Anoop thanks for an intelligent reply. Have we isolated and tested native isolates of microbes for their efficacy in solo and also interaction in consortia. Do we have worked a kind of matrix with relation to temperature and survival of natural microflora and fauna and further multiplication at faster rate to accrue the desired benefits. Solarization in general practiced during hot months in the tropics and subtropics,  by providing soil cover with different coloured polyethene sheets. Though it can be practiced all the year round, but effectivity is obtained during specific months. Killing soil pathogens at the cost of beneficial microbes is the question.

 Dear Malhotra Sahav,

When establishing a new date plantation, certain actions need to be implemented to ensure the long term success of the plantation. One of these actions involves the initial land preparation which should be done prior to transplanting of the plant material (offshoots or tissue culture-derived plants).The purpose of land preparation is to provide the necessary soil conditions which will enhance the successful establishment of the young offshoots or the tissue culture plants received from the nursery. Considering the nature of the date palm, one cannot "save" on this operation and hope for long term sustainability of the plantation.

Critical factors to consider during this planning exercise are summarised as follows:

- Availability and quality of irrigation water;

- Field selection;

- Mechanical actions to be implemented;

- Chemical needs for pre-plant soil improvement;

- Tools and equipment needed for date cultivation;

- Labour needs;

- Irrigation design and installation;

- Leaching schedule;

- Hole preparation;

- Financial requirements and

- Time schedule.

External agricultural inputs such as mineral fertilizers, organic amendments, microbial inoculants, and pesticides are applied with the ultimate goal of maximizing productivity and economic returns, while side effects on soil organisms are often neglected . Mineral fertilizers have limited direct effects, but their application can enhance soil biological activity via increases in system productivity, crop residue return, and soil organic matter . Another important indirect effect especially of nitrogen fertilization is soil acidification, with considerable negative effects on soil organisms.

Soil solarization is an environmentally friendly method of using solar power for controlling pests such as soilborne plant pathogens including fungi, bacteria, nematodes, and insect and mite pests along with weed seed and seedlings in the soil by mulching the soil and covering it with tarp, usually with a transparent polyethylene cover, to trap solar energy. It may also describe methods of decontaminating soil using sunlight or solar power.

The area to be solarized should be level and free of weeds, debris, or large clods, which could raise the plastic off the ground. Transparent (not black or colored) plastic tarps or sheeting 1 to 4 mils (0.001 to 0.004 inch) thick are anchored to the soil by burying the edges in a trench around the treated area. Plastic tarps can be laid by hand for small farms or gardens or by commercial machinery for large farms. To prevent air pockets that retard the soil heating process, there should be a minimum of space between tarps and the soil surface. The soil under the plastic is then soaked with water by inserting one of more hose or pipe outlets under one end of the tarp. If the soaking step is impractical, the soil may be irrigated before laying the plastic, but care should be taken to apply the plastic as soon as possible to avoid water loss. If, however, heavy machinery is used, the soil must be dry enough to avoid soil compaction. The plastic should be left in place 4 to 6 weeks to allow the soil to heat to the greatest depth possible. The plastic should then be removed and the soil allowed to dry to a workable texture. The soil can be planted to a fall or winter crop or left fallow until the next growing season. If the soil must be cultivated for planting, the cultivation should be shallow (less than 2 inches) to avoid moving viable weed seed to the surface. Time of year. Highest soil temperatures are obtained when the day lengths are long, air temperatures are high, the sky is clear, and there is no wind. The heat peak in many areas of California is around July 15. Therefore the best time for solarization of soil in California is in June and July. Good results may also be obtained in May, August, and September, depending on the weather and location.

Soilless potting mixes have long been used for greenhouse production of bedding plants, vegetable transplants and container-grown ornamentals. By avoiding the use of topsoil, the risk pathogenic microorganisms in this media may be reduced, avoiding problems with diseases like damping-off. In addition, topsoil is relatively heavy and dense so it can contribute to poor aeration and drainage in a potting mix. Soil-less mixes should be formulated to have optimal physical and chemical properties that promote germination and healthy seedling growth.

Regards,

Prem Baboo

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwingsyB0ubNAhVKLo8KHQUTD4gQFggbMAA&url=http%3A%2F%2Fwww.fao.org%2Fdocrep%2F006%2FY4360E%2Fy4360e0a.htm&usg=AFQjCNHvwiecwp8qOi1NSO_2tC1A2lvQsA

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwimopeS0ubNAhUOSI8KHfkgADcQFggiMAE&url=http%3A%2F%2Fsolutionsforyourlife.ufl.edu%2Fhot_topics%2Flawn_and_garden%2Fhomemade_potting_mix.shtml&usg=AFQjCNGApjxlmFLSMBy02l87aKL8cjJM3g

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwimopeS0ubNAhUOSI8KHfkgADcQFggoMAI&url=https%3A%2F%2Fwww.agric.wa.gov.au%2Fnursery-cutflowers%2Fpotting-mixes&usg=AFQjCNHrorIl9QhDI0gRoDnUnaQMJV8eZA

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwi23vru0-bNAhWBo48KHX8tDxoQFggbMAA&url=http%3A%2F%2Fwww.farmerfred.com%2Fsolarization.htm&usg=AFQjCNGyNby5cg-9hfH3Cw_7fvgcPSnypw

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjg14u91ObNAhVKOI8KHVYODXMQFggdMAA&url=http%3A%2F%2Fwww.uvm.edu%2Fvtvegandberry%2Ffactsheets%2Fpottingmix.html&usg=AFQjCNFVn0OIL-D6sF4SgH4cqnKaNGr_8g

Thank you Dr. Prem Baboo, for being the first respondent to this question. Your response covers lot of information with special focus on date palm planting. Date is one of the difficult crop to handle and has long gestation period in nursery. Yes the ultimate goal is  maximizing productivity and economic returns through optimum application and utilization of external agricultural inputs . It is true side effects on soil organisms are often neglected. Direct and indirect effects of mineralization are also required to be equally considered for the soil ecosystem . Your critical analysis on soil solarization and soil microflora is equally important. Thanks.

-

Dear Barbara, gratitude for endorsements and upvotes. 

Abhishek, i am delighted to read excellent response from you, compliments. you have detailed information on functions of potting mix and thumb rules about it. Soil solarization details are excellent but cost effective and quick methods are the need which could destruct soil borne pathogens, it is also obvious that friendly microflora will also be affected. But how we can recharge back the soil with the power of useful microbes.

Dear Dr Malhotra , you deserve my warm compliments for tossing up such issues , which have so much of relevance in day-to-day work . Let me respond to your subset of questions; 

How to conceive the idea of suitable potting mixture that could fulfill the requirement of a nursery plant?

The best way could be to observe very closely the excellently performing plants in a population where most of the plants are not in good health . Analyse the physical , chemical and biological properties of soil . And try to simulate such conditions through your own synthesis involving soil, organic manures and a range of microbial cultures . Such simulation study is a must to idealise a plant growing under required optimum conditions.

What are the soil-plant parameters that guide the composition of potting mixture for a given nursery plant ?

Soil should be having some 15-20% of available water capacity , loamy sand -clay loam in texture , organic carbon atleast above 5.00mg/kg , pH somewhere neutral , good microbial load of the potting mixture capable of supporting good plant health , uniformity in growth etc will surely dictate the superiority of a substrate .

Can we perform solarisation during any part of the year or this process is season dependent?

Yes , technically speaking , solarisation should be effectiveduring any part of the year , but most of the studies advocate best results of solarisation during summer months. Solarisation acts in relation to outside atmosphere and inside temperature of 55-600C created  within the solarised platform. We need more studies to make specific recommendations.

How effective is the role of soil solarization or other techniques  in neutralising the soil borne pathogens ?

Yes , solarisation has been observed so afr most effective and safe from killing rhizocompetent beneficial microbes being killed . We need to standardise duration of exposure to solarisation under a given set of temperature and humidity conditions fro a potting mixture having different physico-chemical features.

How can we do value addition to any optimised potting mixture ?

We can do value addition to developed potting mixture by adding cocopit , different combination of textures , aggregate stability , microbes of different functions  , especially in consortium mode , depending upon the type of plants aimed to be grown . 

What are the latest  interventions in the development  of potting mixture dynamics?  

We need to trace the growth of a plant at various stages , and simultaneously observing the nutrient and moisture flow over a period of time  to judge the superiority or inferiority of the potting mixture in terms to supporting the growth of the plants. Use of AMFs , microbes , preferably AMFs driven microbial consortium , us of perlite etc.. could pave the way for much better development of potting mixture . 

What should be ideal potting mixture suiting to dynamic requirements of horticultural crops during pre-evaluation stage ? 

A potting mixture is said to be dynamic , only when it meets all  the requirement of growing plants by supplementing all the essential nutrients , besides optimum soil moisture , besides keeping diseases like damping off , leaf curls, leaf margin necrosis etc at bay. 

Hope , these answers will set the whole discussion into right context .

Anoop thanks for an intelligent reply. Have we isolated and tested native isolates of microbes for their efficacy in solo and also interaction in consortia. Do we have worked a kind of matrix with relation to temperature and survival of natural microflora and fauna and further multiplication at faster rate to accrue the desired benefits. Solarization in general practiced during hot months in the tropics and subtropics,  by providing soil cover with different coloured polyethene sheets. Though it can be practiced all the year round, but effectivity is obtained during specific months. Killing soil pathogens at the cost of beneficial microbes is the question.

Dr Malhotra , wont it be good we take the question  and subsequent discussion one by one .  I think , that will be more meaningful . 

Lets take first question ; why do we need potting mixture and how it be developed ?

Interesting Abhishek , how shall we proceed to develop a potting mixture ?. how shall we develop a hypothesis of a good potting mixture ? Thats my point of contention . 

My point of view for hypothesis is that a potting mixture should contain billions of beneficial microbes, with great water-holding capacity and abundant nutrient content which are available to plants for a longer period without frequent addition of nutrients. It should be cost effective.

Very good response Dr Malhotra. My point of view with potting mixture is it should be replicate with soil in terms of physical, chemical and biological properties of a fertile field soil. 

 Endorsing the comments from both  of you , Dr Malhotra and Dr Shirgure . The best  way to hypothesize the potting mixture with respect to any crop is to observe the crop performance in field . Find an excellent field performing soil , analyse the physical , chemical and biological properties , then try simulate such blend of soil properties to develop a comprehensive and dynamic potting mixture , compatible to a given crop. This will be the first stage of development of  potting mixture . Thereafter , we can continue tailoring potting mixture as per differential requirements of different crops  .

Potting mixes should support developing seedlings. Most potting mixes are soilless to avoid soil borne diseases and promote good drainage. A mix of peat moss, vermiculite or perlite, and compost or organic fertilizers can provide a suitable environment with sufficient water-holding capacity, nutrient content, and aeration for plant growth and development.  Many commercial mixes contain wetting agents to facilitate water absorption by peat moss. The question before us is for an ideal potting mixture what should be pH range,  soluble salts conc. Apart from it what should be the level of nitrate nitrogen , phosphorus, potassium other secondary and micronutrients, sodium contents range etc.

Dr. Anoop and Abhishek what is your opinion about customized potting mixtures for different crops and situations.

Yes , this  could be a possibility , but this customisation will not on the line what we have been discussing , unless you have a complete dynamic  potting mixture . i think , none of you responded to my earlier response , about the clues to be obtained for a dynamic potting mixture ..? How will you imbibe , these  should be the composition of our targeted potting mixture ...? 

Dr Srivastava, this is an excellent clue to serve as a base for developing potting mixture. This will also give an indication, what type of potting mixture will serve a specific crop. 

 There are a variety of potting mixtures. Those designed for terracotta pots are full of organic matter to retain a lot of moisture. Some potting mixes are unusual such as the lumps of bark used to pot a particular type of orchid (Cymbidium) that grows on tree trunks and lives on the moisture and nutrients that run down the bark. This orchid would not survive in ordinary potting mix or soil because it needs excellent drainage that is provided by the coarse bark.

You can make your own potting soil. Start with garden soil, add coarse river sand to create a free-draining soil and coca fibre to retain some of the water. These components should be in a ratio of one third of each. This soil won’t go hard and the roots can penetrate it easily.

The soil used for raising seeds is different. Seedling raising mixes are pasteurised to remove all the organisms such as harmful bacteria and fungi. This is different to sterilisation which kills all living organisms in the soil.

Some plants require potting soil that is specific for their environment. For example, an African violet would grow better in potting soil containing extra peat moss, while a cactus requires sharp (i.e. plenty of) drainage, most commonly perlite or sand. But potting soil is not ideal for all contained gardening. Insectivorous plants, such as the Venus flytrap and the pitcher plant, prefer nutrient-poor soils common to bogs and fens, while water-based plants thrive in a heavier topsoil mix.

The bulk density, total porosity, air porosity and water-holding capacity of mixtures of equal parts of either sand or scoria with peat moss, pinebark, poppy straw and sawdust can be predicted from the respective properties of the ingredients. Total porosity of the media was inversely correlated to bulk density, but there is no clear correlation between air porosity and bulk density. Air porosity increased with pot size. Please see abstract:

http://www.sciencedirect.com/science/article/pii/0304423879900487

 There are as many potting mix recipes as there are plants to grow in them. Many recipes have evolved to use local waste such as brewery sludge or jarrah woodchips. Such products may or may not be suitable as components of mixes in various proportions. Use such a product only if it has the following characteristics:

• desirable physical properties – wood chips may be suitable for large pots but would be too large for bedding plants
• does not contain excessive levels of salt or nutrients as some local peats or animal wastes do
• does not contain any toxic chemicals, such as copper chrome arsenate, PCP or boric acid from timber treatments, phenols as in uncomposted pinebark, or heavy metals as in sewage sludge.
• If it might carry disease, sterilise material before use. Gravels, soils and sand from dieback-infected areas are likely sources of Phytophthora.

Source: https://www.agric.wa.gov.au/nursery-cutflowers/potting-mixes

Very good feedback , full of logics to be fitted into the concept of developing a dynamic potting mixture . Such potting mixtures are crop specific..? Let us know,  what kind of soil and plant parameters should we consider to define the better response of potting mixture ..?

Thank you Abhishek. I liked paper number 3 on optimization of potting mixture.

Best wishes

How do you arrive at physical, chemical and biological environment of the potting mixture necessary for a given crop. 

Thats a good point Dr Shirgure , i appreciate it . Such idea about these issues will come through your field observations . however , you need to see a differential requirement of nursery versus grown up plants

There is a large number of different types of potting mediums available, both commercial and homemade. Many of them often share common ingredients and vary only in the different amounts of the ingredients depending on the stage of growth, type of plant, season and even the type and size of container the particular mix is being used for. Basic needs for health and growth of plants should cater are aeration, moisture, nutrients and support to plant so that plant should not just survive but thrive. As seedling get older the pot sizes will increase accordingly. The potting mix used will need to be heavier and able to retain nutrients. It should also be dense enough to support growing seedlings and be free of pathogens and weed seed.The principle guideline for a potting mix is, the smaller the pot and the younger the seedling the lighter the mixture. Potting mixes for many vegetables, flowers and fruits are often specialized and can vary considerably for different plant types and growth stages.  

Informative feedback Dr Malhotra. Potting mixture is meant for nurseries only . While developing crop-based nurseries , we need to look at the specific requirement s of crops , whether annual or perennial in nature . Fro example , litchi is highly AM-dependent crop , so we need to have AM as one of the important components of potting mixture . 

Dr. Anoop, thank you for analysis.

Let me toss up yet another quarry to all of you , wonderful friends as science ambassadors. what are the methods of disinfecting potting mixtures , besides well known solarisation.  Whether , we can do solarisation during any part of the year , or we should invariably  do solarisation during  summer only..?

Thank you Dr. Raj for important details on the topic.

Abhishek , good information , but the precise data on solarisation effect on soil microbial load of the soil , during various seasons , is distinctively missing . You have initiated a very good discussion , but lets discuss the issue more in depth ...

Good response Dr. Raj. I shall respond to your querry

Drainable porosity of the potting mixture should be maintained so as avoid the water logging induced plant mortality. 

 Organic potting mixes for organic farming systems assume importance. Several kinds of media (compost, peat, and manure-based materials) commonly used in organic potting mix recipes.There is always need for adequate supply of organic nutrients for growth in organic system. The organic sources are often inconsistent and slowly nutrients are released to plants. Can we predict release of nutrients from organic sources.

Infact , this is the reason , we started referring to substrate dynamics . Many account such issues as more  philosophical than scientific . Whenever , we have a potting mixture , it is supposed to be dynamic in terms of fulfilling the nutrient requirement of nursery plants. The point raise dby Dr Shirgure like a potting mixture should have enough drainable porosity to ensure , there is no waterlogging problem to growing such juvenile plants. Likewise,  nutrient release pattern should be  so extended that it should comensurate with the nutrient demand over an extended period. the best course would be the good microbial load of the prepared mixture . 

Even the professionals may have trouble determining the exact water needs of a plant. In order to avoid waterlogging, overwatering in potted plants is of the most concern, Due to waterlogging, nutrients are washed away and mold or fungal issues may develop. An obvious method to prevent overwatering in potted plants is with the use of a moisture meter. Sugarcane Research Institute at Coimbatore has developed a device and patented a soil moisture meter based on traffic light signal based colours. The moisture meter probes are inserted into soil and within 20 seconds, light glows like red or yellow or green. Easy to use and quick in giving result. 

This soil moisture meter costs to Rs. 1100 only.

 Yes it is true we need to trace the growth of a plant at various stages , and simultaneously observing the nutrient and moisture flow over a period of time  to judge the superiority or inferiority of the potting mixture in terms to supporting the growth of the plants. use of mycorhiza, PSB, PGPR could pave the way for much better development of plants . 

Yes , i agree with you , determining moisture content of potting mixture  requires some kind of realistic skills. Multi-inoculation of potting mixture is a kind of value addition in terms service functions of potting mixtures. i willing to know the ideal time of inoculation of potting mixture , since the same potting mixture will be subjected to solarisation ..? How much time lag , shall we give to the solarised potting mixture to recoup its microbial liveliness...?

Anoop compliments for focused reply. 

Let me toss up another quarry to you friends . How can we define the quality criteria of any potting mixture specific to a crop nursery..?

 The important quality characters which a potting mixture should contain are : desirable physical properties, should not contain excessive levels of salt or nutrients. It should be free from toxic chemicals and diseases. Should possess good aborbing capacity and efficient in release of nutrients.

Dr Malhotra, Abhishek and other learned colleagues:This is what i was expecting the quantitative criteria for evaluation of any potting mixture , worth appreciating . But , Abhishek , potting mixture having EC 1-5 mmhos will be too high , especially for those juvenile nursery plants , they seccumb to salt stress , for sure . We need to develop the potting mixture quality criteria ( what Dr Malhotra refered earlier) , and these criteria have to be based on crop nursery based., instead of any potting mixture could be used for raising nursery of any crop. 

Let me add yet another response on this very issue.  Why , the composition of potting mixture has to be dynamic , because fruits have different requirement , vegetables have their own preferences, flowers find in more comfort zone with shallow root system proliferating in a much friable soils, orchids have their choice of substrate , so unless potting mixture is dynamic to a specific crop , i dont think , we will ever be able to meet the dynamic requirements of a potting mixture vis-a-vis different horticultural crops. Unfortunately , i dont see much of the response , for the simple reason , not much work has been done on this very issue. 

Let us bring a concept of substrate dynamics in developing a potting mixture.

Thats a very good point Dr Shirgure . Infact , this is a kind of concept , which has huge application in developing potting mixture , dynamic to suit the requirements of different crops.

 Let me give details about the medium/potting mixture for hydroponic system which is one of the most important decisions a hydroponic farmer has to make.  Different media are appropriate for different growing techniques.

 Diahydro : Diahydro is a natural sedimentary rock medium that consists of the fossilized remains of diatoms. Diahydro is extremely high in Silica (87-94%), an essential component for the growth of plants and strengthening of cell walls.

 Expanded clay : It is made by baking the clay pellets and known under the trade name of 'Hydroton' or LECA (light expanded clay aggregate). Hydroton or expanded clay pellets are suitable for hydroponic systems in which all nutrients are carefully controlled in water solution. The clay pellets are inert, pH neutral and do not contain any nutrient value. The clay is formed into round pallets and fired at high temperatures (1200°C) in rotary kilns. This makes the clay to pop-up and become porous. The main advantage of hydroton is it is light in weight and does not compact over time. This is an ecologically sustainable and reusable growing medium because of its ability to be cleaned and sterilized by washing in solutions of white vinegar, chlorine bleach or hydrogen peroxide and rinsing completely. But there is an opinion that clay pebbles are best not re-used even when they are cleaned due to root growth which may enter the medium. Breaking open a clay pebble after a crop has been grown will reveal this growth.

 Rock wool : Rock wool, also called mineral wool is the most widely used media in hydroponics. It is an inert substrate for both free drainage and re-circulating systems. It is produced by aerosolization of molten mineral compounds which results in a fibrous medium accessible to capillary action that is not degraded by microbiological activity.

Coir : Coco peat, also known as coir or coco, is the leftover material after the fibres have been removed from the outermost shell of the coconut. Coir is a 100% natural growing medium.

 Perlite : Perlite is made from volcanic rock after being superheated into very lightweight expanded glass pebbles. It is used either loose or in plastic sleeves immersed in water. It is also used in potting soil mixes to decrease soil density and facilitates drainage. Perlite generally holds more air and less water. If not contained, it can float if flood and drain feeding is used. It is a fusion of granite, obsidian, pumice and basalt. This volcanic rock is naturally fused at high temperatures undergoing what is called "Fusionic Metamorphosis".

Vermiculite : Like perlite, vermiculite is another mineral that has been superheated until it has expanded into light pebbles. Vermiculite holds more water than perlite and has a natural "wicking" property that can draw water and nutrients in a passive hydroponic system. If too much water and not enough air surround the plant roots, it is possible to gradually lower the medium's water-retention capability by mixing in increasing quantities of perlite.

 Sand : Sand is the cheapest and easily available medium. However, the main disadvantages of using sand are that it is heavy, it does not always drain well and it must be sterilized between use.

 Gravel/Quartz : Quartz or gravel of size

Accept my compliments Dr Malhotra, for such a comprehensive reply. No doubt the role of substrate dynamics is most important in developing a dynamic potting mixture. But most important is to keep in mind the crop requirement as well. 

Yes Dr Shirgure , very thoughtful and educative information indeed. substrate dynamics is most developed fro apple , orchids, mushroom cultivation . we can imbibe some good practices from these crops to be replicated in other fruits and vegetable crops. 

 When selecting a potting mix, there are also a few things to avoid. 

When using fabric aeration containers it’s important to use a heavier soil. A soil that is water retentive will allow the water to stay within the confines of your soil and aerated container so that your plants are getting as many nutrients as possible. Avoid mixes that contain garden soil or topsoil. These mixes are often poorly-draining, and because they many not be sterile, they could contain pathogens or weed seeds. Potting mixes with an unpleasant odor aren’t a smart buy. These may be too rich in nitrogen, or they may contain harmful pathogens or other detrimental ingredients. Skip potting mixes containing mold or sprouting seeds. Commercial mixes labeled as sterile should be free of molds, pathogens, and viable weed seeds.

 One of the most important things a potting soil needs to do is provide roots access to air by letting water drain away from them. In the ground, the soil is usually deep enough to let excess water drain beyond root zones. In pots, however, water tends to accumulate at the bottom, despite drainage holes. The smaller the pore spaces of the soil in the pot, the higher that water layer will reach. Larger pores, formed by adding mineral aggregates to potting soils, readily admit water into the soil, then carry it through the medium and out the bottom. Then, all those large, empty spaces can fill with air.

Perlite, vermiculite, calcined clay (kitty litter), and sand are the mineral aggregates most commonly used in potting soils. Perlite and vermiculite are lightweight volcanic rocks naturally filled with air. I prefer perlite over the others because it does not decompose with time nor lose its aerating ability if the potting mix is compressed. Vermiculite is a valuable additive because it prevents some nutrients from leaching away, and it even provides a bit of potassium and magnesium.

A potting mix also must have ingredients that help it retain moisture. This is where organic materials—usually peat moss, sphagnum moss, or coir—come in. They cling to some of the water that the aggregates are helping to drain. Organic materials also hold on to nutrients that might otherwise wash away.

In addition to peat moss, vermiculite, and perlite, commercial mixes often contain sawdust or various grades of shredded bark. Lime may be added to help balance the acidity of the peat moss, and a small dose of fertilizer can often make up for the lack of nutrients.

Most gardeners make potting soil by combining perlite or vemiculite with peat or sphagnum moss. Two other organic materials that you could add to your potting mix are leaf mold and compost, which offer a wide spectrum of nutrients.

Adding some garden soil to a homemade potting mix contributes bulk while buffering against pH changes and nutrient deficiencies. The reason that garden soil is rarely added to commercial mixes is because of the difficulty in obtaining a steady supply that is consistent in quality and free of toxins such as herbicide residues.

 Read more: http://www.finegardening.com/soil-containers-should-be-good-mix#ixzz4HnArvFJO

Dear Dr. Malhotra

1. Potting soil needs to drain well but still hold moisture. Adding compost or garden soil can be beneficial. Following points may be studies.

Light, Humidity, Water, Growing Medium, Feeding & Fertilizing, Important Requirement. And try to simulate such conditions through your own synthesis involving soil, organic manures and a range of microbial cultures . Such simulation study is a must to idealise a plant growing under required optimum conditions.

2. Potting soil is a combination of several ingredients that are chosen to provide the best drainage, support and nutrition to plants. When dry soil is crushed in the hand, it can be seen that it is composed of all kinds of particles of different sizes. Commercial potting soils and homemade mixes contain similar ingredients, pH somewhere neutral , good microbial load of the potting mixture capable of supporting good plant health , uniformity in growth etc will surely dictate the superiority of a substrate .

Name of the particles Size    limits in mm     Distinguisable with naked eye

gravel          larger than 1                                 obviously

sand             1 to 0.5                                        easily

silt                0.5 to 0.002                                  barely

clay                less than 0.002                          impossible

3. Soil solarization is a nonchemical method for controlling soilborne pests using high temperatures produced by capturing radiant energy from the sun. The method involves heating the soil by covering it with a clear plastic tarp for 4 to 6 weeks during a hot period of the year when the soil will receive the most direct sunlight. When properly done, the top 6 inches of the soil will heat up to as high as 140°F, depending on the location. The plastic sheets allow the sun’s radiant energy to be trapped in the soil, heating the top 12 to 18 inches and killing a wide range of soilborne pests, such as weeds, pathogens, nematodes, and insects. We need to standardise duration of exposure to solarisation under a given set of temperature and humidity conditions fro a potting mixture having differentphysico-chemical features.

BENEFITS

Effectiveness on Various Pests, Fungi and Bacteria, Nematodes, Weeds

Most present- and future- environmental problems such as climate change and conservation of biodiversity are global in scope and require rigorous empirical analyses for any meaningful policy formulation. Though it is relatively easy to access data related to developed countries, data from developing countries is rather difficult to acquire.

4. Most gardeners make potting soil by combining perlite or vemiculite with peat or sphagnum moss. Two other organic materials that you could add to your potting mix are leaf mold and compost, which offer a widespectrum of nutrients.

5. One of the more confusing issues in gardening, especially to new gardeners, is which choose, potting mix or potting soil.

6. Peat Moss is an organic product derived from the slow decomposition of sphagnum moss which accumulates in bogs. The moss decomposes slowly under water. It is harvested by draining the peat bogs and collecting the material by various means. It is the most common ingredient found in North American potting mix formulations. Peat moss has no nutrient value and is acidic.

7. The physical qualities of potting composts are often assessed visually by taking into account such factors as the colour of the product, its elasticity and the presence or absence of fine peat particles. A potting mixture is said to be dynamic , only when it meets all the requirement of growing plants by supplementing all the essential nutrients , An important criterium for potting composts based on frosted decomposed black peat and peat moss is whether sufficient peat moss has been added to the mixture, since this type of peat has a favourable effect on the water and air balance in the compost and on the rate of shrinkage. The skill and experience of the assessor are of course of great importance. Different persons can form quite different opinions of the same batch of compost.

Dr Prem Baboo, very informative response indeed . What is your opinion , do we need to have potting mixture  according to crop species? Can there be an universal potting mixture?

Some good and relevant points Dr Srivastava, with respect to potting mixture. 

Dear Dr. Anoop

Good discussion,

As the name can be made it likely, universal potting soil is an all-rounder. Extremely suitable for many purposes, repotting houseplants, filling terrace- and bloom boxes, planting trees and shrubs and cultivating bedding plants, perennials and vegetable plants. Potting mixture, the common medium for growing plants, is prepared by mixing soil, sand and farm yard manure (compost) in 1:1:1 proportion. Coco peat may be added to an extent of 20 to 50 % by volume to the potting mixture. It can be used for both indoor and outdoor purposes and the pH ranges from 5.5 to 6.5. The main nutrient elements in a potting soil consist of nitrogen (N), phosphorus (P) and potassium (K). Universal potting soil with the RHP quality marks the correct proportion of these elements this is a multipurpose potting and germination mix for home use as well as universal. The mix suits the needs of most loved home plants in small pots and trays, it can be used for repotting in bigger pots and containers as well. The substrate is also suitable for soil improvement in the garden and as a grow bag for vegetables outside or in the greenhouse. The universal potting mixture made by proper ratio providing the right aeration and moisture ratio for your plants’ root system. Lime and standard fertilizer are also added to the mixture, ensuring that your plants have the right amount of main and trace elements available during the first 4 to 6 weeks. This makes Universal Potting Soil suitable for houseplants and patio plants but it can also be used for borders, balcony plants and perennials. Number of other product can be made , e.g. Organic potting soil, Coco peat potting soil, Tub plant potting soil and soil for seeding’s and cutting. Etc.

Whether you use it with houseplants indoors, or for window boxes outside, potting soil is an essential elementin any garden container. That's because potting soil is different than gardening soil: It is lighter and airier, so helps to keep water moving from top to bottom and keep plant roots as healthy as possible. Garden soil, on the other hand, moves water to the bottom and holds it there.

But pre-packaged potting soil can be expensive, particularly if you have lots of containers and flower boxes. Fortunately, you can make homemade potting soil quickly and easily with readily available ingredients.

Regards,

Prem Baboo

Dr Prem  , appreciate your response . i willing to know from your experiences , can we tailor the potting mixture according requirements of different  crops. For example , litchi air alyers are most response to AMFs , so a potting mixture should have enough load of AMFs .  Buddlings of citrus are raised on a clay loam soils , preferably alkaline pH, potting mixture developed for mushroom cultivation has very low bulk density , TPS  raising is done on loam soils , not heavy textured soils, like this.. is there any such standard suitability criteria of potting  mixture ....  

Dr. Prem thanks for response, but how value addition can be done in optimized potting mixture

The course of value addition in any potting mixture would be to microbially load it as much as possible to transform the utility of potting mixture as dynamic as possible. 

 I agree that soil should be having some 15-20% of available water capacity , loamy sand -clay loam in texture , organic carbon atleast above 5.00mg/kg , pH somewhere neutral , good microbial load of the potting mixture capable of supporting good plant health , uniformity in growth etc will surely dictate the superiority of a substrate . But what are the most significant soil-plant parameters that guide the composition of potting mixture for a given nursery plant ?

Yes , thats the point Dr Malhotra , most and distinctively  missing  from the entire discussion . Unfortunately , very little headway has so far been made on these issues, needs better redressal through future studies.  

My view point regarding significant soil-plant parameters that guide the composition of potting mixture, links plant properties, shoot-root relations and root-soil interactions  to uptake of nutrients and their efficiency. But how this knowledge can be precisely used for  customization of potting mixtures. This could be the area for future studies for working out composition of potting mixtures for different crops and situations.

I agree with you Dr Malhotra in principles, but not in outcome in relation to variety of crops. we need to have physico-chemical and biological criteria in relation to every crop to customise the potting mixture  . Look at the kind of work , that we have in hand , simply clueless....when you look at specific crop requirement ...

 Yes we need to have physico-chemical and biological criteria in relation to every crop to customise the potting mixture.

Yes , then only we will be in a position to customise the potting mixture in tune with specific requirements of different corps. i think , in this area , we need to work a lot more ... 

Let me  raise another issue. for how many crops , do we have the soil fertility and crop nutrient requirement criteria..? Are we in a position  to tailor an alternative crop on a soil originally not suitable to be grown ...?

I don't think so, this is the reason we do not have any dynamic potting mixture. 

It is well proved that good microbial load of the potting mixture is capable of supporting good plant health, uniformity in growth etc will surely dictate the superiority of a substrate. But how to ascertain the efficacy of microbial culture for optimum plant growth and development for longer period

Very good suggestions and basic information for customization of potting mixtures. But information on commerciallization and feed back from users is lacking. We need to link with sensor based systems and automation for fulfilling dynamic needs of nutrients and keeping the pH to optimum level.

I think , optimization in pH of potting mixture is the biggest issue , once you have developed a potting mixture suiting the pre-evaluation issues of a specific crop. We nedd to tailor soil pH somewhere 6.5-7.5 for the results of highest order.

Friedns , i got an excellent  paper about the utility of gassified biochar to be used a potting mixture for different hroticultural crops. The abstract is given below: 

Biochar is a renewable, useful material that can be utilized in many different applications. Biochar is commonly produced via pyrolysis methods using a retort-style oven with inert gas. Gasification is another method that can utilize pyrolysis to produce biochar. This method has significant processing advantages; it can be carried out in normal atmospheric conditions, eliminating the use of inert gas, is more amenable to scale up, and provides heat that can be used to generate power and/or help recoup processing costs. In this work, a simple gasification process using a top-lit updraft style cookstove was used to produce biochars from corn stover, wheat straw, and wheat straw treated with glycerin, which were then compared to biochars made using the more conventional retort oven pyrolysis process. The glycerin-treated wheat straw biochar from the gasification process had carbon content > 70% and an ash content of 25% which was equal or better than the same biochar produced using the retort oven. This biochar has also shown successful use as a peat moss replacement in horticultural applications. This shows that gasificationis a simpler,more cost-effective means to produce biochars and shouldbe considered for horticultural and other similar application. 

PDF enclosed for further reading...

Thank you Dr. Anoop, Dr. Abhishek, Dr. Parmeshwer for providing important links and information on biochar related to its benefits. Does quality of biochar differ in with different sources used for preparation of biochar for this purpose. 

Biochar could be effectively used as an amendment in improving the quality of potting mixture. 

Dr Malhotra , you are right , the quality of final product  biochar is hugely dependent upon the composition of feedstock and the temperature of pyrolysis . This is undoubtedly one area , where researchers are eyeing at  from different angles , right from physical amendment to expending the utility of biochar through composting with different organic manures as a part of process of value addition of biochars. 

 Dr Malhotra and other colleagues, another advantage with biochar lies in the fact that biochar out of other organic sources, has the maximum carbon stability in the soil, besides other distinct advantages in terms of decreasing teh bulk density of the potting mixture and facilitating the microbial abundance as well.  . 

Dr. Anoop, there is no doubt biochar will play a greater role in the potting mixture for plant growth. You are aware that different size of pots with varying capacity are available for accommodation of potting mixtures. Normally pots of 10 cm to 1 mt are used. Do we have calculations about the quantity needed for each size of pot/crop. Do we apply biochar at intitial stage of pot filling or it can be done in pot with established plants also. This is open to all colleagues for views.

Nice response Dr Malhotra , loaded with some very good quarries. Let me attach some PDFs in relation to your quarry  about the pot and field  experiments using some vegetable crops and other horticultural crops as well...

Hope , they will be useful in the context of further discussion on a n issue of such a huge significance ..

It is always useful to have a potting mixture carrying lower bulk density to facilitate better plant growth. 

This is where biochar offers very strong competition to conventionally used materials in developing potting mixture.

Thank you anoop ji, i know biochar will bring dynamism in potting mixtures sector. we need to promote it. Can you appraise about the status of biochar application in India. If we need to promote, how we can do this. I am not writing in specificity to potting mixtures, but we need to look for application in other areas too. 

Abhishek , use perlite and vermiculite , no doubt are conventionally used in potting mixture , but of late use of biochar certainly offers better opportunities as a supplement to conventionally used organic manures, for the simple reason , former has better carbon stability and far higher resilience time  in soil , besides imparting lower bulk density for aeration and pore volume related lot of issues..?

Here is your most desired answer , Abhishek . Hope , our colleagues will find this attachment very useful in the context of whole discussion . it will be more interesting to know , look at role of biochar in longer perspective, preferably in combination with compost or composted manures.

Biocha has  a potential to serve carbon requirement of crops for atleast 20 years or so..depending upon the nature of feedstock  and related base material used in developing the biochar-based substrate..?

Yes Biochar will definitely stimulate microbial activity in soil.