Effects of procyanidins on corn growth and nitrous oxide reduction
Che-Jen Hsiao/Tim Griffis
Agricultural nitrogen (N) inputs stimulate the production of nitrous oxide (N2O), a long-lived greenhouse gas with a global warming potential of 298 times higher than that of CO2. Nitrous oxide concentrations have increased by 24% over the past 50 years, with expectations of further increases under future climate change scenarios. Strategies for N loss reduction while maintaining crop productivity are crucial in developing sustainable agriculture. The US Corn Belt is a significant resource for food, fiber, and fuel, but is a globally important N2O source. Procyanidins are plant-derived denitrification inhibitors that could lower N2O emissions. Denitrification, a process that converts soil nitrate to N2O and N2, can be significantly reduced by procyanidins. We have demonstrated that procyanidins reduced denitrification enzyme activity (DEA) and N2O emissions in Minnesota cornfield soils by 10-80%, depending on soil type, procyanidin application rate, crop type, and source of procyanidins. However, the sources of procyanidins in past studies were typically grape seed extracts, which are not economically viable for field applications.
Procyanidins, formed naturally in plants from catechin and epicatechin, offer a cost-effective alternative. Dr. Chi Chen’s lab has developed a method to oligomerize catechin using horseradish peroxidase (HRP; EC 1.11.1.7) and hydrogen peroxide (H2O2) in a potassium phosphate buffer at ambient conditions to produce procyanidin dimers and trimers. This method produces procyanidins at a much lower cost than the commercial grape seed extract we have used (USP Grape seeds oligomeric proanthocyanidins, Maryland, USA). In addition, our procyanidin products had greater inhibitory activities on N2O production than grape seed procyanidin extracts in the microcosm experiments. However, the impact of our procyanidin product on N2O emissions, corn growth, and soil N under field conditions remained to be measured. We hypothesize that adding our procyanidin product to soils will inhibit denitrification, increase plant available nitrate, and potentially enhance productivity.
In this project, we will first conduct a microcosm experiment to establish a dose-response relationship between our procyanidin product and its impact on soil DEA. The results will be used to determine the optimal concentration for the procyanidin application in the field. Next, we will apply our procyanidin product to corn-planted soils in 1.5 m x1.5 m x 1.2 m insulated soil columns within a climate-controlled greenhouse (hereafter the University of Minnesota Mesocosm Facility) to assess the effects of procyanidins on corn growth and N2O emission reduction. Our procyanidin solution will be evenly distributed over the soil surface, together with urea application. Overall, this project aims to evaluate the feasibility of using our low-cost procyanidin product as a soil amendment at the field scale. The results will show whether the procyanidins synthesized via our catechin oligomerization method could offer an economical and effective approach to mitigate N2O emission mitigation and enhance crop nutrition. The success of this project could stimulate more research on cost-effective procyanidin synthesis strategies. This includes incorporating enzyme immobilization and fermentation techniques, along with an expanded exploration of their applications in agriculture.
