Use of Scanning Near-Infrared Spectroscopy as a Quality Control Indicator for Bulk Blended Inorganic Fertilizers

• Published in: Communications in Soil Science and Plant Analysis Vol. 44; no. 1-4; pp. 120 - 135
• Main Authors: Janse Van Vuuren, J. A., Groenewald, C. A.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Philadelphia, PA Taylor & Francis Group 01.01.2013; Taylor & Francis; Taylor & Francis Ltd
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Bulk blended fertilizers; Calibration; Fertilizers; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Generalities. Analysis and diagnosis methods; liquid fertilizers; quality control; Raw materials; scanning near infrared spectroscopy (NIRS); Soil sciences; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Spectrum analysis; Near infrared spectrometry; Compound fertilizer; Quality control; Inorganic fertilizer; Bulk blended fertilizers; Liquid fertilizer; liquid fertilizers; Indicator; Mixture; scanning near infrared spectroscopy (NIRS)
• ISSN: 0010-3624; 1532-2416; 1532-4133
• DOI: 10.1080/00103624.2013.736141

The use of bulk blended fertilizers worldwide has become preferred to compounded chemical fertilizers. This poses new problems in obtaining a representative sample for laboratory analysis. There are huge variations in particle-size distribution, shape of particles, and bulk density. These factors results in separation when attempting to obtain smaller subsamples. Turnaround time of wet chemical analysis by the laboratories (usually 1-2 weeks) further compounds the problem. A procedure was developed to obtain reliable composition results for quality control of bulk blend fertilizers using near-infrared spectroscopy (NIRS) technology. Results are available immediately. Another challenge is obtaining reliable chemical analyses for preparing the NIRS calibrations. To overcome this, an exact formulation is prepared in the laboratory using the raw materials. The size of each such mixture (approximately 500 g) is sufficient to allow the complete sample to be scanned on a scanning NIRS instrument with rotating sample container. All raw materials are also scanned individually. Robust calibrations were obtained in this manner, and special control systems were implemented to ensure and verify the reliability of the results. The results of the NIRS were shown to be acceptable and on par with the chemical composition for the following elements: nitrogen (N), phosphorus (P), potassium (K), and sulfur (S). Better results were obtained for N if separate calibrations were prepared for N sources (urea, ammonium, and nitrate). The best results for all components were obtained using Partial Least Squares (PLS) chemometrics with Standard Normal Variant (SNV) Detrend Pathlength correction and wavelengths between 950 and 1650 nm. Calibrations for other parameters are in process.