SOIL ENZYME ACTIVITY AS INFLUENCED BY Bt COTTON GENOTYPES AND OPTICAL SENSOR-BASED NITROGEN MANAGEMENT PRACTICES.

Cotton is a crop that has a high demand for nutrients. To obtain higher yields nutrients must be supplied as per the crop demand and must be available to the crop. Therefore, a field experiment was conducted at the Main Agricultural Research Station, Dharwad during kharif 2019 and 2020 to assess the soil enzyme activity as influenced by Bt cotton genotypes and optical sensor-based nitrogen management practices. Pooled data revealed that genotypes did not show any significant difference for soil dehydrogenase (P = .2899), phosphatase (P = .0165) and urease (P = .1481) enzyme activity at mid flowering stage. Different optical sensor-based nitrogen management practices significantly (P<.0001) influenced soil dehydrogenase, phosphatase and urease enzyme activity at the mid flowering stage. Nitrogen (N) supplementation at 81-90 % sufficiency index (SI) (43.69 μg TPF g^-1 Soil day^-1) recorded significantly higher dehydrogenase enzyme activity. The N supplementation at 1.1- 1.5 response index (RI) (248.14 μg PNP g^-1 Soil hr^-1 and 22.68 μg NH₄-N g^-1 Soil for 24 hrs) and 81-90 % SI (245.91 μg PNP g- 1 Soil hr^-1 and 22.38 μg NH₄-N g^-1 Soil for 24 hrs) recorded significantly higher phosphatase and urease enzyme activity as compared to N omission treatment. Interaction of genotypes and different N management practices did not differ significantly. The correlation of soil enzymatic activity showed a very strong and positive association (r>0.90) with total nitrogen, phosphorous and potassium uptake at the mid flowering stage of the cotton crop. [ABSTRACT FROM AUTHOR]