Ammonia-oxidizing microorganisms and microbial respiration: Biochar ammonium/nitrate-based fertilizer effects on soil nitrification and crop performance

Abstract

Biochar and N fertilizers can significantly influence the abundance and functionality of ammonia-oxidizing microorganisms (AMO), which are critical for nitrogen cycling and soil health. This study investigates the synergistic effects of combined application of biochar (2% w/w) and different N fertilizers, that is ammonium chloride (NH<inf>4</inf>Cl), sodium nitrate (NaNO<inf>3</inf>) and ammonium nitrate (NH<inf>4</inf>NO<inf>3</inf>) at 200 mg kg⁻¹ each, in affecting the soil nitrification processes and microbial activities and later, these effects were correlated with the growth of Chinese cabbage under acidic soil conditions. Our results indicated that Co-application of biochar with NH<inf>4</inf>Cl reduced cabbage height and biomass by 44.35% and 38.52%, respectively. However, application of biochar in association with enhanced the activity of ammonia monooxygenase (AMO) by 47.87% in comparison with BCN1, which was mainly because of enhanced N absorption by plant leading to its increased growth and biomass. Moreover, BCN3 treatment reshaped the microbial community composition and enhanced the relative abundances of AOA-Nitrososphaera and AOB-norank_d_Bacteria. At the same time, NH<inf>4</inf>NO<inf>3</inf> treatment decreased the relative abundances of AOA-norank_d_Archaea and AOB-Nitrosomonadaceae, which negatively affected the AMO activities. Consequently, application of biochar in conjunction with NH<inf>4</inf>NO<inf>3</inf> could enhance AMO activities, which resultantly, provided more NO<inf>3</inf>⁻-N for cabbage uptake and enhanced its growth as opposed to its collaboration with NH<inf>4</inf>Cl under acidic soil. In conclusions, the combined application of biochar and N fertilizers (NaNO<inf>3</inf> and NH<inf>4</inf>NO<inf>3</inf>) improved plant growth and biomass more than NH<inf>4</inf>Cl application. These results highlight the potential for integrating biochar into fertilization practices to promote sustainable soil health.