The revelation of Alexander's ability to grow more crops was something the nobles were eager to learn about no matter what.
"My lord, is that true? Can it really be done?" Lord Tikba represented the entire ecstatic noble group as he hopefully asked.
Because doubling their food production would double their income.
And so in the days leading up to the swearing ceremony, Alexander gave them a tour of his farms and showed them the various new inventions such as horse collars, and the heavy plow, and the new three-crop rotation method.
And while most nobles were impressed, or at least outwardly pretended to be, some of the bit more stubborn nobles tried to argue with him as they did not think a military man would know anything about farming.
This caused Alexander to simply propose, "Then send some of your men during the autumn harvest. And find out the yield for yourself. Seeing is believing after all."