O empobrecimento causado pela erosão e pela cultura algodoeira no solo do arenito Bauru

The empovrishment of the soil brought about by erosion and cultivation of cotton has been studied in experimental plots where catch tanks were employed to collect soil removed by erosion. These tests have been carried out by the Soil Conservation Department at the Experiment Station of the Instituto Agronômico of Campinas, in Pindorama, and on the "Arenito Bauru" soil type representative of the region. Actually sixty percent of all coffee and eighty percent of all cotton cultivation in the State of São Paulo is on the "Arenito Bauru" soil type. Thus the data collected, although preliminary, are of great interest, and indicate that the empovrishment of the "Arenito Bauru" soil by erosion is extremely rapid. It is also pointed out that the "Arenito Bauru" soils are the most highly erodable of all soil types in the State of São Paulo. A chemical analysis was made of representative samples of the original soils in the experimental plots and of samples of soil carried in the runoff, for the purpose of determining the losses due to erosion. It has been determined that the soil transported in the runoff is proportionally very much richer in mineral elements than was the original soil. The data obtained from analysis of samples showed that soil eroded from the experimental plots contained 2.0 times as much organic material, 2.8 times as much P2O5 ; 2.3 times as much K2O, and 1.9 times as much CaO, as was determined present in the samples obtained from the original soil of the experimental plots. In the runoff water it has determined that calcium was present in larger quantities than other elements. On the basis of data obtained from the experimental plots with cotton cultivation, an evaluation and comparison was made of the amount of mineral elements lost by erosion and the amount used by the cotton crop. It was found that the empovrishment of the soil by loss of organic material and chemical elements was due more to erosion than to utilization of these in the production of harvested cotton. A discussion is given of forms of organic and mineral fertilizers to be employed on "Arenito Bauru" soils, taking into consideration the physical and chemical nature of these soils.