Climate

The Cerrado biome is a neotropical savannah that comprises ca. 2 million km². The area is the second-largest biome in South America, after the Amazon. The Cerrado region includes parts of 11 Brazilian federal states and extends from the equator to the Tropic of Capricorn. 

According to the Köppen classification, the Cerrado exhibits a typical Aw climate (humid tropical savannah) with a distinct dry season between May and September. The temperature and precipitation varies with latitude (south-north) and altitude, which ranges between 300 and 1800 m a.s.l. The annual average rainfall and evapotranspiration rates in the wet season are 750–2000 mm and 900–1100 mm, respectively. More than 80% of the precipitation falls in the rainy season between November and April, and the smallest amount falls in the north-eastern part of the biome (Cochrane and Jones, 1981; Oliveira-Filho and Ratter 2002). The rainfall erosivity increases from east to west (Oliveira et al., 2013). Dry spells of one to three weeks, which are associated with high evapotranspiration rates (5.8 mm per day, Oliveira et al., 2005), frequently occur during the rainy season. The runoff regime is driven by rainfall, with a marked difference in discharge between the dry and wet seasons.

Soils

Cerrado soils are among the oldest on Earth. The soils are mainly derived from the Brazilian shield (Marques et al., 2004; Zinn and Lal 2013), and they are deeply weathered (up to 50 metres or more) and well drained. The landforms include flatlands and plains, hilly areas and high plateaus (Silva et al., 2006). 

 Approximately 50% of the soils are Ferralsols according to the FAO classification (Latosolos in the Brazilian soil classification and Oxisols in the USDA- United States Department of Agriculture taxonomy), while 21% are Arenosols and 12% are Acrisols, which seriously limit crop production because of their very low natural soil fertility (see Figure 2 for the spatial extent). The soils are acidic and have low nutrient availability (Lopes and Cox 1977a; Lopes 1996; Lopes et al., 2004). The total P content for typical Ferralsols is 250-350 mg kg-1 soil, whereas the available P is much lower (Goedert 1983). Lopes and Cox (1977a) found a median concentration of available P of 0.4 mg kg-1, whereby more than 92% of their samples exhibited values less than 2 mg kg-1. The soils have a low effective cation exchange capacity (ECEC < 1.5 cmolc kg-1 clay), high aluminium (Al) saturation (Lopes and Cox 1977a) and high P fixation capacities (Ayarza et al., 2007). The soils of the Cerrado are normally not prone to crusting or compaction, and they exhibit a good soil structure for satisfactory crop growth (Goedert 1983). These soils, including the clayey varieties, are characterised by low a water-holding capacity. The limited rooting depth of many crops is suggested to be a function of Al toxicity and/or Ca and Mg deficiency in subsurface soil layers (Lopes 1996; Joris et al., 2012). 

Low soil pH values, deficiency in plant-essential soil nutrients (e.g., P), adverse soil chemical conditions for root growth, low soil-water retention capacity, and extended dry spells during the rainy season have been detrimental to crop growth (Oliveira et al., 2005). To remove the low soil fertility as a limiting factor for crop production, the land was excessively limed (Yamada 2005), which increased the soil pH by up to 0.25 pH-units per year (Carvalho et al., 2009). Breeding tropically adapted cash crops, applying agrochemicals, and liming practices greatly improved the soil conditions to intensify agricultural land use in the Cerrado (Lopes 1996; Roscoe and Buurman 2003; Jepson et al., 2010).