Mustard is the winter oilseed and the yellow that covers Punjab in January and February in the popular image of it, mostly now in photographs rather than in fields.
Its acreage has collapsed since the Green Revolution. Wheat is procured and mustard largely is not, so land moved and stayed moved. India imports around two-thirds of its edible oil.
The crop feeds the household as well as the market: mustard oil for cooking and for the body, the greens for saag, the residue as cattle cake, and the flowers for bees.
Sarson da saag with makki di roti is the dish Punjab is known for and both its ingredients are crops Punjab has largely stopped growing.
There is a serious argument for bringing oilseeds back into the rotation on water grounds. It runs into the same procurement wall as every other diversification proposal.
Mustard needs a fraction of the water wheat needs and takes far less out of the ground than paddy, which is why every diversification proposal for Punjab includes it.
The oilseed sector was opened to imported palm and soy oil in the 1990s and domestic mustard has competed against that price ever since.
The saag is made from sarson and other winter greens together. What Punjab eats in January is what grows in December, which is true of very little else on the plate now.