Acid soils develop under humid tropical (HT) climatic environment with a loss of some major nutrient elements, and thus the development of acidity in soils is considered to be a sign of chemical degradation. While estimating the area degraded by acidity, tropical Indian soils with strong (pH < 4.5) and moderate acidity (pH 4.5–5.5) only were considered. About 6.98 m ha area is affected by soil acidity, which is about 9.4% of the total geographical area of India.
Soils of HT climate in the states of Kerala, Goa, Karnataka, Tamil Nadu, Western Ghats and north-east hills (NEH) areas are strong to moderately acidic Alfisols, Ultisols and Mollisols and their further weathering in HT climate would finally end up in kaolin dominated Ultisols with considerable amount of layer silicate minerals. Thus siliceous nature of the HT soils (especially the Ultisols of Kerala) is reflected in the SiO2:R2O3 (1.4–5.0) and SiO2:Al2O3 (1.8–6.0) ratios (Pal et al., 2014), suggesting an incomplete desilication process. The amount of SiO2 and its molar ratios are comparable with some of the Oxisols reported from Puerto Rico, Brazil, and other regions of the World. However, in the acidic Alfisols, Ultisols and Mollisols, the process of desilication no longer operates in present day conditions because the pH of the soils is well below the threshold of∼9.
The OC rich Ultisols have less Al-saturation in surface horizons due to the downward movement of Al as organo-metal complexes or chelates, but have higher base saturation than the sub-surface horizons due to addition of alkaline and alkaline metal cations through litter fall, and there is no desilication and transformation of kaolin to gibbsite. In view of contemporary pedogenesis, it is difficult to reconcile that Ultisols (especially of Kerala hitherto considered to be of international reference for laterite) would ever be weathered to reach the Oxisols stage with time frame as often envisaged by the pedologists.
Such OC rich acid soils are not kaolinitic as they are dominated by kaolin mineral (a mixed mineral) as their clay CEC is > 24 cmol (p+) kg-1 determined by BaCl2-TEA for total acidity plus bases by NH4OAc, pH7 method). These favourable chemical and mineralogical endowments help support the economically important forest and horticultural products, cereal crops, tea, coffee and spices. In view of the present successful and economically viable various land uses, it would not be prudent to class them as chemically degraded soils.
The above knowledge is available through a recent review (attached) (Pal et al., 2014. Catena 121:260-278). But it is now made open for inviting valuable and useful comments/ suggestions of our esteemed colleagues all over the globe to accept or reject the finding that ‘acid soils are truly not degraded and never loses their usefulness’ even under adverse HT climatic conditions, and with suitable managements they show enough resilience in producing food and fibre for human sustenance.
I think, that it is better to avoid generalization as "acid soil are degraded", or "acid soil are not degraded", because from pure chemical point of view "acid" means "having pH
Dear Dr. Pal Sir,
Myself working on tropical soils and conducted exploratory, reconnaissance and detailed soil surveys to characterize, classify and map tropical soils of high rainfall high temperature climates with considerable dry period. I am agreeing with the idea mooted by you that all highly acidic soils are not chemically degraded and can be brought back to the cropping condition requirement.
Surface soils and litter of forest or plantation cropped areas will be less acidic and comparatively rich in bases and more than active roots of tree species will form a map in the surface soil of around 20-30 cm and absorb bases and moisture, while tap roots and its secondary and teritiary branches grow vertically downwards and horizontally for its physical strength and absorption of water molecules even during temporary dry spells. For each cation is absorbed by plant root one hydrogen ion is given out on exchange will also create acidity. With continuous application of ammoniacal and phosphatic fertilizers in plantations and annual cropped areas without liming, there is chances of increasing acidity twofold. As the liming materials generally used are sparingly or non-soluble there is chances of development of subsoil acidity, which can be controlled by application of gypsum which will remove or reduce aluminium saturation from exchange complex.
There are some plantation crops like rubber, for which liming was not a practice so far and did not find in recommendations of RRII, for which we advised RRII to have a recommendation for liming as the soil acidity is increasing year by year. Earlier P was supplied with as super phosphate, which contained calcium sulphate. Now ammonium phosphate replaced super phosphate. As a result now rubber estates and coconut plantations in humid tropics face acute shortage of calcium and magnesium along with boron (and zinc) deficiencies, which is going to be a big challenge in cropping of hot humid tropics, where the litter fall from trees are the sources of bases, which the long tap roots extract from distances and after wards it will remain in leaf litter, which will be made available to the active plant root mat by the fast disintegrators(soil fauna) and decomposers (soil microflora and vam)
If this system continues without intensive agriculture and nutrient mining the equilibrium will last without much degradation
anil
@ Dear Michal and Anil
Thanks for your right interventions and making discussion and debate more exciting.
Thank you Dr. Michal sir and Dr. Pal Sir and others!
I wish to add a few more lines: Very high acidity around 4.5 pH also promote disease causing fungi to culminate into epidemics (Like Phytophthora, Pythium etc., diseases caused by them are very common hot humid tropics with high rainfall and high humidity) to dominnate over beneficial bacteria which help in mineralization of organic matter, phosphorus solubilization, nitrogen fixation, nitrification etc which proliferate at slightly acidic pH around pH 6.0. Bacterial fertilizers added to plantations at high acidity will perish immediately if liming not done prior to their introduction.
anil
Can refer one conference paper 9th PSILPH also
anil
The acid soil problem is complicated at the same time much studied.The problem of soil acidity may start at pH of around 6.0.But may not be a real problem for forest and plantation crops and some field crop species.The base saturation is an index of acid soil degadation or detereoration.In the range of pH 5.0 to 6.0 the base saturation may vary from16%to 67%.I believe that the real degradation starts with the presence of soluble Al species below pH 5.0 ( pH 4.7).Some forest systems may maintain certain soil acidity level.But some tree species may decrease the soil pH.There have been reports of decrease in pH when forest trees are harvested .Even aforestestion can decrease the soil pH.Agricutural systems are more prone to pH decrease compared to forest and plantation systems.Recent global meta-analysis of research done indicated decrease in soil pH with nitrogen addition.The last sentences of the paper reads"Global soils are now a buffering transition from base cations(Ca,Mg,and K) to non-base cations(Mn and Al).This calls our attention to care about the limitation of base cations and the toxic impact of non-base cations for terrestrial ecosystems with N deposition. I shall give a few references in my further interactions.
I also join with Dr. Subbarao sir's answer, Fe, Mn and Al are the dominant cations in the systems with very acidity and multi nutrient deficiencies including calcium and magnesium is going to be a big concern along with high Aluminium saturation in hot humid tropics with heavy rainfall apart from detrimental effects of high sub-soil acidity. Surface soils are more buffered due to high organic carbon and supply of bases from leaf litter and have less acidity compared to sub-soils.
anil
@ Indranil - Though pedochemically altered these soils are supporting good agriculture, horticulture,forestry etc , however with some specific species not grown any where.Then why to designate them as 'degraded'?
Fascinating discussion on a equally fascinating question raised by Dr Pal sir. i can share my experiences with regard to acid soils of northeastern region being engaged for growing citrus ( Khasi mandarin , predominantly the major perennial fruit crop after other crops like mango , litchi passion fruit ) . An excellent Khasi mandarin comes out on un-limed and unfertilized acid soils having soil pH 4.5-6.0, right from floodplains of upper Assam to either Jampui hills of Tripura or Lohit/Pasighat of Arunachal Pradesh. And , it is continuing over the last 40-50 years ( Based on our visual observation) with continued sustainable fruit yield without any deterioration in any of the commercially important fruit quality parameters. What could be the decisive factors for such success ( needless to say acid soils are chemically or pdeogenically degraded , such clues so obvious from such crop performances) .? How do you assign such success, either to the phosphorous being more loosely held to organic matter than fixed irreversibly by hydroxy iron /aluminium , thereby, better nutrient environments ( often , we coin bio-availability of nutrients) are naturally available to the plants , since root systems are never damaged . These conditions also predispose such plants to experience a continuous inflow of required carbon sink through recurrent ,since adaptation of stress ( water deficit stress or low temperature stress ) may involve an increased growth of root system , constituting an immediate carbon cost for maintenance of increased biomass , a pre-requisite to better crop performance ..?
@Dear Anoop - Thanks for sharing very important information gathered by you,which will definitely help to define 'degradation' of acid soils.
Dr.Srivastava, soil acidity may not hamper the productivity of mandarin as it is a tree species which obviously had extensive deep root system. The soil acidity is acute problem in surface and immediate subsurface horizon. Besides phosphorus transformation through Fe/Al may be altered by the huge biomass/organic matter produced by these tree in this particular growing situation.
Citrus has basically a shallow root feeding habit ( more than 70-80% feeder roots remain confined to top 0-15 cm depth , regardless of season of the year , many times 100% feeder roots remain confined to top 10 cm only , especially in rainy season , tap roots are poorly developed in all citrus cultivars ) as far as nutrient foraging is concerned. So citrus is able to sustain that acute soil acidity , with an excellent fruit quality for so many years ( more than 50 years, without any additional externally added nutrient source , to say the least ), no way it supplements to consider acid soils a degraded soils , as evident from crop responses in ultimate terms. Let us look at the chemistry of phosphorous fixation and release under varying levels of organic matter content plus soil moisture regimes..?
Dr Anoop Srivastavji,
Will citrus plants show hidden hunger if grown under strong acid environments as in NE especially for K, Ca & Mg?
ANIL
Dear colleagues, we have to see the acid soil degradation issue wholistically.If soil pH falls below a certain level ,say 5.0 or below what will happen to clay mineral Constitution, soil structure, clay loss ,microbial biodiversity, earthworms population, certain plant species survival,weed species diversity, nutritional value of animal ,human and fish food? We have to see or monitor the prevailing conditions whether they are conducive for further acidity development or arresting further degradation.One has to see the degree of degradation and ecosystem functioning. Fragile ecosystems have to be assessed,managed,monitored and conserved.
Dr Anil Kumar , except fro K, we did not find any hidden hunger for Ca and Mg, but surelt with lime/dolomite application , crops responds much better to applied nutrients like N, P, Zn etc.. . Infact , it is impossible to find any true Ca or Mg deficiency in field, but K-deficiency in form of smaller fruit size could be visualized. But , again , in perennial fruit crops, very often , smaller fruit size is linked with greater number of fruits , that hastens the reduction in fruit size. Therefore , we need to differentiate the causes of smaller fruit size, very carefully . in order to identify these nutrient constraints , we undertake leaf analysis , which reveals nutrient deficiencies much better than simple soil test-based interpretation . There is also need to utilise citrus species specific leaf nutrient standards , especially using DRIS norms , already in practice so successfully. And , same stands true with regard to soil test based interpretation. This is one issue...
Physiography of acid soil belts , shifting cultivation, whether or not cultivation is practiced on lands intercepted with conservation practices , they all together dictate , shall we consider acid soils , chemically degraded..? But , again , if there is certain defined pedogenesis of acid soils , how different crops respond so well , and if this is the case, how can we call them as chemically degraded..?
@ Anoop - Your statements in the last three sentences are worth considering. Hope to get more thoughtful inputs to this very important issue of soil science.
Dear Dr. Anoop and Dr. A . Subbarao sir and others,
We have encountered acute Ca, Mg and B deficiencies in almost 80 % of the coconut plantations of Kerala by analyzing surface and sub soils, but plant leaves seldom show deficiencies of Ca and Mg. But in case of B clear cut symptoms are there and seen more if correct all other deficiencies because of law of minimum or limiting factor. But in B deficient plots significant reduction in yield and less number of female flowers or less fruit setting. Here B Ca and Mg deficiency is attributed to inherently low base high rainfall well leached hot tropical soils of Kerala and B defifciency apart from hot tropical high rainfall climate and dry spell making fast decomposition of organioc matter that highly porous nature of soils owing to dominance of kaolinite clay in surface and sub-soils of Kerala. The farm yard manure itself will lack boron as animals are also getting low B diet. This low calcium will also lead to high child mortality and that of elderly people in backward areas along with animal mortality due to low Ca diet. The young calves eating soil is an indication of acute calcium deficiency leading to epidemics. Plants will show low magnesium levels through low chlorophill and yellowing of leaves and poor biomass production and low yield. High Aluminium saturation restricts root growth assisted by low K levels. Disease causing fungal population of Phycomycetes class dominate over beneficial microbes. By correcting surface and subsoil acidity we can save a region from epidemics
anil
Interesting Dr Anil Kumar , how do deficiencies of different nutrients like Ca, Mg, K affect the coconut quality ..? Whether Fe-toxicity compliments the suboptimum nutrition with regard to Mg , K ..? What about Fe-induced Zn deficiency ..?
Dr.Anilkumar, very interesting information. I expect similar wholistic information from different acid soil regions covering/connecting soil-microbial-plant-animal/human system.I shall further interact on your comments.
Dear Drs. ASR, AS,AR and Anil - Thank you all for your valuable inputs in better understanding of the nutritional aspects of acids soils. However, I would like to request you all for your arguments in favour or against the idea mooted here that are acid soils truly degraded or not. This has become very critical issue in soil care when we all know that all soils whether acidic, alkali or neutral, need nutritional care in view of their some specific deficiencies.
Dear colleagues, what criteria should we use for separating degraded acid soils from not so degraded soils? What level of minimum base saturation is desired in acid soils for normal nutrition ?( at least for basic cations ).What is the critrical Al concentration in solution and Al saturation on exchange complex for soil clay mineral destruction and plant physiology impairment ? Will the bases from leaf litter and residues provide sufficient bases to counter H and Al activity in the system under different acid soil environments ?At least in two states in India pH lowering on wider scale reported due to agricultural practices(,Punjab and West Bengal).Can we avoid further degradation of acid soils especially those below pH 5.0 ? How far the plant and microbial diversity is affected with increasing soil acidity ? In words of Dr. Panda acid soils and poverty go together(may not be exact words). Ultimately we have to see human and animal nutrition in those areas.
@Dr.ASR - Thanks for your timely interventions as these are very important issues while our national data on such soils is ~7 m ha.We need to sort out some critical basic issue of soil chemistry and mineralogy including Al- toxicity. Let us wait for other colleagues to provide their further views and suggestions.I must say such discussions and debates will help us in better understanding of soils of our nation.
Thank you Dr Pal Sir and Dr Subbarao sir for taking the issue to meaningful yardsticks to decide whether it is vulnerable to degradation and how to manage it with maintaining /sustaining agricultural production
I have few points here:
Soil reaction with water or CaCl2 should not be below 5.5 if goes below in surface lime (Ca CO3 POWDERED OR BURNED LIME or QUICK LIME (CaO or Ca(OH)2) to make the pH around 6.0-6.5 and apply gypsum (CaSO4 2 H2O) TO BRING SUBSOIL ACIDITY ALSO (UPTO DESIRED LEVEL AND UPTO DESIRED DEPTH)
Estimate organic carbon stocks and see that it is above 9 kg/sq m (MODERATE or higher IN LAND QUALITY BASED ON RATING) in hot humid tropics otherwise to do mulching to make the soil more buffered against moving towards very strongly or extremely acidic condition
Depth of occurrence of pH below 5.0, where high Al saturation is expected, should be below the major root zone of the crop suggested for the area. If not apply lime and gypsum to maintain pH to the level of root zone to avoid decay of roots to high Al concentration
Restrict removal of biomass produced other than economic produce and pool back farm wastes to avoid nutrient mining and make the plants healthy to avoid incidence diseases and their epidemics
Have check of nutrient levels of index leaves of plants and soil to ensure deficiecncy/toxicity or antagonism of any element beyond threshold level
Maintain water saturation not water logging or drying of soil and/or subsoil sediments in case of acid sulphate soils or potential; acid sulphate or acid saline soils
Growing of crops which have some amount of tolerance to acidity Al or Fe toxicity
and breeding of desired plants to impart resistance to extreme acidity or toxicity of some elements for future
Fertility Capability Cassification IS IDEAL to depict the actual soil potentials and solutions for them
wE HAVE TO CONSIDER IN HOLISTIC WAY TO SEE THE VULNERABILITY TO DEGRADATION AND TO SOLVE THE ISSUES
ANIL
@ Dear Anil - Many thanks for your interventions.Would you please inform us about the content of soluble Al measured anywhere in Ultisols, acidic Inceptisols and Alfisols? Moreover it will be nice to indicate the area of acid soils that pH < 5 (excepting the acid sulfate soils) and also the lime requirement of acid soils of Kerala or any southern states that have KCL pH > water soluble pH. These are very critical issue to manage acid soils of the country.
Acid soils to be coined as chemically degraded need a much stronger back up of spatial-temporal crop response data. For example , if a soil is chemically degraded because of the soil pH below 5 , still a crop performs well, will it be appropriate to call that acid soil chemically degraded, despite the fact that many soil mineralogical and structural disorganisation have taken place..? The next important concern would be to define chemical degradation of acid soils in terms of soil pH vis-a-vis crop performance again, since what is chemical degradation for one crop , may not be that destructive to another crop , which warrant redefining of acid soils , if at all , it is to be linked with magnitude of chemical degradation vis-a-vis different soil parameters including most prudent index as soil pH.
@ Dear Dr. Dasog - Many thanks. Pertinent points are placed and worth considering for the future reconciliation on defining degradation status of productive acid soils of India.
@Dr. Anil - I have gone through the document you have sent. Much of its chemical properties was read by me earlier but it does not contain any data on soluble Al of soils,which could be directly related to Al toxicity of acid soils,an unfavourable factor for crop performance. Please indicate what will be the area under acid soils with pH < 4.5, excepting however the acid sulphate soils.
Does liming form a line of management the authors have mentioned in the review?
@Dear Dr. EVSPR- Thanks for your posting.To ameliorate the soil acidity, liming is generally recommended for strong to moderately acid soils of tropical India. However, crop response to liming remains anomalous. In some moderately acidic Alfisols of the Western Ghats, crop response to liming is not observed due to the presence of Ca-zeolites in these soils. Although the aluminium toxicity to plants is a constraint associated with overall low nutrient reserves in Oxisols, Ultisols and Dystropepts, reports on Al toxicity to crops in Indian acidic soils are scarce. Ultisols and Dystropepts of Kerala, Goa, Tamil Nadu, Karnataka and NEH are strongly to moderately acidic, and liming is often recommended to correct soil acidity and improve nutrient availability. Liming is recommended to bring exchangeable aluminium level in the soil to < 1mg kg −1 for maintaining sustained productivity because it improves the general nutrient availability. The KCl extractable aluminium is used for liming tropical acidic pH soils . It is, however, intriguing that despite equally strong acidic Ultisols and Dystropepts of NEH, Ultisols of Kerala, and Alfisols of Goa indicate varying KCl exchange acidity. It is less than 1 cmol (p+)/kg for the Ultisols of Kerala and Meghalaya, and Alfisols of Goa whereas in the Ultisols of Arunachal Pradesh, Assam, Mizoram, Nagaland, Tripura and Dystrochrepts of Manipur, it ranges from 3 to 6 cmol (p+)/ kg. Accordingly, the lime requirement (LR) of these acidic soils varies widely. Lime requirement is around 1 t lime/ ha for Ultisols of Meghalaya, and for Dystrochrepts and Ultisols of other states of NEH, it ranges from 4 to 12 t /ha. A low LR (< 1 t /ha) may be expected for zeolitic soils that contain higher amount of soluble Ca-ions from dissolution of Ca-zeolite but for the gibbsite containing Ultisols (Kerala, Meghalaya) and Alfisols (Goa), the reason for low KCl exchangeable acidity and LR, it is still not clear. Therefore, for soils containing Ca-zeolites and gibbsite, recommendation for LR on the basis of KCl exchangeable acidity needs to be regarded with caution.
Dr.Pal, good information.From the background what I have (from literature and visit),theNorth-east region acid soil ecosystems are more fragile compared to South India acid soil regions.Probably the rainfall distribution, vegetation and crop cover may make large difference. It is worth to compile information on percent base saturation and solution and exchangeable Al in contrasting acid soils from different regions.
Dear Dr. ASR - Thanks. KCL extractable acidity and base saturation for a large number of acid soils of our country are available and a concise table on these two chemical properties are provided in a table of our review paper in Catena (already attached). Unfortunately, no precise information of soluble Al ion is hardly seen. It is again a unfortunate situation that even in the absence of such an important chemical property Indian researchers presume Al toxicity in acid soils of India.
We need more studies on Al chemistry with focus on soluble Al in Indian acid soils with pH in the range 4.0 -4.7(other than acid sulphate soils) and acid sulphate soils pH from 3.5-4.7.We need convenient and accurate method to estimate small amount of Al in solution phase.We also need to include sensitive and important crops to evaluate the Al ion effect on root systems ,nutrient uptake and other nutritional studies.
Dear Dr. ASR - I only wonder why this very important soil property did not get adequate attention of soil scientists/soil chemists for so many years in our country !
Dr.Pal, thank you for your response. Along with Al, Mn and Fe also deserve attention in acid soils in the range I mentioned earlier. One more important aspect is, are the acid soils becoming more acidic especially in India? Under which conditions such pH decrease is observed ? To say in different way ,what soil,climate and management factors are contributing to further acidification of acid soils?
Dr.Abhishek, thank you for providing link to another recent question on this important aspect.Somehow I missed this question.Have you seen any Indian work on this aspect ,especially the effect of trees/cropping system, N fertilizer use , manure use, acid precipitation and afforestation ?
Dear Dr.ASR - I very much appreciate your concern about the possibility of Indian acid soils to become more acidic in future. We at NBSS&LUP developed a knowledge that the formation of Ultisols may be the last stage of soil formation in tropical humid climatic conditions (Chandran et al., 2005. AJSR,43:839-852 & Pal et al., 2012. Geoderma, 189-190: 28-49). Further transformation of Ultisols to more acidic Oxisols is improbable as in acidic soil condition of humid tropical weathering condition, desilication process (the major pedogenic process) is not operative. It is also experienced that Ultisols have more base saturation in the surface than their subsoils due to addition of alkaline and alkaline metal cations through litter fall. It is a very interesting as well as intriguing points to ponder over. Does it suggest that under profuse vegetation cover, such Ultisols would ever become a more base saturated soils? Moreover the release of Al ions is also reduced because of less solubility of Al ions in the present acidic pH ( >> 4.5). Even in the event of release of Al ions, presence of 2;1 weatherable minerals ( more than 10% weatherable minerals are available in such soils) will entrap Al ions in their interlayers. This fact is very much evident from the dominance presence of hydroxy-interlayered clay minerals. Decrease in pH in acid soils may however happen in acid sulphate soils because only at pH below 4.5 Al ions will behave as cations and dominate the exchange complex and that can only happen in acid sulphate soils where biological factors come in to play for causing more acidity.
Our Ultisols are cultivated without much addition of NPK fertilizers. N fertilizer used is mainly urea and there is no record of acid rains in acid soils area of our country like in western Europe and elsewhere. Therefore, we need not to assume at this stage that Indian acid soils like acidic Alfisols and Ultisols under good vegetative cover would turn more acidic in near future.
Dr.Pal ,I appreciate your comments. As I understand, the vegetation may not supply sufficient basic cations in all the acid soils.Also the soluble Al may not be entrapped by 2:1 minerals every where.I am more concerned with agricultural soils under the influence of cropping, irrigation and fertilization..NBSS&LUP has reported acidification on wde scale in some districts of West Bengal state.The following references may give some idea of the scope and extent of soil acidification.
A Global analysis of acidification caused by nitrogen addition. Dashuan Tian and Shuli Niu Environmental Research Letters10(2015).024019.Open Access.
A Global meta-analysis of soil exchangeable cations, pH,carbon, and nitrogen with afforestation. Berthrong et al. Ecological Applications,19(8),2009,pp.2228-2241. can be accessed online.
Acidification of Swedish forest soils.-Epsilon Open Archive http://pub.epsilon. slu.se/13810/
Soil Degradation Due toAcidification. Okazaki M.
www-basin.nies.go.jp/project/lugcc/proceedings/28//Okazaki. pdf
Dear Dr. ASR - Thanks for showing concerns about the acidification of soils under agriculture especially in some soils of WB state. I am aware of it. NBSS&LUP has just reported the present drop in pH as compared to pH measured previously possibly a decade ago. But the causative factors for the decrease in pH still remain to be analysed precisely. Till date no scientific explanation is advanced. So, in its absence considering it is due primarily to agricultural practices may not be a wise thing to assume. Personally, I attended some discussions on this issue held at NBSS but research initiative in this area is yet be taken up.
In majority of acid soils of India developed from acid or basic igneous and sedimentary rocks, presence of vermiculite and smectite even in small amounts is ubiquitous. Therefore, entrapment of released Al ions by these clay minerals in their inter-layers is generally observed.
Anyway, some historical account on lowering pH strictly in Indian soils under long term agricultural practices in the form of scientific communication is always welcome to enrich our knowledge base in this subject area of soil science/soil chemistry.
How shall we arrive at conclusion that a given acid soil is now chemically degraded , and , unless remediative measures are undertaken , growing crops ( annual or prerennial ) would not be remunerative..?. The other side of the coin , blinks brighter considering the fact , how come such soils continue to throw such bumper crops in the absence of any remediative measure..?
Thank you Dr.Abhishek for your valuable and interesting comments and references. I shall go through them .Dr.Pal I appreciate your reply/comments. One interesting finding of Indian longterm experments is decrease in pH of acid soil in the treatment which received N as ammonium sulphate.If the acid soils receive manure application every year. The stable or humic fraction can complex with Al ions and buffer soil pH.
Dear Dr.ASR - I think use of N fertilizers as ammonium sulfate is done with long time ago. However, any science based systematic report on lowering pH values in acid soils that are under long-term agricultural crops in any part of the country is welcome.
Dr.Pal, 3-4 years back I have reviewed the Indian work on acid soils for a seminar presentation. I did not comeacross any critical study on Indian soils on the aspects discussed by this forum.Even today we have good number of longterm experments in different regions of the country. There is scope for formulating a critical study on the aspects discussed by us including Al chemistry, base saturation and composition, trends in pH change overtime, nutrient composition of grain and straw etc.Even a basic chemistry study can be taken up in West Bengal to scientifically validate the NBSS&LUP report on pH reduction in acid soils.
Dear sirs,
I along with my M.Sc.Ag. guide Dr. P.a. Wahid have published an article in Oleagineux in 1989 itself French journal on development of acidity in consequence to continuous application of ammoniacal fertilizers in long term fertilizer experiment on factorial RBD started in 1964 at Coconut Research Station,Balaramapuram, Trivandrum, Keala
Thanks Dr. ASR for your concern in initiating critical study on acid soils of the country. Dr. Anil- Thanks for the important info. Would you please share your paper with me published along with Dr. Wahid?
Dear colleagues, under AICRP Longterm Experments there are 5 centres in acid soil regions where experments are in progress from the last 44 years. Of the five ,three experiments have been in progress without any disturbance(in other two places new experiments are in progress).In Palampur, Ranchi and Bangalore experiments, there was definite decrease in pH in treatments like N alone ,NPK at higer rates of application.pH decrease was less in NPK plus organic manure treatments. pH increased in NPK plus lime treatment.For detailed results one can visit IISS website,www.iiss. nic. in/LTFE html In next interaction I shall provide one published reference each for the three centres.
Dear Dr. Anil - Thanks for sharing an important information. May I know what was the start date of this classical experiment? Would you please inform why ammonium sulphate as N fertilizer was a preferred choice in acid soils?
The experiment started in 1964 with factorial RBD with 9 treatments with 3 replications. N0, N1, N2, P0, P1, P2, K0, K1 and K2 in all permutations like N0P0K0 N1P0K0,..........and final N2P2K2. That point of time ammonium sulphate was the source for N, superphosphate for P and MOP for K. The excess acidity created by ammonium sulphate was neutralized by gypsum contained in superphosphate. Even then there was increase in acidity as noticed in the paper. An interesting observation i have seen there was no coconut palms supplied with N2P0KO did not grow to bunching stage at all even after 21 years of growth in a very deep well drained red fine-loamy or clayeysoil with almost year round well distributed rainfall in Balaramapuram, Trivandrum, Kerala.
Now the scenareio has changed now ammonium sulphate got replaced by urea, even though it is an ammoniacal fertilizer it won't supply free available S, but worst thing happened by replacing super phosphate with ammonium phosphate and its monoammonium and diammonium or tri ammonium versions to supply N and P together and sometimes without MOP only urea and ammonium phosphate as N and P sources. And correction of extra acidiy by gypsum also not happening and in due course along with acidity supply of K and secondary nutrient levels also started declining in tropical soils. this is really alarming this is the main catastrophe happening in Kerala culminating in very low yield levels of coconut compared to neighbouring states
anil
Please have a look at these useful links.
http://academicjournals.org/journal/JSSEM/article-full-text-pdf/A3847D356736
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