Biological indicators of soil health as influenced by plant nutrient sources

Abstract

The research project entitled ‘Biological indicators of soil health as influenced by plant nutrient sources ’ was undertaken to study the changes the major biological properties of a soil undergo when the major nutrients to a crop grown on it are supplied organically or inorganically or in their different combinations and to employ them as tools for evaluating the health of that soil. The investigations consisted of laboratory studies and two field trials at the Instructional Farm, College of Agriculture, Vellayani with Amaranthus var.Arun during May 2012 to July 2012 in two soil types of Vellayani, red loam and lateritic. The ten treatments were laid out in RBD with three replications. The treatments consisted of T1 (Urea+ Rock phosphate+ Muriate of potash) (KAU POP, 2007), T2 (Urea+ Rock phosphate+ Wood ash), T3 (Urea+ Bone meal+ Muriate of potash), T4 (Urea+ Bone meal + Wood ash), T5 (Oil cake+ Rock phosphate+ Muriate of potash), T6 (Oil cake +Rock phosphate +Wood ash) , T7 (Oil cake+ Bone meal+ Muriate of potash) , T8 (Oil cake+ Bone meal+ Wood ash), T9 (KAU Organic POP, 2009), T10 (Control ) The biometric observations viz., plant height, number of leaves, number of branches, stem girth, root length and root volume were all significantly influenced by different treatments. Significant differences were observed among yield attributing characters like leaf weight plant -1, stem weight plant -1,shoot biomass plant -1, root biomass plant -1, biomass yield plant -1 and total yield plot -1. The highest yield plot -1 was recorded by the treatment combination T1 in both soils. With respect to quality characters the treatment combination T5 recorded the highest value for vitamin C and -carotene content in both soils. For crude protein content treatment T6 recorded the highest value in red loam soil and T8 in lateritic soil to both of which T5 was on par. Oxalate content and nitrate content were also influenced by different treatments .T9 registered significantly higher population of earthworm and soil respiratory activity in both soils. Soil microathropod and soil microbial population (bacteria, actinomycetes and fungal) were maximum in the treatment combination T6. In both soils urease activity was maximum for T4 and dehydrogenase activity maximum for T8, phosphatase activity showed maximum values for T2 in red loam soil and T8 in lateritic soil. Soil organic carbon and available N, P, K content in the soils were significantly influenced by various treatments. Regarding Carbon mineralization potential estimated as the organic C content of the soil T5 recorded maximum value in red loam soil and T9 in lateritic soil. The treatment combination T¬6 registered highest values for nitrogen mineralization potential in red loam soil while T1 for lateritic soil.T7 recorded highest values for available P content in both soils and available K content in lateritic soil. Economic analysis of various treatments showed that the combination of inorganic sources of plant nutrients T1 generated higher profit compared to all other treatments in both soils. Taking into account the favourable effect exerted on biological properties of soil, yield and yield attributes treatment T6 which is a combination of N and K in organic form and P in inorganic form to supply the recommended dose of major nutrients to the crop can be adjudged to be the best treatment for economic production of amaranthus in both red loam and lateritic soils of Vellayani. Considering quality of the crop treatment T5 which supplied N alone organically was found to be best.