adminpraised for fixing carbon in the soil, thereby reducing the amount of carbon dioxide – a greenhouse gas – released into the air. It also prevents soil erosion and therefore demands less irrigation.
Brazil has been a major pioneer of the technique since the country adopted it in the 1970s. But its small farmers have been lagging behind, mainly hindered by the high costs of specialised planting machines needed for zero tillage. Now, thanks to cheaper seeding machines and efforts by farming organisations and individual agronomists, small farmers are spreading the word.
Essentially, zero tillage consists of seeding uncultivated soil, as well as rotating crops and constantly covering the soil with crop residues (the parts that remain in the field after harvest). Preventing the soil from being bare has several advantages. It protects the land from heavy rain, leaves cleaner surface waters and helps recharge aquifers – permeable stone layers that supply much of the world’s water. It also cuts soil erosion by up to 90 percent, allowing for 30-60 percent greater rainfall infiltration so less water is needed for irrigation.
In addition, crop residues boost the soil’s organic content and help fix carbon in it. So that zero tillage reduces carbon dioxide emissions far more than conventional techniques.
“With the best systems you have over a ton of carbon sequestered (in the soil) per hectare per year. When you consider there are a hundred million hectares under zero tillage in the world, this is an awful lot of carbon dioxide taken out of the atmosphere,” says British agronomist John Landers, who has promoted the technology in Brazil since the 1970s.
Today, after the United States, Brazil has the second largest area cultivated using zero tillage – some 25,5 million hectares, or more than 60 percent of the country’s cultivated surface. Although zero tillage was initially tested in the United Kingdom, it was the United States who adopted and further developed it in the early 1960s.
The practice was first introduced to Brazil to combat soil erosion. In 1972, Herbert Batz was the first farmer to import zero-tillage-adapted seeding machines in Latin America. “He encouraged me and other neighbours to do the same,” recalls Manoel Henrique Pereira, a pioneer of zero-tillage adoption in Brazil.
Farmer-to-farmer word of mouth then fuelled zero-tillage’s spread throughout Brazil – there was little reliance on government subsidies. In 1979, the creation of a farmers’ club to further the technology was the first step of many. There are now nearly 50 such clubs in Brazil, led by the National Federation of Zero Tillage into Crop Residues (FEBRAPDP).
But the real zero tillage boom came in the 1990s. The area farmed using the technique reached a million hectares in 1991 – 2,6 percent of Brazil’s cultivated area at the time – and has been growing exponentially ever since. Between 1991 and 2004, Brazil increased its grain production from 57,8 million tonnes to 125 million tonnes from a cultivated area of 42 million hectares, 22 million of which was under zero tillage.
This is also the period zero tillage began to gain favour in the Brazilian central savannahs – the cerrado. While zero tillage was easy to apply in the humid sub-tropical southern states, where winter rains allow two harvests a year, the arid cerrado posed a greater challenge. The six-month dry season allows only one annual harvest, which halves the amount of grass and crop residues available to cover the soil.
The problem was solved by growing a tropical pasture alongside the main crop. Following the harvest, this grass is used to feed farm animals. When the rainy season returns, the grass is killed by herbicides and used to cover the soil where the next crop is planted. According to Landers, the herbicides used in zero tillage (mainly glyphosate) are among the most environment-friendly available.
The result is that soils severely eroded by years of grazing, and usually abandoned, can now be used to grow pasture again – and without any fertiliser.
“We have 16 million hectares of pasture in the cerrado, 70 percent of which are degraded. Now we can plant good maize or soyabean crops on these and go back to top quality pastures after three years, which is a real breakthrough,” says Landers, who founded the Zero Tillage Association for the Cerrado Region (APDC). Meanwhile, in the heart of the cerrado, a team from the French International Co-operation Centre for Agronomic Research (CIRAD) has been leading key work in adapting ZT technology for dry regions. The team has, for instance showed the benefits of planting a certain grass species (Brachiaria ruziziensis) alongside the main crop. As well as being easier than other species used as crop residues to control with herbicides, its long roots – up to two metres – allow it to take up more groundwater.
Introducing zero tillage to the cerrado has also slowed down deforestation, as farmers are less likely to cut down trees to open up new pastures.
“Zero tillage has saved the cerrado,” says CIRAD agronomist Serge Bouzinac. “If it hadn’t been adopted, this region would have become a huge pasture and many farmers would have extended the deforestation frontier in the Amazon even further.”- SciDev.Net.
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