Soil organic carbon and clay content as deciding factors for net nitrogen mineralization and cereal yields in boreal mineral soils

Abstract

To achieve appropriate yield levels, inherent nitrogen (N) supply and biological N fixation are often complemented by fertilization. To avoid economic losses and negative environmental impacts due to over-application of N fertilizer, estimation of the inherent N supply is critical. We aimed to identify the roles of soil texture and organic matter in N mineralization and yield levels attained in cereal cultivation with or without N fertilization in boreal mineral soils. First, the net N mineralization and soil respiration were measured by laboratory incubation with soil samples varying in clay and organic carbon (C) contents. Secondly, to estimate the inherent soil N supply under field conditions, both unfertilized and fertilized cereal yields were measured in fields on clay soils (clay 30-78%) and coarse-textured soils (clay 0-28%). In clay soils (C 2.5-9.0%), both the net N mineralization and the cereal yields (without and with fertilization) decreased with increasing clay/C ratio. Moreover, in soils with high clay/C ratio, the agronomic N use efficiency (additional yield per kg of fertilizer N) varied considerably, indicating the presence of growth limitations other than N. In coarse-textured soils, the yield increase attained by fertilization increased with increasing organic C. Our results indicate that for clay soils in a cool and humid climate, the higher the clay content, the more organic C is needed to produce reasonable yields and to ensure efficient use of added nutrients without high N losses to the environment. For coarse soils having a rather high mean organic C of 2.3%, the organic C appeared to improve agronomic N use efficiency. For farmers, simple indicators such as the clay/C ratio or the use of non-N-fertilized control plots may be useful for site-specific adjustment of the rates of N fertilization. Highlights• We aimed to identify simple indicators of inherent soil N supply applicable at the farm level.

Revisiting Biological Nitrogen Fixation Dynamics in Soybeans

“…From the first hypothesis, although higher clay contents may relate to more soil organic matter (i.e., soil organic carbon) and the potential to provide more N, net mineralization rates tend to be reduced in soils with fine texture vs. those with coarse texture due to the capability of clay protection on the decay of the organic matter (Hassink, 1997;Castellano et al, 2012). In addition, Soinne et al (2020) emphasized the role of clay in controlling the supply and mineralization of organic N. For the second hypothesis, the N fixation process has a larger demand on oxygen relative to root growth (Layzell and Hunt, 1990), with this process being more susceptible to poor soil oxygenation (Linn and Doran, 1984) which is exacerbated with high soil clay content (Schipanski et al, 2010). Lastly, this study expands on recent efforts on improving our understanding of the main factors underpinning that the N fixation process is still an unresolved task in our scientific community (Chalk, 2000;Hungria and Vargas, 2000;Borja Reis et al, 2021).…”

Effect of farm management on topsoil organic carbon and aggregate stability in water: A case study from Southwest England, UK

“…(2017) recently developed an index of soil structural quality using the ratio of SOC:clay applied to Swiss arable soils intended to support on‐farm decision‐making, which has been successfully applied by Soinne et al. (2020) and Prout et al. (2020) to farmed soils in Finland and the UK, respectively; the latter used the SOC data provided by the Countryside Survey of England and Wales in 1987.…”

Sustainability of Diversified Organic Cropping Systems—Challenges Identified by Farmer Interviews and Multi-Criteria Assessments

“…Vegetable production grown on open land corresponds to an area of 6,000 ha, and only 15% is under organic production (Statistics Sweden, 2020c). In Scania, cereal-based farming is concentrated on the open plains in the southwest, where soils generally have relatively high clay content (Piikki and Söderström, 2019) and high soil fertility (Soinne et al, 2020). Mixed farming and livestock production are distributed along with the northern and eastern parts, where less fertile moraine soils dominate and where fields are less accessible due to high levels of hinders (landscape features) and other impediment occurrences resulting in smaller sized fields.…”