NODULATION AND ROOT GROWTH OF FORAGE LEGUMES SOWN INTO TALL FESCUE SWARDS

Authors: Staley, Thomas; Belesky, David

Submitted to: Grass and Forage Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2004
Publication Date: 11/1/2004
Citation: Staley, T.E., Belesky, D.P. 2004. Nodulation and root growth of forage legumes sown into tall fescue swards. Grass and Forage Science. 59:399-405.

Interpretive Summary: Renovating tall fescue pastures by introducing forage legumes is difficult, particularly in well-established swards. At present, the cause of this problem is unknown. Although one explanation is that the legume component is unable to form nodules with rhizobia, no literature exists to support it. In this study, we determined that alfalfa, red clover and white clover were well nodulated, when seeded into variously managed, 30-year-old tall fescue swards. However, differences were found for legume root growth, relative to the management technique (live sod < killed sod/rye < killed sod = suppressed sod). These findings suggest that competition for soil moisture, and not nodulation, is the causative factor for poor stands of the legume component in renovated tall fescue pastures.

Technical Abstract: Establishing forage legumes into endophyte-infected tall fescue (Festuca arundinacea Schreb.) swards is problematic, especially in well-established stands of this warm-season grass. A field experiment, using legume interseeding, was conducted to determine if this problem was a consequence of failure of symbiosis establishment (early nodulation) with rhizobia or limiting soil chemical/physical conditions. Specifically, four sward management techniques, providing different tall fescue residue types to the soil, were investigated to determine if legume nodulation and/or root growth, and morphology, were affected. At soil rhizobial populations sufficient for maximal nodulation (> 6 x 104 CFU g-1 soil), substantial nodulation (> 70% nodulation potential) of alfalfa (Medicago sativa L)., red clover (Trifolium pratense L.), and white clover (Trifolium repens L.) occurred and was little affected by sward treatment (killed sod /rye, killed sod, suppressed sod), except under live sod, even at the latest time examined at 29 DAP. Total root lengths (TRL) at Cuts 1, 2, and 3 (16, 22, and 29 DAP) for all species were severely restricted (< 30% root growth potential). The general correspondence of TRL of all legume species with tall fescue residue type, that being live sod < killed sod/rye < killed sod = suppressed sod, suggests that soil moisture was a limiting factor. Root morphological data (TRL sorted by diameter class) also suggest a soil chemical effect at Cut 3, at least for red clover. These results demonstrate that weak stands of various forage legumes, interseeded into a tall fescue sward, were not a consequence of the failure of establishment of rhizobial symbioses. Rather, the inhibition of root growth by detrimental soil chemical/physical conditions is suggested.