Why do farmer's burn fields?

This is probably an incredibly stupid question but I’ll ask it anyway:

My grandmother used to set fire to her cornfields each March/April (often to disastrous results) before planting the next crop. What is the reason for this? Is it just to get rid of the old stalks or does it somehow make the soil more fertile or… what?
For somebody who grew up on a farm I’m amazed how ignorant I am about farming, though admittedly I was always far more involved with the livestock- castrating pigs I can do, but don’t ask me to keep a petunia alive for a week without a feeding tube.

IIRC, it’s a fast method of getting rid of stalks, weeds, etc. since you don’t have to worry that you might have tilled some seeds from previous crops/weeds under the soil and have them pop up again.

My grandfathers both farmed, and though they did it only sometimes, they did it for both reasons. Not sure it’s scientifically proven that it enhances a field’s fertility, but they thought it did.

I should add the disclaimer that this information has come down to me through my dad, as both my grandfathers are dead. And my dad sometimes likes to pretend he knows more than he really does. Aah, now that I think about it, you should take my post with a grain of salt.

burning fields was a widespread practice years ago-in some parts of the country. I know that in Oregon, farmers would grow hay in quite large fields. After harvest they would burn over the fields. The resulting smoke in the air was very unpopular. The reason, according to the farmers and associated agricultural experts at the local universities, was to control insect and disease. So the argument came down to either large amounts of pesticides or large amounts of smoke. Smoke was cheaper and therefor more popular when I was there, don’t know how it is now.

This used to be quite common in the UK. After the wheat or barley crop had been harvested the surplus straw was burned in the field. This practice has now been outlawed . The main reason for this ban was the mess left by the ash blowing around, fires getting out of control , and the huge clouds of smoke which not only blotted out the sun but caused traffic accidents when the smoke drifted onto roads and reduced visibility.

I have also seen fields of sugar-cane set on fire in Trinidad. This is done to burn off the surplus leaves and also to drive out any nasty snakes and spiders before the cane-cutters get to work.

They still burn the sugar cane fields here in South Florida every year, or at least did so very recently.

I kinda remember learning in grade school or high school this was for more than just clearing the field, and the ash added something beneficial to the soil.

We used to sometimes burn our grass/yard in Illinois. It always came back much greener the next year.

Perhaps this is the reason my grandparents said it made the fields “more fertile”–because they got higher crop yields if they burned out insects, pests, and diseases.

Every year here in Iowa, I see a few fields being burned out. So it is still done. Probably because out here, the population density is pretty low, especially out in the country.

I don’t know the name of this practice in english, but in the case of the agricultural communities that burn forested surfaces, cultivate the area until the soil is exhausted some years later, then move and repeat, I’ve been told that this practice had the added benefice of ashes providing a more fertile soil. don’t know if it’s true, though…

I believe that it is still done routinely with cotton stalks after the harvest in many parts of the world to kill boll weevils and the plant that will continue growing year round in places without a freeze.

They still burn the sugar cane fields in Louisiana, but I’m not sure why. The smoke is quite a nuisance. Burning has something to do with the next year’s crop. Department of Agriculture and EPA, as well as farm groups, are working on the problem to see if a cleaner way can be found.

This a quote from the web-site of a sugar plantation in Hawaii :-

Is sugarcane still burned during the harvest?
Harvesting begins with a brief, intense field burn for two reasons. First, the burning boosts the quality and quantity of the sugar we recover. Secondly, it reduces the amount of dried cane leaves reducing the cost of harvesting, hauling and milling. There are also other benefits to burning including the reduction of vermin insects and rodents and it provides natural potash to our acidic soil. Experimentation over many decades still have not produced a more viable method of cleaning off the cane trash

Aside from getting rid of the old stalks and killing off weed seeds, the minerals contained in the remnants of the earlier crop are more readily incorporated into the soil from the ash than if you had to wait for the leaves and stalks to decay. However, this depends on there not being excessive rainfall between the time of the burning and the next growing season. If there is, runoff can wash away the soil and deplete it of minerals.

The traditional form of agriculture in the tropics is called slash-and-burn. During the dry season the farmer cuts the vegetation on a new plot of land and allows it to dry. At the end of the dry season, he burns the cut vegetation and plants a crop at the beginning of the rains. It saves a lot of labor from having to haul off the cut vegetation. However, the runoff of ash contributes to the loss of soil fertility so the practice often cannot be continued in the same place for more than a few years.

Burning off pastures stimulates the growth of young fresh leaves for cattle to feed on. It also will kill off tree seedlings and prevent the pasture from becoming overgrown.

And this man’s a librarian! :smiley:

Gaudere, how I hate you.

I saw a documentary on The Science Channel last week, that wondered if a Spanish explorer really did see a large city in the Amazon Basin. When the researcher found were ‘islands’ of high ground, and causeways connecting them. I don’t remember the number, but the population the evidence suggested seemed to be way too large to support. The programme mentioned ‘slash-and-burn’, and noted what Colibri noted above. How could a large population be supported?

Charcoal was found in the soil. While ash – and its nutrients – is easily washed away by the heavy rains, charcoal seems to persist. Apparently they ancient farmers may have turned their crop waste and jungle wood into charcoal and used that as a nutrient.

Another thing the programme showed was ‘black earth’. Valuable stuff, which is found around the ancient settlement sites. It’s ‘mined’ by the truckload. One farmer said that he sells 60cm of the ‘black earth’ from a plot, and then lets it sit while a similar amount is harvested from the next plot. IIRC, the narrator said that after 20 years the mined site will have regained the 60cm that was removed. Jungle litter (leaves, grasses, etc.) gather and decompose, resulting in very fertile soil. Natural compost.

Don’t some of the minerals in the soil go into the stalks? Burning would return these minerals to the soil. I used to burn my bermuda grass lawn in the winter and then water the ashes in. It seemed to make my bermuda lawn the best one in the neighborhood.

Of course this was hardly a double-blind, scientific test.

Known in Portuguese as terra preta. Here’s a bit more info.

Yes, I sort of touched on that a few posts up. Burning recycles the minerals in the remnants of last year’s crop a lot faster than if you waited for them to decay, which is especially important in temperate areas where decay is relatively slow.