Molybdenum status and critical limit in the soil for green gram (Vigna radiata) growing in Madurai and Sivagangai districts of Tamil Nadu, India
A survey was undertaken during 2008 to determine molybdenum (Mo) status of soils and to establish critical limits in soils of Madurai and Sivagangai districts of Tamil Nadu. A total of 202 surface soil samples were collected from 16 soil series of the study areas based on their percent coverage. The samples were analyzed for extractable or available Mo. Extractable Mo varied from 0.028 to 0.661 mg kg 1 and 0.035 to 0.961 mg kg 1 at Madurai and Sivagangai districts, respectively. Based on the results of a pot culture experiment, the critical limit of available Mo was determined to be 0.043mg kg 1 for green gram [Vigna radiata (L.) Wilczek] (Var; CO 6) in both the districts. Based on this critical limit, we classified the soils into three categories: (1) low: <0.043 mg kg 1 (2) medium: 0.043—0.082 mg kg 1 (3) high: >0.082 mgkg 1. Green gram responded highly to Mo application in soils below the critical limit whereas soils with Mo greater than 0.082 mgkg 1 did not respond. Among rates of Mo application, 0.075 mgkg 1 showed better yield than others. Overall, 3–41% and 7–46% of total area in Madurai and Sivagangai districts were in the low to medium Mo status, respectively. The application of 0.075 mg of Mokg 1 or 0.4 kg ha 1 as sodium molybdate was sufficient to optimize green gram yield in the major soil series of the districts. These results will be useful in decisionmaking to apply Mo for improving green gram yields in the two districts studied.