Intercropping dynamics in a perennial Kernza cropping system

A research agenda has been undertaken to perennialize agrarian landscapes in response to structural issues inherent to annual agricultural production, which compromise the sustainability and resiliency of cropping systems. These issues include soil erosion, nutrient runoff, declining soil organic matter stocks, and poor water relations. Two major efforts to perennialize landscapes have been initiated: agroforestry and perennial herbaceous crop improvement. The former focuses on integrating trees in existing annual cropping systems, and the latter focuses on developing perennial crop varieties to replace their annual counterparts. As it stands, these research agendas have been relatively disparate. However, their merging has significant potential for the future of perennial agricultural research. The integration of novel perennial cereal crops, such as Kernza (Thinopyrum intermedium (Host) Barkworth & D.R. Dewey), perennial rice (Oryza sativa x longistaminata), or Silphium (Silphium integrifolium (Michx.)) into agroforestry configurations could provide numerous beneficial ecosystem services that support the productivity of said perennial cereal crops as well as diversify farm income streams, provide wildlife habitat, and work towards the development and commercialization of multifunctional landscapes. While this field experiment is set within an alley cropping design, the main objective of this thesis was to determine the productivity of Kernza in monocrop and intercrop configurations. This thesis also investigated mechanisms of nitrogen provisioning and sought to reveal the processes driving productivity of Kernza when intercropped with alfalfa (Medicago sativa (L.)). Study 1 of this thesis evaluated the grain and biomass productivity of Kernza, including when intercropped with the perennial forage alfalfa. Monoculture Kernza was grown in both unfertilized and fertilized settings. Alfalfa was also grown in a monoculture. Each of these treatments was replicated four times. Data was taken on both Kernza plant development and the harvestable productivity of alfalfa and Kernza. The results of this study showed that between 2022 and 2024 the fertilized treatment produced 39.27 percent and 67.05 percent more grain than the intercropped and unfertilized treatments, respectively. It also produced 53.74 percent and 44.83 percent more Kernza biomass than each respective monoculture treatment. The alfalfa monoculture produced 63.85 percent more biomass than the intercrop treatment. However, the intercrop treatment reported higher Land Equivalency Ratios than each monocrop treatment, with the average ratio being 1.11 for 2022, 1.60 for 2023, and 1.74 for 2024. The average ratio was 1.17 when the intercrop was compared to the fertilized monocrop and 2.30 when compared to the unfertilized monocrop. Thus, the biculture of Kernza and alfalfa is a more efficient use of land over growing said crops in monoculture settings in Northern Missouri. Additionally, the biculture treatment showed a greater level of resilience to drought than the monoculture treatments, with intercrop yields only dropping by 28.3 percent during a severe drought. In contrast, the fertilized and unfertilized monocrops reported yield reductions of 59.5 percent and 83.4 percent, respectively. Study 2 evaluated N movement through a Kernza-alfalfa alley cropping system. The movement of 15N from alfalfa aboveground biomass to Kernza and pin oak (Quercus palustris (M�nchh.)) was examined across existing vegetative treatments, to simulate the provisioning of N from alfalfa utilized as a green manure. A nitrogen tracer was taken up by the alfalfa, which was mulched and applied to the Kernza and oak as a green manure alongside a control where no mulch was applied. Over one year, N transfer was documented from the alfalfa to the Kernza and oak plants, with four replications for the Kernza and two for the oak. Between mulch application and harvest, 6.79 percent of N in the Kernza leaf and 5.35 percent of N in the aboveground biomass of Kernza was provided by the mulch. After harvest, during fall regrowth, fertilization intensified, with 23.9 percent of N in the Kernza leaf being provisioned by the mulch. A lack of N transfer was found for soil and oak tissue pools. Mechanisms driving N transfer between alfalfa and these pools include the slow rate of alfalfa decomposition and physiologically determined rates and timing of N demand, mediating N mineralization and uptake rates. These findings enhanced our understanding of Kernza-alfalfa N dynamics, including the benefit of ground cover in providing this essential nutrient to perennial cereals, compared to synthetic fertilizer. Overall, this thesis aimed to frame how the two primary forms of field crop-oriented perennial agricultural research can better interact with one another and inform how novel cropping systems integrating trees and perennial cereals can help solve the challenges of contemporary agriculture. Through two experiments evaluating the ecological interactions of these systems, we found that alfalfa provides adequate N to Kernza, driving productivity for both grain and biomass. It is hoped that this thesis can provide a solid foundation for advancing ecologically intensified perennial cropping systems to meet future food security and sustainability needs.