I am not sure you mean by damage by urea. Urea is used to supplement N for crop production and indeed Urea or other chemical fertilizers have played a key role in increasing food production. Excess use of N would have implications for nitrogen leaching (often as NO3-N) and its gaseous loss (NH3, N2O, NOx). The "damage" is generally associated with excess or untimely N use. Organic source of N (and other nutrients) perhaps can help control this damage. The key point is using equal amount of N through organic fertilizers may not help control this "damage". In fact there would be increased losses of N in gaseous forms from organic fertilizers.

Dear Peter, thank you for your answer. Yes i agree with you that urea and other chemical fertilizers have played a key role to increase food production, but excessive use of them have made the soil loose its fertility. For example, in a town nearby the city whe i am located, apple trees do not produce apple fruits anymore. That town was famous for its apple fruits production for several decades, but now the soil stop producing good apple fruits, because of fertility is ruined.

My question is: will the use of organic fertilizer be able to return back soil's fertility which has been already damaged? Thanks

Victor, it is difficult to how the use of urea can make apple trees not to bear fruits. Yes the use of organic fertiliser /manure is helpful as it  should result in general soil improvement, including microbial activities. I suspect the cause is something else. You should get it investigated. But no harm in trying mixing manure in the soil around a few trees.

Thanks, Peter, for your suggestion. Best wishes

i agree with other authors it is nutrient rich land in N is the worrying factor

sustainable agriculture is one of the ways

use of organic fertilizer like Compost/ vermicompost/ green manuring/ application of cow dung etc.

if you want to leach out excess nutrients then irrigation methodology appropriate to your farm/land in consideration is to be used 

Dear Prakash, thank you for your answer. Best wishes

Damage caused by urea fertilizers, can be recovered by application of potassium fertilizers.

Thanks Ashokkumar, do you mean that potassium fertilizer should be used in combination with organic fertilizer? Or potassium should be used alone? Best wishes

Points-of-thoughts from my side: 1. We need to accept the positive impact of all sorts of mineral fertilizers for global yield-increases since 130 years, but perceive increasingly the adverse ecological impacts of any one-sided chemical-applications on soils. (In Germany many aquifers are heavily N-polluted due to excessive N-fertilizers incl. Urea, and animal-sludge / semi-liquid-manure  from animal-factories. 2. Excessive urea-use will destroy important soil-fertility-components and properties and can be replaced / corrected by a) foliar-application of urea, b) using compost, c) esp. horn-meal, bone-meal, etc. d) legume-mixed cropping / intercropping / rotation-cropping. 3. Healing an "urea-sick" soil needs a robust organic-soil-fertility-strategy with b) and c) plus mulching, all sorts of organic material, esp. mature manure and mature compost. 4. In irrigation-areas there is the option of guiding-in silt-rich river-waters into the plots after heavy rains. 5. On small areas permaculture-like practices are advisable. 6. Fallow with utmost triggering of germination & growth of many different species may be considered.

I still find it difficult to understand how the use of urea can make apple trees not bear fruits - to be honest I see no link here. We should not simply assume that the problem is caused by urea use.

Thank you, Bernhard and Peter. Best wishes

Excessive one-sided N-fertilizer-applic. by urea (or any other pure N-fertilizer) can lead to high yields for some time and deplete completely the stock of P, or K, or S, or Mg.....etc. and lead to a stop in flowering. In Ethiopia I heard about dramatic soil-fertility-problems due to false urea-regime on large scale production of teff (Eragrostis tef) and combined with a fully distorted credit-scheme many farmers were sent to prison.

@Bernhard, thanks for your answer. Yes, perhaps the initial increase in production after the introduction of urea fertilizer may cause a linear thinking: if one increase the use of urea then it will also increase production. Then the temptation is great to maximize the use of urea (they call it: intensification), but the soil fertility is ruined as a result. That situation may happen in many countries where the governments push the farmers to increase the production no matter what. Do you know other examples of misuse of urea fertilizer? Best wishes

To all contributors, does anyone know about how to assess soil quality on global scale. I jus found an article discussing how to do that, but do not know the actual report. Thanks

http://www.iuss.org/19th%20WCSS/Symposium/pdf/0341.pdf

Your actual question does not have a simple answer.  First, urea fertilizer does not directly cause soil damage unless grossly over applied.  As others have pointed out, the use of urea alone for fertilization purposes will of course contribute to withdrawal and a decline of available P, K and other essential nutrients over time if they are not also applied on a regular basis.  On a relatively small scale, organic fertilizers may help prevent this, but it is important to remember that the term "organic" simply means the material is primarily carbon based, and it does not imply any particular nutrient content.  For instance, blood meal is a good organic source of N, but not high in P or K.  Bone meal is considered to be a good organic source (which I disagree with, since it is mostly mineral matter) of Ca and P, having little to no N.  Other organic "fertilizers," such as animal manures, may have decent levels of N and P, but lack sufficient K levels to serve as a useful long term fertilizer material.  The real key, in any fertilization program, is to monitor the existing available nutrient supply in a soil, matching that with the nutrient needs of the crop being grown, while applying any that are in short supply, whether from organic or inorganic sources.  Yes, there are benefits to improving  organic matter levels in soils through the use of green manure crops and other organic materials, but all come with a cost.  Green manure crops need nutrients (fertilization) too and some organic fertilizers also pose environmental hazards.  There are no magical solutions and no "one-size fits all" solutions to meeting crop nutrient demands.  Being smart, keeping an open mind, and using good science are the best bets, my friend.

@Robert, thank you for your insightful answer, best wishes

Sorry , i am so late in the discussion , but looking at the utility of the question , i feel , let me add my bit...Robert  has responded really ably with some thoughtful points , we need to look at them . We so often blaim the use of chemical fertilizers towards the deterioration in soil health -related properties , but the story is simply otherwise . As long as , we continue to use chemical fertilizers including urea in tandem with P and  K-fertilizers , balancing them as per crop requirement , i do not think , we need to worry about such problems, unless grossly over-applied ( Robert has rightly pointed out )  . Let me divert your attention towards another side fertilizer use in contemporary agriculture . How many of you think , soil microbes prosper well in fertile than non-fertile soils..? Probably all of you , then , if we use urea simply for meeting out the N-requirement of the crop , how shall it induce such soil damages, where we need  any possible intervention of organic fertilizers..? If at all , there certain damage in soil properties  , lets use composts , green manures/cover crops, and most important soil conservation practices , use  Land capability classification for streamlining the possible  sustainble land uses...

Some thoughts ....