Resposta do arroz irrigado à deficiência hídrica em diferentes fases de desenvolvimento da planta

Abstract

Considering the current limitations and future scenarios of water scarcity, the reduction in water consumption is one of the priorities of the rice industry in Rio Grande do Sul, Brazil. Therefore, alternative techniques of crop water management, such as intermittent flood irrigation, have been proposed. In this irrigation system, the rice crop is not kept continuously flooded so that the soil can be subjected to an alternation between wetting and drying cycles up to a certain level of water deficit. The objective of this work was to evaluate the adaptation of rice to intermittent irrigation in a vegetative and reproductive phases and its impact on the nutritional status and nutrient uptake by the crop. To reach this goal, this work was divided in two charpters. The objective of the first charpter was to determine the effect of levels of soil deficiency at different crop development over the agronomic and productive performance and rice grain quality of three irrigated rice cultivars recommended for the state of Rio Grande do Sul; the objective of the second charpter was to characterize the accumulation of dry matter and nitrogen, phosphorus and potassium (NPK) of rice cultivated under continuous flood irrigation and under soil water deficiency conditions in the vegetative and reproductive phases. The experiment was carried out at Embrapa Clima Temperado Experimental Station, (ETB) located in the municipality of Capão do Leão, State of Rio Grande do Sul, in the agricultural crops 2014/2015, 2015/2016 and 2016/2017, respectively, using cultivars of irrigated rice BRS Sinuelo CL, Puitá INTA-CL and BRS Pampa. In the first study, four rice irrigation managements were evaluated: continuous flood irrigation with maintenance of average water depth of 7.5 cm; irrigation with intermittent water supply, keeping the soil saturated ( 0 kPa or slightly higher); and two levels of soil water deficit, up to 10 and up to 40 kPa in the vegetative (V5 - R0), reproductive I (R1 - R4 + 10 days) and reproductive II (R4 + 10 days - R7) periods. In the second study, treatments with continuous flood irrigation along the cycle were compared to treatments with water deficit of up to 40 KPa applied in the vegetative (V5 - R0), reproductive I (R1 - R4 + 10 dais) and II (R4) + 10 days - R7). In Chapter I, it was concluded that BRS Sinuelo CL, Puitá INTA-CL and BRS Pampa rice cultivars are negatively affected by soil water deficiency of up to 40 kPa imposed in the vegetative phase and in the initial period of the reproductive phase; however, the response is similar when water stress occurs in the final period of the reproductive phase, without exerting negative influence on yield components and, consequently, on grain yield. Soil water deficiency up to 40 kPa did not influence the grain quality of the three cultivars studied. In Chapter II, it was concluded that the response of the cultivars is distinct to soil water deficiency up to 40 kPa when compared to the continuous irrigation treatment - Blade. Dry matter accumulation was negatively influenced by the water deficit in the BRS Pampa cultivar, while cultivar Puitá INTA-CL was affected when the water deficit was imposed during the reproductive period, which includes the flowering phase. As to the cultivar BRS Sinuelo and Pampa, there was an increase in the production of biomass when the water deficit occurred at the end of the reproductive period (maturation). The cultivars Puitá INTA-CL and BRS Pampa accumulated lower amounts of nitrogen when the water deficit occurred in the vegetative period. Phosphorus and potassium absorption is compromised when water stress occurs in the vegetative period, respectively, for cultivars Puitá INTA-CL and BRS Pampa and BRS Pampa. In the other development periods, no effect caused by water deficit was observed. In general, the point of maximum accumulation rate of N and P was different for the cultivars and varied according to the period in which water deficiency occurs.