Manejo de canola em terras baixas: características do dossel, interceptação da radiação e produtividade de grãos

Abstract

The modification of microclimatic conditions in agricultural crops can substantially affect the growth and yield of grains in waterlogged environments. Therefore, the present study aimed to determine the effect of the modification in the spatial arrangement of plants in a canola canopy grown in Umbric Alithic Dark-Grey Ultisol with and without surface drainage in the Central Depression region of Rio Grande do Sul. The study comprised field experiments conducted in 2018 and 2019 using a randomized block design with strips for the surface soil drainage factor and arranged in a 2 x 4 two-factorial arrangement with four replications. Treatments consisted of the presence and absence of surface drains (drainage factor) and the row spacings of 0.17, 0.34, 0.51, and 0.68 m (spacing factor). The canola cultivar Diamond was used in the experiment at a population density of 40 plants m-² after thinning. The drainage grooves measuring 0.25 m in width and depth were opened with a machine around the experimental units. The plants were subjected to phenological evaluations and analyses of growth traits, leaf area, dry matter, final plant density, number of siliques per plant, number of grains per silique, thousand-grain mass, grain yield, and interception parameters of photosynthetically active radiation (PAR). The incident and transmitted PAR on the canopy were measured using handmade sensors containing five amorphous silicon solar cells, with readings every 30 seconds beginning at the rosette stage of the crop. Soil surface drainage (CD) reduced the persistence of water table rise in the soil profile. Waterlogging delayed the necessary plant development to obtain maximum leaf area index (LAI) and the total crop cycle. The highest extinction coefficient of the PAR was obtained at the spacing of 0.17 m, decreasing with the increase in spacing. The radiation use efficiency ranged (EUR) from 1.49 to 3.08 g MJ-¹, and the insertion of drains resulted in a EUR of 11.1 and 31.2% in the different years. Canola branching is affected by soil waterlogging, negatively affecting the yield. The absence of surface drainage (SD) increased the total number of branches by 21.7 and 62.1% in 2018 and 2019, respectively. Drainage positively impacted canola cultivation, especially under intense waterlogging conditions (2018), increasing by 22.0, 469.9, 130.8, 58.7, and 1198.1% the parameters of plant height, number of siliques, grains per silique, thousand-grain mass, and grain yield, respectively. The spacing of 0.17 m resulted in the lowest reduction in the final plant stand and the highest number of grains per silique. The grain yield means were 81.5 and 1,090.2 kg ha-¹ in SD and 1,237.2 and 2,901.1 kg ha-¹ in CD in 2018 and 2019, respectively. In the treatments with drainage, the highest grain yield values were obtained with the row spacings of 0.41 m in 2018 and 0.17 m in 2019. The results of this study highlight that canola cultivation in lowlands is possible and could be profitable in the presence of surface drainage, requiring intermediate spacings around 0.45 m to safeguard the production capacity in the presence of waterlogging.