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Identifying the causes of the yield gap (Yg) is essential to understand and take proactive measures to improve crop management factors. Brazil is the country in the Americas with the highest area of flooded rice (Oryza sativa L.) and the Rio Grande do Sul (RS) state accounts for 73% of the Brazilian rice production. The objective was to determine yield potential (Yp) and Yg in flooded rice and identify key factors associated with high yield (HY) and low yield (LY) farms across the rice production regions in RS, Brazil. Yield and management practices data from farmers were collected by a survey that included 324 site‐year observations fields covering the five major RS production regions during three growing seasons (2016–2018). The Yp was simulated by Oryza crop model. The Yg was calculated as the difference between Yp and the average yield from farmers. Factors related between tertiles were studied by identifying management practices that were associated with high‐ and low‐yielding fields. Rice Yp ranged from 14.2 to 15.9 Mg ha−1 and the Yg was 48% of the estimated average Yp (15.1 Mg ha–1). Our findings indicated that HY fields had 33% higher productivity, rotated more area with soybean [Glycine max (L.) Merr.] (77%), controlled pre‐sowing weeds by only herbicides (56%), sowed 20 d early with lower seeding rate (6%) and had early onset irrigation (5 d) compared to LY fields. These findings are applicable to rice farmers worldwide, and can help to define priorities in research and extension programs at both local and regional levels. Core Ideas: Yield potential average was 15.1 Mg ha−1 and yield gap was 48% of yield potential.Sowing date, irrigation, N fertilizer, rotation, weed and seed rate explained yield variation.The lowest yield gap for sowing date was 12% for the sowing window from 18 October to 3 November.Onset of irrigation delay after V3‐stage decreased yield by 180 kg ha−1 d–1. [ABSTRACT FROM AUTHOR]

Weed competition in southern Brazil is one of the main limiting factors for Oryza sativa L. (flooded rice) yield. Echinochloa spp. (barnyardgrass) occurs at a high frequency. Although the potential for weed interference in this cereal is well known, there is little information available about the impact of nutrient competition on rice. Thus, this study aimed to evaluate the relationship between the increase of the barnyardgrass population and the development and nutrition of flooded rice plants at different stages of development. The treatments consisted of growing populations of barnyardgrass competing with the crop from stage V4, which were: 0, 1, 6, 13, 100 and 200 plants · m-2. The experimental design was randomized blocks with two replications, and the experimental units were plots 1.53 m wide by 5 m long. Plant biomass, nutrient uptake and loss of productivity were determined with three replications. An increase in the barnyardgrass population reduced the dry mass of rice leaves and stems, regardless of the evaluation period and the vegetative or reproductive period. Barnyardgrass plants had a significant impact on the reduced grain yield of a flooded rice crop, mainly due to high nutrient competitiveness, especially N in the vegetative period and K in the reproductive period. Barnyardgrass caused a loss of yield by unit · m-2 of 1.13%. The competition for N between rice and barnyardgrass plants was higher in the vegetative period, while for K, Ca and Mg the highest competition occurred in the reproductive period. [ABSTRACT FROM AUTHOR]

This research aimed to evaluate the phytosociology of weeds in irrigated rice in different soil management systems and crop rotation intensity. Therefore, two field studies were carried out. Study 1 was conducted in an area that has been cultivated since 1994 with three cultivation systems: direct, pre-germinated and conventional ones. Study 2 was carried out in an experimental area in five Integrated Farming Systems, with crop rotation. Phytosociological evaluations were conducted when rice was fully blooming, in the first study, and when grain filling was ending, in the second study. Pre-germinated system of rice cultivation has predominance of aquatic weeds. Conventional system when compared with direct sowing has lower weed densities. Integrated Agricultural Production Systems with higher intensity of crop rotation have been higher infested of perennial species. [ABSTRACT FROM AUTHOR]

Weedy rice (Oryza sativa L.) is the most problematic weed in rice fields due to the few control management alternatives to control it, because of the genetic similarity with the crop. Different cropping systems (regarding soil preparation before sowing) have been used as options to control the persistence and emergence of the weed seedbank. Therefore, the objective of this study was to evaluate the longevity and vertical distribution of weedy rice seeds in the soil seedbank after 22 years of different rice cropping systems. Data was analyzed as a two-way factorial, with cropping systems carried out for 22 years [no-tillage (NT), conventional tillage (CT), wet direct-seeded (WDS)] as one factor and sampling depth (0-2, 2-5, 5-10 and 10-20 cm) as the other factor. The number of whole and deteriorated seeds per m-2 were assessed, as well as the viability (%). No effect between the systems were detected up to 5 cm, however at 5-10 cm CT and WDS showed higher amount of seeds, and WDS at 10-20 cm. As the sampling depth increased, NT showed fewer amount of seeds, while less reduction of the soil seedbank was observed in WDS. CT and WDS spread viable seeds in the soil profile from 0 to 20 cm depth. After 22 years there are viable weedy rice seeds up to 10 cm of depth in the three cropping systems and there is no difference among them up to 5 cm of depth, demonstrating the serious problem of the seedbank for this species. [ABSTRACT FROM AUTHOR]