Every year, after harvest, fields burn.
Rice straw on the plains of South Asia, sugarcane trash in Brazil,
stubble in parts of Africa and Eastern Europe. The reason is usually simple: the window between one crop and the next is short, the combine harvester leaves loose straw everywhere,
and a match is the fastest way to clear a field.
But fire is the most expensive way to clear a field, even if you never see the bill. In this video: what burning really costs your soil, the two families of alternatives, sowing straight through the residue,
and taking the straw away to be used, the conservation agriculture system behind them, how to measure residue cover, how to handle the nitrogen lock-up from straw, and the real problems farmers meet when they stop burning, with their fixes.
Start with the soil.
Burning destroys soil organic matter and nutrients:
most of the nitrogen and sulphur in the residue,
and much of its carbon, go up in smoke.
It kills soil organisms, from the microbes to the earthworms whose burrows let water in.
Removing or burning residues starves the whole soil food web.
Then the air.
Burning releases fine particles, black carbon, carbon monoxide, nitrogen oxides and other gases.
When it coincides with low winds and temperature inversions,
the smoke is trapped near the ground, and contributes to severe seasonal air pollution across whole regions, visible from satellites.
Smoke also causes road accidents through poor visibility.
And burning residues adds to agriculture's greenhouse gas emissions.
So the straw is not waste.
It is fertiliser, soil carbon and soil cover,
and the question is only how to use it without slowing down the next sowing.
The first family of answers keeps the residue in the field.
Machines now exist for exactly the problem that drives burning. A straw management system attached to the combine deals with the straw as the crop is harvested.
Mulchers turn the stubble into mulch. And seeders such as the Happy Seeder sow wheat directly through standing rice stubble, cutting a narrow slot and leaving the straw on the surface as mulch. Zero-till drills do the same where the residue is lighter.
In rice and wheat systems, zero-till wheat sown this way brings earlier sowing, lower cost, and no residue burning.
Earlier sowing matters, because timely sowing itself raises yields in many systems.
Microbial decomposer solutions have also been promoted to speed up straw breakdown, but the field evidence for them is mixed.
And there is a change upstream: shorter-duration rice varieties are harvested earlier, which widens the sowing window and removes some of the pressure to burn.
Sowing through residue is one part of a bigger system: conservation agriculture.
The FAO defines it by three principles, applied together.
First, minimum soil disturbance: seed and fertiliser go into untilled soil through a narrow slot, with no more than about a quarter of the surface disturbed.
Second, permanent soil cover: residues or living cover crops cover at least thirty per cent of the surface right after sowing, and ideally much more.
Third, diversity: crops grown in rotations, sequences and mixtures, including legumes, rather than one crop year after year.
Why does it work?
Residue cover breaks the impact of raindrops and slows runoff, so erosion by water and wind falls dramatically.
More water soaks in, and less evaporates from a covered surface;
in dry climates, that stored moisture is often the biggest benefit. The pores left by old roots and earthworms survive,
and soil life increases.
And fewer passes save labour, fuel and machinery wear. Conservation agriculture covers roughly two hundred million hectares,
around fifteen per cent of the world's cropland, mostly in South and North America and Australia,
and growing in Asia.
How do you know if you have thirty per cent cover?
Use the line-transect method.
Stretch a fifteen-metre tape, or a rope marked every fifteen centimetres to give one hundred points, diagonally across the rows.
At each mark, record whether a piece of residue big enough to protect the soil lies directly under it.
Suppose thirty-eight of the one hundred marks fall on residue.
Your cover is thirty-eight per cent, which meets the threshold.
Repeat the count in three or more places across the field and average them, for a more reliable number.
The same number places your field on the tillage ladder.
Conventional ploughing usually leaves less than fifteen per cent cover.
Reduced tillage leaves fifteen to thirty.
Conservation tillage, by definition, leaves thirty per cent or more,
and zero tillage leaves the most.
Straw and stalks returned to the soil recycle much of the potassium the crop took up, and some of the other nutrients, and they feed soil organic matter. Burning them loses most of the nitrogen and sulphur.
There is one catch. Cereal straw has a high carbon to nitrogen ratio. While soil microbes break it down, they temporarily lock up soil nitrogen, so the next crop can look pale early on. The fix is simple: a little extra nitrogen may be needed while the straw decomposes. Count the potassium the straw returns against your fertiliser plan, too. Your soil test and local advice set the exact amounts.
The second family of answers takes the residue out of the field and gives it a value.
Straw can be baled and collected for biomass power, compressed biogas, pellets and briquettes, paper, and animal feed. Briquettes and pellets made from residues can replace open burning outright.
In mixed crop and livestock farms, especially in Africa and South Asia,
residues are already valuable as fodder, fuel or building material.
There, the challenge is the opposite: so little is left that the soil stays bare. Even then, leaving whatever share you can spare as mulch protects the soil.
Stopping burning is a system change, and farmers meet real problems.
Weeds are no longer burnt or buried, so weed control changes.
Many large systems lean on herbicides at first, which raises the risk of herbicide-resistant weeds;
cover crops, rotations and competitive crops have to be part of the answer.
Heavy residue needs seeders that cut through it, which can be expensive; hire services, and small seeders for two-wheel tractors or animals, have brought them to smallholders.
In poorly drained, cool or wet soils, residue can delay warming and sowing.
Without rotation, some residue-borne diseases,
slugs and rodents can increase.
And yields often dip in the first years while the soil, the weeds and the farmer adjust.
A large global analysis found that no-till alone cut yields by about five to six per cent on average. But the penalty was smallest, and sometimes reversed, in dry climates, and it shrank greatly when no-till was combined with residue cover and rotation, the full system. The economics often rest as much on lower costs and timeliness as on yield.
To recap.
Burning loses most of the residue's nitrogen and sulphur,
kills soil life, and fills the air with smoke.
Keep the residue in the field: chop and spread it at harvest,
and sow through it with a zero-till seeder. Or take it out and use it for feed, energy or pellets.
Aim for at least thirty per cent cover, and check it with a one-hundred-point line transect. Add a little nitrogen while cereal straw decomposes,
and count the potassium it returns.
Expect a learning period, manage weeds with rotation and cover crops, and use the full system: minimum disturbance, permanent cover and rotation.
For the full conservation agriculture guide, visit laisha.ai.
And before you go: Laisha Lens number one is out, our free guide to November, for every climate zone on Earth.
North of the equator, the cool-season crops go in:
winter wheat and garlic in the temperate north,
wheat, barley and lentil on the autumn rains of the Mediterranean,
and on the plains of South Asia the whole rabi season,
wheat, mustard, chickpea and potato.
South of the equator it is spring, and the tropical south sows soybean, maize, cotton and rice on the first rains.
Lens also covers crop residue without fire, the pests worth walking the field for, and a study plan for agri students.
Open My farm's November, choose your zone and up to three crops, and it builds your field jobs, week by week, with the pests to scout for. It is free, and needs no account. Our free November Lens, with your farm's month plan, is on laisha.ai slash lens.
From all of us at Laisha: may your fields do well this season. Thank you for watching.
