Soil Microbial Population and Enzyme Activities as Influenced by Different Nutrient Management Practices in Arecanut and Black Pepper Cropping System of Uttara Kannada District of Karnataka, India

Abstract

The diverse range of microorganisms live in soils and are responsible for the decomposition of organic matter and the mobilisation of nutrients. Thus, they play an important role in the cycling of nutrients in nature. Arecanut and black pepper, these commercial cropping systems are mainly grown in the Western Ghats of Karnataka, where microorganisms play an important role in nutrient cycling, as they are both sources and sinks for mineral nutrition and can carry out biochemical transformations.  A survey was conducted to study the soil microbial population and enzyme activity in arecanut and black pepper gardens at Sirsi, Siddapur and Yellapur taluks of Uttara Kannada district during 2020-21. Geographically, the study area (Sirsi, Siddapur and Yellapur) lies between 140 37’ N - 740 50’ E, 140 20’ N - 740 53’ E, 140 57’ N - 740 42’ E, latitude and longitude respectively. The altitudes of the study area are at 611, 564, and 541 m above mean sea level, respectively. It lies under a tropical monsoon climate; therefore and the weather is hot and humid throughout the year. The mean rainfall of the tract is 2500 mm, with 103 rainy days in a year.  These gardens were classified based on different nutrient management practices as INM, Organic and ZBNF gardens. The soil samples were collected from the rhizosphere of those selected groups of gardens at two depths, 0-15 cm and 15-30 cm. A study revealed that soil biological properties varied significantly among different nutrient management practices and soil depths. The organic areca-black pepper garden has recorded higher bacterial, fungal and actinomycetes populations, which were on par with ZBNF areca-black pepper gardens. The surface soil has exhibited higher bacterial and fungal populations, whereas the actinomycetes population was found to be highest in the subsurface soil. Urease activity among different nutrient management practices varied significantly in the order INM > Organic = ZBNF. Whereas dehydrogenase and acid phosphatase activities varied significantly in the order Organic = ZBNF > INM practices. The microbial biomass carbon (MBC) was recorded as highest in surface soil than in subsurface soil. Similarly, higher MBC was observed in organic areca-black pepper gardens than in other gardens at Sirsi, Siddapur and Yellapur taluks. It was observed from the current study that in organic areca-black pepper gardens due to higher application of organic nutrient sources resulted in higher organic carbon accumulation which resulted in higher microbial population.