Theory 082/Food & Agriculture /Nutrient management
Nitrogen Efficiency Is Synchrony
Efficiency is computed as output per kilogram applied. The timing in between may decide most of it.
Nitrogen use efficiency is set by the synchrony between supply and crop demand rather than by the total applied, so splitting the same dose into better-timed applications can raise efficiency without reducing yield.
01The evidence
Split applications and controlled-release fertilisers raise efficiency at equal total nitrogen, and the gains vary with rainfall timing.
02The tension
Recommendations are built on total dose, with timing as an implementation detail, which predicts uniform efficiency at equal dose.
03The mechanism
Nitrogen that is present when the crop cannot use it is lost to leaching or denitrification. Efficiency therefore depends on how much of the applied nitrogen coincides with uptake demand, which is a scheduling problem.
That makes synchrony the determinant, and predicts efficiency should collapse when supply precedes demand by more than the soil's holding capacity.
04What this is not
Dose models predict efficiency from quantity. This predicts it from timing, which explains variation at equal dose.
05Predictions
- P1Efficiency should correlate with synchrony.
- P2Split applications should raise efficiency at equal dose.
- P3Holding capacity should set the tolerable gap.
06Refutation
Efficiency tracking dose at controlled timing would restore quantity models.
07What it changes
It would make timing the primary recommendation.