MSc.

The present investigation titled ‘Biological characterization of Onattukara soils under coconut based cropping system’ was undertaken during 2013-15 with the objectives of building an inventory on the biological properties of the major coconut growing soils in Onattukara tract of Kerala and studying the impact of the prevalent nutrient management practices followed by farmers on these properties.
Eight soil series of Onattukara viz. Palamel and Attuva (under ‘very good’ productivity class) Vallikunnam and Mynagappally (‘good’) Neendakara and Kandallur (‘average’) Kollaka and Thrikkunnappuzha (‘poor’) were selected (Premachandran,1998). In each series three mature bearing palms in the age group of 15 to 20 years under four levels of nutrient management practices for the last three years (organically, inorganically, both organically and inorganically and none) were selected on the basis of personal interviews and soil samples were collected from a depth of 60 cm within a lateral distance of 2 m from the base of coconut palm. The data generated were subjected to statistical analysis applicable to factorial CRD, the factors being four productivity classes and four levels of nutrient management.
The soil faunal populations, earthworms (1.04 – 3.12 no m-2 soil) and arthropods (76.67 - 158.33 no kg-1soil) were significantly influenced by the nutrient application practices in different productivity classes. The interaction effect was significant for the arthropod population only. All the microbial populations studied differed significantly as a result of nutrient management. The productivity of the soil exerted significant influence only on the bacterial, actinomycetes, fungal and P solubilizer populations while the interaction effects were significant for actinomycetes, fungi, Azospirillum and P solubilizers.
Result of enzyme assay showed that urease activity was not influenced by any of the factors where as Phosphatase and dehydrogenase were significantly altered by both the factors and their interactions. Soil respiratory activity showing significance at all levels was maximum in the ‘very good’ soils under organic fertilization only and minimum in the ‘poor’ soils not receiving any nutrition. Carbon as well as Nitrogen mineralization potentials of the soils showed significant variations in response to management, productivity and their interaction. ‘Very good’ soils under dual nutrition registered the highest values (1.75% organic C and 471.72 kg ha-1available N). The lowest values of 0.61% organic C and 219.69 kg ha-1available N were for the ‘poor’ soils with no nutrition at all.
Details on yield of the palms and management practices (nutrient application as well as plant protection measures) were gathered through personal interviews with farmers whose palms were surveyed. Irrespective of the production and nutrient management and soil productivity classes, there was prevalence of rhinocerous beetle, red palm weevil, leaf eating caterpillar, eriophid mites, root (wilt) disease and leaf rot on all palms.
The results clearly indicate that all the biological properties studied are sensitive indicators of soil health and are highly expressed in ‘very good’ soils receiving nutrients, organically and inorganically and minimum in ‘poor’ soils with no nutrition. But even the ‘poor’ and ‘average’ soils can be made biologically more healthy through systemic and judicious nutrient application through organic or inorganic or a combination of these two sources.