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Open Access
Nutrient dynamics if the rice based cropping systems
(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 1989) Sundaresam, Nair C.; Subromonia, Aiyer, R
Open Access
Exchangeable aluminium as an index of liming for the acidic upland soils of Kerala
(Department of soil science and agricultural chemistry, College of Agriculture, Vellayani, 1987) Meena, K; KAU; Alice, Abraham
Aluminium toxicity is the major factor limiting crop production in the acidic soils and the usual practice of alleviating aluminium toxicity is liming* / The present investigation was carried out to find out the distribution of water s dluhle and exchangeable aluminium in the acidic upland soils of Kerala and to test the suitability of exchangeable aluminium as an index for liming them* It was further programmed to find out the growth, yield and nutrient uptake pattern of two acid sensitive crops namely cowpea and fodder maize in soils under different levels of exchangeable aluminium brought out by the use of different levels of lime* Chemical analysis of eighty soil samples representing the five major upland soil types of Kerala viz* laterlte, alluvial, red loam, sandy and forest a oil have indicated the highest amount of exchangeable aluminium and percentage aluminium saturation in the laterite soils* The soil with 3 high level of exchangeable aluminium and percentage aluminium saturation was selected for conducting a pot culture experiment to test the suitability of using exchangeable aluminium as an index of liming* The exchangeable aluminium content of this soil was maintained at different levels by applying different levels of lime and the performance of these crops in this soil was compared by making biometric observations and by chemically analysing plant and soil samples* From the results of the study it was seen that higher levels of exchangeable aluminium adversely affected the growth, yield and nutrient uptake In cowpea and fodder maize* Maintenance of exchangeable aluminium at 1*26 me/100 g with a corresponding percentage aluminium saturation valua of around 30, by the use of 500 kg lime/ha appeared to be the optimum for maximising the yield of cowpea* But in fodder maize this level of lime was found to be insufficient and complete elimination of aluminium toxicity appeared to be essential for maximising production* Since the critical levels of exchangeable aiuainiua appears to be different for different crop3, it is desirable that lias levels to reduce exchangeable aluminium to such a critical level alono be applied. The results of the present study thus point to the advantage in adopting the exchangeable aluminium level of soil as a better index of liming for various crops grown in the upland acidic soils of Kerala.
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
Nitrogen losses from the rice soils of Kerala with special reference to ammonia volatilization
(Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellanikkara, 1989) Anila Kumar, K; KAU; Rajaram, K P
In order to get a deeper insight in to the N dynamics of selected submerged rice soils, an investigation entitled “Nitrogen losses from the rice soils of Kerala with special reference to ammonia volatilization” was carried at the Regional Agricultural Research Station, Pattambi during 1985 – 87 with the following objectives. 1. To estimate the magnitude of ammonia volatilization losses from submerged rice soils, representing major rice growing tracts of Kerala. 2. To study the factors which are responsible for accelerating the rate of ammonia volatilization under flooded soil conditions. 3. To evaluate the effect of submergence, organic matter application, complementary effect of P and K on ammonia volatilization from the rice soil ecosystem. 4. To identity suitable N carriers capable of reducing the loss of N due to ammonia volatilization from submerged paddy soils. 5. To find out the effect of continuous application of organic and inorganic manures in lateritic submerged paddy soils on the quantum of N loss through ammonia volatilization. 6. To find out the transformations and extent of mineralization of applied urea. With these objectives, in view, a serious of laboratory incubation studies, followed by pot culture trials were carried out and the results were finally verified under field experiment also. Besides these, the plots of permanent manorial trial (dwarf indica) were utilized for estimating the N loss through ammonia volatilization on long term application of organic manures and inorganic fertilizers. In the incubation study for estimating the magnitude of N loss though ammonia volatilization, eight rice soils of kerala viz., sandy, karapadam, kayal, kari, pokkali, kole, poonthalpadam and laterite soils representing the major rice growing tracts of Kerala were incubated with no N and 27 g N m-2 as urea. Air train and acid trapping device was utilized to collect the volatilized ammonia. The results showed that sandy soil collected from Onattukara region registered an increased N loss through ammonia volatilization, whereas in the kole soil of kattukampal, the process was retarded to the lowest level. More than 75 per cent of the volatilization loss was observed within 9 days after urea application. Significant negative correlation was observed between ammonia volatilization and organic matter content, clay fraction and cation exchange capacity of the soil, whereas the coarse sand fraction showed significant positive correlation. Soil sterilization had little influence on ammonia volatilization in any of the soil under study. Another incubation study to assess the impact of quantity of urea applied on the quantum of N loss through ammonia volatilization was carried out using four soil types (sandy, kayal, poonthlpadam and laterite soils) with four rates of N application (9, 18, 27 and 36 g N m-2 ). The results indicated that the N loss through ammonia volatilization had a positive relationship with increased rates of urea application, though not linear. The complementary effect of phosphorus and potassium on the extended loss of N through ammonia volatilization was estimated in another incubation study utilizing the same four soil types with treatment as N alone, N and P, N and K and N, P, K @ 27:13.5:13.5 g N, P, K m-2 respectively as urea, superphosphate and muriate of potash. The results revealed that combind application of urea and muriate of potash was found to be significantly better in reducing the volatilization loss to be significantly better in reducing the volatilization loss of ammonia compared to the treatments, N alone and N and P. The incubation study to find out the influence of depth of submergence on the rate of volatilization of ammonia was conducted using the same soil types and four treatments (soil saturation, 5,10 and 20 cm submergence). The results showed that the soil samples maintained at saturation point recorded double the values for ammonia volatilization, compared to samples kept under submergence of 20 cm depth. The effect of application of organic matter on N loss through ammonia volatilization was studied in the same four soil types with the treatments as no organic matter, 0.25, 0.50, 0.75 kg organic matter m-2 as farm yard manure. The results indicated that application of organic matter was found to reduce volatilization losses considerably in all the soils studied and the lowest value recorded was for the treatment receiving farm yard manure @ 0.75 kg m-2. The relationship between N sources and the extent of volatilization of ammonia was investigated in another incubation study employing the same four soil types and ten different N carriers to supply 27 g N m-2. The relative efficiency of different N carriers in reducing the ammonia volatilization loss was in the order sulphur coated urea > urea mudball > gypsum coated urea > rock phosphate coated urea = neem cake coated urea = ammonium sulphate = ammonium chloride > urea : coconut pith: soil = urea. The pot culture study to trace the pathway of transformation and extent of mineralisation of urea under flooded soil condition consisted of three soil types (laterite, kari and poonthalpadam soil) and two levels of N (no N and 90 kg N ha-1 as urea). The rate of mineralisation of applied urea followed the soil reaction and the mineralisation stopped at the stage of NH+4 formation and hence chances of N loss through denitrification is meagre, unless the soil is aerobic. The second pot culture experiment was conducted with a view to identify the different ways that result in minimum loss of N through ammonia volatilization in sandy and laterite soils. The study showed that the decreasing order of N loss through ammonia volatalization from different N carriers followed the order, urea basal = urea; coconut pith: soil = coaltar coated urea = gypsum coated urea = rock phosphate > coated urea > urea split > urea super granule > urea mudball > sulphur coated urea. The five treatments selected from this experiments viz., urea split, urea mudball, urea super granule, gypsum coated urea and rock phosphate coated urea on reduced ammonia volatilization and high grain yield were compared in another pot culture trial and finally it was verified under field experiments in trial and finally it was verified under field experiments in laterite soil. The results revealed that urea mudball placement in the anaerobic layer of soil was found to reduce the n loss through ammonia volatilization to negligible level. Treatments with surface application of rock phosphate coated urea and urea in split dose ranked second and third position respectively in reducing the volatilization losses. Treatment receiving split application (top dressing of urea at 20 and 40 DAT) reduced ammonia volatilization considerably. Significant positive correlation was found between the cumulative N loss through ammonia volatilization and flood water pH measured at 0800 hrs and 1400 hrs, flood water NH4 – N content and flood water bicarbonate content. The pH of flood water measured at 1400 hrs were significantly higher than the value recorded at 0800 hrs and highest diurnal variation was observed for treatment with urea super granule deep placement. The urea super granule deep placement treatment resulted in increased grain yield in both the pot culture trials and field experiment. However, in field experiment the effect of different N carriers on grain yield was found to be uniform. The periodical N uptake by plants as well as N accumulation in grain and straw at harvest were found to be higher in the case of treatments receiving USG deep placement and urea split application. The effect of long term application of organic and inorganic nitrogen sources in soil on the rate of n lose through ammonia volatilization was studied utilizing the permanent manorial experiments. Plots receiving combined application of cattle manure + green leaves + NPK @ 45:45:45 kg N, P2 o5, K2 o as ammonium sulphate, super phosphate and muriate of potash were recorded the lowest value of n loss via ammonia volatilization when compared to other treatment plots.
Open Access
Nutrient dynamics in the rice based cropping systems
(Division of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 1989) Sundaresan Nair, C; KAU; Subramonia Aiyer, R
The experiment consisting of five cropping sequences viz. rice - rice – rice (A1), sweet potato – rice – rice (A2) cowpea – rice – rice (A3) daincha – rice – rice (A4) and fallow – rice – rice (A5) and six treatments with varying doses of N P and K were conducted to study the performance of the sequences in relation to the nutrients required for optimising the out put from the sequences. The field experiment was laid out at R.R.S., Pattambi in 1980 – 81 and the experiment was conducted for two consecutive years ie. For six seasons. The experiment was started with the summer crop of 1981, namely summer rice (Triveni), sweet potato, cowpea, daincha and a summer fallow wherein the land was ploughed twice and left as such without any crops. The component crops were raised with five treatment variations modified from the recommended doses for each crop. The biometric observations for the summer crops, virippu and mundakan crops were recorded. The indications were that treatments have a significant effect on summer crops virippu and mundakan rice crops of 1981 and 1982. The yield shows that both treatments and sequences have a significant effect. The sequence daincha – rice – rice and the cowpea – rice – rice sequence gave the highest yield. The chemical analyses of plant parts of the summer crops, virippu and mundakan rice crops of both 1981 and 1982 show that the treatments have no effect on the NPK content. The soil study shows that the cropping sequences have a significant effect on soil pH. A pH decrease was noticed in all the sequences, the highest decrease being in the rice – rice – rice sequence. The organic carbon level of the soil is also affected due to the cropping sequence. The rice – rice – rice sequence shows a maximum decrease in organic carbon level and the daincha – rice – rice – rice shows a gain in organic carbon level of the soil. The total nitrogen of the soil shows a decrease in all the sequences and maximum decrease was noticed in sweet potato – rice – rice sequence. The available nitrogen level also was influence both by the sequences and treatments. A decrease in available nitrogen was noted to be a maximum in the rice – rice – rice sequence. The total P and available P levels show an increase in all the sequences and were high in daincha – rice – rice and cowpea – rice – rice sequences. The treatments also have a significant effect in maintain the P level in soils. The total K status of the soil as well as the exchangeable status of K shows a decrease after two year of cropping. The nutrient uptake studies reveal that the maximum NPK uptake takes place in the sequences sweet potato – rice – rice followed by rice – rice – rice and cowpea- rice – rice – rice followed by rice – rice – rice and cowpea - rice – rice. The balance sheet of nutrients reveals that nitrogen and available phosphorus in all sequences show a decrease and increases with decrease in fertilizer levels. The balance sheet of K shows that the soil maintains K levels. The sequence daincha – rice – rice is the best in maintaining a high K status in the soil. An analysis of the economics of cropping sequences reveal that the sequence sweet potato – rice – rice with full recommended dose of fertilizers gave the highest net return, which was followed by Cowpea in – rice – rice and rice – rice – rice. From nutrient balance studies, yield and economic analysis it is clear that any attempt in reducing the quantity of fertilizer for the component crops of the sequences affects the yield, besides deleteriously affecting the fertility of the soils. Any decrease in the fertilizer doses in the sequences will not be economical. With a long range view of enhancing crop output from cropping sequences and maintaining soil fertility, it becomes necessary to enhance and maintain higher fertility levels.
Open Access
Potassium supplying capacity of Neyattinkara- Vellayani soil association and its relationship with potash nutrition of major crops on them
(Department of soil science and agricultural chemistry, College of Agriculture, Vellayani, 1989) Valsaji, K; KAU; Subramonia Aiyer, R
Detailed study on the potassium supplying capacity of Neyattinkara-Vellayani soil association and its relationship to potash nutrition of major crops on them namely coconut and cassava has been made. This soil association represents the red loam soil type and consists of Neyattinkara series tentatively classified under Typic Eutropepts and Vellayani series under Typic Tropudalfs. Soil samples were collected from selected fields under coconut and cassava for the dominant soil types namely sandy clay loam and sandy loam soils under Neyattinkara and Vellayani series. To find the most suitable depth and location of soil sampling for coconut samples were also drawn at two different depths of 0-30 and 30-60 cm from basins and interrows. Empirical methods, quantity intensity studies, electro ultrafiltration studies and foliar diagnostic techniques were employed to decide on the most suitable method for plant available K. The various intensity, quantity and capacity factors which relate the readily available, difficultly available and storage or buffer capacity were assessed for a proper appraisal of the K status and supplying capacity. The various soil K parameters such as total K, water soluble K, exchangeable K, available K, nonexchangeable K, HNO3 extractable K, H2SO4 extractable K, sodium tetraphenylboron extractable K and percentage K saturation were found to be low. The water soluable K formed higher proportion of available K than exchangeable K. Interrelations showed that water soluble K, exchangeable K and available K are in dynamic equilibrium. Nonexchangeable K did not show any relationship with available K indicating that it is a poor source of available K. Quantity-intensity studies showed that the shape of the Q/I curve was similar in all types of soil since they belong to a group of related soils. The Q/I parameters like Are.K, Ko, Kx. KL and potential buffering capacity values were low. The KL values were higher than NH4OAc.K. The free energy values were found to be high indicating easy release rates of K. For both coconut and cassava, the leaf K did not show any consistent relationship with the soil K parameters. Among the Q/I parameters, KL had significant relation with leaf K of coconut. EUF 10 and EUF 35 showed significant relationship with leaf K of both coconut and cassava. Electro-ultrafiltration studies showed that the easily desorbed K was more than the strongly desorbed K indicating easy supply rate. The EUF 30-35 values were related to HNO3.K showing that this fraction included some initially nonexchangeable K. EUF 10 had significant relation with exchangeable K and EUF 35 had significant relation with exchangeable and available K. The buffer parameters BK (EUF 10/EUF 30) and EUF.Q (EUF 30-35/EUF 30) values were low indicating low buffer capacity. The EUF desorption pattern showed that the first peak was within 10-20 minutes and prominent than the second peak. This indicated low reserve K but easy supply rates. The EUF desorption curve of soils with high NH4OAc.K was above that of soils with low NH4OAc.K. This indicated that with increase in NH4OAc.K the easily desorbed K also increased. The yield of coconut and cassava were related to the various K parameters to evaluate the suitability of different methods for available K. In most of the cases NH4OAc method was found to be suitable for both coconut and cassava. Leaf analysis was also found to be suitable. For cassava the result obtained after 41/2 months is meaningless for the current crop. For coconut collection of index leaf is laborious. It was also found that the Q/I and EUF were suitable for coconut. But these methods cannot be followed in routine soil testing because of the high input of laboratory work involved. Considering these aspects it was found that NH4OAc method is the most suitable one because it is simple, cheap and easy to adopt. Based on the NH4Ac.k content the fertility status was found to be low to medium. The various intensity, quantity and capacity factors of soil K, Q/I and EUF parameters revealed that this soil association has low K supplying capacity. Hence heavy dose of K fertilizers is required. Split application is preferable especially in sandy loam soils to reduce leaching losses. NH4OAc.K which was found as a suitable indicator of plant available K varied significantly in basin and inter-row samples of sandy clay loam soils. This K fraction did not vary with depth in both sites. In general, the K nutrient index indicated that the basin samples had a higher level than inter-row and surface samples. Thus basin sampling at 0-30 cm depth was found to be the ideal site of soil sampling for coconut tree.
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.

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