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## Allocation in Crop Modeling

### Leaf Emergence to Grain Fill
- Carbon allocation to different crop pools (leaf, live stem, fine root, reproductive) changes based on crop phenology.
- During the leaf emergence phase (phase 2), allocation coefficients are defined by equations that account for factors like leaf area index and heat units.
- At maximum leaf area index, carbon allocation goes exclusively to fine roots.

### Grain Fill to Harvest
- During the grain fill phase (phase 3), leaf and live stem allocation coefficients decline over time, while the reproductive allocation increases to meet nitrogen demands.
- Nitrogen retranslocation from leaves, stems, and roots occurs during grain fill to support reproductive development.

### Harvest
- At harvest, live leaf and stem biomass is partitioned between biofuel, removed residue, and litter pools based on specified fractions.
- Grain carbon and nitrogen are split between "food" and "seed" pools, with the food pool decaying to the atmosphere over a year.
- Crop yield can be calculated from the annual grain carbon flux to the food pool.

The article describes the detailed mechanisms in the Community Land Model (CLM) for simulating carbon and nitrogen allocation in crop systems over the growing season, accounting for dynamics like retranslocation during grain fill.