Humic Acid Determination in some Compost and Fertilizer Samples

Abstract

Seven fruit-based fertilizer samples obtained from the Ministry of Agriculture in Gaza include (Pow Humus, Humigan, Eptic, Liquid Potasium, Liquid H.A. Organic corrector Mix, Agriful and Agriful Antisal), have been analyzed for humic acid percentage content using sodium pyrophosphate. Zero humic acid content were found in the samples of Eptic, Liquid Potassium, Agriful and Agriful Antisal, which were in agreement with the reported values in the samples. Also, Pow Humus, Mix and Humigan fertilizer samples and two compost samples from the Agriculture school in Beit Hanoon (Gaza Strip) have been determined for their Humic acid contents using International Humic Substances Society (IHSS) method, modified UV-Vis and modified HPLC methods. It was observed that there is no accurate and precise method for humic acid determination. The best recommended method was the IHSS method as giving highest reasonable results but it is time wasting. The HPLC method is the second recommended method with comparing to IHSS method, despite its costs. UV-Vis method gives good results with just the Pow Humus, Humigan and Mix samples. It was found that different humic acid structures resulting from different sources, in addition NaOH solution modified the humic acid structure. These structures have been illustrated using FTIR after IHSS method for humic acid extraction in the fertilizer samples of Pow Humus, Mix and Humigan. Finally, pyrophosphate solution showed higher selectivity and milder than NaOH solution, in contrast it extracted just 30% of humic acid in the samples and the Redox titration of this method was of high errors.