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Corn Yield Response to Nitrogen Fertilizer Timing and Deficiency Level

Dep. of Agron., 210 Waters Hall, Univ. of Missouri, Columbia, MO 65211

View larger version (30K): [in a new window]   Fig. 1. Locations of N-timing experiments.

View larger version (32K): [in a new window]   Fig. 2. Relative yield as a function of timing of a single N application. Conclusions and models are nearly identical for (a) all 28 experiments or (b) the 22 N-responsive experiments. Simple linear models are not statistically significant. (a) Quadratic-plateau or linear-plateau models are highly significant (P = 0.001) but are not significant when data from N applied at silking are omitted. Pre-emergence N applications were randomly assigned vegetative stage values between 0 and 1 to make the data easier to see.

View larger version (23K): [in a new window]   Fig. 3. Degree of N stress observed, as indicated by relative SPAD chlorophyll meter readings, was not a significant predictor of relative yield achieved when N fertilizer was applied at the time of the reading. This was true regardless of the time of the reading and N fertilizer application within the range from growth stage V6 to V13. For all of the above groups, P > 0.40 for simple linear regression. Chlorophyll meter readings were not taken after V13 through a few experiments received later N fertilizer applications.

View larger version (26K): [in a new window]   Fig. 4. Timing of a single N fertilizer application from V6 to V13 did not significantly influence relative yield, regardless of N stress level observed at the time of fertilizer application (as indicated by relative SPAD chlorophyll meter reading). For all of the above groups, P > 0.25 for simple linear regression.

View larger version (18K): [in a new window]   Fig. 5. SPAD chlorophyll meter reading of unfertilized plots, relative to the reading of well-fertilized plots, was a highly significant predictor of the magnitude of corn yield response to N fertilizer.