Abstract
Field experiments were conducted in 1992 and 1993 to examine effects of soil acidity on growth and N2 fixation by “Serala”; sericea lespedeza [Lespedeza juncea (L.F.) var. sericea (Mig.)]. Effects of acidified soil on N2 fixation could not be determined because nodulation was suppressed, apparently by sufficient availability of N. Apparently‐suppressive, mean 1993 levels of KCl‐extractable NH4 and NO3 in zero nitrogen (N) control treatments were 20 and 13 mg‐kg‐1, respectively. In soil acidified with sulfur (S), growth of sericiea lespedeza was significantly reduced (PO.05) when the concentration of water‐extractable Mn exceeded 1.3 mM or calculated Mn2+ activity exceeded 0.4 mM. This occurred at pH values of 4.1 to 4.3 depending on S treatment. At a given value of pH, shoot dry weight production was greater in S‐amended soil than in Al2SO4‐amended soil. Reduced growth in the latter did not appear to be directly related to higher measured levels of toxic Al but may have been caused by a combination of aluminum (Al), hydrogen (H), manganese (Mn), and phosphorus (P) effects. Lespedeza growth was lowest in nonacidified soil with pH values near 6.0, indicating a preference for acid soils by the variety “Serala.”; The demonstrated tolerance of sericea lespedeza to acid soils make it a valuable reclamation species. However, Mn may inhibit growth in acidic soils when the activity of water‐extractable Mn2+ exceeds 0.4 mM, and it may not fix appreciable N2 unless available soil N is quite low.