Purpose Soil organic nitrogen (N) is primarily found in the surface soil, but mineral N is easily leaching along the profile. It is well known that blending biochar with chemical fertilizers is necessary to enhance N stocks and soil fertility in the topsoil. However, there is a lack of comprehensive understanding of the effects of long-term biochar history on the distribution and transformation of soil organic N fractions in the 0–100 cm soil layer. Methods In this study, a nine-year field experiment was conducted with four treatments: no biochar application (CK); 15.75 t ha− 1 of biochar (BC1); 31.5 t ha− 1 of biochar (BC2); and 47.25 t ha− 1 of biochar (BC3). Equal amounts of fertilizer were applied annually for each treatment. Soil samples were collected from five soil layers (0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, and 80–100 cm) in 2013 and 2021 to measure the differences in soil N pools distribution, and the potential N supply capacity of organic N fractions. Results The results showed that biochar combined with chemical fertilizer altered the soil organic N pool distribution, with non-hydrolyzable N dominating in 2013 and hydrolyzable N dominating in 2021. Compared with CK, biochar history increased soil N stocks in the topsoil (0–20 cm), but decreased soil nutrient content and N stocks in the soil (20–60 cm). Although the N stocks in BC2 was the highest among the biochar blended with fertilizer treatment at a depth of 20–60 cm soil, there were no significant differences among the treatments. Redundancy analysis showed that total N, soil organic matter, and C/N were the main indicators, closely related to organic N fractions in the topsoil (0–20 cm) under nine years of biochar history. Partial least squares path modeling illustrated that NH4+-N was primarily obtained from different soil organic N fractions, and the soil N supply potential of the organic N fractions differed under biochar application with chemical fertilizer. Specifically, amino acid N and hydrolyzable unknown N were the main organic N sources in the CK (fertilizer application without biochar), hydrolyzable unknown N in BC1 (15.75 t ha− 1 of biochar blended with fertilizer), hydrolyzable unknown N and amino sugar N in BC2 (31.5 t ha− 1 of biochar blended with fertilizer), and amino acid N, hydrolyzable ammonium N, and unknown N in BC3 (47.25 t ha− 1 of biochar blended with fertilizer). Conclusion This study showed that long-term application of diverse rates of biochar history could promote soil nutrient accumulation in the topsoil, especially at 31.5 t ha− 1, which could increase soil N stocks. These findings could provide new insights into understanding the long-term role of biochar application.

Nine-year biochar history increases topsoil nitrogen stocks and reduces the refractory organic nitrogen fractions in deep soils

期刊论文
发表日期：

2025年5月30日

查看全文

Di Wang,
Shuai Liu,
Liwei Hao,
Qi Yue,
Linlin Jiang,
Yu Lan,
Wenfu Chen

摘要

Purpose

Soil organic nitrogen (N) is primarily found in the surface soil, but mineral N is easily leaching along the profile. It is well known that blending biochar with chemical fertilizers is necessary to enhance N stocks and soil fertility in the topsoil. However, there is a lack of comprehensive understanding of the effects of long-term biochar history on the distribution and transformation of soil organic N fractions in the 0–100 cm soil layer.

Methods

In this study, a nine-year field experiment was conducted with four treatments: no biochar application (CK); 15.75 t ha^− 1 of biochar (BC1); 31.5 t ha^− 1 of biochar (BC2); and 47.25 t ha^− 1 of biochar (BC3). Equal amounts of fertilizer were applied annually for each treatment. Soil samples were collected from five soil layers (0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, and 80–100 cm) in 2013 and 2021 to measure the differences in soil N pools distribution, and the potential N supply capacity of organic N fractions.

Results

The results showed that biochar combined with chemical fertilizer altered the soil organic N pool distribution, with non-hydrolyzable N dominating in 2013 and hydrolyzable N dominating in 2021. Compared with CK, biochar history increased soil N stocks in the topsoil (0–20 cm), but decreased soil nutrient content and N stocks in the soil (20–60 cm). Although the N stocks in BC2 was the highest among the biochar blended with fertilizer treatment at a depth of 20–60 cm soil, there were no significant differences among the treatments. Redundancy analysis showed that total N, soil organic matter, and C/N were the main indicators, closely related to organic N fractions in the topsoil (0–20 cm) under nine years of biochar history. Partial least squares path modeling illustrated that NH₄⁺-N was primarily obtained from different soil organic N fractions, and the soil N supply potential of the organic N fractions differed under biochar application with chemical fertilizer. Specifically, amino acid N and hydrolyzable unknown N were the main organic N sources in the CK (fertilizer application without biochar), hydrolyzable unknown N in BC1 (15.75 t ha^− 1 of biochar blended with fertilizer), hydrolyzable unknown N and amino sugar N in BC2 (31.5 t ha^− 1 of biochar blended with fertilizer), and amino acid N, hydrolyzable ammonium N, and unknown N in BC3 (47.25 t ha^− 1 of biochar blended with fertilizer).

Conclusion

This study showed that long-term application of diverse rates of biochar history could promote soil nutrient accumulation in the topsoil, especially at 31.5 t ha^− 1, which could increase soil N stocks. These findings could provide new insights into understanding the long-term role of biochar application.