An ecological approach to controlling weeds in transplanted lowland rice

Date

10-1979

Abstract

Eleven field experiments were conducted from March, 1978 to August, 1979 at the International Rice Research Institute, Los Banos, Laguna, Philippines. Eight different weed community types were encountered based on a two-dimensional ordination analysis. These were 1) Monochoria vaginalis community type, 2) M. vaginalis- Scirpus supinus community type, 3) M. vaginalis-Echinochloa glabrescens community type, 4) Echinochloa crus-galli ssp. hispidula community type 5) E. crus-galli ssp. hispidula -Scirpus maritimus community type, 6) glabrescens-M. vaginalis community type, 7) E. glabrescens community type, and 8) M. vaginalis-Fimbristylislittoralis-E. glabrescens-S. maritimus community type.

Yield decrease due to weed competition was approximately 42% in the E. crus-galli ssp. hispidula-S. maritimus community, 20% in the M. vaginalis-F. littoralis_E. glabrescens-S. maritimus community, 15% in the M. vaginalis community and the M. vaginalis-S. supinus community and 10% in the E. glabrescens community type when the weed weight was 100 g per m2 in each community.

The plastic response of M. vaginalis to plant spacing and nitrogen was greater than E. glabrescens and rice.

Weeds growing in association with the rice hills were more competitive than weeds growing in between the rice hills. Yield decrease due to weed competition was primarily due to decrease in panicle number per unit area.

Yield reduction due to M. vaginalis competition was greater at 0kg N/ha and 160 kg N/ha than at 80kg N/ha. IR32, a late maturing cultivar, was more competitive than IR38 , an early maturing cultivar, in the M. vaginalis-S. supinus community type but not in the M. vaginalis community. A mixture of two rice cultivarars, IR36 and IR40, was more competitive against weeds than each cultivar grown alone.

The greatest competitive ability against weeds was observed when rice was transplanted at a 10 x 10 cm spacing. However, the highest grain yield was obtained from a 40 x (10 x 10 ) cm spacing when the rice was hand weeded. Competitive ability against weeds increased as age of seedlings transplanted increased while grain yield in the weed free plot decreased with increasing seedling age.

The time of final harrowing was more critical than the degree of tillage in reducing the weed population. Generally, the residual effect of hand weeding in decreasing weed populations was greater than the effect of plant spacing.

Document Type

Master Thesis

Degree

Doctor of Philosophy in Agronomy

College

Graduate School (GS)

Adviser/Committee Chair

Keith Moody

Committee Member

Beatriz L. Mercado, Percy E. Sajise, Enrique P. Pacardo

Language

English

LC Subject

Rice--Diseases and pests, Rice--Weed Control

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 996 1979 A42 K55

Notes

Doctor of Philosophy ( Agronomy)

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