Variabilidade espacial das formas de fósforo em solo sob manejo conservacionista no sistema integrado de produção agroecológica

Abstract

Phosphorus (P) is among the most important elements for the vigor and development of plants. However, it has a strong tendency to react with soil components, making it unavailable to plants. Several factors can affect the dynamics and spatial distribution of P in the soil, including the management system adopted. Conservation systems, with frequent supply of organic matter, can favor the contents of the organic fraction of P, which after mineralization, constitutes a source of P for plants. The aim of the present study was to evaluate the spatial variability of organic and inorganic forms of P in soil under conservation management. In addition, in order to assess the relevance of organic P in agricultural soils, a study of the structure and evolution of scientific production on organic soil P was carried out globally, using a bibliometric approach. In order to assess the structure and evolution of scientific production on organic P (chapter I) searches were carried out for works indexed in the Web of Science database, in the period 1998-2018. To assess the spatial variability of phosphorus forms in soil under conservation management (chapter II), an area consisting of an experimental module for organic vegetable production was studied, with fertilization exclusively based on plant sources. Soil samples were collected at 72 points in the area, with a grid of points every 10 meters. Sampling took place at five depths: 0-0.05 m; 0.05-0.10 m; 0.10-0.20 m; 0.20-0.40 m and 0.40-0.60 m, totaling 360 samples. The labile, moderately labile and moderately resistant fractions were extracted from the inorganic and organic forms of P, in addition to the residual P and total P fractions (sum of all fractions). In addition, some chemical and physical attributes of the soil were determined in order to verify their influence on the distribution of P forms in the area. In the bibliometric study, the number of publications and citations increased linearly over the years, with the largest number of publications in 2015 (73 articles) and citations in 2018 (2754 citations). In the period considered, 80 countries were found publishing studies on soil organic P. Among them, the USA was the most productive, with 207 articles (21.85% of the total), followed by China (13.41%, N = 127) and Australia (11.93%, N = 113). It is concluded that the organic P of the soil represents a relevant scientific theme, which should be considered by governments and countries in their scientific and technological policies. In the study of spatial variability, the results indicate that the management adopted, combined with the characteristics inherent to the soil of the area, influences the spatial variability of the organic and inorganic fractions of P, especially the least stable (labile and moderately labile). The inorganic form had a greater participation in the total P of the soil, except in the depth of 0.20-0.40 m, in which the organic P was more expressive. The spatial distribution of P forms in the area shows that phosphate fertilization must be carried out considering management areas, avoiding that areas with little need for P receive the same amounts as those with deficiency. The information contained in this study can be used to optimize the applications of fertilizers containing P, increasing the productivity of crops, reducing costs and possible environmental problems arising from inadequate fertilization practices.