Unlike the description by Moll et al. (1982), uptake efficiency should be partitioned into two separate components since plant N loss (from flowering to maturity) can be significant.

Fraction of N translocated to the grain should be estimated as Ng/Nf and not Ng/Nt as proposed by Moll et al. (1982) since more N was accumulated in the plant at an earlier stage of growth.

Plants losing significant quantities of N as NH3 would have very high fractions of N translocated to the grain when calculated using Nt instead of Nf.

In terms of plant breeding efforts, this could be a highly misleading statistic.

A second component, the translocation index is proposed that would reflect the ability of a plant genotype or management practice to incorporate N accumulated at flowering into the grain.

3. translocation index Eti=Ng/Nf * (1/Nl)

Ability of the soil-plant system to utilize outside sources of N for food production (grain or forage) depends on the efficiency of storage in the soil. The efficiency of the soil to supply N to plants is strongly influenced by immobilization and mineralization with changing climate and environment.

Over a growing season, storage efficiency will be equal to the difference between fertilizer N added (Ns) minus maximum plant uptake (Nf) plus the difference between total soil N at the beginning and end of the season, all divided by fertilizer N added.

Esg = [(Ns-Nf)-(St1-St2)]/Ns

4. soil (management system) supply efficiency, Es=Ns/(Sv+Sd+Sl) where Sv, Sd and Sl are estimates of soil volatilization, denitrification and leaching losses from the soil, respectively.

Lastly, a composite estimate of efficiency for the entire system (soil and plant) can be estimated as follows

5. composite system efficiency Ec=Eup*Es=Nf/(Sv+Sd+Sl)