Paddy rice ecohydrology pattern and influence on nitrogen dynamics in middle-to-high latitude area

- Soil water (SW) in rice field of middle-to-high latitude area was analyzed.
- SW content presented special temporal-vertical patterns in cold condition.
- Soil temperature forced SW transported with N in surface and subsurface water.
- Ponding on the impermeable soil layer is critical for rice growth in this area.

SummaryPaddy rice in middle-to-high latitude areas has a longer growing period with lower temperature. Therefore, it was hypothesized to have a different soil ecohydrology pattern and nitrogen (N) efficiency. Based on daily monitoring of soil moisture and N concentrations in soil water at four depth layers, the characteristics and their ecohydrological interactions, soil environmental indexes and N dynamics were analyzed. The temporal-vertical observations of soil moisture and soil water acquisition rates demonstrated the existence of an impermeable soil layer at 30 cm, which had lower soil organic carbon content. The soil moisture greater in the upper layer had higher soil organic carbon content, which provided the critical conditions for the rice tillage. Lower than the 60 cm depth, the soil moisture increased and had a peak acquisition rate of approximately 0.0075 cm3 s−1. The concentration of NO3−-N in the water at the soil subsurface was approximately 2.4 times than that of NH4+-N. The NO3−-N had a larger concentration at the deeper layer as a result of downing leaching, but the NH4+-N had a greater concentration in the tops soil layer than the other depths. The soils under the influence of freeze-thawing had the largest TN concentration in surface water at the end of April, which was about three times than that of the peak during the growing period. This study aligned the interactions between the N dynamics with soil microclimatic factors such as temperature, water pH and moisture across the 90 cm profile. The temporal-vertical pattern of soil moisture and the N in soil water provided evidence for the hypothesis that the soil ecohydrology dynamics in this area. These findings were of particular significance to understanding the impacts of paddy rice ecohydrology with N dynamics in middle-to-high latitude areas, which can help to optimize the N availability and water efficiency.