Weighing the value of spring vs. fall nitrogen
Soil Sampling and N Credits
Efficient N fertilizer use requires that the producer gives proper credit for N sources already present before selecting the appropriate N application rate. Significant sources of N include
- soil residual nitrate (determined by soil sampling),
- manure and organic materials (determined by sample analysis),
- legumes (determined according to the previous crop), and
- irrigation water (determined by irrigation water sampling).
Actual N credits from these sources can vary widely, but in many cases the N fertilizer rate can be reduced significantly after accounting for these credits.
Accounting for residual soil nitrate-N has become especially important due to recent weather patterns. Drought conditions can have a significant impact on how much N is left in the soil after harvest. The only way to determine the availability of residual soil nitrate-N is through soil sampling.
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