Fertilizer Schedule Assistant

import pandas as pd
from datetime import datetime, timedelta

def calc_fertilizer(field_id, crop, last_apply):
    req = pd.read_sql("SELECT npk FROM crop_requirements WHERE crop = ?", crop)
    days_since = (datetime.now() - last_apply).days
    if days_since >= 14:
        return f"Apply {req} - overdue by {days_since-14} days"
    elif days_since >= 10:
        return f"Apply {req} - due soon"
    return f"Next application in {14-days_since} days"