Through understanding the variation in NUE the objective of this work was to contribute to the understanding of reducing nutrient (specifically nitrogen) inputs to reduce the environmental impact of crop production and improve crop profitability through enhanced crop nutrient efficiency. Twelve NUE metrics were defined (see table below) with three being chosen as the most informative depending on the question being asked:
1. To indicate efficiency of crop N use to produce yield:
kg grain yield/kg N available (kg/kg)
2. To indicate efficiency of fertiliser to improve crop quality (protein content):
N removed in harvested grain (%)
3. To indicate potential risk of losing applied N to the surrounding environment:
N balance for crop N offtake (kg N/ha), which calculates the net amount of applied N fertiliser left in the field after harvest
|
No. |
NUE metric |
Calculation |
Units |
|
1 |
kg grain yield/kg N available |
kg grain yield / (soil N + N fertiliser) |
kg/kg |
|
2 |
kg grain yield/kg N fertiliser applied |
kg grain yield / kg N fertiliser applied |
kg/kg |
|
3 |
Grain N offtake |
DM yield x grain N% |
kg N/ha |
|
4 |
Total crop N uptake |
Grain N offtake + 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 / (soil N + N fertiliser) |
% |
|
7 |
N utilisation efficiency (grain; NUtE) |
Grain yield (kg/ha) / Total crop N uptake |
kg DM/kg N |
|
8 |
N removed in harvested grain |
Grain N offtake / (soil N + N fertiliser) |
% |
|
9 |
Apparent N 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 for Grain N offtake |
N fertiliser applied – Grain N offtake |
kg N/ha |
|
11a |
N balance for Crop N offtake |
N fertiliser applied - Crop N offtake |
kg N/ha |
This analysis included cereal, oilseed, pea and bean crops, totalling over 4,600 crop entries between the harvest years 2013-2021. The final report was published by Defra and can be found below.
