Microbial Responses to Compost Amendments and Water Pulses in Degraded Dryland Soils

Dryland ecosystems are integral to the global agricultural system and play an important role in soil carbon (C) storage. Despite their importance, drylands are currently facing many challenges including climate-change induced rainfall variability and soil degradation. These challenges are predicted to have effects on the soil microbial communities in drylands. Compost, an organic soil amendment, is a land management strategy that has been proposed to increase soil C storage as well as improve soil conditions in drylands, specifically in restoration and agricultural sites where degradation has affected soil properties like microbial biomass and respiration. Compost additions and rainfall variability may interact to affect soil moisture, an important catalyst for microbial activity. Assessing microbial activity responses under compost applications and variable moisture will aid in understanding how land management strategies will be affected by climate change in the future. This study investigates how soil microbial activity from a degraded dryland restoration site is affected by different compost applications amounts and variable soil moistures. A laboratory incubation study was conducted in a controlled environmental chamber for 60 days. Soils were amended with different treatments of compost (0, 0.35, and 0.70 g cm -2) and water pulses (5, 10, and 15 mm) in a full factorial design. Each treatment received the same cumulative amount of water throughout the incubation, but pulses were administered in different frequencies (every 5, 10, and 15 days). Soil respiration and soil water content were measured daily, and microbial biomass was measured at the end of the incubation to assess treatment effects on microbial activity. Microbial respiration and soil water content increased with increasing compost additions and water pulse sizes. Microbial biomass did not have consistent increases with compost additions or water pulse size. Cumulative microbial respiration was highest with the large-infrequent pulse size and smallest with the small-frequent pulse size. These results suggest that microbial activity and carbon dynamics in soils where compost amendments are used will respond to future changes in precipitation variability. The results of this study can aid in understanding how microbial activity is influenced by compost applications, which will be critical in making informed management decisions in the context of climate change.