Cover Crop Root Contributions to Soil Quality in an Organic Maine Agroecosystem

Root Length Density (RLD) and evolution of inorganic nitrogen from decomposing cover crop root systems in soil were measured within several different crop rotational systems used in Maine and the Northeast in order to quantify the distribution of cover crops roots in the soil profile and root relationship to nitrogen availability for cash crops following a winter cereal cover or legume sod in rotation. RLD was measured for one-year red clover (RCl), two-year old red clover (RC2) stands, and two winter rye (WR) stands within two different rotations (WR-WCC and WR-AYCC) planted the previous fall. RLD was determined immediately prior to tillage. Roots from the treatments were also exhumed and incubated with soil for 70 days at 60°C, over which time inorganic nitrogen was measured to determine nitrogen release from the roots during decomposition. Field and greenhouse grown roots were analyzed for C, N, cellulose, hemicellulose and lignin. As red clover aged it increased significantly in lignin, from 2.57% to 9.9% and decreased significantly in total N by 0.6%. Winter rye had significantly higher C invested in cellulose and hemicellulose and contained a third of the total N found in red clover roots. Incubations of root material from the field exhibited significant differences between treatments in amount of NH~' present, due mainly to the species and age of the root and less to the length of root incorporated. The legumes were consistently higher than winter rye in NH~' release over the incubations. RC2 mineralized more net N in the incubations than RCI, probably due to the denser root material and damage incurred by the clover root borer (Hylastinus obscurus Marsham) prior to root harvest. RLD in 0-5 cm was high for all cover crops and showed no significant differences (a=0.05) between species. There was significantly higher RLD for WR-WCC in the 5-20 cm strata in 2004 and 2005 as well as in the 20-50 cm strata in 2004. Coarse roots were detected only in the red clover treatments and no difference was found between red clovers of different age with respect to coarse RLD. Total cover crop biomass and cover crop roots only incorporated at tillage had no significant differences on broccoli harvestable yield production or biomass production. There were not significant differences in soil mineral N over the season between soils with roots only or total biomass incorporated.