Sodicity cannot be created in pots and hydroponics. There is very wide variation in the field and it is a highly hard to find a piece of land which is uniform in sodicity level. Hence, what is best method for assessing sodicity tolerance level of a plant?
Accurate Sodicity tolerance level assessment method for plants?
Wide variations of sodicity in the field.
Sodicity cannot be created in pots and hydroponics.
An interesting issue , you have raised Dr Nazir. You can not create the sodicity of desired level with desired precision in laboratory. The best way is to identify the salt affected belt , collect the soil samples as many as possible in spatial domain , analyse them for pH and EC in laboratory , and then classify these soil samples in increasing or decreasing order of pH since EC may not increase consistently with pH. Under natural conditions , it is possible to have soils of ESP ranging from 10 to 80 , depending upon the extent of soil salinization. Then , your soils of varying ESP are ready for sodicity tolerance studies under pot culture , but need to be cross verified with field evaluation . After all , the results of these tests will be applied to field only , either to have an alternative crop sequence or as an viable option for reclamation of such soils. The biggest advantage of such plan is that you have soils of varying ESP having same texture and mineralogy. While in hydroponics , test plants will not behave uniformly , but this is again going to be an artificial way of evaluating sodicity tolerance of plants.
The widely used method for studying salinity tolerance is sand culture method, using Hoagland nutrient solution. The use of sand culture will,eliminate the effect of soil texture on salt absorption, if one use soils from different parts of the field, due to differences in soil texture. The results of sand culture are applicable to some extent to field conditions.We have been using sand culture for years with acceptable results. But,as you have pointed out the situation in the field is more complicated, and there are several factors which affect salinity tolerance in plants in the field, in particular, the stage of plant development.Young plants shows different salinity tolerance, but as the plants grow older,they become tolerant to even higher salinity levels in the field. so one , has no choice but to accept the results of sand culture or hydroponics and hoping to apply them under field conditions.
Dear Abbas, we are speaking about sodicity tolerance meaning varying ESP values. Sodic soils (having ESP more than 15 or SAR more than 13) are degraded in physical properties (BD, porosity, degree of clay dispersion). Sand culture studies are OK for salinity tolerance but not for sodicity tolerance. The method proposed by Anoop Kumar is good for preliminary screening but field evaluation (the final test) still remains a problem. Let us hear from other experts.
You are dead right Dr Nazir. In a technique like sand culture, since you take sand , how can you raise ESP beyond 10-15( Sands are not supposed to have high cation exchange capacity to inflict high ESP upon sodiumization ) to test it for tolerance against high sodicity. While in hydroponics , where is the exchange complex , no soil exchange complex at all, and maintaining differential ESP is simply out of question . And these are the candid reasons for results accruing from such exercises, fail to yield reproducible results when evaluated under field conditions. Dr Nazir , let me compliment you for floating an excellent question of very high academic value.
Trials for sodic solis should be done in situ for depth variations and texture. Protocols can be derived from moderation treatments either by Gypsum or Ca organic, using different parcels to grow plants. The main objective is avoiding or decreasing sodicity , selecyng resistant plants does not alleviate the problem. For an issue Bennet thesis can be an example http://www.google.it/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0CEcQFjAE&url=http%3A%2F%2Fwww.cottoncrc.org.au%2Ffiles%2Fae944900-d401-49d1-829b-a00100f2aa0b%2F10323_CCCCRC_Bennett_thesis.pdf&ei=saCbVaWKDcH4ywP-9qnACg&usg=AFQjCNHQvXPjlIAjmDgibZlvyBxgQ3TqkA&sig2=C2IT6P9m6OblMjJnyg802gsodicity.
Hydroponic culture provides a more versatile approach under such adverse situation. However,as support medium, glass or plastic beeds may be tried to avoid any ion exchange reactions.
Anoop Kumar! Thank you for elaborating the problem further and making it crystal clear. Scientists! Please remember that we are speaking about sodicity measured in terms of ESP. It means that the medium of experimentation must have cation exchange complex. Sodicity is quite different from salinity, therefore both must not be confused to be together. Such situation cannot arise in sand culture or hydroponics, as proposed by Bongi and Riaz Waheed. Glass or plastic beds will present artificial conditions and may be used just crude screening. We want some procedure very accurate and very closer to the field conditions so that results are reproducible in all conditions similar to the experimental conditions.
Hence, we want some innovative procedure which could ensure reproducible results and be very nearer to field conditions.
Yes , Dr Nazir , your version is perfectly right in the context of this very pertinent issue . In such studies , exchange reaction is utmost important . Lets listen from our other friends what they have in store to express.
Yes, Anoop Kumar, We are confident to have some good and innovative answers.