Determination of organic matter by infrared spectroscopy (FTIR) in soil barley growers.

Organic matter in soils is useful for the farmer as it complements a series of analyzes to determine soil fertility. A method to determine soil organic matter is called Walkley-Black consisting destroy organic matter, oxidizing it by adding a mixture of sulfuric acid-phosphoric acid and potassium dichromate, leaving digest for a period of time, then make volumetric measurement with ferrous ammonium sulfate unoxidized material and calculating the organic matter in the sample. In this work, we investigated a nondestructive method using near infrared (FTIR). The sample is passed into a quartz cell through a monochromatic light beam which is reflecting layer and said reflectance value is measured and transformed to obtain a spectrum in which each signal corresponds to the absorption bands of sample components. These bands are identified in the near infrared region (400-2600 nm) and ?(CN), ?(CC) and ?(CO) vibration modes. These methods were compared to determine their equivalence used 20 samples of dry soil and homogenized by both methods, performing analysis in triplicate and statistically processing data by a correlation coefficient. The obtained value ri = 0.9197 indicating that both methods are equivalent, a correlation coefficient r = 0.9479 thus confirmed the linearity between the methods, a Student t test with which it was concluded that the values obtained from FTIR method possess an error rate below 10 %, a correlation coefficient of agreement stating rc = 0.9682 concordance and reproducibility of the methods. 35 determinations were performed in parallel which 62 % showed an error rate of less than 10 % and the remaining error rates between 10-25 %. These data were also analyzed for concordance correlation index resulting rc = 0.9883 which confirms the consistency and reproducibility of the data, to the pair of measurements was taken a number of control samples that had results within 10 % acceptable.