Fertility Analysis: Lookback Analysis

The Lookback Analysis is designed to create variable rate field prescriptions similar to the analysis type Soil Fertility. The main difference is that the Lookback Analysis can use either an average yield or measured yield from previous years as an input to take into account the amount of nutrient that may have been spread onto the field previously, but was not accounted for by the resulting yield numbers.
Please Note: Lookback Analysis trades out both Removal Functions and Event Credits in order to gain the lookback capability. Should these functions be desired, referencing a Saved Rx created with these functions using the Lookback Type: Saved Rx may be used.

Soil Fertility vs Lookback Analysis

In the below examples a Soil Fertility analysis is on the left [1] and a Lookback Analysis is on the right [2]. Both of these use the same soil equation and the Soil Fertility uses the same inputs as the Lookback Analysis with the exception of the circled Lookback inputs [3]. In this case we have defined that last year we fertilized with a 200 bu/ac target yield goal, but the actual yield was only 185, leaving un-used nutrient unaccounted for. When the left over nutrients are taken into consideration, the total product rate drops for the current years application from 199 [4] to 189.7 [5] lbs/ac of MAP, resulting in a significant decrease in total product.

Lookback Analysis Options Explained

• Lookback Analysis Type - Target Yield: The Target Yield option makes available a "Previous Yield Goal" input field. Using this option will use the previous years yield goal and performance as the driving factors for the analysis.
• Lookback Analysis Type - Saved Rx: The Saved Rx option makes a "Select Saved Rx" drop-down menu available where the specific previous Rx may be selected. This option uses the nutrient application from a previously applied Rx as well as last years yield performance as driving factors for the analysis.
  Please Note: It may be necessary to expand the field to view/access previously created Saved Rx's.
• Yield Layer - Manual Input: The "Yield Layer" drop down menu allows for measured yield from a previous year to be selected, however if there is not a previous yield layer within the program to select, the "Manual Input" option allows the previous years average to be defined via the "Input Crop", "Average Yield" and "Yield Units" drop-downs.