Harvest Index & Grain vs Total Biomass
Measures partitioning
Enter economic (saleable) yield and total above-ground biomass to get the harvest index, the residue/straw yield and the grain:straw ratio — and judge how well your crop partitions to grain.
Enter your yields
Next: a low HI points to excess vegetative growth (too much N, lodging, shading) or stress at grain fill — balance nitrogen and choose a higher-HI variety.
HI uses oven-dry weights; typical good HI is crop-specific (cereals 0.4–0.5, pulses 0.3–0.4).
Harvest index — key facts
- Harvest index
- economic ÷ biological yield
- Basis
- oven-dry weights
- Residue/straw
- total − economic yield
- Modern cereals
- HI ≈ 0.4–0.5
- Pulses
- HI ≈ 0.3–0.4
- Low HI means
- too much vegetative growth or stress
- Higher HI
- more growth partitioned to grain
- Privacy
- Runs in your browser; nothing uploaded
It is not just how much you grow — it is where it goes
Two fields can grow the same tonnes of biomass yet bring home very different grain. The difference is partitioning — how much of the plant's hard-won dry matter the crop steered into the saleable part instead of leaves and stems. The harvest index captures that in a single number: economic yield divided by total above-ground yield, on a dry basis. Decades of cereal breeding have lifted HI from around 0.3 to roughly 0.45, which is much of where the green-revolution yield gains came from.
This tool returns the harvest index, HI %, residue yield, grain:straw ratio and a performance band from your two yield figures. Use it to check whether a disappointing harvest came from poor partitioning — excess nitrogen, lodging, shade or grain-fill stress — rather than low biomass, and to plan what to do with the straw. Pair it with the Crop Yield Estimator and Seed Rate tools to close the loop from stand to harvest.
Judge partitioning
See how much biomass became saleable grain.
Diagnose low yield
Spot lodging, excess N or grain-fill stress.
Plan the residue
Grain:straw ratio sizes fodder and mulch.
Compare varieties
Higher-HI lines put more growth into grain.
Frequently Asked Questions
What is the harvest index?+
The harvest index (HI) is the share of a crop's total above-ground dry matter that ends up as the part you sell — usually grain. It is a measure of how efficiently the plant partitioned its growth into yield rather than leaves, stems and roots. A higher HI means more of the biomass became saleable product.
How is harvest index calculated?+
HI = economic (saleable) yield ÷ biological (total above-ground) yield, both on an oven-dry basis. For example a wheat crop with 4 t/ha of grain and 9 t/ha of total above-ground biomass has an HI of 4 ÷ 9 ≈ 0.44, or 44%. Using the same moisture basis for both figures is essential for a fair number.
What counts as economic and biological yield?+
Economic yield is the harvested product of value — grain in cereals, seed in pulses, lint in cotton. Biological yield is the total above-ground dry matter the crop grew: the economic part plus all the stover, straw and chaff. Roots are normally excluded because they are hard to recover and measure in the field.
What is a good harvest index?+
Modern cereal varieties typically run an HI of about 0.4–0.5, the fruit of decades of breeding that shifted growth toward grain. Pulses tend to be lower, around 0.3–0.4, because they invest more in vegetative structure and nitrogen-fixing. Values well below the typical band for your crop point to a problem worth investigating.
Why is my harvest index low?+
A low HI usually means the crop made too much vegetative growth relative to grain — often from excess nitrogen, lodging that lays the canopy flat, or shading from dense stands. Stress during the grain-fill window (heat, drought or nutrient shortage) also cuts grain set while the straw has already grown, dragging HI down.
What is the grain:straw ratio?+
It is the weight of grain divided by the weight of residue (straw/stover): residue = biological − economic yield, and the ratio is grain ÷ residue. An HI of 0.44 corresponds to a grain:straw ratio of about 0.79:1. The ratio is handy for planning residue use — fodder, mulch, compost or removal.
How do I estimate residue or straw yield?+
Residue yield is simply the total above-ground biomass minus the economic yield. If you know grain yield and a typical HI for the crop, you can also back-calculate biomass and therefore straw. The tool reports residue yield directly so you can plan baling, incorporation or grazing of the stubble.
Can I raise the harvest index?+
Choose varieties bred for high HI, match nitrogen to need so the crop does not run to straw, manage plant population to avoid lodging and shading, and protect the grain-fill period from stress with timely water and nutrition. Genetics set the ceiling; agronomy decides how close you get to it.
Should I use fresh or dry weights?+
Always use oven-dry weights, or at least the same moisture content, for both the grain and the total biomass. Straw and grain dry at different rates, so mixing fresh and dry figures distorts the HI badly. If you only have field-fresh weights, correct each to a common dry basis before dividing.
What can the harvest index tell me season to season?+
Tracking HI across seasons and fields highlights whether yield gains come from growing more total biomass or from partitioning more of it to grain. A steady HI with rising biomass means good agronomy; a falling HI flags lodging, late stress or over-fertilising that you can correct next crop.