SURVEY OF MOLYBDENUM FERTILITY STATUS IN MARYLAND COASTAL-PLAIN SOILSFOR TOBACCO PRODUCTION

Coastal Plain soils in southern Maryland are typically acid (pH = 5.0 +/- 0.5) with low organic matter (1.2 +/- 0.5%), clay (2.8 to 9.8%), C EC (2.4 to 6.8 meq 100/g), and total Fe contents (4.5 to 34.9 g/kg). T he objectives of this investigation were to assess the status of plant available molybdenum (Mo) in these soils by examining the extractable Mo levels in Ap horizon soil samples and tissue Mo contents in cured tobacco collected across a five-county region. Seventy soil samples re presenting 11 soil series and 198 composite samples of tobacco served as the basis for the surveys. Plant available Mo in soil, estimated us ing a solution containing 0.18M ammonium oxalate and 0.1M oxalic acid as the extractant, ranged from 0.02 to 0.53 mug/g and averaged 0.08 mu g/g Mo. Three of the 11 soil series examined and 30% of the total soil samples exhibited extractable Mo levels less-than-or-equal-to 0.03 mu g/g therefore may have less than adequate available Mo for tobacco. Cu red leaf Mo contents ranged from non-detectable to 7.95 mug/g and aver aged 0.84 +/- 0.95 mug/g Mo. Approximately 15% of the leaf samples con tained less-than-or-equal-to 0.2 mug/g Mo which approaches borderline deficiency for Mo with 12.2% having Mo contents within the range 0.2 t o 0.4 mug/g where growth responses were reported in burley tobacco. Th e causes for the approximate one fourth of the plant samples having le ss than optimum Mo concentrations for maximum productivity for tobacco can likely be attributed to: 1) acid soils associated with inadequate liming programs; 2) very low extractable Mo levels in several soil se ries; and 3) excess input of SO4-2 in fertilizers and acid rainfall in the region which have been shown to inhibit MoO4-2 ion uptake by toba cco plants.