The type of soil found in one place will depend on several factors: the rock type matrix that originated it, the climate, a amount of organic matter, a vegetation that covers it and the time that it took to graduate.
In dry and arid climates, intense evaporation causes water and mineral salts to rise. With evaporation of water, a layer of salts may deposit on the soil surface, preventing richer vegetation from developing.
In humid climates with heavy rainfall, water can seep into the soil and drag the salts deeper.
Some soil types dry out soon after rain, others take a long time to dry. Why does it happen? And does it influence soil fertility?
- Sandy soils they are those that have a larger amount of sand than average (contain about 70% of sand). They dry quickly because they are very porous and permeable: they have large spaces (pores) between grains of sand. The water then passes easily between the grains of sand and soon reaches the deepest layers. Mineral salts, which serve as nutrients for plants, follow along with water. Therefore, sandy soils are often poor in nutrients used by plants.
- The so-called clay soils contain more than 30% clay. Clay is made up of grains smaller than those of sand. In addition, these grains are well-connected, retaining enough water and minerals for soil fertility and plant growth. But if the soil has too much clay, it can get soaked, full of puddles after the rain. Excessive water in the pores of the soil impairs air circulation, and plant development is impaired. When it is dry and compact, its porosity decreases further, making it hard and even less airy.
Clay soil compacted by lack of water
- THE black earth, also called vegetable land, is rich in humus. This solo, called humid soil, contains about 10% humus (composed of organic materials, ie remains of dead animals and plants) and is quite fertile. Humus helps to retain water in the soil, becomes porous and well-aerated and, through the process of decomposition of organisms, produces the mineral salts needed by plants.
Soils most suitable for agriculture have a certain proportion of sand, clay and minerals used by plants, as well as humus. This composition facilitates the penetration of water and oxygen used by microorganisms. These are soils that hold water without getting too soggy and are not very acidic.
- Purple Earth It is a very fertile soil type, characterized by the result of millions of years of decomposition of basalt sandstone rocks originated from the largest volcanic spill this planet has ever witnessed, caused by the separation of Gondwana - South America and Africa - dating from Mezozoic period. It is characterized by its unmistakable red-purple appearance, due to the presence of minerals, especially Iron.
In Brazil, this type of soil appears in the western portions of the states of Rio Grande do Sul, Santa Catarina, Paraná, São Paulo and southeastern Mato Grosso do Sul, especially in these last three states for its quality.
Historically speaking, this soil was very important, since in Brazil, during the late nineteenth and early twentieth centuries, several large coffee plantations were planted in these areas, causing several railroads to emerge and propitiating the growth of cities, such as São Paulo, Itu, Ribeirão Preto and Campinas. Nowadays, besides coffee, other crops are planted.
The name terra roxa is given to this type of soil, due to the Italian immigrants who worked in the coffee farms, referring to the soil with the denomination Rossa earth, as rosso In Italian it means red. And because of the similarity between that word and the word "purple," the name "purple earth" eventually consolidated.
The soil of purple Earth also exists in Argentina where it is known as "tierra colorada", quite present in the provinces of Misiones and Corrientes.