Biodegradation study of slow release waste-based fertilizer: microscopic and FT-IR characterization

NOEMÍ ZARITZKY; LENIN LLIVE; ALINE SCHNEIDER TEIXEIRA; ESTELA BRUNO; LORENA DELADINO

Cesena

Congreso; Food Innova 2017; 2017

Introduction. Yerba mate is a tea-like beverage prepared with dried, minced leaves and stems traditional from Southamerica. A huge amount of yerba mate powder (YMP) 1 is produced as a byproduct of yerba mate production. This waste offers advantages of being cheap, abundantly available, renewable, and biodegradable, acting as a rich source of mineral and organic matter. Fertilizers are vital input materials that limit agricultural production. Exponential population growth and diminishing arable land have motivated people to utilize larger quantities of chemical fertilizers. In this work, urea (U) encapsulated in a slow release YMP system was used to alleviate these problems.Materials and Methods. Yerba mate powder was donated by the Instituto Nacional de la Yerba Mate (INYM, Argentina). Sodium alginate 2% w/v (Cargill, Argentina) was prepared in water. Different amounts of YMP and 2 g of urea (Anedra, Argentina) was dissolved in 100 mL of alginate solution. Then, the blend was forced with a peristaltic pump at 45 rpm (Gilson Minipuls 3, France) into a silicone tube (3 mm diameter) to drop into a calcium chloride solution (0.5 mol/L) (Biopack, Argentina) for 1 min. The capsules obtained were dried in a forced air oven (GMX 9203A PEET LAB, USA) at 70°C until constant weight. Biodegradation studies were performed burying capsules in fine mesh (1 mm) nylon bags (Gasatex, Argentina) 5 cm below the soil surface (35-40 % humidity, Terrafertil, Argentina,) in pots stored under controlled conditions of temperature at 4, 20 and 30°C. After different incubation periods (up to 90 days), the remaining capsules in the cup were picked out, cleaned, dried at 105°C for 30 min and weighted. Urea content was determined by the ureasesalicylate method (Byosystems, Spain). Soil pH (Hach, sensION 3, USA) was measured each time in all beakers. Degradation process effect on capsules was characterized by microbial assays, Environmental Scanning Electron Microscopy (ESEM, FEI, Quanta 200 microscope, Netherlands), Fourier Transform Infrared Spectrometry (FT-IR, Nicolet IS-10, Thermo Scientific, Inc, EEUU) and the spectral analysis was performed with the software Omnic version 9 (Thermo Scientific).Results. Urea released and biodegradation were affected by temperature. Biodegradation was 100% at 20 and 30°C at 60 and 40 days, respectively. Urea was totally released at 30 days at 4°C and at 10 and 5 days for 20 and 30°C, respectively. Microstructure changes and microbial development were observed by ESEM in accordance with bacterial ang fungal kinetic growth. FT-IR confirmed some structural changes due to degradation process.Conclusions. Yerba mate waste is a promising organic source for producing a low-cost and eco-friendly compound fertilizer. The systems demonstrated to be biodegradable and released the total encapsulated urea in soil.