Alfalfa root and shoot mulching effects on soil hydraulic properties and aggregation

Although alfalfa (Medicago sativa L.) stands have been reported to improve soil physical properties, little is known about the specific influences of above- and belowground alfalfa components on soil physical properties. A 2- yr study was conducted to investigate alfalfa roof and shoot mulch modifica tions of soil physical properties and water movement in the root zone of a Kalamazoo loam soil (fine-loamy, mixed, mesic Typic Hapludalf) in southwest Michigan, Four treatments were considered: bare fallow (BF), bare fallow w ith alfalfa shoot mulch (BFSM), alfalfa with shoots removed and roots remai ning (AR), and alfalfa with alfalfa shoot mulch (ASM). Volumetric soil wate r contents were measured by time domain reflectometry (TDR). Development of fine roots was monitored by minirhizotron technology. Alfalfa root systems increased saturated hydraulic conductivity (K-sat) by 57%, total and macro porosities by 1.7 and 1.8%, respectively, and water recharge rate of the so il profile by as much as 5.4% per day. These effects of alfalfa roots on so il porosity were mainly attributed to increased amplitudes of wetting and d rying cycles and high rates of root turnover in the Ap horizon. K-sat was s ignificantly correlated with macroporosity (r = 0.90, P less than or equal to 0.01). Mean weight diameter (MWD) of aggregates From bare fallow soils w as 20% higher when alfalfa shoot mulch was applied, Our results suggest tha t aggregate stability was more affected by C sources from shoot mulch and r oot turnover than by factors specific to root activities such as physical e nmeshment of aggregates and increased soil wetting and drying cycles.