The article discusses how growing a main crop alongside a supplementary crop can affect the main crop's yield. The researchers studied this by comparing different cropping systems over several years to see how intercropping impacts factors like soil erosion, insect control, and nitrogen fixation, in addition to yield. They found that growing a supplementary crop alongside the main crop can have varying effects on the main crop's yield, and it's important to evaluate these effects over a long period of time to fully understand the cropping system.