDTA was performedat six rates for each source namely; 0, 5, 10, 20, 40 and 60 ppm Fe. Experiment II: Iron and calcium carbonate applications were carried out at rates of 0, 10 and 20 ppm Fe, as FeS04 and 0. 2, 4 and 8% C aC03 ” ~periment III: phosphate (KH) application was performed at rates of 0, 20, 40 and 60 ppm P, while Fe waS applied to all treatments at one rate (20 ppm Fe) as FeS04” The determined parameters included the dry matter of sorghum (roots and shoots) as well as the concentration and total uptake of Fe, P, Ca, Mg and Mn in both plant parts. Results can be briefly summarized as follows: Experiment I: At first, it may be profitable to refer that most of the rates of Fe applied in the chelated form occur beyond the optimum rate wh~le the reverse is true in case of FeS04· Accordingly one may expect more adverse effects with Fe-EDTA than treatments with FeS04 particularly at higher rates of Fe application. In view of this sight the results, in general, showed the following: 1. Both of mineral and chela ted sources of Fe (Fe-EDTA or FeS0 4 ) significantly increased sorghum dry weight yield. 2. Iron uptake by sorghum roots, shoots and hence whole plants was promoted with Fe applications showing a maximum value at a rate of about 5 ppm Fe in case of Fe-EDTA and about 20 ppm Fe in case of FeS04· 3. Results show a tendency of Fe accumulation in sorghum roots when FeS04 was the source of iron supply perhaps because of precipitation or adsorption of Fe on root surface or a relatively low mobility of the mineral .Fe form as compared with the chelated one. 4. The possibility of using FeS04 as a source of Fe to growing plants was provided that higher rates than those of chelated iron are needed to compensate the various mechanisms altering Fe availability or its mobility through the plants. . FeS04-tr ated sorghum plants showed higher uptake of P in whole plants than did the Fe-EDTA treated ones, but no 5ig ificant differences occurred in shoots. Calcium ptake by sorghum roots, was increased with increasing the levels of applied Fe. In both roots and shoots there existed more calcium uptake by treatments receiving mineral Fe than those supplied with the chelated fa rm . 7. The concentration of Mg in sorghum roots was not affected neitha by iron sources nor rates, while a signiforms, was obse ved in the shoots. ficant depressi due to Fe application, in both 8. Both so rces resulted in significant differences in total mangan uptake. In roots, shoots and whole plants. Mangan uptake by treatments receiving mineral Fe increased with ncreasing the rate of applied iron, but decreased in th receiving the chelated form. 9. A posit va trend was revealed in sorghum shoots with respect to Fe/Mn ratio with either FeS04 or Fe-EDTA where it was rna e obvious. 10. A nega ive significant relation occurred in sorghum shoots between jFeratio and rate of applied Fe-EDTA. The relation was va y close to significancy in case of FeS04• The P/Fe ra io was higher in sorghum chlorotic plants than in the norm 1 ones. 11. The Fe/1n ratio tended to increase gradually with increasing he rate of applied ironl but only till the maximum yiel was reached. 12. Its show clearly thatl leachates collected from the treated pots during the course of the experiment conta”ned considerable amounts of leached Fel gradually and si nificantly increased with increasing rates the other hand, with FeS04 treatmentsl minute quantitie of leached Fe were recorded indicating that soluble FeS04 applied was converted into insoluble form. 13. Iron extracted from cultures by NH40AC pH 4.8 was increased with increasing the rate of Fe application. 14. Iron fraction extractable by 0.1 N HCl solution significantly increased with increasing the rate of applied Fe where the cu t ure s that received FeS04 yielded higher values than those treated with Fe-EOTA. Experiment II: 1. Results revealed that occurrence of CaC03 significantly reduced he dry matter yield of plants while it was slightly increa ed with Fe applica~ion. 2. Increasi g levels of CaC03 drastically decreased the concentratio and uptake of iron in roots, shtiots and whole plants eit er in presence or in absence of iron. 3. Phosphor s concentration and uptake as well in roots, shoots whole sorghum plants were adversely affected with increasing levels CaC03· 4. Calcium and magnesium uptake contained by sorghum roots significantly increased with increasing levels of CaC0 3, but adverse si9r:ificant trend was observed in plant shoots. 5. The val es of Mn uptake by sorghum roots, shoots and whole plant were significantly decreased with application a f CaCO 3 • 6. Additio of CaC03 tended to decrease the concentration and total ontent of P, Fe, and Mn in both sorghum roots and shoot ~ . In sue unbuffered sand culture, calcium carbonate seems to be an effective factor controlling the concenira-· tion and uptak of Fe, P, Ca , Mg and Mn that may give further eviden e to its importance in the Fe chlorosis phenomenon . • Experiment III: 1. Phosph rus uptake by roots, shoots and whole plants was signifiean ly increased with increasing the rate of P app liea t ion. The PIFe ra io was higher in sorghum shoots than in sorghum roots at all levels of applied P 2. Applicat on of P at a rate of 20 ppm significantll promoted the tot 1 uptake of Fe. Ca and Mg, but further rates failed to· ield significant increments. |