Two crops, rabi and kharif. Wheat is sown in November after the paddy comes off and cut in April. Paddy is transplanted in June, after the date the groundwater law permits, and cut in October.
Between them, in the fortnight either side, the whole machinery of the state moves: the mandis fill, the procurement staff appear, the combines run day and night, and the residue is burnt.
The monsoon reaches Punjab at the end of June and gives it between four hundred and eight hundred millimetres depending on where you stand, which is not enough for paddy. The rest comes out of the ground.
The western disturbances of winter bring the rain that makes the wheat, and a hailstorm in March can take a crop three weeks before harvest.
The Punjabi agricultural calendar runs on the desi months, Chet to Phagun, and on the sangrand, and older farmers still reckon sowing dates by them rather than by the Gregorian calendar.
Baisakhi is the wheat harvest. That is what it was before it was anything else.
A third crop is possible between the two and almost nobody takes it. Moong or a fodder in the six weeks after the wheat comes off would put nitrogen back into the ground, and it competes with the paddy nursery for exactly those days.
Between them is the wheat harvest and the paddy transplanting, six weeks apart, and both have to happen in a narrow window with machinery and labour that are competing for the same days.
That compression is why the stubble is burned. The field has to be clear for wheat within two or three weeks and there is no other method that fits in the time.