Formula used
Gross field area equals area per plot multiplied by plot count. Excluded percentages and fixed exclusions are then removed. The remaining value becomes net planting area.
Pure live seed equals germination multiplied by seed purity. The calculator also applies establishment success and seeding method. A wastage allowance increases the final purchase requirement.
Adjusted crop rate equals base rate multiplied by mixture share. It is then multiplied by the seed adjustment factor. Required seed equals adjusted rate multiplied by hectares.
Dry matter equals fresh biomass multiplied by dry matter percentage. Nutrient mass uses dry matter and crop nutrient concentration. Available nitrogen also uses fixation and availability assumptions.
Total project cost includes rounded seed purchases and entered expenses. Fertiliser value equals available nitrogen multiplied by nitrogen price. Local prices can be entered directly.
How to use this calculator
- Enter direct area or field dimensions.
- Select one crop or build a mixture.
- Check crop rates, bag sizes, and prices.
- Adjust seed quality and field conditions.
- Add sowing, termination, and next-crop dates.
- Enter project costs and nitrogen value.
- Calculate, review warnings, then export results.
Example data
| Situation | Crop plan | Typical rate | Useful purpose |
|---|---|---|---|
| Winter soil cover | Cereal rye with vetch | 70 + 20 kg/ha | Erosion control and nitrogen |
| Fast summer cover | Buckwheat | 55 kg/ha | Weed suppression and pollinators |
| Deep rooting | Tillage radish with oats | 8 + 60 kg/ha | Compaction and nutrient capture |
| Warm-season biomass | Sorghum-sudangrass | 45 kg/ha | High biomass and weed control |
| Legume nitrogen | Red clover | 14 kg/ha | Biological nitrogen fixation |
Green manure guidance
Green manure crops protect bare soil and recycle nutrients. Legumes can add biologically fixed nitrogen. Grasses usually create more fibrous residue.
Mixtures can combine nitrogen, rooting, and weed suppression. Species should match climate and planting windows. Seed availability can also guide choices.
Termination timing changes nutrient release and residue persistence. Younger growth usually decomposes faster. Mature grasses can temporarily tie up nitrogen.
Biomass estimates vary with weather and management. Soil testing improves nutrient planning. Local agronomic advice remains important for final decisions.
Frequently asked questions
What is green manure?
Green manure is a crop grown mainly for soil improvement. It is terminated before or during flowering. The residue then protects or feeds soil.
Why does the calculator adjust seed rates?
Seed lots differ in germination and purity. Field establishment also varies by method. Adjustments help estimate practical seed purchases.
How should mixture percentages work?
Each crop receives part of its full rate. All active shares must total 100%. The calculator checks that total automatically.
Does a non-legume add nitrogen?
Non-legumes mainly capture existing soil nitrogen. They return some nitrogen through residue. They do not biologically fix atmospheric nitrogen.
Why are bag quantities rounded upward?
Seed is normally sold in complete packages. Rounding prevents an under-purchase. Remaining seed is shown separately.
What affects biomass production?
Moisture, temperature, fertility, shade, and soil texture matter. Establishment timing also changes growth duration. Use conservative scenarios when conditions are uncertain.
When should green manure be terminated?
Many crops are terminated near early flowering. Earlier termination decomposes faster. Later termination usually produces more fibrous biomass.
What does carbon-to-nitrogen ratio indicate?
It suggests how quickly residue may decompose. High ratios can slow nitrogen release. Low ratios generally release nutrients faster.
Are nutrient results guaranteed?
No, they are planning estimates. Laboratory testing provides stronger evidence. Crop performance also depends on local conditions.
Can I use imperial field units?
Yes, acres and square feet are supported. Dimensions can use feet or yards. Results can display several area units.