Karst landscapes are distributed worldwide and cover almost 15% of the earth surface. The karst region in southwest China accounts for 5.8% of the national land area. This region is characterized by rapid organic matter loss, poor stability, and rocky desertification. Previous studies found that soil organic matter declines rapidly once natural karst ecosystem is disturbed by humans. Nevertheless, the effects of tillage practices on rapid soil carbon (C) and nitrogen (N) loss in the typical karst calcareous soil still remains unclear.

Researchers from the Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences (CAS), Guangxi Zhuang Autonomous Region, and southwest China investigated the changes of soil C or N, CO₂ fluxes, and microbial metabolic functional diversity under different tillage frequency and maize planting, which was conducted a 1-year experiment.

Researchers found that tillage at different frequencies reduced the total N (TN) content of soil from 0.43 to 0.72 g kg^-1, and TN loss mainly via the fragmentation of 5–8 mm aggregates. Nitrate (NO_3^-) declined sharply with increasing tillage. These findings highlight the importance of preserving large aggregates for maintaining the soil N pool in fragile ecosystems.

Besides, increasing tillage frequency significantly enhance CO₂ emissions in spring, summer, and autumn. This indicated that tillage practice indirectly lowered soil organic C (SOC) by reducing large macroaggregates and microbial biomass, which in turn, enhanced CO₂ emissions.

Furthermore, tillage disturbance significantly decrease microbial biomass, while maize planting significantly increase microbial metabolic activity. Maize planting with no tillage would increase CO₂ emissions through enhanced microbial metabolic activity, but, at the same time, mitigate SOC loss due to an increase in C input by crop residues and roots left in the soil.

The study was supported by the National Key Research and Development Program, the National Key Basic Research Program of China, and the National Natural Science Foundation of China.

The study entitled "Effects of tillage on soil N availability, aggregate size, and microbial biomass

in a subtropical karst region", "Effects of tillage on CO₂ fluxes in a typical karst calcareous soil", and
Microbial biomass, metabolic functional diversity, and activity are affected differently by tillage disturbance and maize planting in a typical karst calcareous soil
was published in Soil & Tillage Research, Geoderma, and Journal of Soils and Sediments, respectively. Details can be found at https://www.sciencedirect.com/science/article/pii/S0167198718312832;

Contact: WANG Kelin

E-mail: kelin@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences