The 25-day trap: Why India's farmers burn their straw every October

Every October, north India's paddy fields burn, and Delhi's air pays the price. Here is why farmers light the fires, how a 2009 law and the combine harvester shaped the crisis, and what satellites cannot see.

In Short

• Farmers have barely 25 days between harvest and wheat sowing
• Fire-spotting satellites pass by midday, so later burning goes unseen
• Madhya Pradesh logged more paddy fires than Punjab so far

Every October, as the monsoon retreats and the light turns amber, north India's fields keep an old appointment with fire.

It begins at dusk. A single orange thread, then another, stitched across the dark horizon like the first stars of a constellation. By morning, the threads have become a veil, and the veil drifts towards cities that are only just learning to call the season winter.

We have a name for this ritual, and a villain to go with it. Stubble burning: the farmer, the match, the smoke. But ask the people who must sow the next crop, and the story grows longer, older and far more tangled than any single match.

THE FIRE THAT KEEPS ITS DATE

Stubble is simply what stands in a paddy field after the grain has been cut: stiff, dry stalks, a foot or more tall, along with the loose straw around them. Paddy is rice before it is milled, and it is the main monsoon-season crop of north India. Burning the stalks is the quickest way to clear the field for what comes next.

This season's fires have already begun. The Consortium for Research on Agroecosystem Monitoring and Modelling from Space, a satellite monitoring group at the Indian Agricultural Research Institute, counted 287 paddy residue fires between September 15 and October 6.

Madhya Pradesh led with 118, ahead of Punjab with 88 and Uttar Pradesh with 65.

Experts quoted in Down To Earth's report on the figures link Madhya Pradesh's rise to farmers there switching from crops such as soybean to paddy, as extreme weather threatens the alternatives. The geography of the fire is quietly widening.

THE MACHINE THAT LEFT THE STALKS BEHIND

There was a time when the field cleared itself. Farmers cut paddy by hand, close to the root, and carried it to the threshing floor, where the grain was beaten free of the plant. The grain went to market, the straw became fodder for cattle, and whatever remained was ploughed into the earth. With nearly two months between paddy and wheat, nothing was hurried.

Then, in the mid-1990s, the combine harvester arrived. It is a single machine that reaps the crop and separates the grain in one pass, finishing in about an hour an acre that once took days of labour.

But it cuts high, and what it leaves behind has to go somewhere.

"When we harvest manually, it cuts close to the root, but when we harvest with machines, we have to leave about a foot," a farmer explained.

THE THREE ROADS OUT OF THE FIELD

A farmer standing before those stalks has three roads. He can clear them by hand and keep the straw for his animals, which costs little money but a great deal of time and labour. He can hire or buy machines that chop the straw and sow wheat through it, which saves time but costs a great deal of money. Or he can light a match, which is fast and almost free.

The machines are the sticking point. Equipment that can cut and clear straw costs between Rs 1.5 lakh and Rs 2.5 lakh, and a tractor strong enough to pull it costs several times more.

"He cannot afford such large implements," the farmer said of the small landholder with two to five acres.

By the usual count, more than eight in ten of India's farmers hold that little land. Low money and high time, or low time and high money: only fire is low on both. For most farmers, the choice is rarely a close one.

THE CALENDAR NO ONE CAN STRETCH

The deeper trouble is time. In the 1960s, the Green Revolution, a national push to end food shortages with high-yielding seeds, fertiliser and irrigation, turned Punjab and Haryana into the nation's granary. Paddy, a thirsty crop that is grown in flooded fields, spread across land that once held far less of it. Decades of pumping dropped the water table.

In response, the Punjab Preservation of Subsoil Water Act of 2009 forbade farmers from sowing paddy nurseries before May 10, or transplanting before a date the state notifies. A nursery is the small bed where rice seedlings are first raised; transplanting is moving them into the flooded field. The aim was to keep the crop from draining groundwater before the monsoon arrives. The aquifer gained time. The farmer lost it.

Push sowing later and harvest drifts later too. Paddy comes off the fields towards the end of October. Wheat, the winter crop, should be in the soil by mid-November. Between the two lies a window of barely 25 days in which a farmer must harvest, clear the field and sow again. Wheat sown late can meet an early warmth that leaves its grain half-filled.

That window is the crux of the matter. "As the farmers have to clear their fields for sowing wheat after paddy harvest, there is no option with them other than burning the stubble," wrote Dr BL Attri, acting director of the ICAR-Directorate of Mushroom Research in Solan. The scale is staggering. By his estimate, India generates 125 to 140 million tonnes of paddy straw a year, and 35 to 40 million tonnes of it go up in smoke.

WHY NATURE CANNOT KEEP UP

Surely, you might ask, the soil can simply digest the straw? It can, but slowly, and the reasons are scientific. Dr Sandeep Sharma, a soil microbiologist at Punjab Agricultural University, explains what makes this straw so stubborn.

"Paddy straw decomposes slowly because it contains resistant lignin and silica, has a high C:N ratio, and often encounters insufficient moisture, low temperature and limited nitrogen," he told India Today Digital.

Each of those terms is worth unpacking. Lignin is the woody glue that keeps plant stems stiff, and few organisms can break it down. Silica is a glass-like mineral that paddy absorbs from the soil and stores in its stalks. The C:N ratio compares carbon with nitrogen. Microbes use carbon as fuel and nitrogen to build their bodies, and straw is almost all fuel. To rot it, they must borrow nitrogen from the soil, which is why the next crop can go hungry.

Temperature matters too. Dr Sharma notes that in Punjab, falling temperatures after the October harvest slow the microbes down. Hence, his sober conclusion: "Complete decomposition within 10 to 15 days is not consistently demonstrated; faster decomposition and timely field preparation are different outcomes." Microbes can clear a field where it lies, but he points to research in which they needed an adequate window of about three weeks. The calendar offers them less.

WHAT THE FLAMES TAKE FROM THE SOIL

If fire is the shortcut, what does it cost? Dr Sharma points to studies from Haryana which found that burning paddy straw heated the soil to about 55°C, reducing populations of bacteria, fungi, actinomycetes and nutrient-solubilising microbes. Actinomycetes are bacteria-like microbes that help break down tough plant material and give fresh soil its earthy smell. Nutrient-solubilising microbes release minerals such as phosphorus that roots cannot otherwise reach.

The news is not entirely grim, and he is careful not to overstate it. "Although many recovered within 30 to 60 days, biomass-recycling activities remained impaired," Dr Sharma says. Repeated burning, he adds, "may cause persistent changes, although permanent damage is not established universally."

Dr Attri paints a harsher picture of the same ground. "Burning completely combusts straw carbon, nitrogen and sulphur into the atmosphere, depriving soil organisms of readily assimilated carbon sources," he says.

The ash left behind, he adds, is alkaline and changes the soil's pH, the measure of how acidic or alkaline it is. He warns of a depletion of organic matter, the decayed plant and animal material that feeds soil life, which he says leaves fields less fertile and less productive.

THE FIRE THE SATELLITES CANNOT FULLY SEE

Almost everything we know about these fires comes from space. Instruments such as MODIS and VIIRS, carried on satellites that pass over India at around 10.30 am and 1.30 pm, sense the heat of active flames. A farmer who lights his field at four in the afternoon has, in effect, struck the match after the cameras have left.

That is not a trivial gap. A 2025 study of north-west India's air suggests that burning may be shifting towards the late afternoon, and its authors caution that their own estimate for 2024 may be an undercount for this very reason. A fire that is missed by the satellites has not vanished. Its smoke arrives all the same.

THE SMOKE AND THE CITY

How much of that smoke reaches Delhi? The same study put crop burning's share of PM2.5, fine particles thin enough to travel deep into the lungs, in Delhi and its neighbourhood at 18 per cent between October 16 and November 30 in 2022, 16 per cent in 2023 and 9 per cent in 2024. On days when plumes blew straight from the hotspots, the share rose to about 50 per cent, though only for two or three days at a time.

Those numbers hold two truths at once. The farmer's fire can turn a city's air toxic in a matter of days. But Delhi makes pollution of its own on all 365, from vehicles, industry, dust and construction, and cool, still winter air holds all of it close. The smoke arrives as a guest. It is rarely the whole of the problem.

WHAT COMES NEXT

So the match is only the final act of a longer play: a machine, a law and a crowded calendar. Which brings us to the question that this fire leaves behind. If burning is so costly, and not burning is so hard, what would it truly take to put it out, and is there a hidden price even for not burning?

In the next part of this series, we follow that question further.

- Ends