I have never grown lablab. But from what I have read, it can tolerate acidic soil. As low as 4.6 and they dont require real fertile soil. So if it were me, I would plant!. Now if it was a huge field or it was a perennial like alfalfa or clover, no way would I do that with out a proper soil test. I would get the lab test on the soil as soon as possible and just be ready to make corrections after the lablab has done its thing. JM2C