Growing and harvesting crops together as they occur in nature is very difficult, so farmers instead use crop rotation, the practice of growing different types of crops after one another. A good crop rotation includes a variety of crops grown in sequence, including cereals (wheat, barley, oats), oilseeds (canola, flax, sunflowers), and legumes (pulses).
Introducing nitrogen-fixing pulses to crop rotations improves the yield and quality of wheat grown in rotation. Although every crop in a diverse rotation is important and brings specific benefits, pulses have been shown to bring extra benefits to rotations.
Pulse crops bring an advantage to cropping systems by leaving nitrogen behind for the following crop in the form of crop residues. But this is only part of the story. Much of the nitrogen fixed by pulses is taken away from the field when the high-protein seeds are harvested, and one study has shown that only 8% of the yield increase of wheat grown after peas could be attributed to the nitrogen benefit that the pulse provides. So what is driving the remaining 92% of the yield increase? This is a complex story, but it involves two components that are essential for crop growth: soil and water.