EFFECTS OF SOIL ACIDITY ON THE GROWTH OF SERICEA-LESPEDEZA

Field experiments were conducted in 1992 and 1993 to examine effects o f soil acidity on growth and N-2 fixation by ''Serala'' sericea lesped eza [Lespedeza juncea (L.F.) var. sericea (Mig.)]. Effects of acidifie d soil on N-2 fixation could not be determined because nodulation was suppressed, apparently by sufficient availability of N. Apparently-sup pressive, mean 1993 levels of KCl-extractable NH4 and NO3 in zero nitr ogen (N) control treatments were 20 and 13 mg.kg(-1), respectively. In soil acidified with sulfur (S), growth of sericiea lespedeza was sign ificantly reduced (P<0.05) 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 giv en value of pH, shoot dry weight production was greater in S-amended s oil than in Al2SO4-amended soil. Reduced growth in the latter did not appear to be directly related to higher measured levels of toxic Al bu t may have been caused by a combination of aluminum (Al), hydrogen (H) , manganese (Mn), and phosphorus (P) effects. Lespedeza growth was low est in nonacidified soil with pH values near 6.0, indicating a prefere nce for acid soils by the variety ''Serala.'' The demonstrated toleran ce of sericea lespedeza to acid soils make it a valuable reclamation s pecies. However, Mn may inhibit growth in acidic soils when the activi ty of water-extractable Mn2+ exceeds 0.4 mM, and it may not flu apprec iable N-2 unless available soil N is quite low.