Crop Diversification Effects on Soil Aggregation and Aggregate-Associated Carbon and Nitrogen in Short-Term Rainfed Olive Groves under SemiaridMediterranean Conditions

Soil particle aggregation and their associated carbon (C) and nitrogen (N) content can<br> provide valuable diagnostic indicators of changes in soil properties in response to the implementation<br> of different agricultural management practices. In this sense, there is limited knowledge regarding the<br> impact of intercropping on soil organic carbon (SOC) and total nitrogen (TN) pools in aggregates. This<br> study aimed to evaluate the short-term effect (4 years) of three crop diversifications in rainfed olive<br> orchards on soil aggregation, SOC and TN concentration and SOC stocks (SOC-S) under semi-arid<br> Mediterranean conditions. Olive orchards were diversified with Crocus sativus (D-S), Vicia sativa and<br> Avena sativa in rotation (D-O) and Lavandula x intermedia (D-L) and compared with monocropping<br> system (CT). Soil samples were collected at two depths (0–10 and 10–30 cm) and analysed for soil<br> aggregate mass, SOC and TN content in aggregate-size fractions obtained by the wet-sieving method.<br> Changes caused by crop diversifications on SOC-S were also determined. Overall, after 4 years,<br> a reduction in aggregation values was observed. However, D-S increased the macroaggregates<br> (&gt;250 m) percentage, Mean Weigh Diameter values, and Geometric Mean Value in the 0–10 cm.<br> Across treatments, aggregate-associated C in 0–10 cm was higher in the D-S treatment, while in<br> the 10–30 cm soil layer, the greatest values were found in CT. Regarding the SOC-S, after 4 years,<br> significant losses were recorded under CT management in 0–10 cm (􀀀1.21 Mg ha􀀀1) and 10–30 cm<br> (􀀀0.84 Mg ha􀀀1), while D-O and D-L showed similar values to those obtained at the beginning of the<br> study. The highest increases in SOC-S were found in D-S, with an increase of 5.88% in the 0–10 cm<br> and 14.47% in the 10–30 cm. Our results showed the high potential of the diversified cropping system<br> to increase soil stability and SOC sequestration.