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Open Access
Impact of eucalyptus and acacia plantations on soil properties in different pedogenic environments in Kerala
(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 1989) Byju, G; KAU; Thomas, Varghese
Eucalyptus tereticornis and Acacia Auriculiformis are two important exotic tree species introduced into our environment through National Social Forestry programme. These two species are said to have many qualities which qualify them for inclusion under the social forestry programme. These fast growing tree species have the unique capability of surviving and regulating their growth to prevailing growth factors. But environmentalists in India and abroad have questioned the feasibility of bringing fertile lands under these exotic species which they claim to have deleterious impact on soil properties, hydrological parameters, biotic associations and long-term socio-economic consequences. However, these arguments do not have a sound scientific basis due to lack of sufficient research data base. So a study was undertaken to find out the impact of these monoculture plantations on soil properties in different pedogenic environments in kerala. Soil profiles were taken from four locations representing different geoclimatic regions of Kerala. The locations were Wynad (Northern forested highland), Kottoor (Southern forested highland), Nileswar (Northern coastal) and Kazhakkoottam (Southern coastal). Altogether thirteen pedons were studied from different locations representing reserve forest, cultivated land, barrenland, Eucaiyptus plantation and Acacia plantation. Pedons were described systematically and subjected to physico-chemical analyses and also for assessing the extent and nature of microflora. Biomass studies and chemical analyses of plant samples have alsobeen undertaken. From the studies, it was revealed that monoculture plantations of Eucalyptus and Acacia have got deleterious impact on soil physical, chemical and biological characteristics. These deleterious effects were more in a forest environment compared to sandy tracts. Increase in gravel content, eluviation of clay, lower silt/clay ratio, increase in bulk density, lower water holding capacity, low moisture content and low water dispersible clay in soils under Eucalyptus in forest areas show that the process of ferrallitisation and soil degradation proceed faster under Eucalyptus. Chemical composition also showed decrease in soil fertility under Eucalyptus. In the sandy tracts, Eucalyptus and Acacia increased the soil organic matter, total nitrogen and available potassium, while almost all other parameters used for the study showed deleterious effects. Active iron ratio (Fe oxalate/ Fe dithionite) was calculated to assess the extent of induration and the results indicated a relative enrichment of crystalline iron oxides in monoculture plantations of Eucalyptus and Acacia which may also lead to induration. A decrease in microbial population was also observed in these plantations except the population of Rhozobium whose number increased in plantations of Acacia which is a leguminous tree. The above results indicated that planting of Eucalyptus and Acacia as monoculture has got very deleterious impact on soil characteristics and fertility . All these throw light on the imminent necessity to have a rethinking about the introduction of monoculture plantations with these exotic species especially in the reserve forest areas.
Open Access
Comparative morphology and physico-chemical properties of some forest and defrosted soils of Kerala
(Department of soil science and agricultural chemistry, College of Agriculture, Vellayani, 1989) Sivadasan, N; KAU; Aiyer, R S
In Kerala, continuous denudation of forests along the Western Ghats region has brought about hastening of the process of laterisation which becomes one of the major constraints to agricultural development. Deforestation of different types of forests such as deciduous, semi – evergreen, evergreen and shola may bring about laterisation to different extents. Deforestation and monoculture with different economically important species and plantation crops may delay or hasten the process of laterisation. The present study is, therefore an attempt to understand more about the effect of different monoculture vegetation such as cashew, eucalyptus, tea and acacia on soil properties in comparison with soils of adjoining virgin soils in deciduous, semi- evergreen, evergreen and shola forest ecosystems respectively. The present study reveals that deforestation has harmful effect on soil irrespective of the type of forest vegetation. It causes mechanical eluviation with higher migration of finer particles from surface downwards, increases bulk density of surface soil and lowers the aggregate stability of the soil. Organic carbon is found to be partly leached off and eroded off along with mineral soil. It is also burnt faster due to denudation. The contents of nitrogen and phosphorus increase while that of calcium and manganese decrease as a result of deforestation. Higher amounts of iron and aluminium are noticed in deforested soil than in virgin soils of the natural forests. The heavy mineral fraction constitutes from 2.5 to 27.6 per cent of the fine sand fraction. The dominant heavy minerals are the black opaques viz., ilmenite, red opaques such as hematite, limonite and goethite, sillimanite and zircon. The lighter fraction of the minerals is constituted mainly of quartz (22.6 to 97.5 per cent) with smaller amounts of feldspars and micas. The heavier fractionof the minerals are found to increase in soil due to deforestation brought about by residual accumulation. The influence of different monoculture / plantations on deforested soil varies with the type of vegetation. Increased root activity exhibited by tea and acacia at lower layers have strengthened the structural stability and improved the single value constants such as low bulk density, higher porosity and water holding capacity of the subsurface soil under these two plantations compared to soils under other plantations and virgin forests. The degree of weathering of soil varies with the type of vegetation. Based on the silt/clay ratio the soils studied can be arranged in the following order according to the observable factors on the degree of weathering : eucalyptus > tea > deciduous > semi – evergreen > cashew > shola > evergreen > acacia. Deforestation and monoculture with cashew, tea and acacia enhance the soil pH while monoculture with eucalyptus lowers the pH of the soil. Acacia is found to enrich the nitrogen status of the soil at a faster rate by its ability to fix atmospheric nitrogen. The study also reveals that ferrallitization advances in shola forest even if the level of organic matter in the surface soil is 5.19 per cent while no significant ferrallitization has been observed in acacia plantation having only 4.07 per cent organic matter in the surface soil though, both the soils fall under the same ecosystem. The critical role played by different type of vegetation in the manifestation of laterisation is yet to be studied. The micropedogenesis of kaoloinite from givvsite and silica in solution is clearly noticeable in laterised layers of the profile. Conversion of ferrouse to ferric iron the also observable in the thin section study of the soils. All soils are laterised with developing argillic horizonds and clay skins. The studies on soils of monoculture plantation crops such as cashew, eucalyptus, tea and acacia in comparison to virgin forest soils offers enough evidences from the present work to show that planted forests / plantation crops favour laterisation in general in comparison to virgin forests. Among the various types of monoculture, eucalyptus appears to enhance laterisation to the greatest extent while cashew and acacia favour laterisation to the least.
Open Access
Studies on the dynamics of forms of soil iron in the acid soils of Kerala during submergence
(Department of Soil Science & Agricultural Chemistry, College of Agriculture, Vellayani, 1989) Harikumar, K P; KAU; Ramasubramonian, P R
The main objective of the study were to understand the pattern of distribution of water soluble, exchangeable, active free oxide, total amorphous, amorphous organic, amorphous inorganic and crystalline forms of iron and their variation under the influence of submergence, the effect of management practices on the variations in the available forms of iron under submergence and the relationship between soil reaction and the forms of iron in the major acid rice soils of Kerala. Viz., lateritic alluvium. Kari, kayal, karappadom, kole and pokkali. The pattern of distribution of different forms of iron studied, varied significantly among the six soils. The water soluble, exchangeable, active, free oxide, total amorphous and amorphous organic forms of iron were maximum in the kari soil, while crystalline iron was maximum in the lateritic alluvium. Kari and kole soils had the highest content of amorphous inorganic form of iron. The minimum content of water soluble iron was recorded in the kole and the lateritic alluvium, exchangeable and crystalline iron in karappadom soil, active, free oxide, total amorphous and amorphous inorganic forms of iron in pokkali soil and the amorphous organic iron in the lateritic alluvium. The total iron was highest in the kole and the lowest in the karappadom soils. Correlation studies indicated that pH had a significant negative correlation with water soluble and exchangeable forms of iron, while electrical conductivity, CEC, organic matter and clay content had positive correlation. Electrical conductivity and organic matter were positively correlated with active iron. Submergence significantly increased the pH and the contents of some of the forms of soil iron. Crystalline iron however, decreased with submergence. Active and free oxide forms of iron had no significant effect. The pH attained peak values on the 20th day of submergence in the lateritic alluvium, 30th day in the karappadom soil and 60th day in kayal, kole and pokkali soils. However, kari soil showed steady slow increases throughout the period of submergence. The addition of organic matter @ 5 t/ha and 2.5 t/ha decreased the pH slightly up to 5th day and then increased and equalled that of the control on the 90th day in all the soils. The decrease in pH was significantly more in the higher level of treatment then in the lower level. Water soluble iron increased significantly due to the treatments in all the soils. The maximum increase was observed in kari soil and the minimum in kayal and karappadom soils. However, the release of water soluble iron due to the higher level treatment was more than that of the lower level. The exchangeable iron also increased due to the organic matter treatment. The maximum increase was observed in the lateritic alluvium and the minimum in karappadom soils. The increase in the content of exchangeable iron due to higher level of organic matter was significantly higher than that due to the lower level. The lime application at full LR and half LR levels substantially increased the pH upto the 5th day in all the soils except in the kari soil, after which it decreased with further periods of submergence. However, in the kari soil, a peak value could be noticed on the 20th day. Water soluble and exchangeable iron decreased significantly due to the lime treatment. The decrease due to full LR treatment was significantly more than that due to the lower level. The active iron neither increased nor decreased significantly due to the organic matter and the lime treatments.
Open Access
Microbial mobilization and immobilisation of nutrients in red loam soils
(Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellanikkara, 1989) Susan John, K; KAU; Alice, Abraham
A field incubation study with four treatments and five replications in RED was carried out in the typical red loam soils (Alfisol) of Vellayani, Kerala to determine the extent of nutrient immobilization and mineralization by soil microorganisms under the influence of various treatments like glucose, paddy straw and inorganic fertilizers during the rainy, winter and summer seasons in 1988-1989. Representative soil samples were collected from the experimental plots before and immediately after the application of treatments and after 21 days of incubation under field conditions. These soil samples were analysed for the status of organic carbon, available N and P and exchangeable K, Ca and Mg. A portion of the soil samples collected after 21 days of incubation under field condition was subjected to chloroform fumigation for 72 hours and after reinoculation with fresh garden soil was incubated for another 21 days. After the specified period, the soil samples were analysed for the status of nutrients mentioned earlier. From the analytical data the amount of nutrients assimilated or immobilized and subsequently released through mineralization was derived and the data subjected to statistical analysis. The study has shown that there is considerable variation between treatments in the extent of immobilization and mineralization of nutrients during the three seasons. Appreciable difference between the treatments was obtained for the contents of organic carbon and available nitrogen during the rainy season, available phosphorus during winter and organic carbon and exchangeable K, Ca and Mg during the summer season. The influence of treatments on the transformation of other nutrients during the different seasons was not appreciable eventhough a variation during the three seasons was noticed between treatments. The extent of organic carbon immobilization and mineralization was maximum during rainy season in the glucose amended plots registering a net assimilation of 18.0 – 23.9% and net mineralization of 14.1 – 17.3% respectively of the total organic carbon content of the soil. Amendment of the soil with glucose, paddy straw and fertilizers did not cause any appreciable difference in the mineralization of organic carbon. The fertilizer treated plots registered the highest rate of nitrogen mineralization equivalent to 26.2 – 34.0 kg N ha-1 during the rainy season. The immobilization and mineralization of available phosphorus was highest during summer with a net immobilization of 4.0 – 16.5 kg P ha-1 and mineralization of 3.0 – 12.5 kg P ha-1. In the case of exchangeable potassium, the net immobilization and mineralization was maximum during rainy season in the fertilizer treated plots. The rates of immobilization and mineralization of calcium and magnesium showed a random trend. The influence of different treatments on the microbial population of the soil has resulted in the highest population of bacteria, fungi and actinomycete during the rainy season in the straw amended plots. The favourable effect of a suitable temperature and moisture during the rainy season has presumably lead to a greater microbial activity and a correspondingly higher rate of immobilization and mineralization of the various nutrient elements.
Restricted
Sulphur status of the Kuttanad soils of Kerala
(Department of Soil Science and Agricultural Chemistry,College of Horticulture, Vellanikkara, 1989) Cicy, P Mathew; KAU; Jose, A I
An investigation was carried out to study the forms and availability of S in the acid saline soils of Kuttanad and to understand whether the application of S containing fertilizers is necessary in this region which is a major rice growing tract of the state. Surface soil samples (0-15 cm depth) were collected during summer. They consisted of 48 karappadam soils, 62 kayal soils and 41 kari soils. The available S in these soils was determined by four different extractants i.e., water, CaCl2 solution, KH2PO4 solution and Morgan' reagent. The physico-chemical properties like pH, EC, organic carbon, available P and available K were also determined in these soils. The fractionation of S was carried out in 39 soils selected from the karappadam, kayal and kari soils. These soils were also analysed for pH, EC, organic carbon, available P, available K, CEC, exchangeable cations and soil texture. The sulphur fractions estimated were total S, organic S, sulphate S and nonsulphate S. All the soils were acidic in nature with a mean pH value of 3.92. The kari soils were extremely acidic, the lowest pH value recorded being 2.7. The EC of the145soils ranged from 0.3 to 13.0 dS/m. Most of the kari soils were saline in nature. The electrical conductivity was negatively correlated with pH. The organic carbon content of the soil varied from 1.23 to 6.72 per cent with a mean value of 2.97 per cent. Kari soils retained relatively high amounts of organic carbon, the maximum value recorded being 6,72 per cent which corresponded to 11.58 per cent organic matter. Increase in organic carbon content of the soil Increased the EC and decreased the pH. In general, the Kuttanad soils were low in available P, values ranging from 1.2 to 10.3 ppm. Available P was positively correlated with pH and negatively correlated with EC and organic carbon. In general, the content of available K in soil was low, the values ranging from 8 to 725 ppm. It was positively correlated with the organic carbon content of karappadam and kayal soils. In general, soils of Kuttanad contained large amount of water soluble S, the mean value being 126.6 ppm. The value ranged from 25 - 395 ppm. On an average, nearly 6,3 per cent of the total S was in water soluble form. Maximum content of water soluble S was found.in kari soils. Water soluble S was negatively correlated146 with pH and positively correlated with EC and organic carbon. Available S extracted by CaCl2 and KH2PO4 ranged from 37 - 2400 ppm and 50 - 2450 ppm respectively. The calcium chloride extractable S and phosphate extractable S were negatively correlated with pH and positively with EC and organic carbon. The mean values of available S extracted by Morgan's reagent for karappadam, kayal and kari soils were .208.3, 481.7 and 571.6 ppm respectively with an overall mean of 419.2 ppm. The magnitude of available S extracted by Morgan's reagent was almost similar to that extracted by the phosphate solution. Available s extracted by Morgan's reagent established significant negative correlation with pH and positive correlation with EC, organic carbon, and available K. Values of available S extracted by the four extractants were significantly and positively.correlated- among themselves, the r values ranging from 0.6459** to 0.9912** .
Open Access
Physico-chemical characteristics, genesis and classification of soils from forest ecosystems in Kerala
(Department of Soil Science and Agricultural Chemistry,College of Horticulture, Vellanikkara, 1989) Elsy, P A; KAU; Venugopal, V K
A study was conducted to evaluate the morphological, physical and chemical characteristic of soil representing different forest ecosystem. In Kerala. Six soil profiles representing predominent vegetation types of Kerala, were selected for the study. The study areas were representative of the tropical evergreen, semi evergreen, moist deciduous, grasslands, hill top evergreen and dry deciduous types of forests. Profiles were excavated in these areas and detailed morphological studies of the soils were carried out. Soil samples representing the different horizons were collected for laboratory characterisation. The interrelationships of various physico-chemical characteristics and the distribution of iron and phosphorus fractions in soils were studied with a view to relate these characteristics to the genesis of the soils. Based on the available data attempts have also been made to classify the soils under soil taxonomy. The surface soils from all the profiles were rich in organic matter and had darker colours, ranging from greyish brown to brown. Increasing redness in the subsurface horizon though noticed in all the soils, was a conspicuous feature observed in the soils from the dry deciduous forests.Weak granular structure in the surface followed by sub- angular blocky structure in the subsurface layers was a feature common to all the soils. Coarse fragments, mostly in the form of secondary latorite gravel constituted a major portion of the soils under investigation.Wide variations in texture was observed between the soils from various ecosystems. Increase in clay content with depth was another feature observed in all the soils. Silt \ was the lowest, among the various size fractions. Positive and significant correlation was obtained between moisture at 0.3 and 15 bar with clay# while available water and clay showed a positive but nonsignificant correlation.The maximum water holding capacity and volume expansion were found to be closely related to the nature and content of clay and organic matter. The soils under dry deciduous forests registered the highest volume expansion and maximum water holding capacity. All the soils under investigation were found to be acidic in reaction. Organic carbon# nitrogen and C/H ratios were high in the surface horizons with decreasing profile trends in soils from most of the locations. Silica constituted the predominant constituent in all tho soils followed by Iron oxide content was less than Al2O3 and showed a positive correlation with clay. The total reserves of MgO, CaO, K2O and P2O5 expected of humid tropical soils.
Open Access
Nutrient management model for compensating spatial soil variability in rubber plantations in Amboori area
(Department of soil science and agricultural chemistry, College of Agriculture, Vellayani, 1989) Anilkumar, J R; KAU; Muhammed, C P
A study of the soils of rubber plantations in Amboori area has been undertaken to investigate the spatial variability of soil properties in those plantations with a view to relating it with the girth of the trees prior to tapping and to work out compensating models for nutrient management. Five plantations of three age groups viz. 1 – 2 years, 4 – 5 years and 6 – 7 years old but prior to the commencement of tapping were selected for this purpose. The plantations were having a slope of 20 – 300 and were planted with the rubber variety RR11 – 105. Soil samples collected from these plantations, from the previously fixed grid points separated by a lag distance (h) of 8 m along the slope, were analysed for the chemical properties such as pH, organic carbon, total and available nutrients. The leaf samples also taken, were analysed to know the nutrient contents in plant. Analysis of variance of the data to establish the variability, correlation and regression studies to relate the girth with nutrient variations in soil and plant, and computation of semi – variance Ý (h) for different lag distances for each nutrient to work out nutrient management models were undertaken. The study showed the existence of considerable spatical variability of soil properties in the plantations under study. Total nutrients such as total nitrogen, phosphorus and potassium were found to be spatially variable and significantly dependent on lag distances. However, three of the five plantations showed less impact of lag distances along the slope on the total nitrogen status of soil. While total calcium did not exhibit significant variations, total magnesium was found to possess spatial variation to some extent. A very significant spatial dependence characterised by an increase along the slope downwards with respect to available nitrogen, was an important observation of the study. Other available nutrients showed lesser degree of variations. Girth of trees when correlated with available nitrogen and organic carbon gave linear regression equations. Nutrient management models in terms of semi -variance were obtained for major nutrients of soil for compensating spatial variability of the nutrients. The models can be helpful in obliterating the effects of spatial variability of nutrients on crop growth. The model will be tested in the field at the Amboori tribal area Research Centre where extensive rubber plantations have been laid out.
Open Access
Influence of form of organic matter on the mineralisation of applied phosphorus in submerged rice soils
(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 1989) Nageeb, P H; KAU; Ramasubramonian, P R
A field experiment to study the effect of incorporation of different forms of organic matter on the transformation of native and applied phosphorous in submerged rice soils and their effects on the growth and yield of rice (Var. Triveni) was conducted in the Instructional Farm of the College of Agriculture, Vellayani during second crop season in 1986. The treatments included the application of three different form of organic materials (farm yard manure,greenleaves and composted salvinia) and two phosphate fortilizers (super phosphate and Mussooria phosphate). Practionation of soil inorganic phosphorous at fortnightly intervals for a period of 90 days and estimation of available P, exchangeable iron and soil reaction were carried out. Observations on the growth characters were made at active tillering, maximum tillering and flowering and yield of straw and grain were recorded. The chemical analysis of the grain and straw for N, P, K, Ca and Mg was also carried out. It was found that in general submergence of soil increased the transformation of both native and added P in to Fe-P, Al-P, Ca-P and saloid – P. Reductant-P and occluded-P fractions decreased with progressive submergence. Submergence of the soil markedly increased the available P status of soil. Phosphorous applied as super phosphate and Mussooria phosphate was recovered in different inorganic fractions in the order Fe-P > Al-P > Red-P > Occluded-P Ca-P >saloid-P. Organic matter addition suppressed the transformation of native and added inorganic phosphorous into different inorganic P fractions (Fe-P, Al-P, Red-P, Occluded-P and Ca-P) and maintained higher amount of added P in the soil in available form during the initial 75 days of submergence. A marked increase in exchangeable iron was also observed with continuous submergence. The process was accelerated by the addition of organic matter. Phosphate application significantly decreased exchangeable iron content in the soil. Submergence of soil resulted in a significant increase in soil pH upto 45 days beyond which it remained more or less constant. Organic matter treatment significantly decreased soil pH whereas addition of P in the form of Mussoorie phosphate increased the soil pH. The growth parameters (tiller count and plant height) recorded a significant increase due to the application of organic matter and phosphorous. The grain and straw yield increased significantly with the application of P fertilizers and organic matter. Application of Mussoorie phosphate plus green leaves recorded the highest grain and straw yield. There was a significant increase in the mineral contents in the plant by phosphorous and organic matter application. The study highlights the importance of organic matter in producing a better response to phosphatic fertilizers by rice in the submerged paddy fields.
Open Access
Heavy metals in fertilizers in relation to their accumulation in soils due to continuous fertilizer use
(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 1989) Sathyaprakasan, S; KAU; Abdul Hameed
The possible heavy metal pollution through continuous use of chemical fertilizers for the last several years, has become a topic of grave concern in recent times. It is possible that such heavy metals if present in soil in sufficient quantities, may enter the food chain and endanger animal and human life. The present study was taken up with a view to establishing whether the accumulation of heavy metals in soils and plants is appreciable so as to pose any health hazards. With a view to achieve the above aim soils and rice plants grown in four major rice soils of Kerala which were receiving high doses of fertilizers for the last several years, and also eight common fertilizers used in these areas were collected and analysed for the heavy metal content with emphasis to cadmium. Soils from plots receiving organic manures, chemical fertilizers and a combination of both from one permanent manorial experiment with tall’ , india rice (25 years under same treatments) and soil, plant and grain from another permanent manorial experiment with dwarf Jeponica rice (13 years old) were collected and analysed for their heavy metal content. A pot culture with added cadmium alongwith fertilizers as per package of practices was also conducted incorporating rice, amaranthus and guinea grass to study the plant to plant variation in the uptake and accumulation of heavy metals in their tissues. The result of the studies showed that the phosphatic fertilizers contained the highest amount of heavy metals and among the phosphatic fertilizers maximum amount of Cd was found in factomphos while Ni and Pb were highest in mussoorie rock phosphate. Among the four soil types investigated viz. the Karappadam, Kayal, Kari and Trivandrum sandy loam the highest content of total Cd Ni and Pb were observed in Karappadam, Kayal and Kari soils respectively. The content of extractable Cd and Pb was highest in Kari soil while the extractable Ni was highest in Kayal soil. The mean Cd and Ni content of rice straw from karappadam soil was found to be the highest where as the rice straw from Kayal soil registered the maximum content of Pb. The results obtained from the Permanent Menurial Experimental trials revealed that the continuous use of organic matter alone or organic matter and chemical fertilizers in combination increased the heavy metal content in soils and plants. In the pot culture experiment with rice there was no significant variation in the total as well as the extractable Cd in the soil after harvest among treatments with 0, 10, 20 and 30 g Cd ha-1. The same trend was observed in the straw and grain as well. The Cd content in amaranthus also was not having significant variation among treatments. But in guinea grass the Cd content was significantly higher in the pot which received the highest dose of Cd viz. 30 g/ha. Since the doses viz. 10, 20 and 30g Cd per heactre were fixed on the basis of annual addition through fertilizers the impact could be much less and therefore the results presently obtained cannot be’,said to be conclusive. Correlation studies revealed that the soil total Cd was positively and significantly correlated to plant Cd content. The extractable Cd was also positively and significantly correlated to soil P. Applied N and P fertilizers were seen to significantly influence plant Cd content. The applied K fertilizers on the other hand were seen to positively enhance plant Cd, Ni and Pb contents.

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