Revisiting the relationships between maize root elongation and penetrometer resistance, air-filled porosity and macro- porosity on a clay loam Mollisol

Analysis of the effects of soil penetrometer resistance (PR) on root elongation and relative classic prediction models mostly ignore the role of macropores, which are important for root to penetrate compacted soils. In this study, undisturbed soil samples were collected from an 11-years tillage experiment (no-tillage and conventional tillage) in Northeast China, and their bulk density (BD), PR, air-filled porosity (AFV), and pore-size distribution were determined. Root elongation of maize seedlings was determined on each soil cores following equilibration at -20 kPa. Our results showed root elongation is significant negatively correlated with BD, PR, and the volume of Pores _{< 6 µm}, while positively correlated with the AFV and macropores (Pores _{> 60 µm}) (P < 0.001). Root elongation rate exhibited a 50% reduction when PR was over 1.3 MPa or AFV was below 10%. A new model has been developed to estimate the rate of root elongation that taken into account the interaction between PR and macropores. The new model had a better performance than previous ones and the root mean square error (RMSE) was 0.13.