Intraspecific Competition, Competition with Weeds, and Spacing Response in Rice¹

Abstract

Intraspecific‐intergenotypic competition, competition with weeds, and spacing response were studied in 25 rice (Oryza sativa L.) cultivars with different growth habits in Lambayeque, Peru. The actual yield of genetically mixed rice populations was always below the yield of the better component genotype in pure populations. The yield of the mixtures seldom exceeded the average yield of the pure populations of the component genotypes. Thus, yield reduction in one genotype as a result of competition was not compensated by the yield increase in another.Intraspecific competition, competition with weeds, and spacing response were highly intercorrelated with each other, suggesting that these were controlled largely by the same genetic factors through the same physiological process. Vegetative vigor, large leaf area, a high rate of N absorption in early growth stages, and plant height were the most significant characters related to competitive ability. Tillering itself was not related to either competitive ability or to spacing response. Tall, vigorous genotypes with a long growth duration were adapted to extremely primitive agronomic conditions. The evolution of cultivars has been accompanied by the evolution of cultural methods and the loss of competitive ability.

Competition between crop and weeds: A system approach

“…A great competitive ability was mainly associated with rapid germination, emergence, and root and shoot growth during the early stages of sorghum development. Other crops also show varietal differences in competitive ability with respect to weeds (soybean: Burnside (1972), McWhorter and Hartwig (1972), Staniforth (1962); wheat: Reeves and Brooke (1977); rice: Sakai (1961), Kawano et al (1974), which suggests that breeding may contribute to reducing yield losses due to weeds.…”

Influência de cultivares de arroz e épocas da adubação nitrogenada nas relações de interferência da cultura com cultivar simulador de infestação de arroz-vermelho

“…Segundo Kawano et al (1974), sob níveis baixos de nitrogênio (N), as plantas de arroz e as daninhas competem inicialmente pelo N do solo e, posteriormente, pela luz. O N é um dos principais macronutrientes necessários para o desenvolvimento normal das plantas de arroz, sendo, na maioria dos casos, o primeiro elemento a ser limitante, como resultado da competição entre cultivo e plantas daninhas (Moody, 1981).…”

Crescimento de Brachiaria plantaginea e Raphanus raphanistrum em convivência com híbridos de milho submetidos a períodos de controle das plantas daninhas

“…Pitelli (1985) relata que as diferentes espé-cies e cultivares de plantas apresentam capacidades diferenciadas de competir com as plantas daninhas. Para Kawano et al (1974), o vigor vegetativo, a maior área foliar, a maior taxa de absorção de nitrogênio nos estádios iniciais de crescimento e as plantas mais altas são características altamente significativas relacionadas com a habilidade competitiva.…”