Higher biochar rates sustain nitrogen supply for perennial trees

Addressing Global Nitrogen Challenges

Nitrogen is an essential nutrient for plant productivity, yet its overuse in synthetic fertilizers often results in significant environmental problems such as greenhouse gas emissions, water pollution, and reduced soil health. Sustainable management practices are needed to improve nitrogen retention and reduce environmental losses, especially for perennial tree crops like Nageia nagi, which require substantial nitrogen inputs over long periods.

Investigating Biochar's Role in Nutrient Management

Scientists from South China Botanical Garden, Chinese Academy of Sciences and Fujian Agriculture and Forestry University explored how different application rates of biochar could influence nitrogen dynamics in fertilized soils. Their study aimed to determine how biochar modifies soil aggregates and associated nitrogen, as well as microbial responses, to regulate nitrogen supply for Nageia nagi over a one-year period. The researchers hypothesized that higher biochar rates would promote microaggregate stability, improve aggregate-associated nitrogen retention, and increase the activity of nitrogen-mineralizing bacteria.

Experimental Design and Observations

The research was conducted using a pot experiment in a glasshouse with a subtropical Alfisol. Biochar, produced from waste mushroom substrate, was applied at two rates: 20 tons per hectare and 40 tons per hectare. These treatments were compared to a control without any amendment and a fertilizer-only treatment. The team analyzed soil nitrogen fractions, soil aggregate stability, microbial community composition, and the nitrogen content of Nageia nagi plants.

Biochar Enhances Nitrogen Availability and Plant Uptake

The findings indicate that biochar amendment, particularly at the higher rate, significantly increased the concentration of inorganic nitrogen compounds such as ammonium and nitrate in the soil compared to fertilizer-only applications. For example, ammonium nitrogen availability rose by 32.8% in the higher biochar treatment compared to the fertilizer-only treatment. This enhanced nitrogen availability led to a substantial increase in plant nitrogen content, with Nageia nagi showing 41.3% more nitrogen in its leaves under the higher biochar application compared to the control. The porous structure and functional groups of biochar were observed to play a key role in retaining and slowly releasing this essential nutrient.

Soil Aggregates as Nitrogen Reservoirs

The study observed that biochar application, regardless of the rate, increased the stability of soil microaggregates. More importantly, the higher biochar rate significantly boosted the nitrogen content within macro- and intermediate aggregates. This modification in soil structure is important for stabilizing nitrogen stocks and ensuring their slow, continuous release. The improved water retention potential attributed to higher biochar rates also likely reduced nitrogen leaching, contributing to its increased concentration in the soil aggregates.

Specialized Microbes Support Nitrogen Cycling

While biochar amendment decreased overall bacterial species diversity over the extended period, it concurrently promoted the abundance of specialized ammonium-oxidizing bacteria, specifically Betaproteobacteria. These microorganisms are essential for nitrogen mineralization, the process by which organic nitrogen is converted into forms usable by plants. The positive relationship between these bacteria and inorganic nitrogen levels in the soil indicates their important role in maintaining nitrogen cycling and supply under biochar amendment.

Sustaining Perennial Crop Nutrition

The research concludes that higher biochar application rates offer a promising approach for sustaining nitrogen supply in agricultural systems, especially for perennial crops. By stabilizing soil microaggregates, increasing nitrogen in larger aggregates, and fostering a specialized microbial community that supports mineralization and slow release, biochar helps meet plant nitrogen needs over longer durations. While these results from a pot experiment are encouraging, further validation through on-field trials will be important to fully confirm these benefits in natural soil systems. This work contributes to developing more effective nitrogen management strategies and promoting environmental sustainability in plantation agriculture.

Corresponding Author:

Muhammed Mustapha Ibrahim and Enqing Hou

Original Source:

https://doi.org/10.1007/s44246-023-00056-2

Contributions:

All authors contributed to the study's conception and design. Material preparation, data collection, and analysis were performed by Muhammed Mustapha Ibrahim, Zhaofeng Chang, Zhimin Li, Jerry Joseph, Ado Adamu Yusuf, and Xianzhen Luo. Data curation, investigation, methodology, writing of the original draft, review, and editing were done by Muhammed Mustapha Ibrahim. Supervision, review and editing, project administration, and resources were provided by Enqing Hou. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.