LAUSR

Abstract Barnyard grass, such as Echinochloa crus-galli var. mitis, Echinochloa crus-galli var. zelayensis and Echinochloa colonum, are the main troublesome weeds in rice (Oryza sativa) paddies. This study aimed to investigate the rice yield (quality and quantity) when grown with these common barnyard grass varieties. A 2-year field experiment was conducted using two high-yielding rice cultivars, Liangyoupeijiu (an O. sativa indica hybrid cultivar) and Nanjing 9108 (an O. sativa japonica cultivar) at different developmental stages from transplant to maturity. Treatments included a weed-free (control), rice grown with Echinochloa. crus-galli var. mitis (Ecm), rice grown with E. crus-galli. crusgali var. zelayensis (Ecz), and rice grown with E. colonum (Ec). The results showed that when barnyard grasses were grown with the same rice cultivar, the order of plant height of the three barnyard grass varieties was Ecz > Ecm > Ec, the growth duration was Ecm > Ecz > Ec and the dry matter accumulation of both Ecm and Ecz was greater than Ec. Compared with the weed-free control, there was no significance difference in rice tiller numbers among the treatments within the same rice cultivar. The Ecm and Ecz treatments for both rice cultivars and the Ec treatment of Nanjing 9108 had significantly lower leaf photosynthetic rate, root biomass, root oxidation activity, and dry matter accumulation at both the heading and maturity stages. Lower rice yield loss was detected for all rice grown with barnyard grass, but the loss in yield differed by treatments. Losses in grain yield of rice were 12.7–42.6% in the Ecm treatment, 22.3–55.2% in the Ecz treatment, and 1.5–12.1% in the Ec treatment. For both rice cultivars, Ecm and Ecz treatments had significantly lower grain yield compared with the control. The Ec treatment for Nanjing 9108 had significantly lower grain yield compared to the control, but there was not a significant difference between Ec and the control for Liangyoupeijiu. In general, the japonica cultivar had a greater loss in grain yield compared with the indicia hybrid cultivar under the same treatment. The degree of yield loss by barnyard grass cultivar was Ecz > Ecm > Ec. Grain quality in head rice, chalky kernel, chalky size, and gel consistency was significantly lower for both rice cultivars in the Ecm and Ecz treatments and also for Nanjing 9108 but not for Liangyoupeijiu in the Ec treatment. We conclude that the reduction in leaf photosynthetic rate, root biomass, root oxidation activity at the grain filling stage, and dry matter accumulation at maturity was caused by interference in canopy light transmission caused by barnyard grass and that these factors resulted in losses in grain yield and quality.