Consumo de água, respostas fisiológicas e desempenho produtivo da cultura do gergelim em função da disponibilidade hídrica

Abstract

Sesame cultivation is of economic interest to the mesoregions of the Zona da Mata and the coast of Alagoas. However, the distribution of rainfall in this region is irregular throughout the year. For this reason, it is essential to know the water requirements of this crop for the region, in order to help producers properly manage their crops and obtain sustainable yields. The aim of this research was to determine crop evapotranspiration (ETC) and the single (Kc) and double (Ke and Kcb) crop coefficients, as well as to evaluate the physiological and productive responses of sesame in the region's rainy and dry seasons. To this end, two field experiments were conducted simultaneously in two growing seasons: the rainy season from February to June 2021, and the dry season from October 2021 to January 2022. Experiment 1 consisted of a set of 25 drainage lysimeters where ETC and crop coefficients were determined using the soil water balance. Crop coefficients were obtained from the ETC/ET0 ratio, where reference evapotranspiration (ET0) was calculated using the Penman-Monteith-FAO method. Ke values were calculated from the ratio of evaporation from the soil surface to ET0, while Kcb was calculated from the ratio of transpiration to ET0. For the rainy season, the accumulated rainfall, ETC and ET0 values were870.1, 450.4 and 476.50 mm, respectively. In the dry season, they were 212.9, 440.1 and 513.40, respectively. The average KC values were 0.26, 0.90, 1.26 and 0.75 for the initial, development, intermediate and final stages in the rainy season, and 0.29, 0.94, 1.17 and 0.59 for the dry season.In experiment 2, in an area parallel to experiment 1, the performance of the crop subjected to different water regimes was evaluated (L1, L2, L3, L4 and L5 referring to water levels of 50, 75, 100, 125 and 150% of the ETC determined in experiment 1), with the treatments arranged in a randomized block design. Evaluations of plant growth variables: plant height (PH), stem diameter (SD), leaf area index (LAI) and total dry phytomass (TDSM) took place every two weeks. When the crop reached full bloom, the following physiological parameters were assessed: relative leaf water content (RAW), leaf water potential in the morning (Ѱw in the morning) and at midday (Ѱw at midday), stomatal conductance (gs), transpiration rate (E), intercellular CO2 concentration (Ci), net photosynthetic rate (A), leaf temperature (Tf), instantaneous water use efficiency (EUAi), PSII quantum efficiency (ΦPSII), maximum PSII quantum efficiency (Fv/Fm) and SPAD index. At the harvest of each cycle, the production components were analyzed: yield, water use efficiency, number of pods per plant, number of grains per pod, weight of 1000 grains and dry mass of grains. The water applied (rain + irrigation) for each treatment was: 904.6; 927.1; 957.7; 979.6 and 1003.6 mm for the rainy season and 419.9; 511.5; 616.1; 721.8 and 815.9 mm for the dry season, in L1, L2, L3, L4 and L5, respectively. In the rainy season, leaf Ѱw ranged from -3.7 to -1.1 MPa at midday for 50 and 150% of ETC, respectively. In the dry period, for these same levels, leaf Ѱw ranged from -1.74 to -0.98 kPa and -3.9 to 1.0 kPa for the morning and midday, respectively. Application of 50% of ETC reduced gs (180 and 303%), E (56 and 97%), Ci (239 and 400%), ΦPSII (36%), Fv/Fm (18%) and increased Tf (8%) respectively, for the rainy and dry periods, compared to 150% of ETC. The highest A values (35.8 and 33.7 μmol CO2 m-2 s-1) were obtained with the application of 109 and 108% of the ETC, respectively. For the dry period, the highest values obtained for the growth variables were: 249.0 cm; 18.7 mm; 6507 cm2; 10.8 m2 m-2 and 16629.8 kg ha-1 , for AP, DC, AF, IAF and MSTa, respectively. In the dry season, the maximum yield was 3114.5 kg ha-1 , with the application of 622 mm (101% of the ETC) of water, which was 20% higher than the average for the rainy season. The maximum PUA (5.78 kg ha-1 mm-1 ) was obtained with 557 mm of water (90% of the ETC). There was little variation in the crop coefficient values in the two growing seasons. Therefore, it is possible to use the same coefficient values for the two seasons in order to facilitate irrigation management in the Rio Largo - AL region. The growth and productivity of the crop varies between the seasons, and the greater availability of solar radiation in the dry season makes it possible to obtain higher yields when compared to the rainy season, as long as it is cultivated with irrigation.

Keywords: Sesamum indicum L., Evapotranspiration, Drainage lysimetry, Irrigation Management.