Accurate and timely estimates of crop physiological growth stages are essential for efficient crop management and precise modeling of agricultural systems. Response of crops to various stress conditions varies with crop growth stage. Because of this, crop growth stages have been increasingly used for scheduling irrigation and fertilizer management practices in the place of using calendar dates. Similarly, crop growth stages also are used in planning pest and disease management practices, since crops are more vulnerable to disease and pest outbreak at certain growth stages. In addition, crop growth stages play a primary role in crop models as they influence all facets of crop growth and development, determining the development and senescence pattern of LAI, allocation of biomass between roots, shoots and seeds, timing of crop nutrient demand and sensitivity to stresses.
Satellite remote sensing has been used to retrieve crop phenological stages (e.g. green-up, peak growth stage) however, most of these stages are different from the crop physiological growth stages (e.g. emergence, silking stage in corn) used in crop management and modeling. As such, to determine crop physiological growth stages, a Harvest team led by Prasad Bandaru developed a framework referred as PhenoCrop by combining satellite remote sensing with the growing degree day (GDD) metric. The PhenoCrop framework includes three different algorithms 1) Downscaling algorithm based on Kalman Filter recursive method to produce high spatial and temporal synthetic remote sensing images 2) Remote sensing-based phenology algorithm to retrieve crop phenological stages 3) Conversion algorithm to determine crop growth stages from remote sensing-based crop phenological stages using predetermined GDD. The current version of PhenoCrop has been found to estimate corn crop growth stages reasonably well in Nebraska for 2015. Efforts are underway to use seasonal weather forecasts to project crop growth stages two weeks ahead of time.
Figure 1. Estimated crop growth stages in Corn for 2015 in Nebraska