Combine harvesters cut paddy high and leave a stiff stubble that will not plough in easily. The gap between the paddy harvest and the wheat sowing is around two to three weeks. Clearing the residue mechanically costs money and time that most holdings do not have.
So it is burnt. Satellite fire counts in Punjab ran into the tens of thousands each autumn until 2023, when the season total was 36,663, and fell to 10,909 in 2024 and 5,114 in 2025. The fires are concentrated in the last ten days of October and the first ten of November.
The smoke contributes to the air quality emergency in Delhi and across the northern plain each November, and the annual argument that follows assigns the blame to Punjab's farmers.
The mechanisms that produced the practice are the short window created by the 2009 groundwater law, the design of the combine, the economics of a small holding, and a procurement system that keeps paddy in the rotation. None of those is a farmer's decision.
Happy Seeder machines, which sow wheat directly through the residue, work and are subsidised, and adoption has been partial. The residue is also a usable fuel and fibre, and the industry to take it has not been built at the scale required.
The window between the paddy harvest and the wheat sowing is about two to three weeks, and the field has to be clear.
The machinery that manages residue in place exists and is subsidised, and it costs the farmer time and diesel on a schedule that has none of either to spare.
The penalties fall on the farmer and the smoke reaches Delhi. That framing is why the argument has gone nowhere for a decade, because it is being conducted between the two parties who can each blame the other.