Abstract
Perennial crops have been proposed as a solution to couple the production of sustainable biomass for multiple uses with several environmental benefits such as soil C storage. Concerns exist that the C sequestered in soil could be lost in a few years after the perennial crops are reverted to arable land. In this study, the current knowledge on the effects of perennial crop reversion on soil C and N was summarized by performing a meta-analysis. One year after the reversion a significant increase of soil C and N stocks (+15% and +12% respectively) were found in the 0–30 cm layer, while in the time interval between the second to fifth year after the reversion, there were no significant increases or decreases of soil C and N. The incorporation of the belowground biomass (BGB) into the soil at reversion plays a key role in the fate of soil C and N stocks after the reversion. In fact, when reverting a multiannual biomass crop there are significant losses of soil C and N. In contrast, when reverting a perennial biomass crop (PBCs) such as rhizomatous herbaceous or SRC woody crops there are no losses of soil C and N. The BGB of perennial grass is mainly composed of root systems and not of a huge amount of belowground organs as in the case of PBCs. The shredding of the BGB and its transformation as particulate organic matter (POM) represent the major pulse C input at the reversion that can undergo further stabilization into a mineral-associated organic matter (MAOM) fraction. Introducing PBCs into crop rotation resulted in an effective carbon farming solution with a potential positive legacy for food crops in terms of achievement of both climate and soil fertility goals.
Highlights
The 21st century will challenge agriculture to produce more food, energy, and goods for a growing human population while respecting the environment [1]
Considering that no significant effects of the reversion were found in the 30–100 cm layer and that this layer was not involved directly in the reversion, the subsequent analyses were limited to data obtained from the 0–30 cm layer
Ledo et al [8,30] evaluated the effect of different land-use conversion into perennial crops (PCs) on soil C, compiling a dataset of 180 studies: potentially, 112 of them are suitable for being included in our meta-analysis once reverted
Summary
The 21st century will challenge agriculture to produce more food, energy, and goods for a growing human population while respecting the environment [1]. This necessitates approaches to mitigate the impact of agriculture on climate and reduce greenhouse gas (GHG) emissions to keep the increase in global mean temperature well below 2 ◦C, and especially for the ambitious target of below 1.5 ◦C [2]. Anthropogenic perturbations that increase the decline of SOC are mainly ploughing, residue removal, monoculture, or the conversion of natural ecosystems to agricultural production [4,6]. In 2015, the “4 per mille” initiative (https: //www.4p1000.org, accessed on 28 December 2021) was launched at the COP21 in Paris, to increase SOC by 0.4% every year to compensate for the C emissions of humankind [7]
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