High organic inputs explain shallow and deep SOC storage in a long-term agroforestry system – combining experimental and modeling approaches
Agroforestry is an increasingly popular farming system enabling agricultural diversification and providing several ecosystem services. In agroforestry systems, soil organic carbon (SOC) stocks are generally increased, but it is difficult to disentangle the different factors responsible for this s...
Main Authors: | , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2018-01-01
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Series: | Biogeosciences |
Online Access: | https://www.biogeosciences.net/15/297/2018/bg-15-297-2018.pdf |
Summary: | Agroforestry is an increasingly popular farming system enabling agricultural
diversification and providing several ecosystem services. In agroforestry
systems, soil organic carbon (SOC) stocks are generally increased, but it is
difficult to disentangle the different factors responsible for this storage.
Organic carbon (OC) inputs to the soil may be larger, but SOC decomposition
rates may be modified owing to microclimate, physical protection, or priming
effect from roots, especially at depth. We used an 18-year-old silvoarable
system associating hybrid walnut trees (<i>Juglans regia</i> ×
<i>nigra</i>) and durum wheat (<i>Triticum turgidum</i> L. subsp.
<i>durum</i>) and an adjacent agricultural control plot to quantify all OC
inputs to the soil – leaf litter, tree fine root senescence, crop residues,
and tree row herbaceous vegetation – and measured SOC stocks down to
2 m of depth at varying distances from the trees. We then proposed
a model that simulates SOC dynamics in agroforestry accounting for both the
whole soil profile and the lateral spatial heterogeneity. The model was
calibrated to the control plot only.
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Measured OC inputs to soil were increased by about 40 % (+
1.11 t C ha<sup>−1</sup> yr<sup>−1</sup>) down to 2 m of depth in the
agroforestry plot compared to the control, resulting in an additional SOC
stock of 6.3 t C ha<sup>−1</sup> down to 1 m of depth. However, most
of the SOC storage occurred in the first 30 cm of soil and in the
tree rows. The model was strongly validated, properly describing the measured
SOC stocks and distribution with depth in agroforestry tree rows and alleys.
It showed that the increased inputs of fresh biomass to soil explained the
observed additional SOC storage in the agroforestry plot. Moreover, only
a priming effect variant of the model was able to capture the depth
distribution of SOC stocks, suggesting the priming effect as a possible mechanism driving deep SOC dynamics. This result questions the potential of soils to store large amounts of carbon, especially at depth. Deep-rooted trees modify OC inputs to soil, a process that deserves further study given its
potential effects on SOC dynamics. |
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ISSN: | 1726-4170 1726-4189 |