Abstract
Precision agriculture is most effective in areas where significant in-field variation occurs. The Palouse region of the Pacific Northwest in the US, a vast area of undulating fertile farmland, has relatively high in-field variation in water retention and crop yield due to regional topography and uneven soil erosion. The regional agricultural systems depend on the soil at or near field capacity towards the end of a wet spring to support crops throughout the summer drought period. Dryland agricultural systems and high in-field variation and changing climate make water retention management practices throughout the region critical. A finite element vadose zone transport model was developed and used to understand the benefits of the targeted application of biochar on water retention and water redistribution in a representative hillslope. The model utilizes measured soil hydraulic properties to predict soil moisture distribution over the dry season. A Redwood Sawdust and Wheat Straw biochar was amended at 4% and 7% concentrations by mass. Biochar amended soils showed an increase in water retention and apparent reduction in unsaturated hydraulic conductivity as the soil approached saturated conditions. After two months of bare field evaporation, the model showed that biochar impacts water redistribution in the soil profile, contributing to positive and negative changes and a net increase in water retention. Model outputs with biochar showed increased retention in and around the amendment area, although the magnitude between outputs varied, with some samples showing minimal effectiveness. Despite the differences in magnitude with targeted biochar amendment, these results indicate that biochar can change water redistribution (up to 0.5%) in a soil profile. Additionally, the developed model shows promise as a field and regional level management tool to determine the best return on investment from biochar application when applied in a targeted manner.
•Selective biochar application in undulating land maximizes return on investment.•The optimum biochar application rate varied based on biochar type.•Finite element analysis model was used as a tool to maximize the biochar benefits.•The model predictions agreed with the observed laboratory experimental data.