Appendix 1

The Cerrado

Location

The wet/dry tropical savannah region, known as the Cerrado, covers approx. 204 million hectares in tropical Brazil. Its development is regarded by Dr. Norman Borlaug - the winner of the Nobel Peace Prize for his plant breeding work that founded the Green Revolution - as the world's most important agricultural expansion zone for this century. But that development depends mainly on soil improvements. As can be seen in the map below (Figure 1.1), the areas of pastures, annual crops, permanent crops and forestry total no less than 47 million hectares. The recent and rapid adoption of Zero Tillage in this region has been phenomenal.

The Cerrado Environment

Climate

Some 86% of the region receives between 1 000 and 2 000 mm of rain per year, and 65% of the area has an annual rainfall average between 1 200 and 1 600 mm, which is where most of the crop production occurs. There is a winter dry season, normally from April to September, and winters are frost-free except for light radiation frosts in some years, mostly in valley bottoms in the latitudes South of about 18º.

Mean annual monthly temperatures range between 20 and 26ºC. High insulation rates make winter daytime temperatures similar to those of summer. The core region of the Cerrado is essentially frost-free.

Topography and Water Supply

Topography is typically rolling, with extensive areas of elevated flat table-lands, and only about 10% of the total area is in slope classes.

About 73% of the region lies between 300 and 600 metres altitude, however, much of the cropped land is in regions of over 600 m, where cooler nights improve the crop's metabolic efficiency because of lower nocturnal respiration rates. Many watercourses cut the topography into wide interfluves. Most are perennial and are used widely for irrigation, which has reached its limits for extraction where there are concentrations of irrigated farming. The core region drains into three main river basins, the São Francisco to the northeast, the Paraná to the south and the Amazon to the northwest.

Vegetation and Fauna

The original vegetation, of which about 35 percent has been cleared, was fire-climax savannah. The vegetation ranges from open grassland to grassland with shrubs and small twisted trees, to light, low tree cover. Medium-sized gallery forests occur along watercourses and on the 7% of soils in the region that are classified as fertile (eutrophic). The vegetation was formed over 100 million years ago, in the Cretaceous period, and has a very high diversity, estimated at about 10,000 vascular plant species (Ratter, 1995).

The animal kingdom is no less diverse: there are 10,000 herbivorous insect species in the bioma, and in the Federal District alone, less than one per cent of the total Cerrado region, 429 species of birds have been reported. These include the rhea, a bird similar to the ostrich, which nowadays can often be seen walking through fields of soybean eating caterpillars. The principal large animal species are the spotted or brown jaguar, various deer species ranging in height from about 50 cm to about 1.5 m, wild pigs, anteaters, maned wolves, which are really foxes, howler monkeys, marmosets, armadilloes, otters, capivara - the world's largest rodent, anacondas up to six meters or more in length, alligators, rattlesnakes, and bushmasters (Bothrops sp.), etc.

Soils

Cerrado soils, which can be up to 25 metres or more deep, are among the oldest and least fertile in the world. Clearing costs are low and crop production easily mechanized, but high fertilizer and soil improvement costs are incurred.

Table 1.1 shows a total area for the Cerrado region of some 204 million hectares, of which latosols, podsolics and quartz sands make up 76% of the total. These soils are all dystrophic. They are therefore infertile and require significant soil amendments for crop production. All of the areas of fertile soils, which do not need soil amendments but which make make up only 7% of the whole, had generally been colonized by 1970.

The main soil types are all of a macro-aggregate structure. This allows for very high infiltration rates when the soils are left in their natural condition, and so runoff is unusual. The predominant clay minerals are kaolinite and gibbsite, of the 1:1 clay type, which results in a very low Cation Exchange Capacity, highly dependent on the organic matter content. Typical values of C.E.C. for dystrophic Cerrado soils are of the order of 5-8 M.Eq/100g soil.

Most Cerrado soils suffer from micro-nutrient deficiencies, especially zinc and boron, while manganese deficiency is common in soya on overlimed soils. Early practice was to achieve a 70% base saturation with liming by incorporating 2 to 5 ton/ha of lime, but this practice was extrapolated from experience with soils of higher C.E.C. in south Brazil. The Embrapa Cerrados Centre has now shown that top yields can be obtained at 40% base saturation, providing the nutrient status is adequate. Calcium deficiency in the subsoil is common and corrected by the application of gypsum, according to clay content. Surface application of lime in Zero Tillage is now the norm, but light applications only can be applied since a high surface pH renders micro-nutrients in the organic matter insoluble.

This figure shows the very rapid loss of organic matter under soybean monoculture, which does not generate enough dry-matter residue to prevent this. Use of a 2-yea soya/maize rotation would have eliminated this tendency, but high transport costs result in a very low maize prices in the region, and this impeded adoption of better rotations.

When soil is cultivated, the organic matter in it is rapidly oxidized, and the soil is left exposed to heavy raindrop impact, which destroys its macro-aggregate structure. This leads to high runoff and widespread erosion on cultivated soils. Physical barriers such as wide and narrow-based contour banks, which were obligatory for credit, were merely palliative measures, for they merely checked overland water flows - and sometimes failed to do that in rainstorms of over 100mm/hour intensity - and they did nothing to prevent soil degradation

Agricultural Development

Beginning in the early seventies, the introduction of the improved pasture grass, Brachiaria decumbens, by IRI Research Institute (IRI, 1990) led to rapid expansion of the area of upland rice as a low-input pioneer crop undersown with pasture.

The first truly tropical and high-yielding varieties of soya - Cristalina, developed by a seed producer, and Doko, bred by Embrapa - triggered an explosion in the area of soya in the Cerrado region from 1978 onwards. In the early eighties, the variety Cristalina made up some 80% of soya planted in the region. From the mid-seventies, the Embrapa Cerrados Centre refined the early basic soil fertility work, which had been led by the IRI Research Institute in the 60's, and pointed the way to initial improvements of the infertile soils through liming and corrective applications of micro-nutrients and phosphorus (Mikkelsen et al 1965).

Table 1.2

Cerrado Situation 1994.

Sources 1. Embrapa 2. WWF 3. APDC estimate 1994
Notes :
1. The summer-planted area of Zero Tillage in the Cerrado region was estimated at 4.3 million hectares in 1999/2000 (source APDC).
2. There are some small discrepancies with the Embrapa's figures in Figure 1.2, probably due to different methodology

Soya was very profitable and it was therefore mainly cultivated as a monocrop. It usually following upland rice as a 1-2 year low return/low input pioneer crop (mainly Brachiaria decumbens). In Table 1.3, the average yields of soybeans and maize in the typical Cerrado State of Goiás are shown, compared to those of Brazil as a whole. It should be noted that for both crops, average yields in Goiás state have been above the national average in the last three years, reflecting in part improved agronomic practices, including ZT. In addition to eliminating soil preparation, Zero Tillage has introduced new principles, especially more crop rotation, biological controls, and second crops for grain, pasture or soil cover.

Table 1.3

Average Soya and Maize Yields for Goiás, a Typical Cerrado State.

Source : Federação de Agricultura do Estado de Goiás.

But the greatest change has been farmers' attitudes: they have become instruments of environmental protection through the complementary effects of Zero Tillage beyond the farm gate.