Does intercropping improve soil aggregation and organic carbon protection? A case-study in the Semi-Arid Mediterranean

Abstract

Intercropping has been claimed to improve the soil structure and soil quality, however its effects on soil fertility parameters in semi-arid Mediterranean agroecosystems remain unclear. The objective of this study was to assess whether intercropping and its combination with N fertilisation are adequate practices to improve the soil aggregate stability and organic matter quality. An irrigated on-farm experiment was established in northeastern Spain to evaluate the effect of seven cropping systems (faba bean-durum wheat, pea-durum wheat, and rapeseed-pea intercropping and the respective sole crops) and two N-fertiliser rates (0 vs. 75 kg N ha−1). Several soil variables were analysed in bulk soil: water-stable macro- and microaggregates, soil organic carbon (SOC), soil total nitrogen (STN), reduced permanganate (Perred), particulate organic matter (POM) and carbon (POC), mineral-associated organic matter (MAOM) and carbon (MAOC) and microbial biomass carbon (MBC) and nitrogen (MBN). Also, SOC, Perred and nitrogen (N) storage within aggregates were determined. Intercropping did not increase the share of water-stable aggregates nor SOC levels, but SOC concentration was higher in macro- (2.34 g C 100 g−1) than in microaggregates (1.89 g 100 g−1). Intercropping did also not affect STN, but the mineral N-fertilised treatment increased both SOC (2.24 vs. 2.08 g 100 g−1) and STN (0.193 vs 0.177 g 100 g−1) significantly in bulk soil. This study showed that after a few years upon establishment, intercropping had not enhanced the soil aggregate stability significantly and as a sole practice intercropping does not improve soil C and N concentrations nor their active fractions.

This work has been funded through the Spanish State Research Agency (aid PCI2020-112297 funded by MCIN/AEI/10.13039/501100011033 and the European Union Next Generation EU/PRTR) within the framework of PRIMA Foundation, call 2019-Section 2\u2014BIODIVERSIFY (Boost ecosystem services through high Biodiversity-based Mediterranean Farming systems), a program supported by the European Union; and the LegITIMada project (2023 CLIMA 00018) through the Departament de Recerca i Universitats, the Departament d\u2032Acci\u00F3 Clim\u00E0tica, Alimentaci\u00F3 i Agenda Rural and the Fons Clim\u00E0tic of the Generalitat de Catalunya. Daniel Plaza-Bonilla is Ram\u00F3n y Cajal fellow (RYC-2018-024536-I) co-funded by MICIN/AEI/10.13039/501100011033 and European Social Fund. Marie Reichmann thanks the European Union for the funding granted to carry out her Master Studies in which context this work was developed. We greatly acknowledge Ramon Pujol Chambert and Ramon Pujol Figueras from Jolbertal SL for the cooperation while carrying out this research in their fields and with their machinery. We also kindly thank Silvia Galit\u00F3, Andreu Dago Malgrat, Josep Maria Perera Llovera, Julia K\u00F6lker, Lucie Jean-Marius and Marta Nadal Arabia for their support in the field and lab.