Benefits of increasing soil organic carbon to reduce drought stress in maize under climate change

Increasing frequencies and intensities of drought periods are likely to aggravate conflicts between agricultural demands and other human and ecological demands for water resources. Improving the natural soil water retention capacity can help to defuse these conflicts and at the same time strengthen climate mitigation, biodiversity, and food security. Increasing soil organic carbon content (SOC) is seen as a promising negative emission technology for the agricultural sector, with the co-benefit of potentially increasing the soil water retention capacity. We tested how different levels of SOC at varying soil depths influence in the transpiration reduction caused by drought stress (Tred_dry) in maize under current and future climatic conditions. We used the SWAP (Soil Water Atmosphere Plant) model validated utilizing information from a long-term lysimeter for a typical Swiss soil and applied it at three distinct climatic regions. A pedotransfer function (PTF) was used to indirectly assess the effects of SOC on soil hydraulic properties that affected the drought stress. Study findings revealed that increasing SOC down to 65 cm depth is beneficial to reduce drought limitations in maize. These benefits are minimal if SOC is only increased in the top 25 cm but become considerable if SOC is increased down to 65 or 135 cm depth. With a 2% addition of SOC down to 65 cm depth, a considerable average transpiration gain of 40 mm can be reached. It appears that a greater or deeper SOC addition would not return substantial extra benefits in terms of offsetting more crop drought stress rooting in the changing climate.