The limited benefits of biochar in limited irrigation maize

Authors: RAMLOW, MATT - Colorado State University; FOSTER, ERIKA - Colorado State University; Del Grosso, Stephen - Steve; COTRUFO, M - Colorado State University

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2017
Publication Date: 12/1/2017
Citation: Ramlow, M., Foster, E., Del Grosso, S.J., Cotrufo, M. 2017. The limited benefits of biochar in limited irrigation maize. Agriculture, Ecosystems and Environment. 269:71-81. https://doi.org/10.1016/j.agee.2018.09.017.
DOI: https://doi.org/10.1016/j.agee.2018.09.017

Interpretive Summary: Biochar (a charcoal created by pyrolysis of biomass at high temperature) soil amendments have been widely promoted for their ability to improve soil fertility in degraded tropical soils and irrigation and fertilizer use efficiency in fertile temperate agricultural systems. Here, we evaluate if a biochar made form wood can produce both agronomic and environmental benefits by ameliorating water stress in deficit irrigation systems, improving crop nitrogen uptake and mitigating greenhouse gas emissions. To evaluate these responses, we established a corn field trial under deficit irrigation treatments with biochar amendment. Irrigation treatments included recommended irrigation (full), recommended irrigation except for non-essential growth phases (limited) and 50% of recommended irrigation (drought). We measured biomass and grain yield, grain nitrogen uptake, soil water content, soil carbon storage and nitrous oxide gas emissions. Drought treatments reduced both grain and biomass yield while limited irrigation showed no significant yield reduction relative to full irrigation. Biochar amendments did not provide any yield improvements. Biochar amendments improved soil moisture by 9.7% over the field season and increased water retention by 7.4%. However, these increases failed to alleviate plant water stress. Biochar delivered significant carbon storage potential and provided a 16.6% reduction in cumulative nitrous emissions across irrigation regimes but was not statistically significant due to high spatial variability in gas fluxes. Both biochar amendments and limited irrigation treatments reduced yield scaled nitrous oxide emissions. This research highlights the importance of targeting biochar application to reduce crop water stress and confirms the diminished potential of biochar to reduce nitrous oxide emissions in field sites.

Technical Abstract: Biochar soil amendments have been widely promoted for their ability to improve soil fertility in degraded tropical soils and irrigation and fertilizer use efficiency in fertile temperate agricultural systems. Here, we evaluate if a woody biochar can produce both agronomic and environmental benefits by ameliorating water stress in deficit irrigation systems, improving crop nitrogen uptake and mitigating greenhouse gas emissions. To evaluate these responses, we established a maize field trial under deficit irrigation treatments with a woody biochar amendment. Irrigation treatments included recommended irrigation (full), recommended irrigation except for non-essential growth phases (limited) and 50% of recommended irrigation (drought). We measured biomass and grain yield, grain N uptake, mineral N mobility, soil water content, soil field capacity, soil C sequestration and N2O emissions. Drought treatments reduced both grain and biomass yield while limited irrigation showed no significant yield reduction relative to full irrigation. Biochar amendments did not provide any yield improvements. Biochar also did not alter mineral N availability within the soil profile or grain N uptake. Biochar amendments improved soil moisture by 9.7% over the field season and increased water retention by 7.4%. However, these increases failed to alleviate the water stress coefficient, an index of how much the water content has dropped below the management allowable depletion, which was best correlated with yield. Biochar delivered significant C sequestration potential and provided a 16.6% reduction in cumulative N2O emissions across irrigation regimes but was not significant due to high spatial variability in N2O fluxes. Both biochar amendments and limited irrigation treatments reduced yield scaled cumulative N2O emissions. This research highlights the importance of targeting biochar application to reduce crop water stress and confirms the diminished biochar N2O emission reductions in the field relative to lab incubations due to drier field conditions and grain N uptake.