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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Water Management Research » Research » Publications at this Location » Publication #394644
Research Project: Improving Soil and Water Productivity and Quality in Irrigated Cropping Systems

Location: Water Management Research

Title: Assessment of biochar adsorption capacity for ammonium and nitrate and implications on soil nitrogen management

Author
item Gao, Suduan
item Hendratna, Aileen
item PFLAUM, TOM - Retired ARS Employee

Submitted to: Journal of Advanced Agricultural Technologies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2024
Publication Date: 10/11/2024
Citation: Gao, S., Hendratna, A., Pflaum, T. 2024. Assessment of biochar adsorption capacity for ammonium and nitrate and implications on soil nitrogen management. Journal of Advanced Agricultural Technologies. 11(2):17–27. http://doi.org/10.18178/joaat.11.2.17-27.
DOI: https://doi.org/10.18178/joaat.11.2.17-27

Interpretive Summary: Observations of the benefits by biochar to effectively retain nitrogen (N) in soil via adsorption have not been conclusive. This research examined the adsorption behavior of the major mineral N species onto biochar to elucidate its role in N management. Laboratory experiments were conducted to determine adsorption capacity of ammonium and nitrate onto seven biochar products from different feedstocks and pyrolysis temperature (PT) and pH effects. All biochar products exhibited some capacity to adsorb ammonium, but very little adsorption for nitrate. Furthermore, ammonium adsorption was highly pH dependent (peaked around pH 9 for all products) that can be reduced by more than half at neutral pH. The results suggest that the role of biochar to retain nitrogen in soil to increase use efficiency may be limited especially in neutral soils. The results, however, do not undermine the benefits of biochar to sequester carbon and improve soil properties as a climate smart strategy and a beneficial agronomic practice.

Technical Abstract: Biochar has the potential to retain nitrogen (N) in soil that can increase its availability, improve use efficiency, and reduce losses to environment, but observations have been inconclusive. The aim of this study was to examine the adsorption behavior of ammonium (NH4+) and nitrate (NO3-) onto biochar and the pH effects to elucidate the impact on N management. Laboratory experiments were conducted to determine adsorption capacity of NH4+ and NO3- onto seven biochar products from different feedstocks and pyrolysis temperature (PT). All biochar products exhibited adsorption capacity for NH4+, but one isotherm fit the best by linear and others by Langmuir (except one) and/or Freundlich equations. Almond shell biochar from 550 oC PT showed the highest adsorption for NH4+ in solution concentration range of 1'200 NH4+-N mg L-1. Almond shell biochar from 900 oC PT had the lowest adsorption capacity at low solution concentration, but adsorption increased linearly and surpassed other products as concentration increased. Two softwood biochar products (500 and 540 oC PT) showed a similar trend. However, NH4+ adsorption was highly pH dependent (peaked around pH 9 for all products) but reduced by more than half at neutral pH. Except for the almond char (900 oC PT), no adsorption of NO3- was observed for other products at 5 or 50 mg N L-1 initial solution concentration. This study shows that biochar products vary tremendously in N adsorption and their ability to retain NH4+ is likely limited especially in neutral soils because of strong pH effects. However, the undeniable benefits of biochar in sequestering carbon and improving soil properties make it a climate smart strategy and an agronomic practice to promote for adoption.