Browsing by Author "Unnikrishnan, R"

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Detritus of plant origin as a food source for Penaeus indicua H. Milne Edwards
(Department of Aquaculture, College of Fisheries, Panangad, 1992) Unnikrishnan, R; Thampy, D M
The objective of the present study was to evaluate the feasibility of using plant detritus as an exclusive food source for the juvenile of Penaeus indicus and also to find out the level of its in corporation in a standard diet for the prawn in place of animal protein sources. When four plant detritus were simultaneously presented to p.indicus juvenile of size 25-32 mm and 110-150 mg, they exhibited best preference for detritus from Rhizophora apiculata, followed by chromolaena odorta, Pistia stratiotes and paddy detritus. Two better preferred plant detritus sources viz. R.apiculata and C.odorata, were subjected to bulk digestion and the improvement in protein level by way of microbial growth during the process of decay was recorded. Since C.odorata showed a better protein level (Max.av.25.716%) on the fifteenth day than R.apiculata (Max.av.7.528%) on the twentieth day, C.odorata detritus was used for the next two feeding experiments: the first to find whether it could be used as exclusive protein source and the second to find the level at which this could be used to replace animal protein source in a standard diet for P.indicus. The first feeding experiment, for a period of 28 days, to evaluate the feasibility of using plant detritus as sole protein source revealed that an exclusively detritus based diet is not suitable for P.indicus juveniles. The detritus based diet produced lower survival, growth, protein sufficiency ratio, protein digestability and high food conservation ratio when compared to that of control diet prepared with clam meal. The second experiment done with eight diets for a period of 21 days revealed that plant detritus could be used for substituting upto a level of 50% of the animal protein source in a standard prawn diet, without producing any adverse effect on growth and survival. While, a diet containing 10% plant detritus fared even better than a diet which was totally devoid of detrital protein. The growth, food conversation ratio, protein efficiency, apparent digestibility and protein digestibility values obtained for various diets did not vary significantly upto a stage where 50% of the animal protein was substituted with detrital protein, beyond which the values declined. The best values were obtained for the diet FD2 and the lowest for the diet FD8.
Sulphur dynamics in major rice-growing soils of Kerala
(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellanikkara, 2022) Unnikrishnan, R; Jayasree Sankar, S
Sulphur has been recognized as an essential nutrient to plants and it is ranked as fourth among major plant nutrients after nitrogen, phosphorus, and potassium. Most of the soils in Kerala are rich in total S and the maximum amount of sulphates has been reported in Kari and Pokkali soils. Representative soil samples were collected from seven different rice growing tracts falling under different agro-ecological units (AEU) of Kerala for the study entitled Sulphur dynamics in major rice-growing soils of Kerala. Five samples each were collected from various locations pertaining to a particular soil type for initial characterisation. In addition three soil and plant samples were also collected from each soil type at active tillering and harvest stage of rice crop. The study aims at understanding sulphur dynamics in major rice soils of Kerala and its relationship with that of carbon, nitrogen and phosphorus. It also envisages at unfolding the antagonism/ synergism between sulphur and other nutrients, if any. Sixteen out of 35 samples belonged to the category of strongly acidic to moderately acidic. It can be concluded from characterisation study that the sandy soils of Onattukara was low in terms of fertility wherein Pokkali soils, Kole land and Kari soils of Kuttanad were high with respect to soil fertility. None of the soils were found deficient in available sulphur with Pokkali soils being the remarkably highest. The low land brown hydromorphic laterite and Onattukara sandy soils had relatively lower sulphur content. The Kari soils accounted for highest microbial biomass carbon and aryl sulphatase activity. The estimated soil pH was slightly elevated at active tillering and harvest stage. The sulphur exhibited an antagonistic relationship with phosphorous, potassium as well as manganese Fractionation of S was conducted at three stages to find out the dominant different forms of sulphur. The Pokkali soils and Onattukara sandy soils had the highest as well as lowest value for all the sulphur fractions before cropping. The Kari soil concluded the highest total organic sulphur at active tillering and harvest stage. All the sulphur fractions were positively influenced by microbial biomass carbon and aryl sulphatase activity. An identifiable positive relation existed between available nitrogen and total organic sulphur as well. The C:S ratio was high in Laterite soil and lowest in Pokkali soil at all the three stages. The Onattukara sandy soil and Laterite soil accounted for the highest N:S ratio wherein Kari soil and Pokkali soil had the lowest ratio. The decreased C:S and N:S ratio contributed to the raised plant available sulphur in soil. Sulphur adsorption experiment was conducted at 25 ℃ as well as 40℃ and quantity-intensity relations were carried out based on data. While The samples from Pokkali and Kari soil exhibited desorption of sulphur at both the temperatures (25 ℃ and 40 ℃) studied, it was found to get adsorbed in the case of Laterite soil and Onattukara sandy soils at both 25 ℃ and 40 ℃.