Crop Diversity Score Calculator
Evaluate farm biodiversity using the Simpson Diversity Index, crop count, rotation length, and legume proportion for organic rotation planning.
About this calculator
This calculator scores rotation diversity using two classic ecological measures alongside organic-farming rotation guidelines. From up to six crop acreages you enter, it computes the Simpson Diversity Index (1 minus the sum of each crop's squared proportion of total planted acres) — a value that rises toward 1 as acreage spreads more evenly across more crops, and falls toward 0 for a near-monoculture. It separately computes the Shannon Diversity Index and derives an "evenness" score by dividing Shannon by the natural log of your crop count, which isolates how balanced the acreage split is independent of how many crops you grow.
These feed into a weighted composite score out of 100: Simpson index at 30% weight, number of distinct crops at 25% (maxing out at 8 or more), rotation length in years at 20% (maxing out at 5+ years, reflecting the USDA organic program's 3-year minimum rotation guidance plus headroom for longer cycles), legume proportion of acreage at 15% (maxing out at 30%, since nitrogen-fixing legumes are core to organic fertility management), and evenness at 10%. Any acreage entered beyond your total farm acres is capped, and acreage left unassigned shows up as an "unallocated acres" output rather than silently vanishing. Note that legume acres are tracked as a separate percentage input and aren't required to also appear inside the six crop-acreage fields, so double-check your entries add up the way you intend before comparing the score across seasons or presenting it to a certifier.
Inputs
Results
Diversity Score (0-100)
79.9
Distribution Evenness
0.91
How to Use This Calculator
- Enter your total farm acreage, then the acreage planted to each of up to six crops.
- Enter your total legume acres (clover, beans, peas, alfalfa) and rotation length in years.
- Read the Diversity Score, Simpson Diversity Index, crop count, legume proportion, and distribution evenness.
- Higher diversity scores correlate with better soil health, pest suppression, and weed control.
- Use results to demonstrate rotation diversity to organic certifiers and soil health program requirements.
How the result changes with Total Legume Acres
| Total Legume Acres | Diversity Score (0-100) | Distribution Evenness |
|---|---|---|
| 25 | 73.6 | 0.91 |
| 38 | 76.9 | 0.91 |
| 75 | 82.4 | 0.91 |
| 125 | 82.4 | 0.91 |
What each input means
- Total Farm Acres
- Total cropland acreage on the farm.
- Crop 1 Acres (largest)
- Acreage of your largest crop.
- Crop 2 Acres
- Acreage of your second crop.
- Crop 3 Acres
- Acreage of your third crop.
- Crop 4 Acres
- Acreage of your fourth crop.
- Crop 5 Acres
- Acreage of your fifth crop (0 if not applicable).
- Crop 6 Acres
- Acreage of your sixth crop (0 if not applicable).
- Total Legume Acres
- Combined acres of legume crops (clover, beans, peas, alfalfa).
- Rotation Length (years)
- Number of years in your crop rotation cycle.
What each result means
- Diversity Score (0-100)
- Composite biodiversity score based on diversity, crop count, rotation, and legume proportion.
- Simpson Diversity Index
- Statistical diversity measure (0 = monoculture, approaching 1 = highly diverse).
- Number of Crops
- Count of distinct crops with non-zero acreage.
- Legume Proportion (%)
- Percentage of cropland in nitrogen-fixing legumes (target: 25-30%+).
- Distribution Evenness
- How evenly acreage is distributed across crops (0-1, higher = more even).
- Unallocated Acres
- Farm acres not assigned to any crop (fallow, habitat, buildings).
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersTotal Farm Acres = 200, Crop 1 Acres (largest) = 60, Crop 2 Acres = 50, Crop 3 Acres = 40 = 9 input(s) provided
- Calculate Diversity ScoreDiversity Score = (79.9 = 79.9
- Calculate Distribution EvennessDistribution Evenness = numberOfCrops > 10.91 = 0.91
- Calculate Simpson Diversity Index0.784 = 0.784
- Calculate Number of Crops6 = 6
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
What does the Simpson Diversity Index actually measure?
It's 1 minus the sum of each planted crop's squared share of total allocated acreage. A single crop scores 0, since one crop at 100% share squares to 1 and the index becomes 1 minus 1. Six equally sized crops push the index close to 0.83, because squaring small proportions makes each crop's contribution to the sum tiny. It only measures how acreage is spread across crops, not which species or plant families are actually grown.
Why are there separate scores for Simpson Index and Distribution Evenness if they both describe diversity?
Simpson Index rises with both crop count and balance combined, while Evenness — Shannon Index divided by the natural log of your crop count — isolates just the balance, independent of how many crops you grow. Two farms growing the same 5 crops can post a similar crop count but very different evenness scores if one splits acreage almost equally and the other is dominated by a single crop, which is why evenness earns its own 10% weight in the composite score.
Do my legume acres need to also be entered inside the six crop-acreage fields?
The two aren't linked automatically. Total Legume Acres is used only to compute legumePct (legumeAcres divided by allocatedAcres) for the legume-percentage score, while the six crop-acreage fields separately drive the Simpson and Shannon calculations. If one of your six named crops is a legume, enter that same acreage in both places — the calculator has no way to know that Crop 3 and your legume total refer to the same ground.
What happens if the acreage I enter across the six crops adds up to more than my total farm acres?
Each crop field is individually capped at totalAcres, so no single crop can exceed your whole farm's acreage, but the six fields aren't cross-checked against each other. If the sum across all six still exceeds totalAcres, allocatedAcres reflects that larger sum and Unallocated Acres (totalAcres minus allocatedAcres) can come out negative — a signal to recheck your entries.
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