Managing Irrigation for Multiple Goals in Organic Systems: Integrating Productivity with Sustainability.

The current drought has incentivized the adoption of more efficient irrigation technology such as subsurface drip irrigation (SSD) to improve yields and water use efficiency of organic processing tomato systems. However, questions remain about the long-term sustainability of this practice and potential tradeoffs for harnessing and building soil health. We will present results of a two-year experiment comparing the impact of various irrigation strategies (single drip, double drip and furrow) on indicators of sustainability, productivity and soil-health-building mechanisms in a tomato-corn organic system at Russell Ranch, a unique long-term trial located at UC Davis. We found no reduction in yields under drip despite concentrated N resources and a sharp decrease in biologically active soil surface in time and space. Although improving water use efficiency is of major importance, we observed potential tradeoffs of drip irrigation on agricultural sustainability of organic tomato production over both short and longer terms. For instance, striking reductions in root size, aggregation and aggregate size under drip might reduce the system’s ability to sequester carbon. Since drip systems provide numerous other benefits such as decreased N-based GHG emissions and weed pressure, a thorough assessment for organic growers and the environment is critically needed.