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We aimed to evaluate the initial growth and physiological characteristics of rice planted following ryegrass in lowland areas. The experiment was conducted in Capao do Leao, Brazil, in Typic Albaqualf. Ryegrass was planted preceding the experiment installation. Prior to rice planting, the area was burndown with herbicide, when treatments were established: ryegrass plants were cut at 0, 15, 30 or 45 cm above ground, resulting in different mulching levels. Rice was then planted, being managed according to local recommendations for the crop. We evaluated the variation in soil moisture levels, rice establishment in density and seedling height, and physiological parameters: relative fluorescence, chlorophyll, flavonoid a nd nitrogen balance indexes. High mulching levels by ryegrass allowed rice five additional days on a dry season, before harmful soil water tension, compared to bare soil; seedlings able to emerge under the ryegrass mulching, grew without considerable barriers; plant physiology in fields with residual ryegrass mulching was little affected, and ryegrass cut up to 45cm height prior to planting rice seem not to affect it. This corresponds to a maximum of about 4500 kg ha-1 of ryegrass straw on soil surface prior to planting rice to avoid damages to crop establishment.

This study aimed to analyze the impact of ryegrass as a soil cover on soil moisture level, initial rice establishment, grain yield and weed control in irrigated rice planted after ryegrass. The experiment was conducted under field conditions in randomized blocks design with four replications. Ryegrass (cv. BRS Ponteio) was planted in autumn and glyphosate was used as a knockdown before rice planting. Ryegrass plants were cut at 0, 0.15, 0.30 or 0.45 m above ground, resulting in different mulching levels. Rice (cv. Irga 424 CL) was planted in spring and was managed according to local crop recommendations. Although positive to the overall cropping system, ryegrass mulching suppressed rice emergence, especially with ryegrass cutting heights above 0.30 m, thus increased seeding densities in rice fields with substantial ryegrass soil cover may be needed. Ryegrass mulching had no significant effect on weed suppression, with positive results being observed only with ≥ 3000 kg ha 1 of ryegrass dry mass mulching. However, the rice yield in relation to the bare soil treatment was 14.3% less when straw quantity was 4500kg ha-1, reinforcing the need for evaluating the benefits and costs of ryegrass as a cover crop in rice production

ABSTRACT: This study aimed to evaluate the potential for glyphosate drift during aerial application using rice plants as sentinels, aiming to determine the effect of drift on irrigated rice crops. For this purpose, a field experiment was performed using an entirely randomized design with four replicates, evaluating different distances from the site of application [control (no application), 0, 12.5, 25, 50, 75, 100, 150, 200, 300, and 400 m]. The experiment was carried out at the Granjas 4 Irmãos farm, located in the Rio Grande city, Rio Grande do Sul State, Brazil. The glyphosate dose application was 1,920 g e.a. ha-1 (Roundup Transorb®, 480 g e.a. L-1 glyphosate isopropylamine salt). A dose-response curve was developed to estimate the drift rate in sentinel plants, by applying increasing glyphosate doses in rice plants and assessing the injury level. The drift rates estimated by the injury level in sentinel plants were 14% (150 m), 13% (200 m), and 5% (400 m). Death of the experimental units was observed for distances between 0 and 50 m, while in distances between 75 and 150 m, 25 to 50% of the plants survived, reducing productivity. In the distances between 200 and 400 m, there was no reduction in productivity when compared to the control, even when the injury levels reached 52 to 82%. Thus, we concluded that a 5% glyphosate drift reached up to 400 m from the application range. Considering the recommendation of zero drift, distances greater than 400 m should be adopted to avoid symptoms in rice plants. We suggest using distances of more than 400 m in future studies.