Our first job is to define the Nitrogen Use Efficiency metrics to calculate and compare in the YEN dataset. Our suggestions are:
|
No. |
Name |
Calculation |
Units |
|
1 |
NUE (yield) |
kg grain yield / kg N available (soil + fertiliser) |
kg/kg |
|
2 |
NUE (yield/fert) |
kg grain yield/kg N fertiliser applied (kg) |
kg/kg |
|
3 |
Grain N offtake |
DM yield x grain N% (= Grain N Yield) |
kg N/ha |
|
4 |
Total Crop N Uptake |
Grain N Yield (kg N ha) + straw N (DM straw x straw N%) |
kg N/ha |
|
5 |
N Harvest Index (NHI) |
Grain N offtake / Total crop N uptake |
% |
|
6 |
N uptake efficiency (NUpE) |
Total Crop N Uptake / N available (soil + fertiliser) |
% |
|
7 |
N Utilisation efficiency (NUtE) |
Crop yield (kg/ha) / Total crop N uptake |
kg DM/kg N |
|
8 |
Grain N recovery |
Grain N Yield / N available (soil + fertiliser) |
% |
|
8a |
Crop N recovery |
Total Crop N Uptake / N available (soil + fertiliser) |
% |
|
9 |
Apparent Fertiliser Recovery |
(Total crop N uptake – soil N) / N fertiliser applied |
% |
|
10 |
Simple Fertiliser Recovery |
Total Crop N uptake / N fertiliser applied |
% |
|
11 |
N balance (Grain) |
N fertiliser applied – Grain N offtake |
kg N/ha |
|
11a |
N balance (Grain & Straw) |
N fertiliser applied - Crop N offtake |
kg N/ha |
We can only assume soil N from RB209 field assessment using soil type, previous crop and over winter rainfall.
We do not have full information on manure N applications, so cannot estimate N from manures for most crops. However we can look at crops with no known manure use separately to those with regular manure history.
For wheat crops we also plan to look at protein content achieved compared to average protein achieved by the variety in the Recommended List, giving an indication of whether N supply was sub or super optimal.
If there are other metrics you think we should include, or we should define any of above differently, please let us know.
