The Fallow Time Calculator helps determine how long a specific area—whether agricultural land or a clinical room—should remain unused before reuse. In agriculture, it supports efficient crop rotation by identifying rest periods for soil to regenerate. In healthcare, especially dental and medical settings, the calculator ensures adequate air clearance after aerosol-generating procedures to reduce infection risk. This tool enhances both environmental sustainability and clinical safety by offering clear, data-backed time intervals for fallow management.
This calculator falls under agricultural planning and healthcare safety tools.
formula of Fallow Time Calculator
1. Fallow Time in Agriculture (Crop Rotation)
Fallow Time = Total Rotation Period − Active Cultivation Time
Where:
- Fallow Time = Time a field stays uncultivated (e.g., in months or years)
- Total Rotation Period = Duration of the full crop cycle (e.g., 3 years)
- Active Cultivation Time = Time when crops are actually grown (e.g., 2 years)
This helps farmers allow the soil to rest and regain fertility before planting again.
2. Fallow Time in Aerosol Clearance (Medical/Dental)
Fallow Time = −(60 / ACH) × ln(1 − (P / 100))
Where:
- Fallow Time = Time in minutes needed to achieve required aerosol clearance
- ACH = Air Changes per Hour in the room
- P = Desired percentage clearance (e.g., 99, 99.9)
- ln = Natural logarithm
This formula is based on air exchange theory and assumes even air distribution in the room.
Example Conversion Table for 99.9% Clearance
| ACH (Air Changes per Hour) | Fallow Time (Minutes) |
|---|---|
| 6 | 69 |
| 10 | 41 |
| 12 | 35 |
| 15 | 28 |
| 20 | 21 |
| 30 | 14 |
This table assumes perfect mixing and provides a fast reference for common ACH values used in clinics and labs.
Example of Fallow Time Calculator
Agricultural Example:
Suppose a field has a 4-year crop rotation plan and is planted for 3 years.
Fallow Time = 4 years − 3 years = 1 year
So, the land should be left uncultivated for 1 year to complete the cycle.
Medical Example:
A dental clinic has a room with 12 ACH and needs 99.9% aerosol clearance.
Fallow Time = −(60 / 12) × ln(1 − 99.9 / 100)
= −5 × ln(0.001)
= −5 × (−6.9078)
≈ 34.54 minutes
So, the room should remain unused for about 35 minutes after an aerosol procedure.
Most Common FAQs
The main purpose is to let the soil recover its nutrients and moisture, helping improve yield and reduce pest buildup for future crops.
Yes, especially when procedures produce aerosols. It ensures that air contaminants are reduced before another patient or staff enters the room.
Yes, besides agriculture and healthcare, it can be useful in cleanrooms, industrial ventilation planning, and even environmental hazard zones.