PG Thesis
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Item Influence of soil solarisation on soil ,icroflora plant growth and incidence of diseases(Department of Plant Pathology, College of Agriculture, Vellayani, 1989) Chandran, C R; Peethambaran, C KThe influence of solarization on soil microflora, plant growth and incidence of disease was studied during 1985-87 at Madavoor on collar rot of cowpea caused by Rhizoctonia solani Kuhn. The effectiveness of solarization was tested in open and partially shaded conditions in coconut garden using 0.05mm transparent polythene sheets as the mulch. The atmospheric temperature during the period of solarization ranged from 28.50C to 34.20C. The increase in soil temperature, as a result of solarization was more in open field than in partial shade. The soil temperature variation in open nonsolarized treatments was 100C while it was 12.50C in solarized plots. Corresponding figures for partially shaded conditions were 5.50C and 70C respectively. Maximum soil temperature recorded at 15cm depth in open solarized soil was 42.50C. Based on the experimental data two statistical models (1) for predicting soil temperature under polythene mulch and (2) for predicting collar rot of cowpea were developed during the study. Soil solarization significantly reduced collar rot of cowpea. Least incidence of the disease (3.6%) was noticed in open nonirrigated solarized treatments while maximum incidence (24%) was recorded in shade irrigated control. The interaction effect of shade, solarization and irrigation was not significant. Solarization reduced the total fungal population in open conditions while the population of bacteria was not significantly changed. In the case of actinomycetes population, a slight increase was noticed in solarized plots. The nematode population was significantly reduced by solarization in open field. Eventhough solarization substantially reduced weed population in open, it was less effective under partially shaded conditions. Growth parameters like height and number of leaves per plant were not significantly influenced by solarization. But it improved the stand of the crop and yield. An yield increase ranging from 7.62 to 21.69 per cent was obtained in solarized plots over the control. Availability of nitrogen, phosphorus and organic carbon was improved by solarization while there was no change in the level of potassium, calcium, PH and electrical conductivity.Item Effect of biofertilizers on the growth, yield and nitrogen economy of sesame grown in summer rice fallows(Department of Agronomy, College of Horticulture, Vellanikkara, 1995) Indu K Paul; Savithri, K EA field experiment was conducted in the rice fallows of Agricultural Research Station, Mannuthy, during the summer season (January – April) of 1995, to find out the effectiveness of biofertilizers on the growth, yield and N economy of sesame. The experiment was laid out in randomised block design with 1.4 treatments replicated thrice. The treatments included were, the recommended dose of inorganic N,@30 kg/ha alone, inoculation of Azospirillum or Azotobacter along with 50 percent, 25 percent or no inorganic N, either with or without lime and an absolute control. Most of the growth characters, yield attributes and yield were highest in the plots applied with the recommended dose of 30 kg inorganic N/ha alone. The crop nutrient uptake and available soil nutrients were also higher in the above treatment. The better initial physical, chemical and biological conditions of the soil, along with the added inorganic N fertilizer @30 kg/ha might have contributed to a better nutrient supply from the initial growth period itself. Though, both the microbes, Azospirillum and Azotobacter showed almost similar performances regarding various parameters, a slightly better response was shown by Azospirillum in most cases. This might be due to the fact that Azospirillum is a better root colonizer than the freeliving Azotobacter, which led to better nutrient uptake and ultimately yield of the crop, compared to Azotobacter inoculated treatments. Lime application, along with the inoculation of acid tolerant strains of the microbes, had no profound influence on the parameters studied. Thus, the study revealed the necessity of the application of recommended dose of inorganic N fertilizer @30 kg/ha for sesame grown in summer rice fallows. It also showed the lesser possibility of inorganic N substitution with Azospirillum or Azotobacter inoculation in such a situation. Moreover, liming could not bring about any significant influence on the activity of acid tolerant strains of either Azospirillum on Azotobacter.Item Assessment of nitrification rate of Kerala soils and agronomic factors influencing it(Department of Agronomy, College of Horticulture, Vellanikkara, 1989) Marykutty Zacharias; Vikraman Nair, RThe present study 'assessment of nitrification rate of Kerala soils and agronomic factors influencing it' was conducted during June 1987 to November 1988 at the College of Horticulture, Vellanikkara, Trichur. A series of laboratory incubation studies were conducted using a total of 22 soil samples including 20 samples drawn from five soil types (laterite red, alluvial, forest and black soils ) of Keralaand two from Coimbatore (red and black). The presence of Nitrosomopas was observed in 11 soil samples and that of Nitrobacters in all soil tested. The nitrification rate was high for alluvial and black soils and low for the red laterite soils.Item Urease activity in rice soils of Kerala(Department of Agronomy, College of Horticulture, Vellanikkara, 1989) Saraswathi, P; Balachandran, P VAn investigation on the urease activity of rice soils of Kerala was conducted at the College of Horticulture, Vellanikkara during the period 1987-1989. Representative soil samples were collected from six rice soils of Kerala, namely , laterite karppadam, kari, kayal, kole and black soil . The kinetics of urease activitywas worked out employing Lineweaver-Burk equation of double reciprocal plot. The effect of different factors like pH, soil submergence and rice rhizosphere on soil urease activity was investigated . A comparision of the efficiency of the different methods of urease assay was also made. The radioassay and autoradiograph of the plants which were allowed to absorb 14 C - urea were also done.Item Nutrient content and decomposition of leaf litter of Acacia mangium Willd as affected by season and field conditions(Department of Silviculture and Agroforestry, College of Forestry, Vellanikkara, 1995) Ramakrishna Hegde; Gopikumar, KA detailed experiment was conducted at the College of Forestry, Kerala Agricultural University, Vellanikkara, Thrissur, during the period from 1993 to 1995 to study the nutrient content and pattern of leaf litter decomposition of Acacia mangium Wild. During south west monsoon and north east monsoon seasons. The experiment was conducted both in home garden and open area. The rate of decomposition was faster in all the study situations. The initial nitrogen, lignin, C:N ratio and lignin : nitrogen ratio of leaf litter were found to exert profound influence on the rate of decomposition. The decomposition rate was found to be a function of time, soil moisture and soil temperature. The nutrient release pattern in almost all cases followed a characteristic biphasic model with an initial rapid phase followed by a slower latter phase. Among the different nutrients, potassium showed a faster rate of mineralisation in most of the situations while calcium and nitrogen mineralised slowly. Among the several mathematical models tried to predict the absolute amount of nutrients in the residual mass, the second order hyperbolic function was found to be good fit in most of the cases. Though the PH was not altered significantly by the decomposing litter mass, the content of most of the nutrient elements is found to be drastically influenced.