Systems to prescribe and deliver fertilizer over agricultural fields and related methods

One or more non-transitory storage media storing instructions which, when executed by one or more computing devices, cause performance of a method of prescribing spatially-variable application rates of one or more nutrients for an agricultural field, the method comprising:

• based on multiple images of the agricultural field, calculating an average modified normalized difference vegetation index (NDVI*) map for a crop across multiple prior crop-growing seasons for discrete pixels of the multiple images of the agricultural field;
• identifying a target yield for the crop in the agricultural field for an upcoming crop-growing season, wherein the target yield is based upon historic performance or expected performance;
• calculating a provisional average nutrient application rate of a nutrient based on a replacement amount of the nutrient consumed at harvest for the crop and the target yield for the crop in the agricultural field;
• determining an average nutrient credit of the crop in the agricultural field for a prior crop growing season of the multiple prior crop-growing seasons;
• estimating a nutrient loss based on a volatility of the nutrient;
• calculating a final average nutrient application rate of the nutrient for the target yield for the crop in the agricultural field based on the average nutrient credit, the estimated nutrient loss, and the provisional average nutrient application rate;
• computing a linear slope for a spatially-variable nutrient application guide based on the final average nutrient application rate and a median NDVI* value of the average NDVI* map;
• forecasting a day of the year (DOY) for one or more growth stages of the crop in the agricultural field, wherein forecasting the DOY for one or more growth stages comprises calculating an apparent emergence date (AED) of the crop in the agricultural field based on a plurality of NDVI* values as a function of a plurality of DOY values, wherein calculating the AED comprises performing a linear regression on the plurality of NDVI* values as a function of the plurality of DOY values;
• prescribing spatially-variable nutrient application rates of the nutrient across the agricultural field based on the linear slope to the NDVI* map for each of the discrete pixels and the DOY for the one or more growth stages;
• communicating the prescribed spatially-variable nutrient application rates to farm equipment or to a user device of a user associated with the farm equipment;
• and
• applying, by the farm equipment, the nutrient to the agricultural field, wherein the nutrient is applied to the agricultural field consistent with the prescribed spatially-variable nutrient application rates computed from the linear slope to the NDVI* map for each of the discrete pixels and the DOY for the one or more growth stages.