Effects of Mineral Nutrition on Iron Toxicity Severity, Leaf Chlorophyll Levels and Grains Solubles Sugar of Floody Lowland Ratoon Rice (Oryza sp) Nerica L 14 under Rainfed Regime

Field fertilization trials were conducted on 15 cm high rice stubble in lowland rainfed rice to determine mineral nutrition (N-, P-, K-, Ca-, Mg-, and Zn-) effects on iron toxicity, agromorphological parameters, average contents of leaf chlorophyll and grains soluble sugar contents of Nerica L 14. Four complete block design of seven randomized treatments was used. Results indicate that iron toxicity occurred in unfertilized ratoon crops grown on undeveloped gleysol containing some iron concretions in upper layer. Characteristic symptoms covered about 6-25% of the field. Nitrogen fertilization totally corrected these symptoms, significantly increased (p = 0.00) chlorophyll a (0.21 mg.g-1 FL), b (0.30 mg.g-1 FL) and total (0.51 mg.g-1 FL) average contents of the three primaries functional leaves, height (60.11 cm) and tillering (8.56 tillers/plant) average of ratoon rice. In addition, Zn applied to soil induced an increase in grains soluble sugar content (3.23 mg glucose/g DM). Conclusion: iron toxicity, mainly caused by antagonism between Fe2+ and K+ as well as Fe2+ and Mg2+, also remains a constraint to rice ratoon cultivation. Its effects on agromorphological and agrophysiological parameters can be corrected by mineral fertilization and nitrogen applies particularly.