Nitrogen dynamics affected by biochar and irrigation level in an onion field

Authors: Gao, Suduan; Wang, Dong; Rana Dangi, Sadikshya; DUAN, YINGHUA - Chinese Academy Of Agricultural Sciences; GARTUNG, JIM - Retired ARS Employee; QIN, RUIJIN - Oregon State University; TURNI, THOMAS - University Of California - Cooperative Extension Service

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2019
Publication Date: 1/7/2020
Citation: Gao, S., Wang, D., Rana Dangi, S., Duan, Y., Gartung, J., Qin, R., Turni, T. 2020. Nitrogen dynamics affected by biochar and irrigation level in an onion field. Science of the Total Environment. 714. https://doi.org/10.1016/j.scitotenv.2019.136432.
DOI: https://doi.org/10.1016/j.scitotenv.2019.136432

Interpretive Summary: Biochar has the potential to retain nitrogen (N) in soil and reduce losses to the environment, but field data are limited. This research investigated the effects of biochar and its interactions with irrigation level on N movement in soil, volatilization, and leaching losses in an irrigated onion field. Three irrigation levels (50%, 75%, and 100%) and three biochar amendment rates (0, 29, and 58 Mg/ha) were studied. Irrigation showed much larger impact than biochar on crop yield, N accumulation in soil and leaching. There were no apparent benefits to reduce ammonia and nitrous oxide emissions by biochar. Higher leaching loss was observed from high rate of biochar incorporation. Thus, irrigation management must be considered in developing practices with biochar amendment for soil and N improvement.

Technical Abstract: Soil amendment with biochar has many potential environmental benefits, but its effects on the fate of nitrogen (N) under irrigated conditions are inconclusive that warrants further investigations. The objective of this research was to determine the effects of biochar and its interactions with irrigation level on N movement in soil and environmental losses. A three-year study was conducted in an onion field. Treatments included three irrigation levels (50, 75, and 100% of a reference that provided sufficient water for plant growth) as the main treatments and three biochar amendment (0 or control, low char -applied first year at 29 Mg ha-1, and high char - added char again in second year for a total 58 Mg ha-1) as sub-treatments in a split-plot design. During the growing season, a similar amount of N fertilizer was applied three times in the first year and weekly for thirteen weeks in the second year. Ammonia (NH3) volatilization, nitrous oxide (N2O) emission, and soil pore water nitrate (NO3-) concentration during growing season as well as annual N (total and NO3-) changes in soil profile were determined for two years. Direct N leaching was collected from early spring through growing season in the third year. Ammonia volatilization was not affected by biochar amendments or irrigation levels but rather by fertilization frequency with higher total loss (5-8% of total applied) when N fertilizer was applied fewer times in larger quantities than weekly application in smaller quantities (3-4%). Not affected by fertilization frequency, N2O emissions loss was much lower (= 0.1% of applied N) for both years. Data on soil pore water N suggested highly dynamic changes in NO3-. By the end of each growing season, soil NO3- concentration increased significantly with higher accumulation from lower irrigation levels, but most of the accumulated NO3- was leached by winter rain. There was no significant biochar effect on total N gas emissions or soil nitrate accumulation, but significant irrigation effect and interaction with biochar were identified on soil NO3-. High leaching appeared associated with biochar amendment and higher irrigation level. Improvement on N management in irrigated systems must consider irrigation management strategies in developing practices associated with biochar.