Phytosociological Characterization of Weeds as a Function of Residual Herbicides Applied to Rice Grown Under Sprinkler Irrigation

Abstract

SUMMARYWe aimed to characterize the weed community in sprinkler irrigated rice, previously applied with residual herbicides for two years, as well as to infer about sustainability of the management applied to the fields based on an ecological approach. The experiment was conducted during the cropping seasons 2013/14 and 2014/15, under sprinkler irrigation. Rice was planted in the second-half of October, using the cultivar PUITA INTA CL. Herbicides were applied in pre- and post-emergence (sequential application) of crop and weeds. Ryegrass (Lolium multiflorum) was planted in winter. In May 2015, soil samples were collected for the soil seed bank study. Phytosociological characterization of weeds emerged from the seed bank was conducted from May 2015 to January 2016, until soil seed bank depletion. Echinochloa crusgalli, Fimbristyllis sp., Cyperus esculentus and Killinga brevifolia were the weeds to which most concern should be directed when growing rice under sprinkler irrigation in lowland areas of Southern Brazil. Their competition strategies are based on density. Herbicides used should be efficient in controlling at least these four weed species. A selecting action of herbicides on weed species was botanically characterized, as the weed species reported after two cropping seasons depended on the herbicide treatment applied.

Competitive Ability of Rice Cultivars in the Era of Weed Resistance

“…In such study, C. esculentus, E. colona and Fimbristylis sp. were also among the most important weed species, similarly to what was observed in Southern lowland rice fields [39].…”

“…Most academic studies that find significant differences on the impact of distinct biotypes of the same weed on rice are probably due to the application of inadequate experimental and statistical methods [39]. Most of these studies adopt designs that simply lack enough statistical power to identify any real difference between plant biotypes.…”

“…Weed composition of rice fields located in the lowlands of Southern Brazil was assessed and the authors reported the list of weed species found highlighting the ones with the highest potential to interfere in rice growth and development, thus impacting rice grain yield. The main results of this study are summarized in Table 1 [39].…”

Physiology of Weeds in Intraspecific Competition

“…6;2018 Weed dry mass ( Figure 1D) differed greatly among species; hairy beggarticks, morning glory and hairy fleabane dry mass accumulation depended on plant density, where a higher number of plants into the area resulted in a proportional increased dry mass accumulation. This is a probable indicator that the competitive ability of these species may be centered on Density, one of the most notable phytosociological parameters in plant community dynamics (Concenço, Andres, Teló, Martins, & Moisinho, 2017). Alexandergrass, on the other side, seems to center its competitive ability most probably on dominance (Galon et al, 2014) since its dry mass per area was high from low plant densities onwards.…”

Adaptability and Stability of Soybean Cultivars in Lowland Production System

“…The monoculture of flooded rice favored the selection of weeds resistant to the main herbicide used in lowlands production system, significantly reducing yield and making it impossible to grow rice in many farms in the Southern of Brazil (Concenço et al, 2017). Soybean is the main alternative for crop rotations in the lowland production system, supporting the integrated pest and disease management, and allowing the maintenance of rice farming technologies for high yield and farmers' profit (Zanon et al, 2015;Sartori et al, 2016a).…”