One reason producers grow pulse crops is for their nitrogen benefits. Properly inoculated pulse crops are able to fix atmospheric nitrogen into a form usable by the crop, thereby removing nitrogen fertilizer from production costs. Fertilizer input costs are reduced and producers can grow high protein pulse crops and receive rotational benefits in the subsequent year’s crop.
Sheri Strydhorst, a grad student with the agriculture department at the University of Alberta, said research conducted at Lacombe, Barrhead and Edmonton is examining nitrogen fixation and rotational benefits of tannin-free faba bean, narrow-leafed lupin and field pea.
Read Also
VIDEO: Green Lightning and Nytro Ag win sustainability innovation award
Nytro Ag Corp and Green Lightning recieved an innovation award at Ag in Motion 2025 for the Green Lightning Nitrogen Machine, which converts atmospheric nitrogen into a plant-usable form.
Strydhorst said faba bean has the highest rate of nitrogen fixation, followed by lupin and field pea. Nitrogen fixation provides large quantities of available nitrogen to the plants so they can produce high protein seeds.
Based on 2004 results, tannin-free faba bean seed contains 26.2 percent protein, narrow-leafed lupin seed 34.1 percent protein and field pea seed 21.6 percent protein.
In the research project, hard red spring wheat was grown on faba bean, lupin, pea and barley stubble without nitrogen fertilizer. Early in the growing season, wheat plant heights and canopy densities differed depending on the previous year’s stubble type.
These early season differences translated into seed yield differences. Wheat grown on pea stubble had the highest yields, wheat grown on faba bean or lupin stubble had moderate yields while wheat grown on barley stubble had the lowest yields.
Based on nitrogen fixation rates, these yield results may be unexpected. One may expect faba stubble to produce the highest yields since it’s the crop with the highest nitrogen fixation rates. However, high rates of nitrogen fixation are required to produce high protein faba bean seed.
With most of the nitrogen exported off the field in the grain, less nitrogen is available for next year’s crop.
The high protein benefit of the faba bean seed – 26.2 percent protein – in combination with high faba bean seed yield, is balanced by the reduced amount of nitrogen available to next year’s crop.
Although field pea has lower nitrogen fixation rates, the highest wheat yields were produced on pea stubble. This may be related to faster breakdown rates of the decomposing pea straw, increasing nitrogen availability.
Because field pea has a lower seed protein content of 21.6 percent, less nitrogen is exported off the field in the grain. The lower seed protein content of the field pea seed is balanced by the increased amount of nitrogen available to next year’s crop.
Nitrogen fixed by a pulse crop is partitioned into the harvested seed and into the soil for next year’s crop. All pulse crops balance the fixed nitrogen differently.
Most nitrogen fixed by faba beans is contained in its high protein seed, leaving moderate amounts of nitrogen for next year’s crop. With field pea, a large quantity of the fixed nitrogen remains in the soil as usable nitrogen to next year’s crop. With high protein seed or high soil nitrogen levels, pulse crops have great nitrogen benefits.
