Studies on the Nutrition of Rice Plant with Reference to the Occurrence of the So-called "Akagare" Disease : VI. Changes in the growth, nutrients-absorption and metabolism in plant as influenced by the excessive supply of ferrous iron

Abstract

In order to make clear the relation between the excessive ferrous iron and the occurrence of Akagare, several experiments were carried out. Results of experiments are as follows: 1) On adding surplus Fe++ to the culture solution, tiny blackish browh spots appeared on the lower leaves. These leaves, subsequently, turned brown or reddish brown and died off. Heavy nitrogen fertilization, lack of phosphorus and potassium, concomitant addition of butyric acid, and low pH of soution intensified such effect of Fe++ as described above. 2) Discoloration of leaves due to surplus Fe++ occurred most severely at the vigorously tillering stage, and more severely at the booting stage of the plant. At the same time severe brown discoloration of grain due to surplus Fe++ occurred at the stage of heading and flowering. 3) The yield of rice was decreased extremely by the addition of surplus Fe++ at the booting and early ripening stage, and to a less extent at the vigorously tillering stage. 4) Resistance to the surplus Fe++ which showed a close relationship with the accumulation of starch at the base of shoot was generally parallel to the resistance to Akagare in rice varieties. 5) Nutrients absorption was inhibited in the order P2O5, MnO>K2O, SiO2>NH4-N, CaO. Respiratory rate and cytochrome oxidase 'activity of root were retarded by surplus Fe++, while respiratory rate and peroxidase activity of leaf blade were promoted, irrespective of the decrease of cytochrome oxidase activity. Both the content of protein-N of leaf and the content of total sugar and starch of shoot were decreased, while the content of soluble-N was increased by Surplus Fe++. 6) The fact that quite the same tendency was observed as to the changes in respiration and metabolism with both the plants subjected to excessive Fe++ in this work and those affected by Akagare in previous works, suggests that the excessive ferrous iron has some relationship with the occurrence of Akagare.