Comprehensive information on Nitrogen Use Efficiency for cereal crop production Response Index (RI)

N Fertilizer Optimization Algorithm (NFOA)

1.   Predict potential grain yield or YP0 (grain yield achievable with no additional N fertilization) from the grain yield-INSEY equation, where;

INSEY = NDVI (Feekes 4 to 6)/days from planting to sensing (days with GDD>0)
YP0 = 0.74076 + 0.10210 e 577.66(INSEY)   units: (YP0 in Mg/ha)

2.   Predict the magnitude of response to N fertilization (In-Season-Response-Index, or RINDVI).  RINDVI, computed as; NDVI from Feekes 4 to Feekes 6 in non-N-limiting fertilized plots divided by NDVI Feekes 4 to Feekes 6 in the farmer check plots (common fertilization practice employed by the farmer).  The non-N 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 (YPN) fertilization based both on the in-season response index (RINDVI) and the potential yield achievable with no added N fertilization, computed as follows:

YPN       = (YP0)/ (1/RINDVI)
= YP0 * RINDVI  units: (YPN in Mg/ha)

Limits must be imposed on the above whereby RINDVI cannot exceed 2.0, and where YPN cannot exceed the maximum obtainable yield (YPMAX). YPMAX 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., YPMAX for dryland winter wheat produced in central Oklahoma would be 7.0 Mg/ha).

4.   Predict percent N in the grain (PNG) based on YPN (includes adjusted yield level)

PNG = -0.1918YPN  + 2.7836
units: (PNG in %)

  1. Calculate predicted grain N uptake (predicted percent N in the grain multiplied times YPN)

GNUP = PNG*(YPN/1000)   units: (GNUP in kg/ha)

  1. Calculate predicted forage N uptake from NDVI 

FNUPNDVI = 14.76 + 0.7758 e 5.468NDVI
units: (FNUPNDVI in kg/ha)

  1. Determine in-season 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) = YP0

GDD                    Growing Degree Days = (Tmin + Tmax)/2 – 4.4C

RINDVI                         = 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.

RIHARVEST                 = 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

RISV                      = 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.

YPMAX                  = 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)

YP0                       = 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)

YPN                             = Predicted or potential yield that can be achieved with additional (topdress) N fertilization based on the in-season response index (RINDVI) (units: Mg/ha)

                             = (YP0)/ (1/RINDVI)

                             = (YP0)*(RINDVI)

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 YPN/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

                     YPN cannot be > YPMAX

                             RINDVI cannot be > 2.0

 

Figure 1.  Predicted yield achievable with added N fertilization (YPN) based on RINDVI as a function of predicted yield that can be achieved with no added N fertilization (YP0), where YPN = (YP0)/ (1/RINDVI).

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 in-season estimates of yield and plant nitrogen uptake. J. Plant Nutr.