Influence of woodchip size and nitrogen fertilization on carbon dioxide and nitrous oxide emissions from soils amended with orchard biomass

Authors: Gao, Suduan; Hendratna, Aileen; Thao, Touyee; CULUMBER, MAE - University Of California - Cooperative Extension Service; Poret-Peterson, Amisha; ZUBER, CAMERON A.T. - Cooperative Extension Merced County; HOLTZ, BRENT - University Of California - Cooperative Extension Service

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2024
Publication Date: 2/25/2024
Citation: Gao, S., Hendratna, A., Thao, T., Culumber, M., Poret-Peterson, A.T., Zuber, C., Holtz, B. 2024. Influence of woodchip size and nitrogen fertilization on carbon dioxide and nitrous oxide emissions from soils amended with orchard biomass. Soil Science Society of America Journal. 1-13. https://doi.org/10.1002/saj2.20650.
DOI: https://doi.org/10.1002/saj2.20650

Interpretive Summary: Whole orchard recycling (WOR) is a conservation practice that can incorporate up to 80 tons per acre orchard biomass as woodchips into soil to increase soil organic carbon (SOC), improve soil properties, and recycle nutrients, but there is a wide concern over nitrogen (N) immobilization and greenhouse gas (GHG) emissions from woodchip decomposition. This research investigated how woodchip particle size could affect C and N dynamics by interacting with N fertilization in an eight-month incubation experiment. Results showed that woodchip particle size strongly affected woodchip decomposition rates, carbon dioxide (CO2) and nitrous oxide (N2O) emissions as well as SOC and soil C and N. The smallest woodchips (<1.6 mm) enhanced initial decomposition with the highest CO2 emission rates but released lowest total emissions and increased SOC in the end. Larger woodchips (>1.6 mm) showed lower initial decomposition rates, reduced the initial N immobilization risks, but released higher total CO2 due to higher emission rates than the smallest woodchips at later times. Nitrogen fertilization suppressed woodchip decomposition by reducing CO2 emissions in larger woodchips (8-9%) compared to the smallest woodchip size (1%). This research increased our understanding on woodchip decomposition affected by woodchip size that can be used in WOR management.

Technical Abstract: Incorporating large amounts of woody biomass into soil, such as in whole orchard recycling (WOR), can promote carbon sequestration, nutrient recycling, and ecosystem health in agricultural fields. Yet uncertainty regarding the effects of WOR on soil carbon (C) and nitrogen (N) dynamics remains a critical concern, which can influence farm management decisions. The objective of this research was to evaluate the effects of woodchip (WC) size and interaction with N fertilization on carbon dioxide (CO2) and nitrous oxide (N2O) emissions. An eight-month controlled laboratory incubation experiment was conducted, which incorporated WC (4% w/w, equivalent to ~40 ton per acre) in four sieved sizes (0.2–1.6, 1.6–3.2, 3.2–6.4, and 6.4–12.7 mm) with and without N fertilizer applications. All treatments with WC showed a similar pattern in CO2 emissions, with peak emissions observed within the first week that decreased drastically afterward. The occurrence of the peak delayed as WC Size increased. The peak increased significantly as WC size decreased, while total CO2 emissions showed a different trend. The finest WC (<1.6 mm) yielded the lowest total CO2 emissions, but increased soil C the most. Nitrogen application reduced total CO2 emissions by 1% in the smallest WC size and by 8-9% for those larger than 1.6 mm. The N2O emissions spiked following each fertilizer application with lowest total emissions from the smallest WC size, suggesting substantial N immobilization. The results imply that larger WC sizes can delay C mineralization and reduce initial N immobilization risks, but the smallest WC size may have stabilized and increased SOC, which relies on further examinations. This research increased our understanding on WC mineralization that can be used in WOR management.