Preparation, characterization and nitrogen availability of nitrohumic acid as a slow-release nitrogen fertilizer

ABSTRACT

Nitrohumic acids (NHAs) are considered as promising slow-release N fertilizers. In this study, NHA was produced from six organic feedstocks, including coal, leonardite, municipal waste compost, sewage sludge, and apple and beech biochars via nitration using nitric acid. The nitration process was conducted in two ways: (i) after humic acid (HA) extraction (NHA_D), and (ii) before HA extraction (NHA_ID). The prepared NHAs were then characterized using FT-IR and CHNS analysis. Additionally, N mineralization of NHAs was investigated in a sandy loam soil sample. The FT-IR spectra showed that both methods of nitration loaded nitro (NO₂) groups into the HA structure. However, the CHNS analysis indicated the highest rate of N increase for NHA_D (106%) and NHA_ID (113%) extracted from leonardite. Moreover, on average, the total acidity and carboxylic groups of the HAs increased by 7.5% and 14.5% after the nitration processes, respectively. The highest extraction yields of NHA_D (26.1%) and NHA_ID (42.1%) were also obtained from leonardite. Although the extraction yield of NHA_ID was on average two times higher than that of NHA_D, NHA_D indicated a higher soil N availability (1.4 times). We concluded that the NHA_D extracted from leonardite could be considered as an alternative slow-release N fertilizer.

KEYWORDS:

• Nitrohumic acid
• slow-release fertilizer
• FT-IR
• extraction yield
• nitrogen mineralization

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.