Avaliação de sensor de turbidez comercial para determinação de K disponível em solo

Abstract

Nutrient availability is essential so the crop can reach its maximum yield. Potassium is an element that has a great influence on this matter since it has several functions in the plant like regulation of osmotic pressure. Its deficiency leads to repercussions on enzymatic processes and an elevated concentration of oxygen-reactive species. Plants absorb potassium from soil, so it is important to assess if the quantity of this nutrient is enough for its growth. Usually, the determination of available potassium is done through chemical extraction where a solution is applied to displace the weakly adsorbed potassium in the electronegative surface of the clay minerals and organic matter present in the soil. Several extracting solutions are available that use different mechanisms to displace the potassium. In Brazil, one of the most employed reagents is the Mehlich-1. The determination of extracted potassium is usually achieved through atomic emission. Therefore, this work proposes a turbidimetric method for the determination of potassium, due to the lower costs of turbidimetric sensors available in the market, in addition to its reduced size and practicality which makes it more feasible in situ analysis. Extraction time, sample mass, and extracting solution were evaluated to achieve this. For the turbidimetric method, the use of sodium tetraphenylborate was assessed for the precipitation of potassium, its volume applied, and the time of precipitation. The ideal conditions found for the extraction were: 10 minutes of extraction, 0,5 g of soil, and diluted Mehlich-1 as extractant. The volume of tetraphenylborate applied was 2 mL and an ideal time of precipitation of 25 minutes. The provisory results indicate the possibility of using the sensor for the determination of available potassium in the soil. It was possible to achieve a calibration curve with good linearity in the range of 0 to 10 mg L-1 of K with the turbidity sensor used. Furthermore, the result for sample A applying the turbidimetric method was near the results obtained by F AES and MIP OES. However, more results are necessary to consolidate its real applicability.