Preliminary design for establishing compost maturity by using the spectral characteristics of five organic fertilizers

Abstract

The maturity of compost is involved in the availability of nutrients to crops and improvement of soil properties after fertilization. In the past, the determination of composts maturity mostly required analysis in the laboratory previously and it must consume a lot of time and cost. This study was conducted to use Fourier Transform Infrared (FTIR) spectroscopy and solid ¹³C Nuclear Magnetic Resonance (¹³C NMR) spectroscopy to understand the mature characteristics of five type of common composts. The FTIR analysis showed that all composts contained aromatic groups. In addition, the surface of five composts contained the functional groups including hydroxyl group, carboxyl group, amino group etc. However, these functional groups changed along with maturity degree. It is recognized that the aliphatic group located at 2930 cm⁻¹ and 2850 cm⁻¹ showed a decreasing peak, and amino acid at 1385 cm⁻¹ was disappearing gradually due to the decomposition of organic matter by bacteria. There may be used to identify the maturity degree of composts. Increase of aromatic group at 1650 cm⁻¹, carboxy (–COOH) and phenolic OH group at 1385 cm⁻¹ may prove the full maturity of composts. ¹³C NMR analysis showed that five type of matured composts are mainly consisted with aliphatic groups and aromatic groups. The surfaces of the composts contained C–O bonds (ester, ethers, carbohydrate and other functional groups), COO⁻ (carboxyl and ester carbons) and C=O bond (aldehydes and ketones). The strength of different absorptive characteristics of FTIR and ¹³C NMR may be a clue to identify the maturity of composts for the design of detective instruments in the future.