you may consult with any agronomy book

Sir, really your question is very interesting and very tough to answer. Only experienced person who is working on these aspects can answer.

Sir, really your question is very interesting and very tough to answer. Only experienced person who is working on these aspects can answer.

Dr Rao , as discussed through pervious conversation , in perennial crops like citrus , mango , guava, the tap root could go down up-to  much deeper , but the feeder roots , the roots responsible for absorbing nutrients  , remain concentrated in top 15-20 cm only as established through radiotracer technique.  . And sometimes , during rainy season , these feeder roots get concentrated to top 10 cm only . For such perennial crops , getting significant amount of nutrients from sub-surface  seems much less compared to surface nutrition , it could be 80% from surface soil and rest 20% from sub-surface . These scenario , you would find under drip irrigation  , but under flood irrigation  it could a difference of another 105 maximum , because of again root configuration /architecture .  Nutrients like N, P , K , Ca, Mg, Fe , Zn , B continue to pose problem with respect to both yield and quality .

Dr.Srivastava, I have come cross  references on subsoil root activity in citrus and other crops much beyond the range you have mentioned(not in black soils alone).With average management many farmers are getting good yield of mango and other crops utilizing the subsoil nutrients.So let us invite opinion of other colleagues working under different crop, soil and climatic conditions.

Dear Subba,

Anoop is correct and feeder roots are typically shallow whereas the deeper roots may take up water from considerable depths.

Paul

Thanks Paul , I hold your opinion correct .  The first question comes to my mind Dr Rao , that why do we need to stress upon the subsoil nutrition  when there is already  major proportion of feeder roots concentrated in 0-20 cm , and the contribution of nutrition from  subsoil could be very small to the extent which is  irrelevant in the context of meeting the significant amount of nutrient requirement of the perennial crop like citrus , without denying the subsoil root activity. Such kind of  situation comes only when crop is poorly fertilized , and feeder roots are not in a position to take up the required nutrients from the surface soil .  Pleas refer to excellent work done by IIHR , Bagalore on this aspect where they advocated to use the term  root activity,  instead of  root concentration/density.  Hope , Paul will throw  some more light on this issue.  

Several scientists measured  subsoil root activity using radioisotopes,uptake of stable isotopes and actual depletion of water and nutrients.They reported subsoil root activity (Up to 75% activity) in deeper layers,45-more than 100 cm in different citrus species ,around 45-200 in mango etc.I understand that feeder roots  may be contributing to  substantially  to uptake of nutrients  under good management of nutrition but even under those situations the subsoil may be providing nutrients originally present in soil  and those leached from applied fertilizers and manures  and also brought from irrigation water. So information is needed on  subsoil  contribution to water and nutrient uptake by orchard tree crops especially from deeper layers.

Please go through the following paper to get  insights into subsoil root activity and its contribution to nutrient uptake from subsoils by tree crops.

Subsoil root activity in tree-based cropping systems by Johannes Lehmann

Plant and soil  255 :319-331,2003

I thank all the followers and participants of this useful topic for their valuable contributions.I believe that there is a need for generating more information on the role of subsoil root activity in mobilizing and tapping nutrients by the tree crops.