A Study to Refix the Critical Limit of Copper in the Major Rice Growing Soils of Tamil Nadu, India

Aims: To refix the critical limit of Cu in the soils of the major rice-growing tracts of Tamil Nadu.

Study Design: Completely Randomized Design and Randomized Block Design.

Place and Duration of Study: Department of Soil Science and Agricultural Chemistry, Tamil Nadu Agricultural University between 2015 to 2018.

Methodology: The pot culture study was conducted in the laboratory followed by the field trials in the selected farmers'plot itself. The soil and plant samples are analyzed for soil copper and the data were statistically analyzed by following the standard procedures.

Results: The Cu deficient soils showed a significant response to the application of graded levels of Cu. For obtaining higher rice production in severely Cu-deficient soils (L1 to L9: 0.33 to 0.95 mg kg-1), the Cu fertilizers may be applied @ 1.50 kg ha-1 i.e. 6.0 kg CuSO4 ha-1 (+ NPK) while in moderately Cu deficient soils (L10 to L13: 1.28 mg kg-1), the Cu level @ 1.00 kg ha-1 i.e. 4.0 kg CuSO4 ha-1 (+ NPK) increased significantly the grain and straw yields and in soils having high initial Cu status (L14, L15: 1.91, 2.12 mg kg-1), the Cu level @ 0.50 kg ha-1 i.e. 2.0 kg CuSO4 ha-1 (+ NPK) showed a significant increase in grain and straw yields.

Conclusion: The present investigation was carried out with the objective of re-fixing the critical limit in wetland soils and accordingly the critical limit for DTPA - Cu in wetland soils and rice crops at the panicle initiation stage was re-fixed as 0.93 and 4.82 mg kg-1, respectively. Based on this, it is possible that a graded dose of micronutrient fertilizers (Cu) may be prescribed to rice crops for the major rice-growing soils.