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The nitrogen (N) sufficiency approach to assess plant N status for in-season N management requires a non-N-limiting reference
to make N recommendations. Use of reference strips in fields with spatially variable soils and the impact this variability
has within N enriched reference strips are not well understood. Consequently three strategies were investigated to evaluate
the impact of spatially variable sandy soils within reference strips in two commercial center pivot-irrigated corn fields.
Evaluation strategies were: (i) ignore soil spatial variability throughout the reference strips, (ii) account for soil variability
in the reference strips based on second-order NRCS soil map units, and (iii) account for soil variability based on apparent
electrical conductivity (ECa) data as a surrogate for soil texture differences in the reference strips. A sufficiency index (SI) calculated from radiometer
measured canopy reflectance data (SIsensor) and from SPAD chlorophyll meter data (SImeter) at two growth stages during corn vegetative growth were used to assess N sufficiency within the N enriched reference strips.
By ignoring soil spatial variability in the reference strips, corn in the sandier soils was designated N deficient. Accounting
for soil spatial variability using NRCS soil mapping units improved N sufficiency designations of corn in the reference strip
for the different soil types contained within the reference strip but tended to designate corn in lighter texture areas within
a mapping unit as N deficient. Use of ECa as a surrogate for soil texture typically performed best for classifying corn N sufficiency throughout the reference strip
and is recommended as a method to obtain reference strip normalizing values in fields with spatially variable sandy soils. 相似文献
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The yield in any given field or management zone is a product of interaction between many soil properties and production inputs. Therefore, multi-year yield maps may give better insight into determining potential management zones. This research was conducted to develop a methodology to delineate yield response zones by using two-state frequency analysis conducted on yield maps for 3 years on two commercial corn fields near Wiggins, Colorado. A zone was identified by the number of years that yield was equal and greater than the average yield in a given year. Classes producing statistically similar yield were combined resulting in three potential yield zones. Results indicated that the variability of yield over time and space could successfully be assessed at the same time without the drawbacks of averaging data from different years. Frequency analysis of multi-year yield data could be an effective way to establish yield response zones. Seventeen percent of the field #1 consistently produced lower yield than the mean while 43 of the field produced yield over the mean. Corresponding values for field #2 were 6% and 42%.The remainder of the fields produced fluctuating yields between years. These spatially and temporally sound yield response maps could be used to identify the yield-limiting factors in zones where yield is either low or fluctuating. Yield response maps could also be helpful to delineate potential management zones with the help of resource zones such as electrical conductivity and soil maps, along with the directed soil sampling results. 相似文献
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