Nitrogen availability in biochar-based fertilizers depending on activation treatment and nitrogen source

Area of Science:

• Agricultural Science
• Environmental Chemistry
• Materials Science

Background:

• Biochar-based fertilizers (BBFs) offer potential for sustainable agriculture.
• Optimizing nitrogen (N) concentration and release rates is crucial for fertilizer efficacy.
• Olive tree pruning waste presents a viable feedstock for biochar production.

Purpose of the Study:

• To develop novel BBFs with enhanced nitrogen content and slow-release characteristics.
• To investigate the impact of different activation and N-doping methods on BBF properties.
• To correlate the chemical forms of N in BBFs with their potential soil availability.

Main Methods:

• Pyrolysis of olive tree pruning at 400°C and 800°C to produce pristine biochars.
• Activation of biochars using ultrasonication, hydrogen peroxide (H2O2), or nitric acid (HNO3).
• Enrichment of activated biochars with nitrogen using urea or ammonium sulfate.

Main Results:

• Nitric acid activation of low-temperature biochar created carboxylic groups, enhancing N enrichment.
• Urea treatment resulted in BBFs with up to 7.0% N, significantly higher than H2O2 activation (2.0% N).
• Water-soluble and hydrolyzable N fractions constituted up to 14.5% and 60% of total N, respectively, indicating slow-release potential.

Conclusions:

• Nitric acid activation combined with urea doping is an effective strategy for producing high-N, slow-release BBFs.
• The chemical forms of N in BBFs (water-soluble, hydrolyzable, non-hydrolyzable) suggest progressive N availability for plants.
• These BBFs show promise as sustainable alternatives to conventional fertilizers, improving soil nutrient management.