This past week I found myself on the pampas of Argentina. The romantic gauchos are largely gone, although painstakingly reconstructed by a few men who love horses and dapper period costumes. Modern highways and trailer trucks now cross the endless spaces and the grazing cattle have been largely replaced by large-scale mechanized agriculture: especially of maize and of soybeans, genetically modified (GM) to resist herbicides.

The soil is black and rich, and when it rains the water soaks into the plains, instead of running off. So harvests can be bountiful, but in the 1990s, mechanization squeezed some 60,000 smallholders off of their land. Most landowners with less than 100 hectares no longer farm own land, but rent it to pools of investors, and the Argentines use the English word “pool� even when speaking Spanish. Los pooles took over the land. Wealthy investors from Buenos Aires gave money to managers who rented small farms and then hire other people to plant them in maize or soybeans, applying some mineral fertilizer and a lot of herbicides, to save labor.

The pool of investors use the land until they have degraded it, and then they give it back to the families that own it, and then they look for more land to spoil, at a profit.

Thus I found myself with some other international extension experts on one corner of La Fe, a large farm in Buenos Aires province. Maximiliano Eize and Patricia Carfagno were two young researchers who had come out to explain their trial. The landowners had been coming to them asking what to do when their farms were trashed and returned.

Maxi (as he is called) and Patricia worked for five years in the west of the Province, 250 km away, where it is drier. They had successfully tried mixes of vetch, oats and wheat as cover crops, which farmers were then starting to adopt. Now, here in the east of the province, the researchers were starting again; in wetter conditions the results would be different.

The basic idea: after the harvest, the land lies fallow for a few months, building up lots of weeds. Thanks to the GM soybeans, the crop can be sprayed with lots of herbicides, so only the nastiest species survive now.

The new technology being tried here is to plant wheat, oats, vetch or a mix of vetch and one of the grains. Maxi and Patricia had a whole string of plots with the different treatments. “Which one works the best?� I asked.

“That’s what we’ll see at the end of this year,� Maxi said, speaking like a true scientist.

But Maxi and Patricia doe realized that they need to come up with a soil conservation strategy that is profitable, even for the greedy pools of investors. Planting vetch and cereals in the off season must increase yields in the following crop of maize or soybeans, and be cheap to do. Earlier experience on the pampas suggests that an off season cover crop may increase the maize yield by 1.5 tons per hectare, enough to appeal to the cold logic of the pools.

Cover crops are an old idea. Years ago in Honduras many farmers tried mucuna, also known as the velvet bean, a legume so robust that when I planted it in my garden, the mucuna grew right over my orange trees, blanketing them in a thick, green mat.

Honduran farmers tried to plant the mucuna in between their maize, only to have to fight back the mucuna as it took over their crop. But farmers and scientists both learn from experience, and they eventually learned to plant mucuna in an off-season, or in an off-year, to give life back to exhausted soils. In our video, farmers show how they plant mucuna once the maize is at least two months old, so the mucuna benefits from residual soil moisture and has taken off before the dry season sets in.

I thought that mucuna in some form might work for the land destroyed by the pools.

As luck would have it, I just happened to have a DVD in my backpack, with a video on mucuna, filmed with a group of farmers in Togo, in West Africa. I gave Maxi and Patricia each a copy of the DVD. As experts in cover crops, they had read about mucuna, but had never seen it, so they were keen to watch the video.

Technology improves with experiments and with experience. I have no idea if mucuna will ever flourish in the pampas or if the pools of investors will be persuaded to take better care of the land. But I came away with a renewed conviction that the people who own the land should be the ones who work the land. The land rental “market� is flawed, and gives perverse incentives to free-riders who mine the soil.

Some economists like to sniff at smallholder farmers as “inefficient�. We see here that the big farmers that economists romanticize about, with their tractors, motorized herbicide sprayers and GM soybeans, may make efficient use of some worker’s time, but they can make a mess of the land, a resource we cannot make more of.

Watch and download the video Reviving soils with mucuna mentioned above. The video is available in English, Spanish and more than ten other languages.