Converting temperate long‐term arable land into semi‐natural grassland: decadal‐scale changes in topsoil C, N, ¹³C and ¹⁵N contents

Abstract

Summary Converting arable land to permanent grassland remains an efficient option for increased carbon (C) storage in agricultural land. We quantified changes in C and nitrogen (N) in topsoil from the Sandmarken experiment (initiated in 1894 in Denmark) before and after its conversion to semi‐natural grassland in 1998. Because of different fertilizer application in the arable phase, the grass was established on soils with different initial fertility. Archived soils sampled during 1942–2012 from plots subjected to different treatments in the arable phase were analysed for C, N, 13C and 15N. With crop yields, topsoil C contents and the C‐TOOL model, we estimated mean C inputs in the arable phase of 0.4, 1.4 and 1.7 Mg C ha−1 year−1 for unmanured, mineral‐fertilized and animal‐manured plots, respectively, and C inputs in the grassland phase of 3.2–3.8 Mg C ha−1 year−1. In the arable phase, topsoil showed mean losses of 0.10 Mg C and 0.012 Mg N ha−1 year−1, whereas δ13C increased by 0.002‰ and δ15N by 0.013‰. Grassland establishment reverted losses of C and N to gains of 0.29 Mg C and 0.017 Mg N ha−1 year−1; δ13C now decreased by 0.065‰ and δ15N by 0.074‰. Fertilizer history did not affect these changes markedly. Converting this low‐yielding sandy soil from arable to grassland use provided an overall annual gain of 0.39 Mg C and 0.029 Mg N ha−1 in the topsoil. Changes in δ13C and δ15N indicated a reduced rate of C turnover and a less leaky N cycle under grassland. Highlights Assessed change in C and N storage with change in land use from arable to semi‐natural grassland Overall soil C sequestration was 0.39 Mg C ha−1 year−1 because C loss was avoided from continued arable use Soil δ13C and δ15N decreased when arable land was converted into grassland In the grassland phase, the modelled C input was not affected by fertilizer history

Roots are key to increasing the mean residence time of organic carbon entering temperate agricultural soils

“…In temperate soils, grasslands store roughly 30% more SOC than cropland soils (Poeplau et al, 2011). This SOC stock difference between croplands and perennial systems is often explained by alterations in net primary production (NPP) and its appropriation (Haberl et al, 2007), and thus total OC input differences (Hu et al, 2019; Post & Kwon, 2000). However, in central Europe, grassland NPP is similarly appropriated as cropland NPP, resulting in similar total OC inputs.…”

Spatial variability of saturated hydraulic conductivity and its links with other soil properties at the regional scale

“…Over a longer time span, conversion of arable land into grassland that can serve as carbon and water storage may be an efficient option (e.g. 67 ).…”

Cereal straw incorporation and ryegrass cover crops: The path to equilibrium in soil carbon storage is short

“…Therefore, one also may consider that incorporation of 4 Mg straw ha −1 provides an overall C sequestration of 0.43 Mg C ha −1 year −1 because this SR avoids the C loss observed for soil with straw removal (the legacy effect). Hu et al (2019) illustrated the importance of including the legacy effect in estimates of potentials for C sequestration by pointing out that overall C sequestration of land use change from arable to semi‐natural grassland consisted of both a gain due to grassland establishment and an avoided SOC loss associated with continued arable use.…”