Influence of compost and biochar on soil biological properties under turfgrass supplied deficit irrigation

Abstract

Turfgrass landscapes are commonly maintained using deficit irrigation. Here we follow-up a prior study, which surveyed turfgrass establishment in plots amended with biochar or compost or a mixture of both and unamended control plots. Following establishment, the plots were differentially irrigated at either full (85% ETo replaced) or deficit (50% ETo replaced) levels for four years and sampled for analysis. Relationships between soil chemical parameters and microbial community biomass and profiles based on phospholipid fatty acid analysis and high throughput sequencing of bacterial/archaeal 16S rRNA genes were determined. Compared to the unamended control soils, compost amended soils with or without biochar underwent greater shifts in soil physiochemical and biological properties than those receiving biochar. Although the impact of compost on the microbial community lessened with time, even 5 years after its incorporation, compost amended soils had increased microbial biomass by 127% and 157% in full and deficit irrigated plots compared to unamended plots. Bacterial/archaeal communities compositionally were more divergent in response to deficit irrigation in the unamended soils than in those amended with compost or biochar. Both soil amendments resulted in reduced relative abundances of nitrifying bacteria and archaea. In compost-amended soils many taxa associated with plant growth promotion and carbon cycling increased in relative abundance, whereas no such effect was observed with biochar. Altogether, these results provide mechanistic insights into how organic amendments affect turfgrass systems and their associated soil microbial communities under full and deficit irrigation regimens.