Low-disturbance farming regenerates healthy deep soil toward sustainable agriculture - Evidence from long-term no-tillage with stover mulching in Mollisols

Dynamic responses of soil microbial communities to seasonal freeze-thaw cycles in a temperate agroecosystem

Soil freeze-thaw cycles (FTCs) are common in temperate agricultural ecosystems during the non-growing season and are progressively influenced by climate change. The impact of these cycles on soil microbial communities, crucial for ecosystem functioning, varies under different agricultural management practices. Here, we investigated the dynamic changes in soil microbial communities in a Mollisol during seasonal FTCs and examined the effects of stover mulching and nitrogen fertilization. We revealed distinct responses between bacterial and fungal communities. The dominant bacterial phyla reacted differently to FTCs: for example, Proteobacteria responded opportunistically, Actinobacteria, Acidobacteria, Choroflexi and Gemmatimonadetes responded sensitively, and Saccharibacteria exhibited a tolerance response. In contrast, the fungal community composition remained relatively stable during FTCs, except for a decline in Glomeromycota. Certain bacterial OTUs acted as sensitive indicators of FTCs, forming keystone modules in the network that are closely linked to soil carbon, nitrogen content and potential functions. Additionally, neither stover mulching nor nitrogen fertilization significantly influenced microbial richness, diversity and potential functions. However, over time, more indicator species specific to these agricultural practices began to emerge within the networks and gradually occupied the central positions. Furthermore, our findings suggest that farming practices, by introducing keystone microbes and changing interspecies interactions (even without changing microbial richness and diversity), can enhance microbial community stability against FTC disturbances. Specifically, higher nitrogen input with stover removal promotes fungal stability during soil freezing, while lower nitrogen levels increase bacterial stability during soil thawing. Considering the fungal tolerance to FTCs, we recommend reducing nitrogen input for manipulating bacterial interactions, thereby enhancing overall microbial resilience to seasonal FTCs. In summary, our research reveals that microbial responses to seasonal FTCs are reshaped through land management to support ecosystem functions under environmental stress amid climate change.

High leaching potential combined with a low leaching amount of fertilizer-derived nitrate in conservation tillage cropland of Northeast China

Stover mulching in no-tillage farming has been widely proposed as an optimized agricultural management practice to increase soil carbon storage and improve fertilizer nitrogen (N) use efficiency in current agroecosystems. However, the regulation of soil internal gross N transformation dynamics on NO3--N leaching potential in response to long-term conservation tillage practices is still lacking. Here, based on a combination of 15N-tracing incubation and in situ monitoring experiments, we investigated the effect of 9-year no-tillage and maize stover mulching on the vertical migration of fertilizer-derived NO3--N into a deeper soil profile and the associated gross NO3--N transformation dynamics in the Mollisol of Northeast China. The net positive NO3--N production rates (varied from 3.14 to 6.22 mg N kg-1 d-1) were observed across all management practices in the studied Mollisol, indicating a relatively high NO3--N leaching potential in the cropland of Northeast China, which was further confirmed by an average of 7.4 % fertilizer-derived NO3--N being vertically transferred to the 80-100 cm soil layer after a complete maize growing period. Compared with traditional ridge tillage, long-term stover mulching in no-tillage farming significantly reduced total NO3--N production by decreasing autotrophic nitrification while simultaneously enhancing total NO3--N consumption by stimulating nitrate reduction and microbial NO3--N immobilization, revealing a markedly reduction of net NO3--N production in the no-tillage agroecosystem. Therefore, converting traditional ridge tillage toward no-tillage with maize stover mulching can effectively decrease fertilizer-derived NO3--N leaching amounts and thus formulate targeted mitigation strategies for sustainable agriculture in Mollisols of Northeast China.

Effects of tillage patterns and stover mulching on N2O production, nitrogen cycling genes and microbial dynamics in black soil

Stover-covered no-tillage (NT) is of great significance to the rational utilization of stover resources and improvement of cultivated land quality, and also has a profound impact on ensuring groundwater, food and ecosystem security. However, the effects of tillage patterns and stover mulching on soil nitrogen turnover remain elusive. Based on the long-term conservation tillage field experiment in the mollisol area of Northeast China since 2007, the shotgun metagenomic sequencing of soils and microcosm incubation were combined with physical and chemical analyses, alkyne inhibition analysis to elucidate the regulatory mechanisms of NT and stover mulching on the farmland soil nitrogen emissions and microbial nitrogen cycling genes. Compared with conventional tillage (CT), NT stover mulching significantly reduced the emission of N2O instead of CO2, especially when 33% mulching was adopted, and correspondingly the nitrate nitrogen of NT33 was higher than that of other mulching amounts. The stover mulching was associated with higher total nitrogen, soil organic carbon and pH. The abundance of AOB (ammonia-oxidizing bacteria)-amoA (ammonia monooxygenase subunit A) was substantially increased by stover mulching, while the abundance of denitrification genes was reduced in most cases. Under alkyne inhibition, the tillage mode, treatment time, gas condition and interactions between them noticeably influenced the N2O emission and nitrogen transformation. In CT, NT0 (no mulching) and NT100 (full mulching), the relative contribution of AOB to N2O production was markedly higher than that of ammonia oxidizing archaea. Different tillage modes were associated with distinct microbial community composition, albeit NT100 was closer to CT than to NT0. Compared with CT, the co-occurrence network of microbial communities was more complex in NT0 and NT100. Our findings suggest that maintaining a low-quantity stover mulching could regulate soil nitrogen turnover toward proficiently enhancing soil health and regenerative agriculture, and coping with global climate change.

Can artificial ecological corridors be used for ecological restoration of cultivated land in Chinese Mollisols?

Artisficial ecological corridors (AECs) are internationally recognized as a standard method for restoring the regional ecological environment. However, the coupling relationship between AECs and soil quality has rarely been studied. Harbin, a typical mollisols region in the cold area of China, has severe soil problems and remediation is urgently needed, yet AEC research in this region is lacking. Based on the perspective of soil restoration, the construction factors of ecological corridors are quantitatively evaluated. It can predict the long-term impact of AECs already built along Harbin's Ashi River on soil chemical indices. This research studied the ecological restoration of secondary woodland, cultivated land within the ecological corridor, and cultivated land outside the influence range of the corridor under the influence of continuous recovery time and different locations in the corridor (distance from the Ashe River). Soil samples were taken from 5 plots, with a total of 161 samples, and 12 indices of soil ecological characteristics were monitored. The result are as follows: It is believed that the quality restoration of mollisols through ecological corridors has great application potential. Based on the low-cost natural restoration of ecological corridors, the highest values of total phosphorus (TP) and soil organic matter (SOM) in soil indices were detected in corridors (restored for more than 10 years). In addition, after ten years of recovery, pH and electrical conductivity (EC) in the ecological corridor returned to normal from high levels in cultivated land that far exceeded the reference values. The recovery process of mollisols mass begins to decrease, then increases, and finally reaches and exceeds the reference value of standard mollisols. The redundancy analysis of soil samples found the distance to be a key factor affecting soil total nitrogen (TN), SOM, and cation exchange capacity (CEC). Recovery time is a crucial factor affecting soil total organic carbon (SOC), pH and EC. According to the TN, SOM, and CEC mollisols indices, the ecological corridor's unilateral width is 125-150m. According to the SOC, pH, and EC indices of mollisols, the AECs should complete a natural recovery cycle of a minimum of 13 years. This study reveals the change mechanism of soil quality in mollisols area corridors based on recovery time and location. This research offer ideas and a scientific basis for worldwide governments in mollisols to formulate mollisols restoration policies.