What could be possible reasons for soil to have higher pH values (8+) and can somehow the soil pH be reduced to 7? Through which techniques/methods?
I am new in the field of Soil Science. I realized the pH in most of Punjab region of Pakistan is on the higher side. I also read that ideal range for pH for better crop productivity is 6.8 to 7.0. However, tests show that pH values range from 8.2 to 9.0 in my region.
What could be possible reasons for higher pH?
Possible remediation strategies? Short term, long term? Economical.
You cannot change the soil's pH over the long term. If one needs to make the soil more acid and it's on a large scale, the chemicals of choice are sulfur or ammonium sulfate. You would still need to apply yearly as the soil will revert back to its original pH. It's always better to let the soil dictate the selection of plants as the addition of these chemicals to the soil also affects the microbial and invertebrate communities and thus diminishes the soil as a living organism.
Dear Irfan, parent material, time, relief, topography, climate and organisms are responsible for higher soil pH.
Possible remediation are application of S or ammonium sulfate. Clay soil are more resistant to change than sandy soils as clay soils are more chemically active and buffered than sands. Ammonium sulfate will produce faster shift than sulfur. Ammonium sulfate may also provide N and faster green up of plants.
But the reducing pH is a temporary process. Due to inherent chemical properties of parent material, alkaline soil will gradually return to their initial pH. This means you need re-treatment of soil every two or three years as change in parent material is not practically possible.
The soil could possible saline soil i.e. high accumulation of soluble salts. The region could also be suggestive of salinity if it is found in arid or semiarid climatic zone. If it is what I speculate and if the pH is not greater than about 8.5, appropriate drainage systems and sufficient amount of water can help.
National Bureau of Soil Survey and Land Use Planning
Soils with pH > 8.5 are alkali or saline-alkali soils like those of NW part of IGP, India. Such soils with very low productivity are amended through the application of gypsum and rice as first crop.It is a very common practice in IGP, India. You can log in to the website ICAR-CSSRI, Karnal for more details on the reclamation methods.
National Bureau of Soil Survey and Land Use Planning
Indian experience is however indicates that flashing of salts by fresh water in both alkali and saline-alkali soils with pH > 8.5 , ESP>15 and ECe > 4mmhos /cm through drainage system, does not work because of enormous dispersion of clay colloids due to the huge presence of carbonate and bicarbonate of Na,which impairs drainage.
All answers above very clearly define the reasons for the pH=8 of the soil and techniques of pH reduction. This could be a good research proposal but as such it is not possible to permanently reduce the pH of soil.
Soils may be alkaline due to over-liming acidic soils. Also, alkaline irrigation waters may cause soil alkalinity and this is treatable, but alkaline soils are primarily caused by a calcium carbonate-rich parent material weathering (developing) in an arid or dry environment.
Ammonium sulfate and sulfur coated urea fertilizers will have a small effect tolower pH. For example ammonium sulfate fertilizer 21-0-0 at 10 lbs per 1000 square feet can change the soil pH from 7.5 to 7.4. These are good choices for maintenance of acid loving plants. You can also add organic matter, such as compost or composted manure, to your soil annually and mulch with acidic organic mulches, such as pine needles. Adding organic matter slowly lowers your pH over time, while increasing microbial life and improving the structure of your soil. The availability of many plant nutrients in soils, including iron, zinc, copper, and manganese, is reduced at high pH values. Iron chlorosis in plants, caused by inadequate iron, is a common problem in alkaline soils.
Phosphate, a macronutrient, may also be limited in these high pH soils due to its precipitation in the soil solution. A soil pH value above 8.5 indicates the presence of sodium. High-sodium soils may reach pH values up to 10. Such high-sodium soils are termed “sodic” soils, and they may also be saline. Sodic soils contain so much sodium that the soils become dispersed and almost impervious to water. To remediate sodic soils, gypsum or sulfuric acid is added, and the soil is leached.
other choices are:
Add organic matter. Many types of organic matter, like compost, composted manure, and acidic mulches (e.g. pine needles) can gradually lower your soil pH over time. ...
Add aluminum sulfate. ...
Add sulfur. ...
Add sulfur-coated urea. ...
Add another acidic additive. ...
Grow alkaline-tolerant plants.
Treatment of High pH Soil
Fertilizers and chelates can be added to soil to increase concentrations of plant nutrients. It is important to note that addition of phosphate fertilizer alone will further reduce the availability of other nutrients.
Lowering the pH of alkaline soils, or acidifying the soil, is an option. Elemental sulfur can be added to soil as it forms sulfuric acid when it reacts with water and oxygen in the presence of sulfur-oxidizing bacteria. Iron and aluminum compounds can be added to soil, as they cause the release of hydrogen when they react with water. Sulfuric acid may also be added directly.
Additions of appreciable amounts of organic matter will help to acidify the soil as microbes decompose the material, releasing CO2 which then forms carbonic acid. Organic acids are also released during humus decomposition. Peat and peat moss are highly acidic forms of organic matter but can be costly.
Application of acidifying fertilizers, such as ammonium sulfate, can help lower soil pH. Ammonium is nitrified by soil bacteria into nitrate and hydrogen ions.
Soils naturally containing carbonates, or lime, are very difficult to acidify, and it may take years before a significant change in soil pH is seen. Even then, the carbonatic parent material will continue to weather, producing more soluble carbonate and buffering the soil solution pH.
Many plants can tolerate pH values between 7 and 8, and some actually thrive at these higher pH values. Choosing plants that grow well in mildly alkaline soils can be selected. This is the most reasonable “treatment” option for soils that have developed from carbonatic parent material.
Vegetable garden plants such as asparagus, beets, cabbage, cauliflower, celery, carrots, lettuce, parsley and spinach grow well in soils whose pH is between 7 and 8.
Alkaline-tolerant landscape plants include boxelder, Japanese barberry, hackberry, Russian olive, sargent crabapple, mockorange, locust, bridalwreath, and arrowwood.
Soil carbonates are the main reason for high pH value. The calcium carbonates usually maintain a pH upto 8.3. If the pH higher than this in this case Na in exchange site or Na bi(carbonate)s are present in the soil and therefore a pH above 9 can be observed. To eleviate the deletereous chemical, physical and biological effects of high pH soil can be treated variety of chemicals. Sulfur, gypsum, H2SO4 are commonly used treatments. Fe(II/III)SO4 can also be used. The effect of Iron sulfate can be in two ways: during the formation of iron hidroxide 2 or 3 mol of H ion is given off. This correct the excessive pH, newly precipitating Fe-oxides can coat carbonate surfaces which can reduce the efficiency or solubility of Ca-carbonates to controle pH at around 8-8.3.
In my own professional experience, you cannot change soil pH over the long term - no matter what you do. None of the chemical-based products can do this so they need to be applied annually. The down side is that these chemical treatments allso undermine the soil's microbial community, thus reducing the presence of mycorrhizal fungi. Compost material such as composted coffee and black tea grinds will acidify soil but also have to be applied annually. This is good for small areas as they do not negatively impact the microbial community.
The best advice is to ALWAYS plant to the pH and not vice versa. Plant what prefers the pH you have, not what you wish for.
Of course changing pH of a highly calcareous soil is nearly imposible. However alkaline soils can be amalioaretad by addition of S, CaSO4, Fe(II, II) sulfate, H2SO4. This practice will reduce the ESP value below 15 where a soil has a pH below 8.5. The critical point is even if you can reduce pH towards 7 during the early growth stages (e.i. 30 days) this will be very benefial for plant nutrient uptake especially those with low mobility in the soils.
Soil pH greater than 8.5 indicates higher amount K, Ca and Mg contents which will fix phosphorus, reduce the soil micro nutrients and cause serious wilting of crops as a result of osmosis.This situation arises from continuous use of irrigation water with salt content and use of basic fertilizer Calcium Ammonium Nitrate and excessive over liming practice regardless the soil pH.To correct soil pH to 7,the researcher will take soil samples of the site and determine the soil pH ,the K ,Ca,Mg and Na contents and soil buffering capacity in order to calculate the amount of acidic fertilisers such as Urea, ammonium nitrate to add to the soils to reduce the soil pH.However, the researcher must be careful in getting the correct quantities to apply because dislocation of soil equilibrium is very dangerous to prevent nutrient antagonism and other soil conditions that will reduce crop yields significantly.
All answers provided above are quite informative and gives a clear understanding of alkaline soils. At high soil pH 8+, carbonates [high concentrations of sodium carbonate (Na2CO3)] become the dominant form of alkalinity . Alkaline soils are basically product of the underlying alkaline parent materials found mostly in arid environment or due to excessive liming of acidic soils. All the reclamation methods suggested above are very good but bear in mind that manipulating the pH especially reclamation or improvement of saline-sodic soils can be very expensive, and improvement will take time, and more especially it requires expertise.
Possible short term remediation strategy is the application of ammonium sulfate which is less expensive.
Long term remediation strategies will be regular application of organic amendments such as compost and manure, in addition to selecting plants that tolerate high soil pH conditions.
The german wikipedia article on the punjab region states that issues with salinity in soils in the punjab region is related to water management to a substantial degree. Sadly no scientific sources are provided in this article however the general statement is quite logical. The punjab region is generally very arid. Vast areas are watered with the water of large rivers. This water is quite rich in salts compared to the lacking rain water. That has caused ground water levels to rise and this water comes back to the surface in many lower ground areas where it evaporates at fast rates. When this water evaporates the salts in this water accumulate which causes the anthropogenic salinity of the soils. Considering that the basic issue in this case is the accumulation of salts I would not recommend adding more salts or other mineral compounds trying to balance them out. As others have mentioned before chemical treatments have a very temporary effect on soil pH anyways. This is likely to be especially true due to the ongoing accumulation of salts.
I am not sure if saline soils that accumulate salt through high evaporation and low precipitation can be treated effectively at all but the first step would have to be to reduce evaporation in the effected areas to stop the process which is responsible in the first place or at least slow it down. Maybe water management in the region should be done more effective in certain ways. Higher fields could be watered less, just the amount that crops can evaporate on site to prevent a salinification of lower ground soils. If higher ground sites used to be forested maybe Agroforestry systems may help increasing the evaporation on higher ground sites in order to reduce the ground water flow that is draining the salts to lower ground areas? The woody compounds of agroforest systems could also be used to produce organic matter for an annual treatment of saline sites.
Some of the water that is saved in this process could be used to wash out excess salts in lower ground soils? This may only be a valid option after ground water levels are lowered well below the lower ground soil surface. Maybe precipitation from monsoon season could help drain excess salts? Some lower ground saline soils may also be situated in former floodplains of large rivers that have been 'secured' with dams. This will also have a major impact on ground water systems and salinity.
I am really not an expert but I have a basic understanding of soil chemistry and I just read very little on the punjab region. What I have wrote are just ideas that came to my mind so I am not quite sure whether I have made general mistakes in my thoughts so maybe some of the other experts could discuss my ideas? I am sure though that water management will be the key to dealing with salinity issues in this region.
the higher pH and the resultant alkalinity might be a direct response to the existing phyllosilicates which I suppose to be members of the smectite –group and calcareous material such as calcite and even dolomite. You cannot exclude other salt minerals driving the grade of alkalinity to a higher level but this would be mere speculation because of lack of any information on the soil composition. Any piece of advice as to the remediation of the soil spraying any fertilizer or other chemical compounds would be a bit premature. You might even achieve the opposite effect in creating new compounds such as encrustation or duricrusts which extract and bind elements and ingredients significant for the plant nutrition and result in an immobilization of elements and thereby reduce the availability of plant to take up elements and chemical compounds. I keep my answer rather general since the basis for any fruitful discussion is the knowledge about what we are going to discuss upon. We neither know the mineralogical/ organic composition of the soil substrate nor its position as to the overall landforms (geomorphology, hydrology).
Actually , high exchangeable sodium in the soil is one of the main reason for high pH of the soil beside the other reasons explained above. Course textured soils are generally less affected by exchangeable Na than are fine textured soils.
Higher amount of salt deposition in soil due to excess irrigation and imbalanced fertilizer use is the main cause of higher pH. And as we all know that soil itself act as a buffer i.e. which resist to drastic change in its pH. To lower down pH from 8 to 7 is very tedious process and require all ameliorating measures viz., mechanical, chemical and biological etc to lower down the soil pH and it require long time also. So 'prevention is better than cure'. Judicious use of all inputs while cultivating the soil is very much important aspect.
What Archana has not included in causation is found in urban environments. Construction rubble is often buried in tree planting areas along the street. That ongoing leachate combined with what leaches from the surrounding concrete pavement keeps the pH range of urban soils too high for many of the tree species one plants in an urban area, affecting nutrient uptake and thus long term growth.
Many factors aspropsed above by researchers are responsible for alkalinity/sodicity. As soils take time to reach this cond through long mismamanagent of area, soils, cropping, irrigation by alkaline water or canals or rivers excessively open to STP water can take long time for amelioration by only organic composting, as Archana has also proposed
The alkalinity is the result of the soil formation processes and soil management practices. In natural soils the soil formation is the key processes. The lack of precipitation and the accumulation of alkaline and alkaline earth elements especially Ca, Mg and Na. The richness of carbonates is also the other requirement. So alkaline soils have high exchangeable Na, high residual carbonates (CO3 and HCO3). The excess of carbonates react with Na in soil solution and some OH ions given off. This ions increase the pH above 8.5. To reduce the pH in a reasonable range, soils should be amended with gypsum, elementel sulfur, H2SO4, FeSO4 etc. Gypsum and elementel sulfur correct the alkalinity in a longer period, wherease incorporation of FeSO4 and H2SO4 act quicker. FeSO4 could be recomended due to safer application than the H2SO4.
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