Differential Weed Suppression Ability in Upland Rice Cultivars

Abstract

Twenty‐five upland rice (Oryza sativa L.) cultivars were evaluated in 2 yr of field experiments in the Philippines. The research was conducted with low and moderate levels of handweeding to determine the extent of cultivar differences in weed suppression ability. We sought the plant characters that may confer superior competitiveness, and determined their practical significance in contributing to weed management. A large significant variation was observed in the dry weight of weeds (0.84 to 3.89 Mg/ha) associated with the different cultivars. Several cultivars had consistently low weed weights in both weeding treatments across years. Weed weights for the five most competitive cultivars were 75% lower than for those of the five least competitive cultivars. Grain yields were negatively correlated with weed weights, in both weeding treatments in both years (r = −0.48** to −0.59**‐significant at P = 0.01). Plant height, which ranged from 0.73 to 1.35 m, was the character most strongly related to low weed weight, with negative correlations that varied from −0.76** to −0.88** among weeding levels and years. Leaf area index (determined at 60 d after seeding) was also negatively correlated with weed weight, but tiller number was not significantly related to weed weight. The minimum plant height necessary to adequately suppress weeds was approximately 1.00 to 1.15 m. Cultivars with superior yield potential were identified that had a minimum height of 1.0 m, with weed suppression ability similar to the tall traditional cultivars.

Competitividade relativa entre cultivares de arroz irrigado e biótipo de arroz-vermelho

“…A provável causa de os competidores apresentarem maior crescimento naquela proporção pode estar relacionada à estatura de plantas, tornando-os mais eficientes na captura da luz solar e impondo sombreamento à cultura (Garrity et al, 1992). Deve-se ressaltar que, em experimentos substitutivos, existe pouca evidência de haver mudanças qualitativas devido ao aumento da população, ou seja, a dominância de uma espécie sobre a outra raramente muda com a alteração da população (Cousens & O'Neill, 1993).…”

Competitividade de cultivares de arroz irrigado com cultivar simuladora de arroz-vermelho

“…Entre as características morfológicas, a estatura de planta é a que mais relaciona-se com o baixo crescimento de plantas daninhas, em virtude do sombreamento imposto pela cultura (Kwon et al, 1991;Garrity et al, 1992;McDonald & Riha, 1999;Bennett & Shaw, 2000). Plantas cultivadas com elevada estatura reduzem a quantidade e a qualidade da luz incidente sobre as infestantes.…”

“…Todavia, Garrity et al (1992) concluíram que a altura mínima necessária ao arroz para adequada supressão de infestantes encontra-se entre 100 e 115 cm. Por sua vez, cultivares com estatura elevada, mas que não apresentam colmos grossos, geralmente apresentam baixo potencial de rendimento e são mais suscetíveis ao acamamento (Ni et al, 2000).…”

Interferência de Brachiaria plantaginea com a cultura do arroz, cv. Primavera

“…Segundo Garrity et al (1992), o arroz de terras altas não compete bem com as plantas daninhas, a menos que o controle seja precoce e bem realizado. Experimentos conduzidos por Merotto Jr. et al (2002) indicaram que a presença de plantas daninhas até 15 DAE diminuiu o crescimento do arroz.…”