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How much nitrogen can pulses supply to the next crop?

Howard Cox, DAF QLD

Growing pulses can increase soil nitrogen (N) stocks. Researchers in QLD have developed some rules of thumb to estimate pulse-N contribution to the next cereal crop. The rules apply to chickpeas and faba beans.

Calculating N from pulses

Good crops

In a good chickpea or faba bean crop:

Extra N (kgN/ha) = grain yield (t/ha) * 20

For example, a good chickpea crop yielding 3 t/ha will supply an extra 60 kgN/ha.

Another rule of thumb from southern NSW suggests using grain yield (t/ha) * 18 to calculate additional N contribution.

Poor crops

In a semi failed crop:

Extra N (kgN/ha) = crop biomass (t/ha) x 10

For example, a frost affected crop with a biomass of 1 t/ha will supply 10 kgN/ha.

Should you change your N rate?

Consider reducing N fertiliser if the pulse crop has supplied more than 40 kgN/ha. Consider N contributions less than 40 kg/ha a boost to soil reserves. The next crop probably still needs normal N rates.

Use soil tests as well

Always check soil N stocks with soil tests. The amount of N a pulse fixes varies and is affected by:

  • crop species
  • soil conditions (moisture, organic matter, N levels)
  • seasonal conditions
  • crop performance

If available soil N is > 100 kg/ha,  pulses are unlikely to have fixed much N. In high N soils, pulses take advantage of the existing N rather than fixing their own.  

More

Webinar: How to check your pulse-N

The best resource on fertiliser N and legumes in the northern region

Think twice before sowing chickpeas into high nitrogen soils

Adding N with Legumes

How effective are high nitrogen rates for canola wheat rotations

How to account for stubble nutrients next season

 

 

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