The study looked at how much nitrogen fertilizer is needed by a type of pigeonpea plant called ICPL 87 at different stages of growth. They found that adding nitrogen at the flowering stage increased grain yield in one type of soil but not in others, suggesting that the plant's natural nitrogen-fixing ability may not be enough in certain soils. This shows the importance of improving the plant's ability to fix nitrogen, especially in heavy soils like Vertisols.