Lessons from Long Term Fertilizer Experiments


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Long term fertilizer Experiments - Effect on Soil Properties and Crop growth

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Lessons from Long Term Fertilizer Experiments

  1. 1. LESSONS FROM LONG TERM FERTILISER EXPERIMENTS Dhakshinamoorthy, M., Santhy, P., Selvi, D., Savithri, P. and T.M.Thiyagarajan Directorate of Soil and Crop Management Studies Tamil Nadu Agricultural University, Coimbatore-641 003 The continuously growing population and increasing demand for food call forgreater reliance on agriculture than had ever been witnessed. The mining of nutrients fromsoil for ages along with their losses due to erosion and other causes if allowed to continuewould severely limit crop production in the coming years. Fertiliser inputs haveundoubtedly proved to be one of the major components of raising the soil productivity.The increasing demand for plant nutrients grew by leaps and bounds with the introductionof high yielding varieties which even under the best possible management cannot be metfrom the inherent soil fertility . The present day agriculture all over the world has thereforebecome much dependent upon chemical fertilisers to produce more and more from theshrinking land area. Since the early days of use of chemical fertilisers there has been someapprehensions regarding the soil fertility and crop yield being adversely affected by theirprolonged usage. As a sequel to these had come the worlds oldest classical manurialexperiments started by Lawes and Gilbert at Broadbalk fields in Rothamsted (England).The succeeding decades saw permanent manurial experiments being set up in several partsof the world. India started three such experiments after the Rothamsted model towards theend of the last and the beginning of the present century at Kanpur (U.P.), Coimbatore(Tamil Nadu) and Pusa (Bihar) followed by some more permanent field trials at otherlocations. These classical experiments did provide valuable information on the effect ofrotational cropping , use of bulky organic manures, nutrient application alone or incombinations on crop yields, nutrient uptake and on changes in soil physico - chemicalproperties of the soil. The change over of the cropping pattern based on high yieldingtechnology and multiple cropping and breaking of the age old yield barrier gave newdimensions to agricultural production strategy in the country. The yield levels and thenutrient input requirements have gone up several folds with a rapid turnover of thenutrients in the soil plant systems. Multiple cropping, irrigation and pest control measures,all directed towards achieving higher levels of production, necessarily have a much greaterimpact on soil and crop environment than ever conceived before. It becomes imperative,therefore, to examine how far the soil, which is one of the greatest natural resources canbe manipulated without seriously damaging the long term viability of the farm on whichthe livelihood of all ultimately depends. There is a general agreement that long termexperiments play an important role in identifying the soil constraints that limit crop yieldsand help in monitoring the soil conditions so as to protect the crop plants and food chainfrom attaining harmful concentrations of various environmental pollutants in the years to
  2. 2. come, besides maintaining soil fertility and productivity through suitable soil ameliorativemeasures as necessary warrants. The Indian Council of Agricultural Research sponsored an All India CoordinatedResearch Project on Long Term Fertiliser Experiments during the Fourth Plan Period toexamine as to what would happen to soil fertility and productivity on a long term basisunder high input soil management technology. Thus, a new set of statistically designedfield experiments in keeping with the modern intensive system of agriculture were startedat eleven selected centres in 1971. Six more centres were added during 1996 to providemore wider representations for the major soil-climatic zones of the country. The treatments adopted at these centres essentially consisted of 50, 100 and 150 %optimum NPK, 100 % NPK with handweeding , ZnSO4 application @ 25kg ha-1 , S freesources of NPK fertilisers and FYM @ 10 t ha-1, 100 % optimum NP, 100 % optimum Nand a control. The lessons learnt from these Long Term Fertiliser Experiments will bediscussed in this paper.RESPONSE IN CROP YIELDS Balanced application of 100 % NPK with FYM @ 10 t ha-1, produced highestgrain yield response in almost all the soils and cropping systems. However , 150 % NPKrecorded the highest yield response in alluvial soil of Barrackpore and New Delhi and thered loam of Bangalore and Hyderabad. Among the various cropping systems studied, rice-wheat rotation followed at Pantnagar on foot hill (Terai) soil produced the highest averagegrain yield of the order of 10.7 t / ha / year over the years with an additional output ofabout 4 t / ha of cowpea fodder. Similarly, the grain yield under maize-wheat, rice-rice andsoybean-wheat cropping systems averaged from 7.5 to 7.7, 6.9 to 7.5 and 4.1 to 6.5t/ha/year, respectively. Thus, the importance of balanced NPK nutrition and FYMincorporation was very much evinced in maintaining yield stability.(Santhy et al., 1998a) In order to evaluate the net trend in yield over years in each treatment andcrop the average yield in each treatment in each year was related to time in a semilogfunction as Y = at b, _1where Y is yield in kg ha , t is the time in months and a and b are constants. A negative bvalue is an indication of declining trend and a positive one , for yield sustainability. The results indicated that in finger millet a declining yield growth overyears occurred in control and 100% N treatment whereas in other treatments the yieldgrowth was sustainable. In maize sustainable yield growth over years occurred in alltreatments including control. But in grain cowpea the yield growth was sustainable onlyin 100% NP, 100% NPK + ZnSO4 and 100% NPK + FYM treatments whereas in othertreatments the yield growth was found to be declining (Table 1). 2
  3. 3. Table 1. Temporal effect of Treatments on yieldTreatments Finger millet Maize a b a bControl 639 (-) 0.0006 118 0.0103100% N 916 (-) 0.0010 317 0.0061100% NP 2392 0.0007 1525 0.004050% NPK 2101 0.0015 1212 0.0048100% NPK 2101 0.0015 1480 0.0045150% NPK 2416 0.0012 1737 0.0040100% NPK + ZnSO4 2276 0.0010 1772 0.0035100% NPK + FYM 2724 0.0011 1920 0.0039100% NPK + HW 2441 0.0006 1669 0.0037100% NPK (S free) 2392 0.0006 1604 0.0040 (Murugappan et. al., 1997)RESPONSE TO NPK Mean response of rice to N ( kg grain / kg N ) was found to be 18 kg in newalluvium of Barrackpore, 6 to 10 kg in red loam of Hyderabad, 8 to 14 kg in laterite soilof Bhubaneswar and 12 kg in Terai soil of Pantnagar. While response of wheat to N was17 kg at Pantnagar, it was only 4 to 5 kg in medium black and acidic sub-montane soil.The N failed to give any response in acidic red loam soils(Ranchi and Bangalore). Poorresponse to N in medium black and acidic red loam soil was to be due to inadequateavailability of P. Response to P was found to be very high in acidic red loams (Bangalore andHyderabad) medium black soils (Jabalpur and Coimbatore) and acidic sub-montane(Palampur) soils where P has been found to be one of the major soil constraints limitingcrop production. Response to P in alluvial soils of New Delhi and Ludhiana have beenfound to be quite encouraging (8 to 13 kg grain / kg P 2O5 ). Effect of K on yield was found to be quite high in light alluvial sandy soil ofLudhiana and red loam of Hyderabad . Increasing response to K was recorded in acidicred loam, acidic sub-montane, foot hill and even in K rich medium black (Jabalpur) soilwhen N and P were not limiting. Response to K was not observed in the mixed black soilsof Long Term Fertiliser Experiments at Coimbatore centre. 3
  4. 4. EFFECT OF CONTINUOUS N APPLICATION Application of N alone had a deleterious effect on soil productivity resulting indiminishing yields in acidic red loam (Ranchi and Bangalore) and sub-montane (Palampur)soils where P and K were deficient. Even though the mixed black soils of Coimbatorecentre have medium P and high K status, continuous application of N alone has reducedthe yield to a tune of 70% over 100% NPK in finger millet and maize (Santhy et. al.1998 b) and Jayasree et. al. 2000). This ensures the importance of P and K in determiningthe response to N suggesting the need for balanced nutrition.EFFECT ON SOIL PHYSICAL PROPERTIESBulk Density Ploughing and cultivation increase soil aeration and the physical disruption causedby intensive cultivation can result in break down of soil aggregates and produce a tilth thatis very fine and loose. The reduced aggregate stability is associated with increasedporosity and aeration and a decrease in bulk density within the plough depth. Such areduction in bulk density was observed due to combined application of 100 % NPK +FYM in some intensive cropping systems (Table 2).Table 2. Bulk density of soils (Mg m-3) under intensive cropping systemsTreatments Location/Soil type/Cropping system Barrackpore Hyderabad Bhubaneswar Pantnagar Coimbatore Alluvial Red loam Laterite Silty clay Inceptisol loam Rice-Wheat- Rice-Rice Rice-Rice Rice- Finger Jute Wheat- millet - Cowpea Maize - fodder Cowpea fodder1. 100 % NPK 1.44 1.68 1.63 1.32 1.402. 150 % NPK 1.40 1.62 1.55 1.33 1.413. 100 % NP 1.41 1.58 1.62 1.29 1.424. 100 % N 1.46 1.78 1.61 1.28 1.365. 100 % NPK 1.40 1.34 1.56 1.31 1.30+ FYM6. Control 1.46 1.53 1.65 1.33 1.44C.D.(P=0.05) 0.014 0.12 0.08 0.008 0.063 (Anon., 1989 and 1999) No appreciable changes in B.D. were observed between the uncultivated A2horizon and the cultivated Ap horizon of an Andisol under long term cultivation in Japan.This has been attributed to the fact that the depletion of organic matter associated withcultivation was low (Table 3). The application of 100% NPK with FYM recorded a 4
  5. 5. reduced bulk density value of 1.30 Mg m-3 compared to other treatments which could beascribed to better aggregation. (Anon., 1999)Table 3. Effect of cultivation on soil propertiesProperty Uncultivated A2 horizon Cultivated Ap horizonOrganic C (g.kg-1) 93.9 ± 7.3 81.2 ± 14.2Total N (g.kg-1) 5.76 ± 0.53 5.46 ± 0.76C/N ratio 16.3 ± 0.7 14.8 ± 0.9Bulk density (Mg.m-3) 0.56 ± 0.06 0.61 ± 0.04 (Higuchi & Kashiwagi, 1993 )Porosity Soil porosity is influenced by the amount of clay and the arrangement of soilparticles. An increase in clay content is likely to increase the capillary porosity.Aggregation of soil particles into stable structure is bound to result in the properdistribution of capillary and noncapillary porosity. Continuous incorporation of cattlemanure increased the porespace in the OPM and NPM experiments at Coimbatore.Increase in total and noncapillary porosity and a decrease in capillary porosity due to thecontinuous incorporation of 100 % NPK have been observed in an intensive croppingsystem involving Fingermillet-Maize-Cowpea fodder (Table 4 ).Table 4. Effect of intensive cropping and continuous fertilisation on soil porosity(%)Treatment Total porosity Capillary porosity Non capillary porosity100 % NPK 56.14 38.26 17.87150 % NPK 56.98 39.47 17.51100 % NP 52.11 35.76 17.15100 % N 52.24 34.88 17.36100 % NPK + FYM 58.85 40.86 20.50Control 54.18 36.61 17.57C. D. (P=0.05) 2.04 2.82 2.85 (Anon., 1999)Hydraulic conductivity Intensive cultivation results in less organic carbon, low porosity, few water stableaggregates, a smaller mean weight diameter of water stable aggregates and lowersaturated hydraulic conductivity (Arvidsson and Hakansson, 1996). This is due to the factthat ploughing largely restores the macroporosity of the soil within the plough layer. Aslight increase in saturated hydraulic conductivity has been observed in Barrackpore 5
  6. 6. alluvial sandy loam soil and in Vertic Ustropept of Coimbatore under FYM treatment. Buta reduction in hydraulic conductivity was observed in laterite soils of Bhubaneswar underFYM treatment due to reduction in non capillary porosity.(Table 5 )Table 5. Hydraulic conductivity under intensive cropping (cm.hr-1)Treatments Barrackpore* Bhubaneswar* Coimbatore Alluvial sandy Laterite sandy loam Inceptisol sandy clay loam loam100 % NPK 0.095 3.02 1.81150 % NPK 0.099 3.00 1.87100 % NP 0.095 3.02 1.66100 % N 0.095 3.03 1.73100 % NPK + FYM 0.106 2.90 2.61Control 0.088 3.09 1.44 *(Nambiar and Abrol, 1989) (Anon., 1999)PHYSICO-CHEMICAL PROPERTIESSoil reaction ( pH ) Suresh Lal and Mathur (1988) reported that continuous application of fertilisersfor eight years lowered the soil pH. However application of FYM alone had eithermaintained or slightly increased the pH but the incorporation of fertilisers with itdecreased the same (Prasad et al., 1983). The rise in pH under FYM treatment was due tothe deactivation of Fe3+ and Al3+ with concomitant release of basic cations (Ca2+,Mg2+ andK+ ) during its decomposition. They also stated that the pH of the control plot had alsoincreased after 28 years of continuous cropping. This may be due to the release of HCO 3-1and OH-1 into the soil solution for the uptake of anions such as nitrate, phosphate,sulphate, molybdate and borate. However, no perceptible change in soil reaction was observed in near neutral toalkaline soils after a decade of intensive cropping and manuring under the ICARs LongTerm Fertiliser Experiments including Coimbatore centre (Santhy et. al., 1999) (Table 6).But there was an increase in acidity in acidic red loam soil of Bangalore and Ranchi andsub-montane soil of Palampur. Maximum acidity was observed in 100 % N treatment, theeffect being more pronounced in acidic red loam soil where urea and ammonium sulphatewere used as N source. The increased acidity may lead to a decline in productivity in acidsoils in the long run.Electrical conductivity ( EC ) The major source of salts to the soil is irrigation water and wherever the irrigationwater used contains considerable quantities of salts, it will result in increased electricalconductivity of the soil over the years (Wang and Fang, 1978 ). In general, the electricalconductivity of the soil does not vary markedly due to long term manurial practices(Anon., 1979), unless the schedule involves the addition of heavy doses as in the case ofgypsum (Singh and Abrol,1988). Long term application of lime and K to a TypicHaplustalfs soil increased the soil electrical conductivity where as continuous applicationof inorganic fertilisers alone (N, NP and NPK) for 14 years did not change the electrical 6
  7. 7. conductivity in a sandy loam soil (Kapur et al., 1986). In the Long Term FertiliserExperiments at Coimbatore centre, continuous cropping and manuring did not alter thesoil electrical conductivity to any appreciable extent (Table 6).Table 6. Effect of intensive cropping on soil physico-chemical propertiesTreatments pH Electrical conductivity (dSm- 1 )50 % NPK 8.1 0.95100 % NPK 8.2 0.75150 % NPK 8.2 0.80100 % NPK + FYM 8.1 0.63Control 8.1 0.62CD (P=0.05) 0.05 0.03 (Santhy et. al., 1999)Cation exchange capacity ( CEC ) The cation exchange capacity of a soil is influenced mainly by the content oforganic matter and clay fraction. Since long term application of manures and fertilisers islikely to alter the organic carbon status of the soil, significant changes in soil cationexchange capacity as a result of manurial practices over the years has been quoted in thepast (Krishnamoorthy and Ravikumar, 1973). Continuous application of N and compost torice crop in a permanent manurial experiment at Cuttack increased the cation exchangecapacity of the soil (Table 7).Table 7. Effect of N and compost on CEC of rice soils ( C mol. p + kg-1 ) N levels (kg ha-1) Compost levels ( t.ha-1) 0 9.2 Mean 0 21.6 22.1 21.8 22.4 21.7 22.1 21.9 44.8 21.6 22.9 22.2 67.2 22.2 22.9 22.5 89.6 21.3 22.6 21.9 Mean 21.6 22.5 (Patnaik et al., 1989) The cation exchange capacity of a sandy loam soil (Typic Ustochrept) waspractically unaffected due to the continuous application of inorganic fertilisers to a fixedmaize-wheat rotation (Kapur et al., 1986 ). Higher CEC was recorded under 100 % NPK+ FYM in a Long Term Fertiliser Experiment at Coimbatore and this has been attributedto the build up of humus due to the application of FYM and the presence of higheramounts of crop residues (Sheeba, 1994).SOIL NUTRIENT STATUSNitrogen 7
  8. 8. In a Long Term Fertiliser Experiment at Coimbatore, continuous intensivecropping was found to have a general depletion in the total N status of the soil. The orderof depletion of soil N reserve with crops in the rotation was found to be Maize > Cowpeafodder > Finger millet. The available N was also depleted in all plots including the controldue to intensive cropping except in plots receiving 100 % NPK + FYM ( Table 8 ).Table 8. Total and available N status in a Long Term Fertiliser Experiment(mg kg-1)Treatments Total N (mg. kg-1) Available N (mg. kg-1) Finger Maize Cowpea Finger Maize Cowpea millet milletControl 288 293 281 62 66 62100%N 516 509 510 72 71 75100%NP 516 511 512 77 73 7950%NPK 434 432 432 73 69 74100%NPK 523 531 532 76 74 77150%NPK 553 544 544 77 80 80100%NPK+ ZnSO4 553 540 541 75 74 77100%NPK + FYM 664 593 631 92 86 91100%NPK + HW 490 492 487 77 73 75100%NPK (S free) 497 486 487 74 72 72 *C.D.(P=0.05) 12.59 5.59 *Treatment Crop interaction effect (Velusamy, 1996) Cultivation is an oxidative process since it typically promotes good aeration andconsequently promotes rapid decomposition of organic matter and mineralization oforganically bound N. Mineralized N may be denitrified or leached besides fulfilling cropuptake and this may explain the reasons for depletion of N under intensive cropping. Crop rotations have been suggested to reduce soil N depletion. Olsen et al.(1970)found that crop rotation reduced NO3 leaching at a depth of 1.2 to 1.5 m by 34 to 82 percent compared to continuous corn. They found that the decrease in solution NO 3 wasdirectly proportional to the number of years in oats, meadow or alfalfa and attributed thisto the combined recovery of NO3 by shallow rooted oat crops followed by deep rootedalfalfa crops. In a Long Term Fertiliser Experiment on sugarcane for 11 years in a slightly acidicsoil, there was a drastic reduction in soil NPK status in the control treatment due tointensive cultivation . Application of NPK with FYM improved the soil fertility ( Rabindraand Gowda, 1986). Muthuvel et al.(1977) reported that the available N content washigher in the organic manure treatment than in the fertilised plots due to optimummicrobial population and quicker mineralization enhanced by FYM application. Balanced application of NPK at 100 % level reflected in a positive balance of N inalluvial soil of Barrackpore, Ludhiana and New Delhi , medium black soil of Coimbatore,red loam soils of Bangalore and Hyderabad, acidic sub-montane soil of Palampur and 8
  9. 9. laterite soil of Bhubaneswar. Negative N balance was observed in medium black soil ofJabalpur, acidic red loam soil of Ranchi and Terai soil of Pantnagar. (Nambiar and Ghosh,1984)Phosphorus In the Old and New Permanent Manurial experiments at Coimbatore, theplots receiving inorganic P and cattle manure recorded higher available and total Pcontent. In the Long Term Fertiliser Experiments, considerable build up of P was noticedin 100 % and 150 % NPK treatments at Barrackpore, Ludhiana and Delhi. Depletion of Pwas noticed in 100 % N alone as compared to control, probably due to greater removal ofP for enhanced plant growth brought about by N application. Depletion of P (from theinitial level) after 10 years was 37, 47, and 77 % at New Delhi, Barrackpore and Ludhianawhile it was 37, 42 and 66 %, respectively under control (Nambiar and Ghosh, 1984).Similar results have been observed at Coimbatore centre. The P reduction in the soil wasfor a continuous addition of N alone was from 490 to 423 ppm in total P and 4.92 to 2.00ppm in available P over a period if 20 years in the medium black soils of Coimbatore(Jayasree et. al., 2000).Potassium In ongoing Long Term Fertiliser Experiment at Coimbatore centre, continuouscropping even with the recommended dose of NPK + FYM had a declined on total aswell as available K status of the soil. The depletion was of high magnitude in situationwere no K additions were done (Murugappan et. al., 1999). The non exchangeable Kgenerally showed a declining trend indicating the role of this form of K in meeting the croprequirement when the soil available pool remains constantly under K stress. The total Kalso showed a declining trend with the progress in the number of crops, as a result of Kremoval by the crops which far exceeded the fertiliser K input into the soil. The availableK also decreased due to crop uptake over and the quantity of fertilisers applied (Table 9).Table 9. Content of K fractions in soil under Long Term Fertiliser Experiments (mg. kg-1)Treatments Water Exchange- Nonexcha Lattice-K Total K Available- soluble-K able K ngeable-K K50 % NPK 16 215 813 2621 3685 238100 % NPK 20 231 899 2620 3788 255150 % NPK 24 244 1036 2620 3939 273100 % NP 7 108 514 1621 3275 127100 % N 10 126 707 2627 3485 139100 % NPK 23 254 971 2618 3890 281+ FYMControl 12 183 813 2643 3665 198CD(P=0.05) 1 13 80 NS 89 13 (Santhy., et al.,1998b) 9
  10. 10. Similar results indicating a depletion in available K under intensive cropping hadbeen observed by Nambiar and Ghosh (1984 ).Organic matter Organic matter is the centre of nearly all life activities in the soil. It servesas a source of food for microflora, fauna and other living matter in the soil. Long termrecycling of crop residues can improve the organic matter content of soil as a result ofincreased dry matter production( Bhat et al., 1991). The rotation which included only acereal crop gave only a lower organic matter status as against a rotation with a greenmanure or legume crop( Havanagi and Mann, 1970 ; Campbell et al., 1991). The organicmatter is higher under continuous cropping than under fallow ( Jansen, 1987 ). The resultsof 15 years of Long Term Fertiliser Experiments at Ludhiana, Hyderabad, Bhubaneswar,Palampur and Coimbatore showed that organic matter levels increased due to intensivecropping ( Nambiar and Ghosh, 1984).Secondary and micronutrients A decrease in exchangeable Ca and Mg by fertiliser additions but increaseunder FYM treatment had been observed by several workers(Prasad and Singh, 1981 ;Suresh Lal and Mathur, 1988; Patiram and Singh, 1993 ).The results of Long TermFertiliser Experiments from Barrackpore, Bhubaneswar and Coimbatore centres haveshown that the available S content was decreased due to intensive cropping especiallywhen S free fertilisers were added. Addition of S containing fertilisers and FYM with 100% NPK maintained or improved the S status of the soil ( Nambiar and Ghosh, 1984). Asteep decrease in DTPA-Zn over years due to intensive cultivation of Coimbatore centrewas observed (2.58 to 0.90 mg kg -1). However the ZnSO4 application @ 25 kg ha-1 tomaize alone resulted in an increase in the available Zn status of the soil (2.86 mg kg -1)(Selvi et. al., 2000). Zinc deficiency symptoms were not observed at Barrackpore evenafter the 14th crop cycle ( Anon.,1989). Prasad et al.(1994) observed a similar pattern ofdepletion of micronutrients under continuous maize - wheat rotations. The biomass C, N and P were all found to be the highest for the contentapplication of 100% NPK + FYM. The activity of phosphorus enzyme was higher for theintensive application of 100% NPK + FYM which was on par with 150% NPK (Santhy,et. al., 2000). The biomass C : N ratio was narrower in the case of 100% NPK + FYMand wider in unmanured control than 100% NPK. Depletion of P and K widened theratio in case of 100% N application (Selvi, et. al., 2000).CONCLUSIONS The data collected from experiments conducted over a period of 30 years indicatedlittle response to N fertilizer in the absence of P application on Vertic Ustochrepts(Coimbatore) and Chromusterts (Jabalpur). Application of N fertilizer alone had adeleterious effect on crop yields on both Haplustalfs (Ranchi) and Hapludalfs (Palampur),and the crop yields in respect of N treatment were lower than the yields from unmanuredplots. The yield of crops appreciated markedly with the application of P fertilizer in 10
  11. 11. combination with N, which showed further improvement with balanced use of N, P and Kfertilizers. The integrated use of organic manures and chemical fertilizers was found to bequite promising in maintaining stability in crop production through correction of marginaldeficiencies of secondary and micronutrient elements in the course of mineralization on theone hand and providing favourable physical and soil ecological conditions on the other.The deteriorating productivity was found to be associated with the imbalance in secondarynutrients like S and micronutrients like Zn. The original productivity could be restoredwith the application of nutrients which were otherwise yield-limiting. The role of S inmaintaining productivity was more marked in respect of certain crops than others in themultiple-cropping systems. Its effect was more marked on kharif rice on bothEutrochrepts (Barrackpore) and Haplaquepts (Bhubaneswar) after 2 and 3 annualcropping cycles, respectively, as the available soil-S (Morgan’s-extractable S) dropped toaround 4 mg kg-1 soil. No perceptible change in soil pH was observed over the years (1971-99) in respectof soils with neutral to alkaline in reaction but the soil pH decreased by 0.9 - 1.0 from theinitial values on both Haplustalfs (Ranchi) and Hapludalfs (Palampur) under N treatment.However, incorporation of farm yard manure along with NPK fertilizers showed somemoderating effect on soil pH. Appreciable improvement in soil organic carbon over theinitial level was noticed at optimal to superoptimal (100-150%) NPK doses on almost allthe soils except on Hapludolls (Pantnagar), Eutrochrepts (Barrackpore) and Haplustalfs(Ranchi), where considerable reduction in organic carbon was noticed. However, theinitial level of organic carbon was maintained with NPK + FYM treatment. The available soil-N improved appreciably at optimal to superoptimal (100-150%)NPK doses over the initial levels on almost all the soils. It declined to a very low level inunmanured plots. The available soil-P at optimal to superoptimal (100-150%) NPK doseswas raised from low to high status on Chromisters (Jabalpur), medium to high onUstochrepts (Delhi), Haplustalfs (Ranchi), Hapludolls (Pantnagar) and Vertic Ustropept(Coimbatore), high to very high on Eutrochrepts (Barrackpore) and Haplustalfs(Palampur) and low to very high on Ustochrepts (Ludhiana). An appreciable build-up inthe available soil-K (N NH4Oac-extractable K) was noticed even at the optimal (100%)NPK dose on Ustochrepts (Ludhiana and Delhi) and Haplustalfs (Ranchi) and it was atsuperoptimal (150%) NPK dose on Hapludalfs (Palampur) and Hapludolls (Pantnagar).However, available soil-K declined over the years on Vertic Ustropepts (Coimbatore),Chromusterts (Jabalpur) and Tropaquepts (Hyderabad) even at superoptimal NPK dose,indicating considerable soil mining of its available K. The highest depletion in availablesoil-K was noted under NP treatment. Incorporation of farm yard manure (along withoptimal NPK dose) improved soil physical properties like bulk density, total porosity andhydraulic conductivity over other treatments. REFERENCESAnonymous. 1989. Annual Report of the AICRP on Long Term Fertiliser Experiments, ICAR, New Delhi. 11
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