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 (Per_red), 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, Per_red 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.