DECOMPOSITION OF BLUE GRAMA AND ROUGH FESCUE ROOTS IN PRAIRIE SOILS

The mass of grass roots of blue grama (Bouteloua gracilis (HBK.) Lag. ex Steud) and rough fescue (Festuca campestris Rydb.) to a depth of 13 cm is similar but the carbon contents of their respective soils are q uite different. The objective of the present study was to determine so me of the physical and chemical changes of blue grama and rough fescue root masses during decomposition under both Brown (Mixed Prairie) and Black Chernozemic (Fescue Prairie) soil-forming conditions. Roots of each species in fine-mesh nylon bags were buried in the Ah horizon of both a Brown and a Black Chernozemic soil. Sixteen collections were ma de between November 1987 and June 1989 to determine diminution, loss o f dry matter and gross energy, and changes in the concentration of car bon, nitrogen, methoxyl groups, alkaline-soluble organic acids and phe nols, structural and nonstructural carbohydrates, lignin, and monosacc harides. Differences in substrate quality were only partially responsi ble for the increased decomposition of root mass in the Brown Chernoze mic soil-forming environment. Comminution of root mass was significant ly greater under the Mixed Prairie than under the Fescue Prairie condi tions for both species. The nitrogen content of blue grama roots incre ased (from 1.17 to 1.56%) while that of rough fescue decreased (from 1 .53 to 1.26%) significantly over the duration of the experiments at bo th sites. Methoxyl group content and energy levels were not useful par ameters. Organic acid, phenols, and nonstructural carbohydrate content s decreased with time. Lignin concentration displayed a significant up ward trend for both species (from 232 to 280 for blue grama and for 20 5 to 247 mg/g for rough fescue) in the Black Chernozemic soil only.