Experimental study of the effect of tillage gradient along the slope transect on soil respiration rates under agricultural fields of Indian Himalaya

Soil erosion-induced redistribution of soil organic carbon (SOC) plays a crucial role in shaping the net carbon exchange between the soil and atmosphere, with ongoing debates surrounding the overall direction of this exchange. Within the field landscape, tillage-induced soil redistribution and SOC stocks along the slope transect alter the spatial variation in respiration rates and influence SOC storage. The primary objective of this study is to analyze the impact of tillage gradients along the slope transect on soil respiration rates and carbon storage. Utilizing the data from a long-term simulated agriculture experiment field spanning nearly a decade, we quantified the effects of different tillage and erosion gradients on soil respiration rates and carbon storage within the globally significant region of the Indian Himalayas. The soil respiration rates were measured in weekly intervals from different tillage practices- No-till (NT), Minimum tillage (MT), and Conventional tillage (CT); the measurements were taken continuously from the field surfaces of each practice along the slope transect (from upslope to downslope) for five years, from 2018 to 2022. Daily measurements were undertaken before and immediately after tillage during Maize and Wheat crop cycles, using a portable infrared gas analyzer EGM-5 (Environmental gas monitor; PP System). Additionally, we analyzed the concentration of SOC using a CHN analyzer at alternate yearly intervals from 2016 to 2022. Our findings reveal that, following five years of continuous field measurements of soil respiration rates, the downslope position of CT and MT exhibited higher rates than the eroding midslope position. Remarkably, despite higher soil respiration at the downslope, SOC stock at this position surpassed that of the midslope within CT. This observation underscores the tillage-induced redistribution of SOC, deposition at downslope positions, and the simultaneous enhancement of mineralization on carbon storage. This study interprets valuable insights into the continuous burial of SOC at downslope, resulting in enhanced Carbon storage despite enhanced mineralization rates at Conventional Tillage. In conclusion, the increased SOC stock at the depositing downslope of CT, coupled with heightened mineralization, significantly contributes to soil erosion-induced net carbon sequestration.