Biocarvão de casca de pequi: desempenho como remediador dos efeitos da salinidade da água de irrigação

Abstract

Allied to water availability, water quality is a determining factor to be considered in irrigated agricultural systems, whose analysis allows predicting the feasibility of its application, especially regarding the deleterious effects resulting from salinity in the soil-water-plant system. In this perspective, the objective was to evaluate the pequi bark biochar (Caryocar brasiliense), as an alternative to mitigate the effects caused by the use of saline water in irrigation. For this, three biochars were produced: without chemical modification (BC) and activated in two proportions of magnesium, 1:20 (BCA-20) and 1:5 (BCA-5) (residue/ MgCl2), in three granulometric classes (G1 < 0.5 mm; 0.5 < G2 < 1.0 mm and 1.0 < G3 < 2.0 mm). The tests were carried out in two phases: in aqueous and in soil matrix, using different application conditions. Through adsorptive tests, in the first phase of the study, biochars of intermediate granulometry were analyzed at four levels of application (0.5; 1.0; 1.5 and 2.0 g) in synthetic saline water, with electrical conductivity (EC) of 4.5 4,5 dS m-1. Based on tests, the percentage of sodium reduction (Na+) was evaluated and the sodium adsorption ratio (SAR) of the final extracts was calculated. The second phase of the study was carried out in soil columns, with a clayey texture, conditioned with the respective treatments at an application rate of 1% (m/m). Furthermore, for comparison purposes, additional treatments relating to the application of Mg solid and in solution were evaluated. From the simulation of irrigation with synthetic saline water, through a leaching test, the simultaneous influence between the granulometric levels of the biochars and the interaction time of the treatments (incubated and without incubation) was evaluated. Effects on soil attributes were evaluated: hydraulic conductivity (K0), clay dispersed in water (CDW), EC and pH. in addition, two additional tests were established: the application of BCA-20G2 in two dosages (1 and 4%); and the comparison of the influence of saline, distilled and supply water, when applied to the soil. Para os testes em água, foi observado baixo percentual de adsorção of Na+, with a maximum removal of 9.8% for the BCG2. Still, BCA-5G2 reduced the SAR by up to 76%, proportional to the increase in the doses used, but with an increase in the EC of the extract of up to 14 dS m-1. In soil matrix, the incorporation of biochar promoted satisfactory improvements, especially the BC with larger granulometry. K0 values reached 76 cm h-1 when not incubated and 52 cm h-1 when incubated. The control treatments, without biochar, showed lower values, 38 and 21 cm h-1, respectively. For the incubated soils, there was an increase of 93.8% in pH, a variation mainly associated with the previous correction of soil acidity by liming. Regarding the effects of CWD, the treatments did not confer attenuation and satisfactory improvements to the soil by the application of Mg. For additional tests, low influence was observed regarding dosage variation and activation proportions (BCA-5G2 and BCA-20G2). Finally, the application of saline irrigation water, when compared to the others, resulted in a reduction in K0, in addition to an increase of 0.83 dS m-1 in the EC of the soil, reflecting a high salinization potential. From a general perspective, the application of biochar proved to be favorable for the intended purposes.