Dinâmica do banco de sementes do solo e potencial de revegetação campestre após cultivos agrícolas

Abstract

The aim of this work was to evaluate the dynamics of soil seed bank (SSB), as well as the potential of revegetation in the field under no - tillage system. The experiment was carried out in the Eldorado do Sul city, in a native field area submitted to a succession of corn - black oat + vetch - soybean agricultural crops. The treatments were composed by the SSB collection in three depths (0-5 cm, 5-10 cm and 10-20 cm) in five evaluations (at the end of the 3rd, 4th, 5th, 6th and 7th cultivations), when most of the spontaneous species was at the end of the cycle, but before the crops were harvested. For the SSB evaluation, soil samples were collected and germinated in a greenhouse, with the seedlings being counted and identified. Four germination cycles were performed to evaluate the maximum possible number of seeds in the SSB. The statistical analysis consisted of a descriptive analysis of the mean number of seeds, and species in each depth of collection by evaluation and multivariate exploratory analysis (ordering and grouping) through the MULTIV computational application. Seventy species belonging to twenty five botanical families were identified, with the main families being Poaceae and Asteraceae. The number of species and seeds underwent oscillations along the evaluations, with a tendency to decrease and stabilize a few dominant species. A higher number of species and seeds was found at depth of 0-5 cm, characterized by the predominance of exotic species. The 5-10 and 10-20 cm layers showed predominance of native species. From the analysis of ordering and grouping, there was a clear modification in the SSB, with a decrease in native species and increase of exotic species throughout the evaluations. Up to the fourth crop SSB has the potential of natural revegetation due to the predominance of native species. The sequence of agricultural crops in the no-tillage system results in degradation of the SSB, which will not be sufficient to provide native revegetation due to the predominance of exotic species, more adapted to the environment modified by the crops. Considering the small amount of material available on SSB in Rio Grande do Sul, the importance of carrying out other studies on the subject, both in the native grasslandd and in agricultural areas, is emphasized. There is also a need for advances in the methodology for collecting and overcoming seed dormancy of native species, as a way to cover the largest number of species, especially those classified as transient.