Abstract
Although the study of Phosphorus (P) in soil has received attention in the last years, the mobility and its transformations in no-till (NT) with use of cover crops intensively are still poorly understood. Techniques such as X-ray absorption near edge structure (XANES) and chemical fractionation of P have been used to analyze the chemical speciation of P in soil, considered appropriate tools to verify the effects of soil management as the crystallinity of minerals changes over time. It is known that crop rotations have the ability to promote the differentiated solubilization of P by organic acids (OA) production, depending on the species grown over time. The aim of this work is to analyze the influences on the adsorption and solubilization of P from the crop production systems over time in three long-term experiments in soils with different mineralogy and crop rotations. The soils are of clayey texture, classified as the experiment I) Rhodic Hapludox, II and III) Typic Rhodudalf. Experiments are conducted in NT areas at the Experimental Lageado Farm, located at UNESP / FCA, in Botucatu-SP, Brazil, under a randomized block design with four replications with plots subdivided in experiments I and II. These experiments (I and II) have been conducted since 2003 and 2006, respectively, with the same crop rotations with three annual cycles since then. While experiment III has been conducted since 2006 with four crop production systems. In the experiments I and II, soil samples (2011, 2013, 2015 and 2017), and for experiment III (2014 and 2017) will be analyzed by the XANES technique. The inorganic fractionation of P in the samples to be collected in 2017 in the three experiments will also be performed. Part of these samples (from 2017) will be used for the analysis of the OA, responsible for the solubilization of P, by High-performance liquid chromatography, as well as in crop residues. It is expected that crop production systems will influence the differentiated adsorption of P forms over time according to the cover crops used in the rotations, as well as in the types and quantities of OA and the consequent solubilization of P and that this response between the systems as well as the types of soils. From this, the most efficient crop production systems over time in the availability of P in the soil to the commercial crop in question will be sought, either by the production of OA and solubilization and/or by desorption of chemical P forms.
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