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ThesisItem Open Access Leaf litter dynamics in acacia and eucalyptus plantations(Department of soil science and agricultural chemistry, College of Agriculture, Vellayani, 1997) Moossa, P P; KAU; Venugopal, V KAn investigation entitled “Leaf litter dynamics in Acacia and Eucalyptus plantations” was undertaken to study the leaf litter production, litter decomposition and nutrient release characteristics, and impact of Eucalyptus and Acacia monoculture plantations on the soil physico-chemical and biological characteristics during 1994-97. One hectare each of Acacia auriculiformis, Eucalyptus tereticornis and a moist deciduous forest coming under the Kulathupuzha range of Kerala Forest Department were selected for the study. Field experiment were conducted to determine the leaf litter production and decomposition characteristics of plantation and natural forest. Leaf litter collected at monthly intervals showed that highest litter production was in Acacia (9.4 t ha-1 year-1) followed by natural forest (6.67 t ha-1 year-1) and Eucalyptus (4.68 t ha-1 yaer-1). Pattern of litter production was unimodal in Acacia and natural forest while in Eucalyptus it was bimodal. Chemical analysis of litter samples of plantations and natural forest revealed that with respect to nutrient content fresh and leaf litter of Acacia and Eucalyptus is superior to natural forest whereas litter quality in terms of water soluble components, polyphenols, lignin and cellulose were superior in natural forest. Annual dry matter loss of leaf litter by decomposition followed the order natural forest > Acacia > Eucalyptus. Nutrient release pattern of major and micro nutrients were also worked out for the leaf litter during the process of decomposition and natural forest litter recorded the highest mobility for all the nutrients on decomposition. Improvement in soil physico-chemical properties were noticed due to leaf litter decomposition in the monoculture plantation and natural forest. Biological activity in terms of earthworm and nematode under monoculture plantation was significantly lower than that of adjacent natural forest. Microbial content of soil below the litter bag during different months of decomposition were low in Eucalyptus and Acacia. Chemical analysis of the profile samples of various plantations revealed lower nutrient status in respect of major and micronutrients compared to natural forest. The physical properties of the soil also recorded as unfavourable change in the monoculture plantations as compared to the adjacent natural forest. Proximate anlysis of soil organic matter and humus characterization of the soil organic matter separated from various plantations indicated a low rate of humification and condensation under Eucalyptus. Low humic acid and fulvic acid content in humus and dominance of fulvic acid over humic acid was also noticed in Eucalyptus plantations. Functional group analysis of humic acid and fulvic acid showed that humic material separated from natural forest contained higher quantity of total acidity, contributed by COOH and phenolic group compared to plantation soils. UV, IR, DTA and TGA analysis of humic acid and fulvic acid separated from various plantations showed no variation with respect to natural forest. Allelopathic effect of fresh leaf and leaf litter extract of various plantations on the germination and growth of rice and cowpea followed the order Eucalyptus > Acacia > natural forest and as the concentration decreased from 1: 2 to 1: 10, the allelopathic inhibition also decreased significantly. Allelopathic effect of soil extract also followed the order Eucalyptus > Acacia > natural forest. Thus it can computed that though the leaf litter production and litter quality of monoculture plantations are comparable with that of natural forest, leaf litter decomposition and nutrient released were significantly lower than that of natural forest. Soil physico-chemical properties, soil fertility and biological activities were also adversely affected by monoculture plantations.ThesisItem Open Access Morphological, physical and chemical characterization of the soils of North Kuttanad(Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellanikkara, 1997) Manorama Thampatti, K C; KAU; Jose, A JAn investigation was carried out at the College of Horticulture, Vellanikkara during 1992 to 1995 to evaluate the morphological, physical and chemical characteristics of soils of North Kuttanad and to assess the extent of toxic factors that pertained in the soil due to restricted movement of water under the influ- ence of Thanneermukkom regulator. The study was carried out in three parts, viz., (1) Morpho- logy and physicochemical characteristics, (2) Fertility characteristics and (3) Toxicity chara- cteristics. Fifteen soil profile were drawn from North Kuttanad to study the morphology and physicochemical characteristics of the area. The fertility characteristics were studied by collecting 97 surface soil samples (0-15 cm depth) from 27 padasekharams of the area during rainy and summer seasons (before and after the closure of Thanneermukkom regula- tor). Toxicity characteristics of the area were studied by collecting bulk soil samples (0-25 cm depth), surface water and ground water from the above sites during the same period. Morphological and physicochemical properties of the soils showed great degree of variation. Soils were dark brown to black in colour, sticky and plastic, subangular blocky in structure and sandy to clayey in texture, with random deposits of lime shells and humus. Presence of faint to prominent reddish yellow or brown mottles, rice roots and root canals were some of the special characteristics observed in the soil profiles. Soils of the area were highly acidic and mildly saline. Both soil acidity and salinity increased with depth. Organic carbon, CEC and ECEC of the area were higher compared to other parts of Kerala, but the base saturation was comparatively lower. The area was rich in almost all the essential nutrients except P. Fe, Al and S were present in toxic concentrations. Potential acidity of the area was very high and more than 70 per cent of it was contributed by hydrolytic acidity and the rest by exchangeable acidity. All the acidity characteristics increased with depth. The profile IX was grouped under order Inceptisol and all others under order Entisol. On evaluating the fertility characteristics of the area it was observed that the area experienced an increase in soil acidity and availability of N, P, Fe and Zn and a decrease in salinity, CEC, ECEC and available K, Ca, Mg, \.10 and Cu. However, the availability of all nutrients except P was above the deficiency level. Fe was present in toxic quantities. On a general comparison with that of pre-barrage period, the area experienced a reduction in salinity and an enhancement in soil acidity and availability of K, Ca and Mg. The Na content was reduced considerably in response to the reduction in salinity. The exchangeable and water soluble cations followed the same trend as that of available cations. Among the exchangeable cations Ca was the dominant basic cation instead of Na which occupied the same place during pre-barrage period. Acidity characteristics of surface samples behaved similar to that of profile samples. Pot- ential acidity and hydrolytic acidity recorded higher values during rainy season while exchangeable acidity was greater during summer. Among the components of exchange- able acidity exchangeable Al3+ dominated during rainy season, and exchangeable H+ dur- ing summer. The overall influence was greater for exchangeable A13+ as evidenced from the higher correlation coefficient (0.862**). The general soil properties and acidity characteristics of the bulk soil samples were similar to that of surface samples, showing a reduction in pH, EC, CEC and available, exchangeable and water soluble cations during summer compared to the rainy season. Among the different fractions of Fe, free and available forms were present in large quantities while exchangeable and water soluble forms were present in negligible quantities. All the fractions expressed a higher concentration during summer indicating more chances for severe Fe toxicity during that period. Mn was also present in large quantities. Compared to Fe, the concentration of different fractions of Mn were very small. The availability of Cu and Zn were also above the critical levels. The area was rich in AI. Reverse to that of Fe the different fractions of Al showed a lower concentration during summer. The free Al content was three times lesser than that of free Fe, while in exchangeable form Al expressed a higher concentration. The water soluble AI was very low. Surface water and ground water of the area were mildly acidic and saline during rainy season and they showed an increase during summer. The acidity exceeded the permissible maximum but the salinity was maintained below the permissible limit for agricultural and domestic purposes. Among the various elements present in water, Na and Cl- were the dominant ions expressing greater concentrations during summer in both surface and ground water. Based on SAR they were rated as moderately unsafe for irrigation during summer. The concentrations of K, Ca and Mg were within the permissible maximum for agricultural and domestic purposes. P was present only in traces. The Fe content was greater for ground water than surface water and it exceeded the permissible limit for drinking water. Though Mn was absent in ground water, it has already reached up to the permissible maximum in surface water. Al content exceeded the permissible maximum for domestic purposes. Cu, Zn, Cd and Pb were not detected in water. SO4-S, NH4-N and NO2+NO3- N contents of both surface and ground water were well below the critical levels suggested, but Cl' contents of both were sufficient to cause specific toxicity effect. The chlorinated hydrocarbon pesticides identi _ fied in the area were (X-HCH, y-HCH and DDT. They showed higher concentration during summer. Among the chlorinated hydrocarbons, DDT was present in larger quantities, though it was banned for agricultural uses, followed by (X-HCH. The concentration of y-HCH was comparatively small. The accumulation of fertiliser residues in the area was not so negligible. The highest concen- tration was observed for NH4-N during addi- tional crop season, at the time of basal dressing, both in soil and water. During punja season, a decrease of 55 to 60 per cent in soil and 10 to 12 per cent in water for NH4-N was observed. The content of N02+N03-N was comparatively low in soil due to continuous submergence. In water it was not as low as that of soil, indicating a major portion of N02+NOrN retained in water. P content of the area was very low. Its loss through drainage water was nil. A sizable quantity of K was also subjected to loss through drainage water, though the extent of loss was well below the level of N. Here also highest concentration was noted during additional crop season at the time of basal dressing both in soil and water. The study indicated that the area is subjected to severe pollution due to the accumulation of native toxic factors as well as residues of pesticides and fertilisers. The closure of Thanneermukkom regulator aggravates the situation by restricting the water movement.ThesisItem Open Access Increasing phosphours use efficiency in banana cv. nendran(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 1997) Shehana, R S; KAU; Alice AbrahamThe efficiency of phosphobacterin culture in increasing the availability of phosphorus from MRP and the resultant effect on the growth and yield or banana, cv. Nendran was evaluated by conducting laboratory incubation and field studies at FSRS, Kottarakkara during 1993-96. Representative soil samples from the field at FSRS, Kottarakkara were mixed with MRP, PS, FYM and lime in different combinations and incubated at 60% WHC for 90 days. There was only a slight variation in the pH of soil upto 20 days due to the effect of different inputs. After 20 days, the soil showed a tendency to become slightly acidic reaching a mean value of only 5.6 from the initial pH of 5.7. The P solubilising effect was maximum with a combination of PB, FYM and MRP. At the end of 90 days incubation, out of the 100 ppm P applied as MRP, a maximum of 19.31 ppm P became available in this treatment. P solubilised in the unamended soil was only 3.90 ppm and in the other treatments receiving FYM, lime and MRP either alone or in different other combinations, the values ranged from 9.2] to 16.73 ppm. ,-. The application of 3/4 level of the recommended P along with PB, FYM and mulch has produced a significant positive effect on growth and yield characters compared to all the other treatments including the treatment as per package of practices recommendation of the KAU. The highest bunch yield of 10.68 kg plant-1, which was significantly superior to the yield in all the other treatments was recorded by plants supplied with 3/4 level of recommended P as MRP, 10 kg FYM and PB inoculated with proper mulching. The increase in yield in this treatment was 7.55% higher than the yield from plants given fertilizers as per the POP recommendations of the KAU. The second highest bunch weight of 9.93 kg plant-1 was recorded by the plants which received the full recommended level of P along with N and K (POP recommendation). This yield was on par with the yield obtained in the treatment where only 1/2 the recommended level of P was used along with PB, FYM and mulch. The use of FYM and mulching was round to be an essential practice to obtain the maximum benefit from the use of PB. It may be concluded from the results of the study that for increasing the efficiency of utilization of applied P to banana in the acidic laterite soils, a combined application of MRP and PB along with FYM and mulch is essential. This package was found to be very effective in increasing the available- P status or soil, promoting plant growth and increasing the yield of banana with a lower level of P than what is recommended at present. For achieving a higher net return from banana cultivation along with other inputs like FYM and mulch, the use of 3/4 level of P and PB inoculation may be considered as a viable alternative to the present POP recommendation.
