My Jastro grant was used to support me in my research to look at how soil organic carbon management effects wheat yield and nitrogen losses—specifically nitrous oxide. Carbon and nitrogen cycling are tightly linked in agricultural soils and there is increasing evidence that greater soil organic carbon (SOC) inputs may negatively impact soil nitrous oxide emissions. In this study, we are examining these potential tradeoffs through the planting of wheat in a controlled greenhouse trial.

Soil samples were taken from the University of California’s West Side Research and Extension Center (UCWSREC) in Five Points, CA. These agricultural fields had been part of a 22-year study conducted by Jeffrey Mitchell that examined improvements in soil health between cover cropping/no-till systems and conventionally tilled systems in arid regions. As a result, we were able to take soil cores (12’’ diameter x 10’’ depth) from soils of known soil organic carbon (SOC) levels. The no-till cover cropped cores represent the higher SOC samples, and the conventionally tilled, no cover crop cores are the lower SOC samples. Over the course of this study we will apply nitrogen fertilizer at three different rates (0, 100, and 200 kg/ha).

Over the duration of the study period, the pots will be planted with 8 wheat plants that are evenly spaced in a circle within the pots. In the center of these pots we have placed a 4’’ diameter PVC ring upon which a gas flux chamber will be placed during sampling periods. This ring will remain in the pot the entire length of the trial to minimize disturbance.

We developed the methodologies for the sampling and growing conditions based on similar research, although most studies of this type occur in the field. Therefore, adapting methodologies from the field to the greenhouse has been a major part of this project. However, the methodology has been set and we are now in the implementation phase of the project.

Starting in early February the cores will be prepped for planting and the first gas samples will be taken. Soil samples will then occur at minimum once per week through the trial period, and more often after fertilization events. Samples will be analyzed for nitrous oxide fluxes over time using a gas chromatograph.

Anticipated results will provide an indication of how managing for SOC will impact yield, nitrogen fertilizer requirements, and nitrogen losses in soils. As communities here in California and beyond implement more soil fertility-based strategies for mitigating climate change, it will be important to understand how to balance all of these processes and inputs within the soil profile.

The data collected from this study can be used to develop baseline management strategies for future projects and inform the development of soil health practices not just in California, but in farming communities around the world. The overarching objectives are widely applicable to farming systems around the world. Climate change mitigation and soil fertility are issues that are at the forefront of conversations at the global level. The data from this research project, and the conclusions that are drawn from it, can help inform conversations on the role of soil fertility, SOC, and nitrogen cycling in food security.
 

In addition to funding from the Henry A. Jastro Graduate Research Award, this project would not be possible without the help and support of multiple people: Dr. Jeffrey Mitchell and his crew down at WESREC provided access to their fields and assisted with two long days of soil sampling. Bruno Pitton allowed us to use his flux chambers and PVC collars. Dr. Bruce Lindqust has provided access to his lab and gas chromatograph for sample analysis. Last but not least, my advisor Dr. Cameron Pittelkow and my fellow lab mates, Zhang Zhenglin and Santiago Tamagno, have assisted in sampling, methodology planning, and hours of assistance in getting this project up and running.