Chemical, Thermal, and Spectroscopic Analysis of Organomineral Fertilizer Residue Recovered from an Oxisol

Core Ideas The joint use of analytical techniques helps us to better understand the characteristics and chemical processes that may influence the efficiency of fertilizers. Differential scanning calorimetry, X‐ray diffractometry, and Fourier transform infrared spectroscopy techniques are helpful in capturing the differences in compounds and mineral presence in fertilizers before and after application to the soil. Organomineral and inorganic fertilizers have different capacities to make P available in the soil. Different methods of organomineral fertilizer production result in different capacities to provide P, so that the granulation process resulted in lower P solubility than the granule mixture. Understanding the behavior of different organomineral phosphate fertilizers will help the delivery of available P to plants. We evaluated differences in the characteristics and P availability of granulated organomineral fertilizer (OG), an organomineral granule mixture (OM), and an inorganic granule mixture (MM) and their residues (OGr, OMr, and MMr, respectively) after four 35‐d cropping cycles. Soil‐available P content, X‐ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and soluble P content analyses of the fertilizers and residues were performed. The OM soil had higher available P content after the crops than those with OG and MM. The OGr had the highest total P, water‐soluble P, and P soluble in neutral ammonium citrate and water and a more intense DSC peak related to the remaining monoammonium phosphate than OMr and MMr, indicating that OG had the highest capacity to provide P over time. The XRD and FTIR analyses showed the predominance of aluminum phosphates and the possible formation of low‐solubility compounds in all residues. Differential scanning calorimetry showed a change in the characteristics of the organic matter of OG and OM after application, indicating that these fertilizers have different solubilities and capacities to make P available. The granulation process of OG results in lower capacity to provide P than the granule mixture used for OM. The joint use of several analytical techniques helps clarify fertilizers' characteristics and the chemical processes that influence their efficiency and may be helpful for improving the management and manufacture of organomineral phosphate fertilizers.