An interesting question .Surely , the evaluation of soil temperatue at various depths will reveal the ultimate effect on given crop rhizosphere ecology and the recalcitrance level of carbon within the rhizosphere...

Global warming has been widely debates in scientific, political and social communities over recent decades; furthermore, it has caused changes in various ecological processes and has potential to change ecosystems’ stability1–3. In spite of comprehensive studies to investigate responses of various ecosystem processes to rising air temperatures4–7 under global warming, much less is known about changes in soil temperatures and their impact on below-ground processes8–13, particularly deep in the soil profile. Temperature change can affect most soil processes, including decomposition and formation of soil organic matter14,15, mineralisation/immobilization of nutrients (N, P, K, etc.)16,17, and the subsequent nitrogen transformation (nitrification and denitrification) processes18,19. Any change in these processes can alter soil carbon and nutrient dynamics, soil fertility and productivity, and greenhouse gas emissions, with effects of ecosystem function and global climate change15,20–23. Soil respiration, as a key temperature-dependent process, is biologically mediated; its rate increases exponentially with temperature, roughly following the Q10 ≈ 2 rule (rate doubles for every 10 °C increase in temperature) for a wide temperature range24–28. In addition, several plant processes, including seed germination, seedling emergence, early developmental and growth processes, root extension and growth, are all sensitive to soil temperature change29–31. Rising soil temperature directly and indirectly impacts these processes, potentially leading to changes in productivity and stability of ecosystems.

Soil temperature is an important physical property that regulates evaporation, aeration and chemical reaction taking place in the soil. Soil temperature strongly influences biological processes such as seed germination, seedling emergence and growth, root development and microbial activities. The depth of sampling differ according to your objectives. For example to analyse of the available macro and micro-nutrients that are related to crop growth and nutrient uptake, sampling is done to a depth of 30 cm. In general people avoid first 5 cm depth as it influences by ambient temperature. Depth wise soil sample should be taken as per needs of the researcher.

I am agreeing with the vies given by the other researchers. But it is a parameter to compute emission of green house gases

It is basically for study of root zone depth as per crop root for effective activities of rhizosphere and beneficial Microorganisms.

Dear Prof Anoop, Tarafdar, Prashan, and Suchit Rai, thank for your explanations. That is very useful for me. I asked because several researcher use different soil depth for the same purpose, for example during measure the soil respiration.

Emission of GHGs depend on soil temperature also. Taking of soil temperature at different depth helps to support or correlate emission data.

Thanks Choundary, so if we only measure the soil temperature , for example, at 10 cm , is that fine we generalized that number into the whole soil profile. When we measure a soil respiration on the soil surface and temp at 10 cm depth , the Rs number often reported or assumed from the whole profile of depth. is this appropriate, or we should make a correction?.

How far the depth of crop rhizosphere affects the depth of soil temperature to be measure..??

Dr. Srivastava, I think it is between 30 and 60 cm, depends on crop root behavior. Therefore, there is no point to measure soil temperature below 60 cm depth and above 10 cm depth (as it affect by ambient temperature).

Shall we stick to the effective rooting depth of a given crop or the depth of soil where ecological behaviour of the soil is dictated by the free air exchange , called heat transmission properties of the soil.....