Mr Rodrigo Antón1, Dr Iñigo Virto1, Dr Henar Urmeneta3, Dr Alberto Enrique1, Dra Delphine Derrien2, Dr Gregory van der Heijden2

1Departamento de Ciencias-ISFOOD, Universidad Pública de Navarra, Pamplona, Spain, 2Biogéochimie des Ecosystèmes Forestiers, INRA-Nancy, Champenoux, France, 3Departamento de Estadística e Investigación Operativa, Universidad Pública de Navarra, Pamplona, Spain

The conversion of rainfed agricultural land to irrigation is a widespread strategy for increasing yields and the variety of crops cultivated. It can also have other repercussions in the agroecosystems. From the soil functioning perspective, changes in soil organic carbon (SOC) can be expected, as not only inputs from crop residues can change, but also the conditions for incorporation and mineralization of these inputs can be affected. The objective of this study was to identify and quantify the changes induced by this land-use change in SOC dynamics in a semi-arid Mediterranean region.

A 7-years C3-C4 chronosequence on a calcareous Mediterranean soil was used for this study. Maize and wheat are grown under two different management conditions: irrigated and rainfed. The dataset includes data on SOC stock (0-30 cm), crop residues inputs and d13C signatures of total SOC and the particulate organic carbon fraction (POC, >53mm). A two-compartment model (fast and slow cycling pools) was fit on the data to provide quantitative estimates of the turnover rates of SOC in the irrigated and non-irrigated maize plots

Results show that irrigation increases SOC stocks, both total and POC fraction. This increase is related to a raise by 72±9% of plant productivity and a faster turnover rate in the fast cycling pool. Contrary to what is commonly acknowledged for acidic or neutral soil, POC is not a good proxy for the fast-cycling C pool in the studied calcareous soil. This questions the suitability of analytical methodologies to isolate POC, and calls for a revision of POC correspondence with the soil labile C pool under certain conditions.

Biography: PhD student at the Science Department-ISFOOD at Universidad Pública de Navarra (UPNA). He joined UPNA in 2013 after completing his postgraduate education at the Institut Agronomique Méditerranéen de Montpellier. Since then, he has participated in a number of projects related to soil quality and management.

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