Soil, and Carbon, and Crops…Oh My!
Sophie Smith weight soils in the Greenhouse lab for carbon fractionation.
As a vital ecosystem that sustains plants and animals, soil is one of the most (if not the most) crucial aspect of an agricultural system. Therefore, maintaining good soil health is crucial to any farming operation [1]. One of the many ways to accomplish this is by using cover crops. Cover crops are unharvested plants that are used to provide a variety of ecosystem services, such as erosion control, increased water retention, improved soil structure stability, increased soil carbon storage, and more [2]. These crops can be implemented into almost any cropping system to improve overall soil health during times of the year when cash crops are not typically grown [2].
My time in the Tully Agroecology Lab has been focused on assessing long-term soil organic carbon dynamics among five unique cropping systems with varying degrees of cover crop use in each rotation, along with other variations in management (i.e. tillage, manure inputs, crop rotation length). Cover crop use among these five systems includes cereal rye after corn, a vetch and cereal rye mix after soybean or wheat, and triticale in between years of perennial alfalfa [3]. This project is critical in understanding best management practices to build soil organic carbon in agricultural operations.
My own work in the lab has included a series of soil processing tasks, or preliminary steps, that must be completed to determine the carbon content and storage capacity of the soil. The first of these steps involves fractionating soils, a process which involves wet sieving the soil to distinguish and sort the different aggregate sizes using a set of mesh strainers decreasing in size [4]. At the end of this process, holistic soil samples have been separated into one of the following categories: large and small macroaggregates, microaggregates, silt and clay, and floating particulate organic matter. The separated soil aggregates are then dried and weighed for greater comprehension of the soil sample’s overall stability as well as the carbon stabilized within these fractions [4].
Once aggregates are dried and weighed, the next part of my work is to prepare the aggregates for carbon analysis. I finely grind the samples, sieve out any sand particles (>250 um), and weigh tiny subsamples (0.25 g) that are then packed to be sent to another lab for elemental combustion. This process will tell us the percentage of organic carbon contained within the soil aggregate in question, allowing for a greater understanding of which management practices are most beneficial for building soil health.
References:
[1] Allen, Diane E., et al. “Soil Health Indicators Under Climate Change: A Review of Current Knowledge.” Soil Biology, vol. 29, 3 June 2011, pp. 25–45., https://doi.org/10.1007/978-3-642-20256-8_2.
[2] Schipanski, Meagan E., et al. “A Framework for Evaluating Ecosystem Services Provided by Cover Crops in Agroecosystems.” Agricultural Systems, vol. 125, Mar. 2014, pp. 12–22., https://doi.org/10.1016/j.agsy.2013.11.004.
[3] Cavigelli, M., Spargo, J., & Teasdale, J. “Increasing Crop Rotation Diversity Improves Agronomic, Economic, and Environmental Performance of Organic Grain Cropping Systems at the USDA-ARS Beltsville Farming Systems Project.” Crop Management, vol. 12, April 2013. https://doi.org/10.1094/CM-2013-0429-02-PS
[4] Six, J., et al. “Soil Structure and Organic Matter I. Distribution of Aggregate‐Size Classes and Aggregate‐Associated Carbon.” Soil Science Society of America Journal, vol. 64, no. 2, Mar. 2000, pp. 681–689., https://doi.org/10.2136/sssaj2000.642681x.