Calibração de sensores de umidade do solo em beterraba irrigada sob salinidade

Abstract

Drought and salinity are the abiotic stresses that most cause loss in agriculture, and numerous irrigation management strategies are adopted in order to reduce production losses. In situations where there are high concentrations of salts in the soil or irrigation water, moisture sensors are still barely recommended due to loss accuracy. Beetroot (Beta vulgaris L.) is a vegetable with nutritional and economic relevance, which presents very different physiological alterations to water and saline stress, mainly in terms of sugars and osmoregulation. The objective was to evaluate the water status of the soil and plant, as the physiological processes of the beet during a salinization process under controlled moisture ranges and different levels of salinity of water. The performance of sensors with different principles and costs under conditions of saline and non-saline soil was also studied. For this, 3 experiments were conducted, one in randomized blocks with a 5x3 factorial arrangement with five salinity levels of irrigation water (0, 2, 4, 6 and 8 dS m-1) and three levels of soil moisture (moisture contents 100, 90 and 80 % of field capacity). Water potentials were determined in soils and in beetroot, biometric variables, production, leaf succulence (LS), osmotic adjustment (OA) and membrane damage. Two more experiments were carried out with soil moisture sensors, the first one was in a 5 x 2 factorial arrangement, with 5 levels of electrical conductivity (EC) of the water used for artificially salinizing the soil (0, 2, 4, 8 and 16 dS m-1) and two soil moisture sensors (resistive and tensiometer) in randomized blocks with 4 repetitions. The second experiment was carried out in non-saline and salinized soil during the beetroot cultivation with different levels of brackish water, being evaluated in a 5 x 2 factorial arrangement, with 5 being the EC levels of the water used during irrigation (0, 2, 4, 6 and 8 dS m-1) and two soil moisture sensors (resistive and tensiometer). In both experiments, the sensors were calibrated and the respective static indices were obtained (discussed in Chapter III). From chapter 2, it stands out the beetroot coexistence strategies to abiotic stresses with regard to OA, LS, and reduction of water potential in the plant, in addition to the higher productive capacity, when cultivated with salts. The resistive sensors and the tensiometer presented calibration equations with high coefficients of determination independent of soil salinity, however the electrical resistivity measured using the low cost sensor YL-69 is significantly affected by soil salinity, contrary to what happened with the tensiometers that showed low variation for both experiments. It is concluded that moderate values of salinity and soil moisture promote gains in production, OA and LS in the beetroot crop and that the use of low cost sensors is possible in salinity conditions when calibrated, without loss of data reliability.