Investigations into near Infrared Analysis as an Alternative to Traditional Procedures in Manure Nitrogen and Carbon Mineralisation Studies

Abstract

The objective of this investigation was to determine the feasibility of using near infrared (NIR) reflectance spectroscopy to determine nitrogen and carbon mineralisation rates and extents in dairy manures. Ground soil samples from studies in which manure was incubated with soil for various time periods (0 to 112 d) were scanned in the near infrared (1100 to 2498 nm) using a scanning monochromator equipped with a rotating sample cup. Control samples (soil alone) were also scanned and tested. Calibrations for ammonia, nitrate, total N (ammonia and nitrate) contents and carbon evolved as carbon dioxide were developed. Calibration values for ammonia and nitrate were determined on potassium chloride soil extracts using a Technicon autoanalyser. Carbon dioxide values were determined by titrating evolved carbon dioxide that was trapped using potassium hydroxide solution. All calibrations were developed using Partial Least Squares regression analysis. Results using 593 samples from several mineralisation experiments have shown that, while NIR reflectance spectroscopy calibrations for ammonia, nitrate, total N and evolved carbon dioxide may be possible, their development will require great care with respect to the samples to be covered by the calibration. While it appears that the source of the manure, with respect to the diet of the animal(s), was not a serious consideration, manure storage conditions prior to incubation had a strong influence on calibration results. In addition, separate calibrations appear to be needed for control and non-control samples. In summary, results presented here, indicate that NIR reflectance spectroscopy may have potential for analysing manure-amended and non-amended soils from mineralisation experiments, but further work is needed to determine its true potential.