Abstract
Barley (Hordeum vulgare L.) was grown in a greenhouse under a combination of treatments that tested the effects of two types of biochar amended with fermentation solids and dairy lagoon effluent at high and low levels of phosphorus fertilization. We hypothesized that a modified biochar dosed with iron in combination with a dairy amendment would yield the greatest photosynthetic assimilation rates of CO2 and water use efficiency. Furthermore, we hypothesized that these rates may differ between photosynthate demand represented by plant developmental stages, specifically the tillering, stem elongation, and heading stages. We found that photosynthetic assimilation was greatest at the tillering stage. Plant water use efficiency increased with commercially available fertilizer. Plant biomass at harvest was greatest among the chemical fertilizer (high and low levels of phosphorus fertilization) and low-level fertilization of dairy lagoon, fermentation solid, and an iron dosed biochar. The results suggest that while the dairy-amended biochar can maintain plant growth, it is not necessarily achieved through improved photosynthesis or water use.