How Growing Peas Reduces the Need for Nitrogen Fertilizer

Farming is a business. And like any business, finding success often means finding smart ways to get more done with less.

And if that’s good for the environment, too? So much the better.

That’s one reason many Roquette farmers choose the yellow pea. “I decided to grow legumes to reduce my fertilizer usage,” says Baptiste Laloux, who grows peas for Roquette in northern France. “My goal is to increase yield, whether it is peas or the yield of wheat, which will be grown later.”

So how does the humble pea plant help a farmer increase yield of multiple crop types? One big advantage comes from nitrogen.

Plants need nitrogen. It’s one of the nutrients crops need most abundantly – and they can only get it from the soil.

Typically, different forms of nitrogen are cycled through the soil, and forms usable by plants come from the decay of organic carbon (organic matter or soil microorganisms). But the amount of nitrogen released is not always abundant enough in soil to nourish the crop for maximum growth or yield.  That’s why nitrogen is a key component in so many commercial fertilizers.

But legumes, including yellow peas, provide another way.

Legumes have built-in nitrogen “fixers.” Most pea plants flourish in symbiotic relationship with rhizobia, bacteria that live in nodules in the legumes’ roots. Rhizobia shelter in the nodules and get food (nutrients) from the pea plant – and in return, they transform inert atmospheric nitrogen gas found in the soil into a form of nitrogen that the peas can use.

Effectively, that means a pea plant lives with its own nitrogen factory – and farmers do not need to add costly commercial nitrogen fertilizers like they have to with most other crops.  The rhizobia can supply up to 80% of the peas’ nitrogen, with roughly 1/3 going into the seed. The remainder of the pea’s nitrogen requirements (roughly 20%) come from nitrogen cycling in the soil.

And pea plants aren’t the only ones that benefit.

The next crop gets a boost, as well. Legumes are typically rotation crops. After a season growing peas in one field, farmers rotate to another crop: Wheat and canola are common choices. And thanks to a growing season with pea plants adding nitrogen to the soil through decomposition of the nodules, the following crop is stronger.

How much stronger? That depends on the region. In Europe, a well-nodulated pea crop can give the following wheat crop up an increase of up to 600 pounds per acre. In Western Canada, the nitrogen benefit for the following crop is more conservative, with farmers getting an increased protein level in their wheat when they fertilize their wheat crop normally. 

That saves farmers money – and it saves the planet resources.

“We believe that by growing peas, we reduce our use of mineral fertilizers at least 100 kilos per hectare,” says Laurent Rosso, director of Terres Univia. “This offers solutions in the agro-ecological transition of farms.”