Effect of planting method, fertilizer management and plant growth regulator on lodging in lowland rice.

The experimental growth regulators Hoe 78784 and PP-333 significantly reduced lodging in all rices. However, they did not affect significantly the crop vegetative characteristics and yield components, except by decreasing plant height when both growth regulators were applied at booting stage, decreasing internode elongation, and increasing the number of vascular bundles, and the thickness and diameter of the third and fourth internodes. The new experimental plant growth regulator Hoe 78784 when applied at booting prevented lodging and significantly increased grain yield of IR 21820-154-3-2-2-3. But when applied at 30 DT, it significantly decreased grain yield of all test varieties due to shortened panicle length and increased unfilled spikelet percentage. Hoe 78784 applied at heading did not increase yield nor did it prevent lodging. Lodging was correlated to crop nutrition, particularly with N. Increasing N application rate enhanced lodging, but combining N with P or K minimized lodging. Increasing applied P or K also decreased lodging, regardless of N level and rice variety. Phosphorus and K fertilizer application increased bending resistance; improved rice morphological characteristics, necessary to reduce lodging, such as a wider culm diameter; and stimulated development of schlerenchyma tissues and vascular bundles in the culm. In direct seeded and transplanted rices, no correlation was found between plant height and lodging incidence. Vegetative characteristics and yield components did not significantly differ between planting methods. Higher culm K content, observed in transplanted than direct seeded rice, increased lodging resistance. Phosphorus and Si contents did not affect significantly the culm strength. Generally, N and K contents greatly determined the occurrence of lodging.