Carbon Budget of an Agroforestry System after Being Converted from a Poplar Short Rotation Coppice

Giovanni Pecchioni,Cristiano Tozzini,Iride Volpi,Federico Dragoni,Alberto Mantino,Vittoria Giannini,Simona Bosco,Marcello Mele,Giorgio Ragaglini

doi:10.3390/agronomy10091251

Abstract

Poplar (Populus L. spp.) Short Rotation Coppice systems (SRCs) for bioenergy production are being converted back to arable land. Transitioning to Alley Cropping Systems (ACSs) could be a suitable strategy for integrating former tree rows and arable crops. A field trial (Pisa, Central Italy) was set up with the aim of assessing the C storage of an ACS system based on hybrid poplar and sorghum (Sorghum bicolor L. Moench) and comparing it with that of an SRC cultivation system. The carbon budget at the agroecosystem scale was assessed in the first year of the transition using the net biome production (NBP) approach with a simplified method. The overall NBP for the SRC was positive (96 ± 40 g C m−2 year−1), highlighting that the system was a net carbon sink (i.e., NBP > 0). However, the ACS registered a net C loss (i.e., NBP < 0), since the NBP was −93 ± 56 g C m−2 year−1. In the first year of the transition, converting the SRC into an ACS counteracted the potential beneficial effect of C storage in tree belowground biomass due to the high heterotrophic respiration rate recorded in the ACS, which was fostered by the incorporation of residues and tillage disturbance in the alley. Additional years of heterotrophic respiration measurements could allow for an estimate of the speed and extent of C losses.

Highlights

A Short Rotation Coppice (SRC) is defined as a growing multi-stemmed woody material that is subject to short rotations, usually of less than five years, and harvested using converted agricultural machinery [1]
Due to the fact that the poplar woody biomass was removed from the system through harvesting, the results showed that the C output, like the C input, was higher in the SRC than in the Alley Cropping Systems (ACSs)
Our results show that the total C content in the belowground biomass (CBGB ) is 47% in the ACS and 33% in the SRC of the total C

Summary

Introduction

A Short Rotation Coppice (SRC) is defined as a growing multi-stemmed woody material that is subject to short rotations, usually of less than five years, and harvested using converted agricultural machinery [1]. Hybrid poplars are fast growing trees suitable for SRC in Northern and Central Italy [3,4] and covered 6000 ha in 2016 [5]. Despite their high biomass potential, SRC pure stands have some limitations:. SRC-based Alley Cropping Systems integrate rows of fast-growing trees into conventional arable systems and they are currently under investigation, especially in Central Europe [10,11,12,13], while there have been few experiments with them in Mediterranean environments [14,15,16]. SRC-based ACSs, belonging to agroforestry systems, can couple the production of biomass and food, while delivering other ecosystem services, such as soil erosion reduction, improved nutrient cycling, soil faunal diversity and soil fertility conservation [17,18]

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