Long‐term management changes topsoil and subsoil organic carbon and nitrogen dynamics in a temperate agricultural system

Abstract

SummarySoil organic carbon (SOC) and nitrogen (N) contents are controlled partly by plant inputs that can be manipulated in agricultural systems. Although SOC and N pools occur mainly in the topsoil (upper 0.30 m), there are often substantial pools in the subsoil that are commonly assumed to be stable. We tested the hypothesis that contrasting long‐term management systems change the dynamics of SOC and N in the topsoil and subsoil (to 0.75 m) under temperate conditions. We used an established field experiment in the UK where control grassland was changed to arable (59 years before) and bare fallow (49 years before) systems. Losses of SOC and N were 65 and 61% under arable and 78 and 74% under fallow, respectively, in the upper 0.15 m when compared with the grass land soil, whereas at 0.3–0.6‐m depth losses under arable and fallow were 41 and 22% and 52 and 35%, respectively. The stable isotopes 13C and 15N showed the effects of different treatments. Concentrations of long‐chain n‐alkanes C27, C29 and C31 were greater in soil under grass than under arable and fallow. The dynamics of SOC and N changed in both topsoil and subsoil on a decadal time‐scale because of changes in the balance between inputs and turnover in perennial and annual systems. Isotopic and geochemical analyses suggested that fresh inputs and decomposition processes occur in the subsoil. There is a need to monitor and predict long‐term changes in soil properties in the whole soil profile if soil is to be managed sustainably.Highlights Land‐use change affects soil organic carbon and nitrogen, but usually the topsoil only is considered.Grassland cultivated to arable and fallow lost 13–78% SOC and N to 0.6 m depth within decades.Isotopic and biomarker analyses suggested changes in delivery and turnover of plant‐derived inputs.The full soil profile must be considered to assess soil quality and sustainability.

Species and Genotype Effects of Bioenergy Crops on Root Production, Carbon and Nitrogen in Temperate Agricultural Soil

“…Poeplau et al [61] calculated accumulations of SOC of 10 to 50% within 10 years from arable to grass and arable to woodland land use conversions, which covers the kinds of proportional increases we found here (up to 12% increase in the 0-0.3 m depth and up to 43% increase in the 0.3-1.0 m depth from 4 to 6 years). The subsoil may also be affected by land use change [61,62] and accumulation rates may be greater where the subsoil SOC stock was low initially [17]. Berhongaray et al [43] also calculated greater sequestration rates under SRC willow and poplar at 0.3-0.6 m depth compared to 0-0.3 m depth.…”

A deeper look at the relationship between root carbon pools and the vertical distribution of the soil carbon pool

“…Soil organic matter losses coincide with a shift from perennial plant systems to annual cropping systems that introduced frequent tillage, subsurface drainage, and differences in organic matter inputs, including considerably different rooting systems (Davidson and Ackerman, 1993;Huggins et al, 1998;Guo and Gifford, 2002). The effects of changes in soil management, such as increased soil disturbance and aeration, the addition of fertilizers, and changes in residue amount and quality, have often been cited as primary factors in the changes of soil organic matter from native levels (Buyanovsky et al, 1987;Huggins et al, 1998;David et al, 2009;Gregory et al, 2016). The role played by changes in rooting systems, on the other hand, is difficult to study and has received less attention.…”

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

“…The 13 C of grass sampled in 2011 and 2012 (−29.0 to −29.8‰) was 1-2‰ smaller than the 13 C for arable crops grown at the Askov Lermarken site (Bol et al, 2005;Kanstrup et al, 2011). Similarly, Gregory et al (2016) found more negative values for grass than for wheat plant material in an experiment at Rothamsted Research, Harpenden, UK. A selective accumulation of recalcitrant plant residue components that has small 13 C content (e.g.…”

“…Similarly, Gregory et al . () found more negative values for grass than for wheat plant material in an experiment at Rothamsted Research, Harpenden, UK. A selective accumulation of recalcitrant plant residue components that has small 13 C content (e.g.…”

“…In temperate climates, long‐term arable management may reduce the pre‐arable soil C content by 30 to 60% (Guo & Gifford, ; Poeplau et al ., ; Kopittke et al ., ). In particular, large losses occur when converting permanent grassland to arable rotations dominated by annual crops (Johnston et al ., ; Gregory et al ., ), with rapid losses of C in the early phase after conversion and slower losses as the arable land use continues.…”