Mulching improves soil-plant water status and yield in experimental drought conditions

Climate change-driven drought events are becoming increasingly common across Europe. These events can dramatically affect crop production, leading to significant yield losses and an overall deterioration of yield quality. Furthermore, irrigation is often not possible or allowed during long drought periods due to water scarcity. This problem requires crop management adaptations that provide more stable yields during challenging environmental conditions. To this end, organic mulch materials are being used as an agroecological solution. However, the effects of this management practice are not always straightforward, which has led to contradictory observations regarding their effect on crop yield. Here, we investigate the effect of applying an organic grass-clover mulch layer on the soil-water relations of celery (Apium graveolens Tango L.) during an extreme drought event. A full-factorial setup was used with (i) plants growing on a rainfed field with supplementary irrigation and plants subjected to drought using a movable rainout shelter and (ii) soil with and without organic mulch. Based on soil moisture and soil water potential sensors, and below-ground ERT (Electrical Resistivity Tomography) measurements, it was observed that the soil below mulched areas maintained a higher soil water content for a longer period of time compared to the soil in areas without mulch. Plant growth was monitored over time by combining manual measurements and drone data. Plants subjected to drought with mulch were significantly larger compared to plants without mulch, resulting in yields comparable to rainfed fields without mulch. Furthermore, the stomatal conductance and leaf water content of plants in mulched fields tended to be higher compared to plants in fields with no mulch. However, rainfed fields with mulch provided an even higher yield, indicating that the positive effects of the organic mulch were probably also mediated by a buffered soil temperature and an additional nitrogen input. Overall, organic mulch appears to buffer the soil-plant water relations of celery during drought, providing more stable yields under a changing climate.