Integrated efsfect of vermicompost and nitrogen fertilisers on soil urease enzyme activity and yield of onion – radish cropping system

A field experiment was conducted at Hyderabad on a sandy loam soil during kharif (onion) and rabi (radish) seasons of 2007–08 with a view to study the effect of integrated use of vermicompost (0, 5 and 10 t ha⁻¹) and nitrogen fertilizers (0, 60, 90 and 120 kg N ha⁻¹) on soil urease enzyme activity and yield of onion-radish cropping system. Among the different combinations, application of 10 t vermicompost ha⁻¹ + 120 kg N ha⁻¹ (V₂N₃) recorded significantly highest fresh onion bulb yield (24.45 t ha⁻¹) at harvest. However, the bulb yield at V₂N₃ was on par with the yield obtained at V₂N₂ (23.43 t ha⁻¹). The radish crop grown during rabi responded favorably to the residual and cumulative treatments and the highest radish yield of 18.45 t ha⁻¹ and 23.43 t ha⁻¹ was recorded in residual and cumulative treatments at V₂N₃ level. The soil urease enzyme activity at different growth stages of onion and radish revealed that there was increase in enzyme activities upto active growth stages (30 days after transplanting for onion and 15 days after sowing for radish) of crops and later showed a decrease. The results showed that integrated application of 10 t vermicompost ha⁻¹ + 120 kg N ha⁻¹ (V₂N₃) recorded significantly highest urease activity at 30 (90.86 ug of NH₄⁺-N released g⁻¹ soil h⁻¹), 60 (75.30 4g of NH₄⁺-N released g⁻¹ soil h⁻¹), 90 days after transplanting (63.62 4g of NH₄⁺-N released g⁻¹ soil h⁻¹) and at harvest (38.72 4g of NH₄⁺-N released g⁻¹ soil h⁻¹) of onion. The cumulative and residual effects at different growth stages of radish revealed that the urease activity was higher in cumulative treatments than residual treatments.