UC Davis

Agricultural stakeholders are becoming increasingly aware of the need for sustainable food systems. In a shift from an agricultural paradigm that prioritizes yield, there is now growing interest in multifunctional food systems that simultaneously promote environmental integrity while also providing adequate yield and nutrition. An investigation into how current and proposed alternatives to annual grain systems address the multifaceted objectives of food system sustainability is necessary given that annual grains currently comprise nearly 70% of earth’s cultivated land and provide majority of the world’s food. Furthermore, it is crucial to conduct research on these grain systems in highly productive and economically valuable agroecological regions, such as California (CA). As the largest and most diverse agricultural state in the U.S., CA provides market opportunities while also heralding what current and future food systems must overcome to maintain food supply amid projected water and weather extremes. Thus, we investigated the multifunctionality of a tilled annual wheat system and two proposed alternatives, no-till annual wheat production and novel perennial grain production, in the Mediterranean climate of California. We measured plant and soil parameters for three years in intermediate wheatgrass or IWG, no-till annual wheat, and tilled annual wheat at four nitrogen rates. IWG had significant fluctuations in aboveground biomass (AGB) and had the highest soil carbon (C) mineralization at each soil depth. No-till wheat had stable AGB and the highest soil C stabilization and microbial biomass in the topsoil, which suggests plant productivity and a lack of soil disturbance over time are key factors underpinning enhanced soil C stabilization and gains in microbial biomass in the topsoil. Yield stability, soil carbon storage and nitrogen use efficiency (NUE) were then compared among the three systems using a multifunctionality framework. IWG had large interannual fluctuations in grain yield and NUE, while annual wheat (till and no-till) had stable grain yields and higher NUE than IWG. Soil carbon gains in IWG and no-till wheat relative to the tilled wheat were contingent upon N fertilization and constrained to the topsoil, while tilled wheat stored carbon at depth and across the whole soil profile. Finally, soil microbial community composition and soil carbon were compared in tilled annual wheat and IWG during the final year of the experiment. Bacterial community composition was more sensitive to soil depth than crop type, whereas fungal community composition was influenced largely by crop type. While the fungi : bacteria ratio was higher in IWG at deep soil depths, tilled annual wheat had a higher abundance of fungal taxa known to positively correlate with soil carbon and higher soil carbon mass than IWG at the 60-90 cm soil depth. The two major takeaways from this three-year field experiment were: 1) sampling the subsoil (> 30 cm) is crucial when comparing system-level soil carbon storage potential of annual and perennial grain systems; and 2) plant productivity underpins numerous components of agricultural multifunctionality and thus plant adaption is of utmost importance when designing and implementing future food systems.