The impact of organic amendments on soil hydrology, structure and microbial respiration in semiarid lands

- Higher microbial respiration was associated with greater hydraulic conductivity.
- Soil microbial respiration interacted with structural stability and pore size.
- Macroporosity was much more sensitive to amendments application than microporosity.
- MSW-treated soils with higher CO2 emission had more WSA > 0.25 mm and macro-pores.

Few studies have considered the effect of organic amendments on soil microbial activity and its contributions to hydraulic conductivity under field conditions in semiarid region soils with different textures and degrees of aggregate stability. This study was performed to investigate the relationship between selected soil properties and hydraulic conductivity in response to different types and application rates of organic amendments. For this purpose, urban municipal solid waste (MSW) compost and alfalfa residue (AR) were applied at different rates of 0 (control), 10 Mg ha− 1 and 30 Mg ha− 1 to clay loam and loamy sand soils under field conditions. Results show that after two years, MSW-treated soils had lower soil organic carbon (SOC) compared to those treated with AR due to higher CO2 emissions from the soils treated with MSW. Higher microbial respiration and mineralization quotient (qmC) in the MSW-treated soils resulted in higher levels of water stable aggregates (WSA > 0.25 mm) and more macro-pore fraction, leading to greater hydraulic conductivity, with larger increases at the higher rate of application (i.e. 30 Mg ha− 1). Relative to the control treatment, the application of MSW caused greater increases in microbial respiration in the clay loam soil than in the loamy sand soil, whereas the reverse was found for AR. Apart from soil texture, aggregate size was found to play an important role in controlling the carbon stock and microbial respiration of soils and consequently hydraulic conductivity. The macro-pore fraction was more sensitive than the micro-pore fraction to the application of organic amendments. Correlation analysis indicated that during the reclamation process higher levels of microbial respiration, SOC, water stable aggregates and macro-pore fraction were associated with greater soil hydraulic conductivity.