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Organic Nitrogen Management for Greenhouse Gas Reduction in Agroecosystems

Nutrient inputs to agricultural soils as animal manure or green cover crops can add large quantities of co-located labile carbon (C) and nitrogen (N).

Animal manure is often applied in cropland around CAFOs. Both manure and cover crops are often used as fertility inputs in organic agriculture. These organic amendments are often considered slow-release fertilizers for N (when low in ammonium) when compared with synthetic fertilizers, because organic N needs to be mineralized by soil microbes for that N to become available to plants. Ideally, when N mineralization and crop N uptake are well balanced, mineral N does not accumulate in the soil. One can visualize the process as a conceptual seesaw that goes down on one end due to N mineralization that adds mineral N, but that is gently returned to the horizontal position through N uptake that removes the mineralized N.

However, it is challenging to manage annual crop production on such bucolic rhythm. And when considering nitrous oxide (N2O), a powerful greenhouse gas, the gentle seesaw may well be a catapult. Why? Mainly for two reasons. First, easily decomposable residues can trigger high microbial activity that consumes oxygen (O2) and creates hypoxic pockets (or layers) in the soil while organic N is being mineralized. Second, the composition of the organic amendments is hard to control, in part because the composition of cover crops varies and in part because the composition of manure varies. A rational response by farm operators is to overshoot the application rate to avoid N shortages. These two conditions have the potential to favor large N2O emissions in bursts resembling catapult releases, because without fast mineral N uptake (or even with it) N mineralization is not lowering a seesaw but tensing and loading the denitrification catapult.

In this seminar, Dr. Armen Kemanian (Professor, Production Systems and Modeling, Department of Plant Sciences at Penn State University) presents field data obtained in Central Pennsylvania and in Sardinia, Italy, that indicates that large N2O emissions do happen in cover cropped and manured soils, particularly with inversion tillage that buries and packs manure or cover crops residues in a thin soil layer. This research suggests that controlling the rate and timing of organic input additions, as well as preventing the co-location of legume cover crops and manure, could mitigate N2O emissions.

About Dr. Kemanian

Dr. Kemanian’s research program seeks to develop and promote productive and environmentally friendly agroecosystems. His research program combines model development and application with foundational research on the carbon and nitrogen cycle, biomass crops and polycultures deployment, and agroecosystem and landscape design. Understanding, modeling, and developing technologies to control soil carbon storage and nitrous oxide emissions have been a major component of Dr. Kemanian research portfolio.

Event Date Start-End

March 08, 2022 / 09:00 AM - March 08, 2022 / 10:00 AM