Desenvolvimento de spot test para determinação de fósforo em solos com quantificação por imagem digital

Abstract

Soil analyses are done to evaluate the availability of nutrients for plants and the reaction of the soil. It thus serves for the prescription of correctives and fertilizers. In general, plants need 16 elements for proper development and growth. Thirteen of these elements, commonly referred to as nutrients, may be available in the soil or may be complemented by the use of mineral and/or organic fertilizers. Among these elements is phosphorus, which is indispensable for plant growth and production, interfering in the processes of photosynthesis, respiration, energy storage and transfer, cell divisionand cell growth. It contributes to the premature growth ofroots, quality of fruits, vegetables, grains, and seed formation. Because it interferes in several vital processes in plants, there must be an adequate supply of phosphorus from germination, especially in short cycle plants. Plants, when young, absorb larger quantities of phosphorus, and there is a rapid and intense growth of the roots in environments with adequate levels of the nutrient. The determination of the phosphorus present in the sample, by spectrophotometry, is based on the chemical transformation of this substance into a colored complex. In this work, we proposed the development of a spot test for the determination of phosphorus in soil, with quantification by Photometrix® application in an environment with controlled lighting, using the results obtained in the classical methodology of analysis for comparison purposes. The standard analysis methodology was adapted to the proposed system, reducing the use of reagents by 60%. The results obtained were excellent accuracy when compared to the certified value, and a relative standard deviation of 1%, linearity of 0.1­1 mg/L, detection limit of 0.02mg/L, and quantification limit of 0.03 mg/L. Thus, the use of the spot test associated with detection by the Photometrix application, in a controlled light system, shows to be a promising alternative to traditional absorbance measurements in the determination of phosphorus in soil samples.