Balanço hídrico sequencial, consumo de água e necessidade de irrigação do milho no Rio Grande do Sul

Abstract

Water is one of the most important resources in agriculture and must be used efficiently, especially in irrigated agriculture. Accordingly, the objective of this study was: (i) to simulate the daily soil water balance (SWB) and the irrigation requirement of maize at the physiographic region level in Rio Grande do Sul (RS); (ii) to simulate the evapotranspiration deficit in non-irrigated areas, for different regions and sowing dates; and (iii) to quantify the requirement for supplementary irrigation, through the simulation of the soil water balance, and to estimate the water demand for the current area irrigated by a center pivot in some hydrographic basins of RS. The SIMDualKc model was used in the SWB simulation, for sowings on 10/05 and 10/20, for the 2010/2011 to 2021/2022 harvests. The input data in the model were the soil physical and water characteristics, meteorological data, crop data, soil cover, percolation parameters, and surface runoff, additionally to non-standard information, such as basal crop coefficients (Kcb) for the four phases of the crop development curve. The SWB showed that there are differences in the water requirement and irrigation requirements of maize for the Physiographic Regions of RS, which is due to meteorological and edaphoclimatic factors. The SWB indicated a lower water requirement for sowings performed on 10/20 for most regions, with the exception of Serra do Nordeste. Higher values of evapotranspiration (ETc) were found for the physiographic region of the Serra do Sudeste, while a higher necessity for supplementary irrigation was observed for the physiographic region of the Encosta Inferior do Vale do Nordeste. Lower ETc values were found in the southeastern region of the state, for the physiographic regions of the Grandes Lagoas, Depressão Central, and Litoral, which also have the lowest water requirements. The highest current evapotranspiration deficit (ETc act) was 214 mm and 204 mm, for the sowing dates of 10/05 and 10/20, respectively, in the region of Campanha-Bagé. The highest consumption of water for irrigation occurred in the hydrographic basins of Alto Jacuí, Ijuí, and Piratini. The Piratini hydrographic basin occupies the highest percentage of flow, with about 7.3% of the basin flow for the 10/05 sowing and 7.2% for the 10/20 sowing. The simulation of the water balance proved to be important for quantifying the water requirement of maize and the supplementary irrigation depth during the cycle, in order to estimate the water withdrawn from the springs in the different watersheds.