Consumo de água e componentes da evapotranspiração da cultura do trigo em diferentes cenários climáticos: uma aproximação ao modelo SIMDualKc

Abstract

Water is an abiotic factor, essential in several biological, physiological and chemical processes of plants in general, directly interfering in crops potential yield. Thus, quantifying the plant water requirements in order to avoid losses due to water deficit, especially in the phenological stages that directly affect productivity and grain quality, is necessary. The objectives of this study were: (a) to evaluate the soil water balance during the whole crop cycle of wheat in two climatic scenarios (temperate and tropical), aiming to identify the occurrence of water stress in the period in which yield and grain quality are affected and (b) to calibrate and validate the SIMDualKc soil water balance model to estimate evapotranspiration (ETc) and soil evaporation (Es) during the wheat development cycle and; (c) to evaluate water use and wheat crop grain yield in dry and humid climate scenarios, including the derivation of the basal crop coefficients (Kcb), according to climatic variability of each site. Field studies were carried out in a dry (Cerrado - Scenario I) and wet (Santa Maria - Scenario II) region, using wheat, irrigated by sprinkling, in the 2017 and 2018 crop growing seasons. The water balance model SIMDualKc was used to simulate soil water balance in both scenarios. The results showed good agreement between the observed and simulated values of soil available water (ASW), with a regression coefficient (b0) ranging from 1.00 to 0.99 for Scenario I and II, respectively, a coefficient of determination (R2) equal of 1.00 and an average RMSE (root mean square error) of 4.90 mm. The calibrated and validated Kcb values were 0.1 and 0.15 for the initial phase (Kcb ini), 0.9 and 1.0 for the intermediate phase (Kcb mid) and, in the final stages, the values were 0.25 for both scenarios. The result of the soil water balance showed that wheat cultivated in the Brazilian Cerrado (dry climate) presented higher water use (ETc), when compared to wheat cropped in the South region (humid climate). A slight water deficit was observed in the 2017 growing season, nearly at the end of the reproductive stage, in both areas, stage as there is a higher crop water demand, which resulted in a reduction in grain yield. Results also had shown that the SIMDualKc model was an appropriate tool for scheduling and management the irrigation events, as well as for improving crop and water productivity upon wheat in contrasting climatic scenarios in Brazil.