Possibilidades de recuperação do Campo Cerrado

Resumo

Pedologic, geologic, hydrologic and climatic studies were performed for an 1.800 ranch situated near Itirapina, a small town 120 miles NNW from São Paulo, in order to deduce the adequate land utilization. The study is particularly important for solution of the problem of the "campo cerrado", a typical fire-climax sub-xerophytic vegetation of very sandy, poor, acid, dry, but extremely deep uniform soil in a humid climate with pronounced dry season (Cwa). It is a short grass prairie with a dense (in Portuguese "cerrado") stand of shrubs and small tortuous trees, which transpire liberally, but their sub-xerophytic character is brought about by extremely deep rooting, subterranean trunks and even branches (Andira humilis), in order to allow the roots to reach the deep ground water at 50 to 70 ft depth "Campo cerrado" is a result of geological (thick layer- of decomposed or unconsolidated sandstone), climatic (pethumid mild summer, and semi-arid to arid almost frost-flee winter) and human (intermittent fire since pre-Colombian times) features.

            Geological prospection resulted in discovery of important fault with throw of almost 400 ft, and of a small extrusive basalt layer associated with conglomerate and fluvio-lacustrine faces of the triassic eolian Botucatu sandstone, besides some corrections of existing geological map of almost 11/2 mile to the inch scale, in which many cretaceous Bauru ss spots must be considered as Triassic Botucatu ss.

            Although climatic data do not exist for the ranch nor the town, the general climatic mapping of the State of São Paulo was good enough for elaboration of an efficient table of normals by interpolation (1 305 mm of annual rainfall and 19 8° C mean temperature; 250 mm rain and 22 1;2°C in the rainiest and hottest month (Jan); 18 mm rain and 16°C in the driest and coldest month (July.)

            Chemical and physical analyses of 10 soil samples showed that the worst "campo cerrado" (1 500 acres), suitable for afforestation with eucalypti as the only economic land utilization with amelioration of the soil, is when total clay content is under 4%, pH below 4 3/4, total organic matter less than 0,6%, excn cations below O 5 m e, CEC up to 5 1/2 m e, and cation saturation not higher than 8%, all these data refined to the upper foot of the soil profiles. The extreme minimal found were 1 9% clay, pH 4 4, org matt 0,45% exch bases O 20 m e, CEC 3 9 m e, and 5% cation saturation. Eucalypti are the only trees able to withstand such poor soil conditions because their roots are able to reach quickly the water table when properly planted (complete extermination of ants, healthy seedlings, and planting season restricted to Oct -Dec in order to have good enough rooting before the beginning of the dry season in April).

            Green manuring of the better soils with 2 tons pulverized limestone + l/2 ton rock phosphate + 40 kg potash muriate per hectare, immediately followed by cultivating (before complete decomposition of the freshly incorporated org matter) can produce fair crops of good forage and cane, manihot, sweet potato, peanut, pineapple and even cotton, if these cultures receive additional chemical fertilizers Corn and many tropical fruit trees are suitable with heavy addition of farmyard manure. Irrigation would secure high yields and possibilities of planting beans and peanut also in Febr -March, besides October, but there is enough water for a liberal supply of 50 acres only.

            The campos cerrados of this ranch are good representatives of those of the whole State of São Paulo, in which they are in continuous expansion, reaching already 20% of the State. Frequent burning of them is usually considered by the uncultured rural population as their only use, in order to provide pasture, because in the dry season the deeply rooted vegetation starts budding and sprouting soon after fire, without any need of rain, and thus the cattle finds forage in places where otherwise there is almost nothing edible. Nevertheless every fire impoverishes the soil, and the buds and sprouts are too poor and scattered to keep the cattle fed and healthy.

            Afforestation with eucalypti is a solution because with fall of leaves they transfer to the surface the chemical richness absorbed from great depth of soil, and already lost by leaching, thus improving the poor soils, besides a yield of 40 ms of wood per year/ha during some 30-40 years without replanting, because they continue to grow after cutting them every 6-7 years. In this part of the world eucalypti exhaust rich clayey shallow soils, and improve poor sandy deep ones.