Dear Sir, Thank you for your response

1) I wish to perform perform experiment.

2) I think it will be advisable if I study nutrient availability in soil and correlate it with plant nutrient uptake. Only soil chemical analysis would not reflect availability per say. Especially if the organic amendment is more of a soil conditioner rather than a nutrient source which will degrade and release nutrients

3) The motivation of the experiment is sustainable fertility improvement. That is improve soil properties for its agronomic function (pH, CEC, WHC, nutrient availability). Organic amendments are known to improve these properties. Thus the focus is more on studying interaction of organic amendment wrt these properties rather than its ability of release nutrients. Nutrient release if taking place will be a plus point, however main objective is improve soil properties in long term. The second point is interaction of an organic amendment will vary depending on soil used. Yes, so I have selected 4 soils in Maharashtra, India and where pH is a superficial indicator of fertility, it is affected by various soil properties and processes, which vary with regional soils. Thus I feel it important to study effect of organic amendment on properties and processes relevant to native soils beyond measuring pH at few growth/ incubation point of time.

Back to my query, So properties and processes that occur in native soils will interact with the organic amendment and this will shift the nutrient availability in a given pH range. Now it will be interesting to observe the direction and magnitude of this shift. Or whether such shift occur or not.

Then it will be useful to study pH range relevant to a broad category of plants. Since I have freedom to modify pH of organic amendment (OA) to be used. I intend to study soil + OA at 4 pH levels 6 - 6.5, 6.5 -7, 7 - 7.5 and 7.5 - 8. And Study nutrient availability (uptake in plant).

How is this beneficial? - It allows me to propose the pH at which OA should be maintained so that after addition to native soil, it will serve its purpose more effectively.

I could be incorrect in two ways, 1) The presumption that the OA will interact with processes and properties of native soils distinct enough to conduct this type of study. 2) The methodology I have proposed could be in-efficient and there could be a better way of doing the same study.

Valuable insights and encouragement of experts will help in a big way.

Regarding application rate, I think 2 to 5 T/ Ha would be economical range for Indian farmers (although knowledge is universal, economics is variable). For experimental purpose would be good to study upto 10 T/Ha.

Sincerely,

Rohan

The question is not simple as you clearly appreciate.  On opening cultivation to 10 cm can lose 10 t of C/ha.  To make appreciable, semi permanent changes in properties requires 20-40 dry tonnes/ha as a single addition.  At these rates the microbial community undergoes major changes for several years especially in low C soils.

You need also make sure that there is no N draw down.

Yes. pH is important.  So proposing to study a number of soils is ambitious. Ca is not usually deficient, so using CaCO3 is not a bad approach. 

The plant growth responses are typically greater than can be explained by the mineral nutrition.  Physical differences related to water supply and to microbial communities may be responsible. 

Contact me if you like, Paul.

[email protected]

Hi Rohan,

If I could understand your query well, you wish to find a pH range at which availability of a particular nutrient is highest to the plants. Then keep in mind that the availability of any nutrient depends on several factors (viz. soil clay type, CEC, EC, organic matter content and type, relative availability of other nutrients and ions, and of course the soil reaction i.e. pH). Also the soil reaction which is measured in terms of pH is in itself dependent on several factors like organic matter content and type, availability of cations and anions, environmental conditions governing redox reactions, availability of water and aeration in the soil etc. This makes it practically impossible to maintain a fix range of pH in field condition. So even if you find the idle pH at which availability of all the nutrients is at optimum in your lab experiment, it will have very little practical use. Also there are well established pH ranges for different nutrients at which their availability is at maximum, and the optimum pH at which almost all the essential nutrients are available is 6.5-7.5, as stated by Dr. Hani Antoun. I attach herewith a photo of nutrient availability at various pH ranges, have a look on that, however, I wish you would already know the same.

So in my opinion if you wish to study the effect of various organic amendments on soil pH and nutrient availability, you should not bother about fixing the pH for whole incubation period because organic amendments not only release the nutrients through their decomposition but also alter the soil pH by producing various organic acids. The production of specific type of organic substance on decomposition is peculiar characteristics of a particular organic amendment which in turn alters the soil pH along with other changes and if you fix the pH for all organic amendments, they will lose their peculiar characteristics. Therefore, for all practical purposes, it would be prudent to study the pH and availability of nutrients in the soil under investigation at following stages:

1)       Before incorporation of the amendment into the soil

2)      At various intervals (e.g. 15 days)  during incubation period

3)      At the completion of the crop cycle (i.e. at the harvesting of the crop)

4)      At the completion of your experiment if it is a long term experiment not the one crop cycle experiment.

By doing so you will have the idea of nutrient dynamics how it changes with time after application of particular amendment and also you can draw a correlation between the changes in pH vis-à-vis nutrient availability brought about by the application of organic amendments. At the end of the experiment you would find an organic amendment which facilitates the availability of nutrients in the soil, and the reasoning for the same may be that it (the amendment) altered the soil pH towards a favorable range.

This is the common procedure that most of the soil scientists and we the agronomists follow in our research. However, you as a chemist might be thinking of some different idea.

Dear Dr. Milham, Sir thank you for your response. I have done a preliminary soil chemical analysis of study region. Based on 24 samples spread across the region, the pH range is 7.5 to 9. The organic amendment that I am studying is alkaline with pH range 9.6 to 10.6. I suspect this system will further raise pH beyond the optimum range. Thank you for sharing your contact, I will write to you in details about amendment and objectives.

Dear Mr. Deo, Pls allow me to clarify: I am not looking to find optimum pH range, it is known. As you have pointed, nutrient availability depend on soil clay type, CEC, EC, organic matter (its quality to be precise), native microbial interactions and of course pH. At the same time we are saying, an organic amendment would change most of these parameters on which nutrient availability is dependent. My question precisely is, Which of these parameters are specific or peculiar of region? Here you will appreciate that EC, CEC, pH are a metric that represent certain chemical characteristic of a soil. And if I add say chemical fertilizer of ash (foreign material) these are going to change. Native properties or processes are not a metric, in fact they will govern the dynamics of this metrics. For example: soil mineral properties will form organo-mineral complexes, native microbial species will perform differently under certain environmental conditions. Now the idea is not to get bothered by all this dynamic inter relations, however single out one property and study how native soil properties and processes affect the performance of a soil amendment. At the same time attempt to create technique which would be beneficial to farming and scientific community. And therefore I am exploring how an organic amendment (OA) can perform more efficiently under native conditions. In this case the native soils of study region are in pH range 7.5 to 9, have sufficient Ca. With a long term fertility approach, a low biodegradability organic amendment would mean low nutrient release, low formation of acid functional groups. In the case an alkaline (pH > 9.5) OA will take soil pH beyond the optimum range or it is not clearly known how it may respond. Therefore a study.

Also please excuse me if my queries or propositions sound naive, I am an engineer and not a chemist.

Thank you

 Good response from DNS. Also the soil reaction which is measured in terms of pH is in itself dependent on several factors like organic matter content and type, availability of cations and anions, environmental conditions governing redox reactions, availability of water and aeration in the soil etc. This makes it practically impossible to maintain a fix range of pH in field condition.

U

Mr.Oak ,the soil samples analysed by you  have pH in the range of 7.5 to 9.0.Probably they may be Vertisols and associated soils or swell-shrink soils common in the state of Maharastra.There is no justification to reduce the pH of those soils below 7.0 as such soils may not be occurring naturally.If  you desire to utilize your organic amendment having pH9.6-10.6,then choose an acid soil having pH less than 6.0 or even 5-5.You can lower the pH of soil by amending with elemental sulphur.Do you want to lower the soil pH and again increase it by adding organic amendment and study the nutrient avalability.?As pointed out by Dr.Milham,one may not bring about much change in soil reaction by adding 2-5 tonnes/ha of organic amendment.You may have to apply 15-20 tonnes/ha of OA and continue the practice for several years,at least 4-5 years ,to bring  about some change in soil pH,humus status and nutrient availability.I appreciate all the colleagues for good discussion on the subject.If you apply the OA with pH 9-6-10.6 in neutral to alkaline pH soils(like your soils) there may not be appreciable increase or decrese in soil pH.Humus status and nutrient availability may increase provided sufficient decomposable organic amendment is added and the practice is continued for a number of years.

Generally You can adjust soil PH by using ammendments like Lime and Gypsum in Acidic and Alkaline PH range to bring to near nutral as per your pH requirement 

I am agree with Dr Subba Rao. It is normal that we use amendment to improve acid soils with lime or another. But if pH of your soils is over to 7,5 you don´t need apply amendment, becuse almost crops grow in neutral pH. But if your soil is alkaline and you want to improve it you will have to apply acid amendment as some manure, purines, others.

In our experience (Mérida, Venezuela) with acid soils (pH = 4.8) and FA texture (mountains) we can use 1.000 kg/ha of lime to get pH = 5.4 (after 1 year), depending only of rain.

In flat soils, with high temperature and high relative humidity, Fa or aF texture, pH = 5.2, after 2 years applying manure tea ph was 5.4, organic matter 0,8% to 2.0%, P (5 ppm to 25 ppm). Under cacao (2 years).

Thank you everyone for your contribution. This is becoming a wonderful discussion.

One clarification fundamental about my question is: I want to add the organic amendment not to increase pH. OA provides various benefits: improves cation exchange capacity (and therefore fertilizer use efficiency), water and nutrient retention and availability, soil micro-flora (if good C/N is present), soil physical properties. However if this OA is alkaline (specified pH range) in nature, I thought it might increase pH towards an undesirable higher end.

1) The interest in OA is because of all these various advantages it provides to improve soil quality. Now these properties are also a boon to alkaline soils. Therefore I wished to test its effects on these soils, however to avoid higher increase in pH and thereby negative effect interfering with the main objective. A study should restrict increase in pH beyond a certain limit and maintain pH range in a comparable range if not at an absolute value (which is practically impossible).

The concerns seems to be sorted as experts are unanimous that pH increase will not be to high at mentioned rates.And I initiate a study with this much understanding. By measuring alkalinity added by the OA and balancing the control to that much alkalinity using lime.

2) The importance for studying this effect in neutral to alkaline soils is their major presence in Maharashtra. In this state acidic soils are present along a narrow strip of western coast (Konkan) and western ghat. Paddy is the major or rather the only substantial crop in the region. This restricts applicability of study of this OA.

My presumption is that interaction of any organic amendment with soil is very unique. For example, Maharashtra state have 72 agro-ecological zones (classified based on soil type, precipitation and temperature). Organic amendment will interact uniquely in each of the zone. The magnitude of uniqueness will be less or extreme depending upon similarity/ dissimilarity  between zones.

To select soil from two zones and study the uniqueness of soil - OA interaction remains to be a highly interesting research inquiry to me. And there would be different approaches for undertaking such study based on interaction of the OA with processes that govern soil properties. 

Dear Rohan

Organic matter act as buffering agent. It tries bring the pH of the soil to the near nutral through its decomposition and various chemical reactions. i wish yuou all the best for your studies

Chandrashekar 

I think the addition of Organic matter affects soil physical properties ,help cation -anion exchange ,this cations & anions react with each other according to it,s presence &   abundance in the soil. for example, if  Sodium, Calcium, ammonium, carbonate are available in the soil, the  cation -anion exchange lead of the reaction between the ammonium,Sodium, Calcium & carbonate to give Carbonic acid, which is weak acid decomposed quickly to carbon dioxide & water this make some Calcium cation-free and these calcium suppress Sodium from Fixed compounds & lift Phosphorus & Micro- nutrient available to the plant  

Soil by nature is a complex and dynamic resource developed over a period may be for centuries due to different factors of soil formation. Whereas, pH is a singular property which provides information on soil reaction acidic, neutral or alkaline. It is not static but dynamic. It is not possible to make pH static by any means on addition of organic matter. It is a futile exercise that leads you nowhere except to confusion. None can draw any meaningful and reproducible conclusions. I suggest you to be very precise with a clear focus on your objective(s) in soil research. 

Allow me to add some comments and suggestions, although most aspects have already been addressed:

1. OM may reduce soil pH initially due to the production of organic acids, but in the long run, because OM in terms of acid-base theory could be regarded a cation-carboxylate, the complete decomposition of the latter increases pH, hence most organic fertilisers tend to have a positive lime value.

2. Agree with Maria Ormeño, it’s certainly easier to start with a low soil pH, adding lime to adjust soil pH to the desired initial value (after allowing for some time to react).

3. Having said this, would it not be an option to go the other way round? One of the least interfering mineral acids might be sulfuric acid, as others (HNO3, H3PO4, HCl) introduce nutrients and chloride. Dilute sulfuric acid could be added as such, or bentonite-S could be added, which is widely used in India as a source of S. Would also be more gentle, longer lasting.

4. Finally, I also agree with Dr Reddy – do not overdo it. Maintaining soil pH in a narrow range is a research project in its own, and also a misconception: Even when bulk soil pH could be adequately maintained in the desired range, it could be argued that rhizosphere pH – certainly more relevant for nutrient uptake – is completely different, and the gradient that develops depends on all sorts of things like clay content / buffering capacity / OM (that you added and changed) / or even pH (that you changed). Suggest to adjust soil pH to meaningful values and monitor how things develop.

Good success with your experiment!

Dear Rohan,

for conducting experiment with an objective to examine the efficiency of organic manures under different pH level:

(1) the most practical approach, in my opinion, will be to use field/ naturally occurring soils of graded pH (acidic, near neutral and alkaline) and incorporate organic matter of one source (with known composition/)quality). Recommendations drawn from such experiment will be practical and useful.

(2) When you change pH of your soil by adding acid or alkali from outside, availability or solubility of many nutrients in it gets altered. Even microbiological properties of the soil is also altered. Effect of organic manure observed by adding it to such modified soils, will not have any practical value and utility.

This is my personal opinion and to the best of my knowledge and experience. You may have a serious thought over it.

I Agree to some extent with Dr Dilip Kumar, in that the modification of soil pH by liming or acidification changes - on short notice - not only soil pH, but also soil nutrient dynamics and soil biota. As the changes are in full sway while running the experiment, this may reduce the significance of the findings.  

On the other hand, comparing soils of different native pH doesn't make it much easier: The soils may not only differ in nutrient dynamics and soil biota, which would be now in equilibrium with soil pH, but soils may differ in structure, texture, nutrient reserves, SOM etc. So, somehow soils are compared that differ in many parameters, not just pH, reducing the significance of the findings.

The 'silver bullet' might be to take samples from a liming experiment. Here all soil parameters were originally the same and the soil would be in equilibrium.