Balanced application of fertilizer P and K had been shown to enhance apparent n recovery in long-term experiments. Methods and time of fertilizer application also have significant influence on uptake efficiency. Crops, even varieties of same crop vary in their efficiency in uptake of nutrients.

The following link may be seen for earlier discussion on the topic

https://www.researchgate.net/post/How_can_I_assess_the_new_formula_about_N_use_efficiency/2

The link below may also be seen

http://horttech.ashspublications.org/content/21/3/266.full

There is no such report where apparent N recovery or recovery efficieny was 100% in cereal crops. This is an age old challenge for all the agriculturists to cross the boundary of 50% REN in cereal crops. I think there is some mistake in calculation. What nutrient management options have you taken for increasing N use efficiency?

Apparent N recovery of more than 50% had been reported for cereals:

https://eurekamag.com/pdf.php?pdf=002905766

file:///C:/Users/Nilay%20Bora/Downloads/04-AJ-96(4)=1039-1049-YangSM.pdf

https://www.researchgate.net/profile/Nps_Yaduvanshi2/publication/231841900_Substitution_of_inorganic_fertilizers_by_organic_manures_and_the_effect_on_soil_fertility_in_a_rice-wheat_rotation_on_reclaimed_sodic_soil_in_India/links/56022f1a08aed9851827d07c/Substitution-of-inorganic-fertilizers-by-organic-manures-and-the-effect-on-soil-fertility-in-a-rice-wheat-rotation-on-reclaimed-sodic-soil-in-India.pdf

Article Substitution of inorganic fertilizers by organic manures and...

Hi Sampriti,  

In the term: ‘Apparent N recovery’, the word apparent means: it is not the ‘real’ added (fertilizer) N recovery, as it incorporates the recovery of both ‘added N’ and ‘soil N’.

In some situations, the root system of the plants in the ‘fertilized plot’ explore a greater soil volume (due to larger root system) leading to greater soil N uptake in the fertilized plot relative to a smaller soil N uptake by plants with a smaller root system in the ‘non fertilized plot’.  If the difference in soil N uptake becomes substantially high compared with the amount of N added in the fertilized plot, ‘Apparent N recovery’ calculation will give a value higher than 100%.

I am curious to know.. what is the N source added?

Dear Sampriti,

in addition to Susanthas´ valuable comment, calculated recovery rates of more than 100% of applied fertilizer N might also be explained by so called „priming effects“. Real priming effects had been defined as strong short-term changes in the turnover of soil organic matter caused by comparatively moderate treatments of the soil (Kuzyakov et al. 2000) and are generally ascribed to interactions between living and dead organic matter (Kuzyakov 2010). In your particular case, the applied fertilizer might have boosted soil organic N mineralization by affecting soil microbial biomass activity.

Article Kuzyakov Y.. Priming effects: interactions between living an...

Article Kuzyakov Y, Friedel JK, Stahr K.. Review of mechanisms and q...

I fully agree with Dr. Santos that it may be a case of over fertilization. You can check the N concentration. Depending of the plant species, development stage, the nitrogen uptake should not exceed between 2 and 5% of the plant dry weight for optimum growth.

Primary assumption behind the Apparent N Recovery (ANR) calculation is:  Soil N uptake in the ‘Fertilized plot’ is similar to the soil N uptake in the ‘Control plot’.

Assuming this assumption is correct, ANR is estimated using the following equation:

 ANR = [(UF - U0)/NF] x 100

Where,

NF = Fertilizer-N rate (kg per ha),

UF = N uptake in fertilized plot (kg per ha), and

U0 = N uptake (kg per ha) in non-fertilized plot.

If that primary assumption is not met, ANR estimate could give an unrealistic value. My first comment and the ‘priming effect’ explained by Kai-Ewe are two examples where that assumption can fail.

I think it is maybe the results of  long term experiments. In the experiment, the soil availibilty of control(no N supply) declined significantly, but the availability of plot suppied N fertilzer continuously could be increased or no declined, and which led to markedly difference between control and fertlization plot,  so the apparent N recovery  could be more than 100%. I don't think it is a realistic value. In the N recovery test, the hypothesis is the N availibility of  plots tested is equal or no difference among the plots. 

Is it that the recovery had been calculated at very low dose of fertilizer, and the soil N supply is very high!!

This is likely to occur with organic fertilizer.  If it is an inorganic fertilizer N source, then it is likely to occur at low rates of N.

 I'm guessing this is not a 15N study and that the results rely on the difference in N uptake between the control and the plus N treatment(s).

The fertiliser is simply helping the crop access soil N.  That is, you appear to be mining the soil N reserves, probably by accelerated decomposition of the organic matte.r 

So no.  It's probably not sustainable.  

Yes , it could be a possibility , unless nitrogen release from control versus treated plots is precisely worked out. This often happens where organic minutes are involved.