N
Fertilizer Optimization Algorithm (NFOA)
1.
Predict potential grain yield or YP_{0} (grain yield
achievable with no additional N fertilization) from the grain yieldINSEY
equation, where;
INSEY
= NDVI (Feekes 4 to 6)/days from planting to sensing (days with GDD>0)
YP_{0} = 0.74076 + 0.10210 e ^{577.66(INSEY) }units:
(YP_{0} in Mg/ha)
2.
Predict the magnitude of response to N fertilization
(InSeasonResponseIndex, or RI_{NDVI}).
RI_{NDVI}, computed as; NDVI from Feekes 4 to Feekes 6 in
nonNlimiting fertilized plots divided by NDVI Feekes 4 to Feekes 6 in
the farmer check plots (common fertilization practice employed by the
farmer). The nonN limiting (preplant
fertilized) strip will be established in the center of each farmer field.
3.
Determine the predicted yield that can be attained with added N (YP_{N})
fertilization based both on the inseason response index (RI_{NDVI})
and the potential yield achievable with no added N fertilization, computed
as follows:
YP_{N
}=
(YP_{0})/ (1/RI_{NDVI})
= YP_{0} * RI_{NDVI }units: (YP_{N} in
Mg/ha)
Limits
must be imposed on the above whereby RI_{NDVI }cannot exceed 2.0,
and where YP_{N} cannot exceed the maximum obtainable yield (YP_{MAX}).
YP_{MAX} is determined by the farmer, or previously defined as a
biological maximum for a specific cereal crop, grown within a specific
region, and under defined management practices (e.g., YP_{MAX} for
dryland winter wheat produced in central Oklahoma would be 7.0 Mg/ha).
4.
Predict percent N in the grain (PNG) based on YP_{N}
(includes adjusted yield level)
PNG
= 0.1918YP_{N} +
2.7836
units: (PNG in %)
 Calculate
predicted grain N uptake (predicted percent N in the grain multiplied
times YP_{N})
GNUP
= PNG*(YP_{N}/1000)
units:
(GNUP in kg/ha)
 Calculate
predicted forage N uptake from NDVI
FNUP_{NDVI}
= 14.76 + 0.7758 e ^{5.468NDVI
}
units: (FNUP_{NDVI} in kg/ha)
 Determine
inseason topdress fertilizer N requirement (FNR)= (Predicted Grain N
Uptake  Predicted Forage N Uptake)/0.70
FNR
= GNUP – FNUP
units:
(FNR in kg/ha)
Definitions
INSEY
In Season Estimated Yield = NDVI (Feekes 4 to 6)/days from planting
to sensing (days with GDD>0) = YP_{0
}_{
}
GDD
Growing Degree Days = (Tmin + Tmax)/2 – 4.4°C
RI_{NDVI
}= NDVI from plots receiving adequate but not excessive
preplant N, divided by NDVI from the farmer check (specific to that field)
where preplant N may or may not have been applied.
RI_{HARVEST
}= Maximum observed grain yield (treatment average with N
fertilizer) divided by the observed grain yield from plots where no N was
applied either preplant or topdress
RI_{SV}
= Estimate of RI (spatial variability), using the average NDVI
value from a random sensor sample (100 m in length) collected in a farmers
field + 1 standard deviation, divided by the average NDVI value minus 1
standard deviation.
YP_{MAX
}
= Maximum obtainable yield level for a specific environment
determined by the farmer, or previously defined as a biological maximum by
research agronomists for that crop, and for that region (units: Mg/ha)
YP_{0
}
= Predicted or potential yield based on growing conditions up to
the time of sensing, that can be achieved with no additional (topdress) N
fertilization (units: Mg/ha)
YP_{N
}= Predicted or potential yield that can be achieved with
additional (topdress) N fertilization based on the inseason response
index (RI_{NDVI}) (units: Mg/ha)
= (YP_{0})/ (1/RI_{NDVI})
=
(YP_{0})*(RI_{NDVI})
PNG
= Percent nitrogen in the grain estimated from multiple
observations, over years, using various different wheat varieties (likely
to be region specific) (units: %)
GNUP
= Predicted grain N uptake (predicted percent N in the grain
multiplied times YP_{N}/1000) (units: kg/ha)
FNUP
= Predicted forage N uptake estimated from the calibrated
relationship with NDVI (units:
kg/ha)
FNR
= Fertilizer nitrogen requirement estimated by subtracting
predicted forage N uptake (FNUP) from predicted grain N uptake (GNUP)
(units: kg/ha)
Restrictions
YP_{N}
cannot be > YP_{MAX
}_{
}
_{
}RI_{NDVI}
cannot be > 2.0
Figure
1. Predicted yield achievable
with added N fertilization (YP_{N}) based on RI_{NDVI }as
a function of predicted yield that can be achieved with no added N
fertilization (YP0), where YP_{N} = (YP_{0})/ (1/RI_{NDVI}).
Lukina,
E.V., K.W. Freeman, K.J. Wynn, W.E. Thomason, R.W. Mullen, G.V. Johnson,
R.L. Elliott, M.L. Stone, J.B. Solie, and W.R. Raun. 2001. Nitrogen
fertilization optimization algorithm based on inseason estimates of yield
and plant nitrogen uptake. J. Plant Nutr.
