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Legume Nitrogen Credit & Free N for the Next Crop

Credits soybean

N credit/haTotal creditUrea-equivalentValue saved

“This tool gets better every time someone says what confused them.

Pick the legume and area to get the nitrogen credit, the nitrogen fixed, the urea-equivalent and the fertiliser value saved on your next crop.

Enter your legume

Legume crop

Fixes ≈ 120 kg N/ha, credits ≈ 45 kg N/ha

Field area

Unit

Your result

45 kg N/ha

Nitrogen credit to the next crop

45 kg

Total N credit

98 kg

Urea-equivalent

120 kg

N fixed (total)

1 ha

Area

What this means

Legumes fix atmospheric nitrogen through rhizobia living in their root nodules. A part of that nitrogen stays behind in the roots and crop residues as a credit that reduces the next crop's N-fertiliser need. Your soybean leaves about 45 kg N/ha (45 kg over 1 hectare), worth roughly 98 kg of urea.

Next: cut the following crop's N dose by ~45 kg/ha (≈98 kg urea) and inoculate seed with the right rhizobium to maximise fixation.

Credits are typical ICAR/extension values; actual fixation varies with inoculation, soil N and how much residue is removed.

Legume nitrogen credit — key facts

Source: rhizobia in root nodules
Green gram: ≈ 25 kg N/ha
Groundnut: ≈ 40 kg N/ha
Soybean: ≈ 45 kg N/ha
Berseem: ≈ 80 kg N/ha
Urea-equivalent: credit ÷ 0.46
Boost it: inoculate seed, retain residues
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The crop before pays for the crop after

Legumes do something no other crop does: with rhizobia living in their root nodules they pull nitrogen straight out of the air. Some of that nitrogen leaves the field in the grain, but a real share stays behind in the roots and residues, and as it breaks down it feeds the next crop. That carried-over nitrogen — the legume credit — is free fertiliser you have already grown, and a well-planned rotation turns it into lower urea bills without lower yields.

This tool gives the nitrogen credit per hectare, the total credit, the nitrogen fixed, the urea-equivalent and the value saved from the legume you grew and your area. Use it to cut the next crop's basal nitrogen by the right amount, and remember to inoculate the seed and retain the residues to keep the credit high. Pair it with the Fertilizer (NPK), Crop Rotation and Green Manure tools to plan a low-input, high-fertility rotation.

Cut the urea bill

Leave out the N the legume already fixed.

Plan the rotation

Put a legume before a hungry cereal crop.

Value the saving

See the credit in kg of urea and money.

Maximise fixation

Inoculate the seed and keep the residues.

Frequently Asked Questions

What is a legume nitrogen credit?+

Legumes fix atmospheric nitrogen with the help of rhizobia bacteria in their root nodules. Part of that nitrogen stays in the roots and crop residues after harvest, and as it breaks down it becomes available to the following crop. That carried-over nitrogen is the legume nitrogen credit, and it directly reduces the N fertiliser the next crop needs.

How is the nitrogen credit calculated?+

Each legume has a typical credit in kg N per hectare based on how much nitrogen it leaves in residues and roots. The total credit = credit per hectare × your area. The tool uses standard values such as green gram ~25, cowpea ~35, groundnut ~40, soybean ~45, pigeon pea ~50 and berseem ~80 kg N/ha.

What are typical credits for common legumes?+

Typical residual credits (kg N/ha) are around: green gram 25, cowpea 35, groundnut 40, soybean 45, pigeon pea 50 and berseem 80. Forage and green-manure legumes that are turned in whole leave the most; grain legumes that export nitrogen in the seed leave less, which is why the values differ.

How do I turn the credit into urea?+

Urea is about 46% nitrogen, so the urea-equivalent of a credit = credit ÷ 0.46. A 45 kg N/ha credit is therefore about 98 kg of urea per hectare you can leave out of the next crop's basal dose — the tool shows both the N and the urea-equivalent so you can adjust your fertiliser plan directly.

Does the legume need to be inoculated?+

For best fixation, inoculate the seed with the correct rhizobium strain for that legume, especially in fields that have not grown it recently. The right rhizobium forms effective nodules, and effective nodules fix more nitrogen — which means a larger credit for the crop that follows.

Why retain the residues?+

Most of the credit lives in the roots and the crop residues. If you remove or burn the residues you take much of the fixed nitrogen with them and shrink the credit. Retaining or incorporating residues keeps that nitrogen in the field and lets it mineralise for the next crop.

Does the credit reduce my fertiliser bill?+

Yes — the credit is nitrogen you do not have to buy. The tool multiplies the urea-equivalent by your fertiliser price to show the value saved, so you can see the rotation paying off and confidently cut the next crop's basal N by the credited amount.

How long does the credit last?+

Most of the benefit shows in the first crop after the legume, with a smaller residual effect sometimes carrying into the second. Plan your fertiliser around the immediately following crop, and re-assess for later crops rather than assuming the full credit repeats.

Does soil and climate change the credit?+

Yes — fixation and residue breakdown depend on soil type, moisture, temperature, the legume variety and how well it nodulated. The standard values are good planning figures; in poor-nodulation or very dry conditions the real credit can be lower, so adjust based on your own results.

Are the figures exact?+

They are solid planning figures drawn from typical published credits. Actual nitrogen left behind varies with the legume, yield, residue management and season, so use the numbers to set your next crop's N and fine-tune with soil tests and your own field experience.

Related farming tools

Fertilizer (NPK) Calculator Crop Rotation Planner Green Manure Calculator Nutrient Use Efficiency Calculator Soil & Fertilizer Farming Hub

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Legume Nitrogen Credit & Free N for the Next Crop

Enter your legume

Legume nitrogen credit — key facts

The crop before pays for the crop after

Cut the urea bill

Plan the rotation

Value the saving

Maximise fixation

Frequently Asked Questions

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