Rice and red rice interference. II. Rice response to population densities of three red rice (Oryza sativa) ecotypes

Abstract

Red rice, which grows taller and produces more tillers than domestic rice and shatters most of its seeds early, is a major weed in many rice-growing areas of the world. Field experiments were conducted at Stuttgart, AR in 1997 and 1998 to evaluate the growth response of the Kaybonnet (KBNT) rice cultivar to various population densities of three red rice ecotypes. The ecotypes tested were Louisiana3 (LA3), Stuttgart strawhull (Stgstraw), and Katy red rice (KatyRR). Compared with KBNT alone, LA3, the tallest of the three red rice ecotypes, reduced tiller density of KBNT 51%, aboveground biomass at 91 d after emergence (DAE) 35%, and yield 80%. Stgstraw, a medium-height red rice, reduced KBNT tiller density 49%, aboveground biomass 26%, and yield 61%. KatyRR, the shortest red rice, reduced KBNT tiller density 30%, aboveground biomass 16%, and yield 21%. Tiller density of rice was reduced by 20 to 48% when red rice density increased from 25 to 51 plants m−2. Rice biomass at 91 DAE was reduced by 9 and 44% when red rice densities were 16 and 51 plants m−2. Rice yield was reduced by 60 and 70% at red rice densities of 25 and 51 plants m−2, respectively. These results demonstrate that low populations of red rice can greatly reduce rice growth and yield and that short-statured red rice types may affect rice growth less than taller ecotypes.

Competitividade relativa entre cultivares de arroz irrigado e biótipo de capim-Arroz (Echinochloa spp.)

“…Esse comportamento mostra que as espécies são competitivas e que uma não contribui mais que o esperado para a produtividade total da outra (Radosevich, 1987). Por pertencerem à mesma família botânica, esperava-se que os cultivares de arroz e o capim-arroz explorassem o mesmo nicho ecológico e competissem pelos mesmos recursos do ambiente, apresentando diferenças em competitividade, pois estas foram verificadas em espécies aparentadas, como, por exemplo, entre arroz x arrozvermelho (Pantone & Baker, 1991;Estorninos Jr. et al, 2005) e entre sorgo x sorgo-de-alepo Tabela 1 -Diferenças relativas para as variáveis área foliar e massa seca aérea dos cultivares de arroz IRGA 417 ou BR-IRGA 410 e de capim-arroz, aos 50 dias após a emergência. FAEM/UFPel, Capão do Leão-RS, 2006/07 ou entre sorgo x biótipos silvestres originados do sorgo cultivado (Hoffman & Buhler, 2002).…”

“…Em todas as comparações, verificaram-se diferenças entre os cultivares de arroz e o capim-arroz, o que demonstra que ambos não se equivalem em termos de competição pelos recursos do ambiente, destacando-se o capim-arroz como mais competitivo que os cultivares. Utilizando os três índices para definir competitividade, foi verificado que o sorgo cultivado foi mais competitivo que Sorghum halepense (Hoffman & Buhler, 2002) e que o nabo forrageiro foi mais competitivo que genótipos de soja (Bianchi et al, 2006 (Pantone & Baker, 1991;Hoffman & Buhler, 2002;Estorninos Jr. et al, 2005;Fleck et al, 2008;Rigoli et al, 2008). O conhecimento da dinâ-mica e da competitividade entre plantas -em especial, o arroz irrigado e o capim-arroz -torna-se fundamental para a tomada de decisão de controlar a planta daninha em determinada população que não irá causar interferência negativa sobre a cultura, ainda mais considerando-se que o fluxo potencial de emergência de capim-arroz por safra pode ser de até 2.400 plantas m -2 em áreas de monocultivo (Melo et al, 2004).…”

Crop Growth and Yield Losses in Wheat Due to Little Seed Canary Grass Infestation Differ with Weed Densities and Changes in Environment

“…Weeds can incur a grain yield loss of 48% in wheat (Khan and Haq, 2002). However, the magnitude of weed-related losses depends on the type and density of a particular weed species, its time of emergence, and the duration of the interference (Estorninos et al, 2005;Hussain et al, 2015;Fahad et al, 2015). Crop yield usually declines with increased weed density and interference duration and yield losses are more severe when resources are limited and weeds and crops emerge simultaneously (Zimdahl, 2007).…”

Weed growth and crop yield loss in wheat as influenced by row spacing and weed emergence times

“…Weeds are omnipresent pests that compete with crops for water, nutrients, space, and light; host pests and diseases; and release allelochemicals into the rhizosphere (Khaliq et al, 2013a(Khaliq et al, , 2014a. The magnitude of weed-related losses, however, depends on the type and density of a particular weed species, its time of emergence, and the duration of interference (Estorninos et al, 2005;Hussain et al, 2015). Yield losses are most severe when resources are limited and weeds and crops emerge simultaneously (Zimdahl, 2007;Hussain et al, 2015).…”