Emergência e crescimento inicial de plantas de arroz e capim-arroz em função do nível de umidade no solo

In lower than expected rainfall years during the early post-sowing stage, Echinochloa seeds tend to germinate and emerge before rice, increasing the competition along the rice development. The objective of this work was to evaluate the effects of water level in soil, expressed as water potentials, on the emergence level and speed, as well as early growth of rice and Echinochloa sp. plants, under controlled environmental conditions. The trial was conducted in a randomized block design with four replications. Lowland soil was used, for which a water retention curve was previously drawn. The experimental units were composed of plastic bottles filled with exactly 400 g of dry soil, and the treatments were water potentials (yw) of -0.03, -0.07, -0.1, -0.3 and -0.5 MPa, where rice and Echinochloa plants were grown. The emergence curve was built for each water potential and species, and 20 days after emergence, three plants of each experimental unit were collected for water content, fresh and dry mass, and total emergence evaluations. Echinochloa plants showed better emergence levels under reduced water potentials than rice plants, but were less efficient in mass accumulation in the early days of development. Plants of both species did not show water stress under low water potentials, and the optimal water level in the soil was more specific for rice emergence, around -0.07 MPa.