Changes in soil organic carbon under perennial crops

This study evaluates the dynamics of soil organic carbon (SOC) under
perennial crops across the globe. It quantifies the effect of change from
annual to perennial crops and the subsequent temporal changes in SOC
stocks during the perennial crop cycle. It also presents an empirical
model to estimate changes in the SOC content under crops as a function
of time, land use, and site characteristics. We used a harmonised global
dataset containing paired-comparison empirical values of SOC and
including different types of perennial crops (perennial grasses, palms,
and woody plants) with different end-uses: bioenergy, food, other bioproducts, and short rotation coppice crops. Salient outcomes include: a
20-year period encompassing a change from annual to perennial crops
led to an average 20% increase in SOC at 0-30 cm (6.0 ± 4.6 Mg ha-1
gain) and a total of 10% increase over the 0-100 cm soil profile (5.7 ±
10.9 Mg ha-1). A change from natural pasture to perennial crop
decreased SOC stocks by 1% over 0-30 cm (-2.5 ± 4.2 Mg ha-1) and
10% over 0-100 cm (-13.6 ± 8.9 Mg ha-1). The effect of a land use
change from forest to perennial crops did not have significant impacts,
probably due to the limited number of plots; but the data indicated that
while a 2% increase in SOC was observed at 0-30 cm (16.81 ± 55.1 Mg
ha-1), a decrease of 24% was observed at 30-100 cm (-40.1 ± 16.8 Mg
ha-1); perennial crops generally accumulate SOC through time,
especially woody crops; and temperature was the main driver explaining
differences in SOC dynamics, followed by crop age, soil bulk density, clay
content and depth. We present empirical evidence showing that the FAO
perennialization strategy is reasonable, underscoring the role of
perennial crops as a useful component of climate change mitigation
strategies.