Phosphorus fractions in the vineyard soil of the Serra Gaúcha of Rio Grande do Sul, Brazil

Abstract

The study aimed to evaluate the accumulation of P fractions in a vineyard soil profile with successive applications of phosphate fertilizers. In January 2010 an area was selected of native forest and a vineyard at age 33 with a history of phosphate fertilizer application, in Bento Gonçalves, Rio Grande do Sul state. Soil samples were collected from 0-5, 5-10 and 10-20 cm layers, prepared and submitted to chemical fractionation of P. The excessive application of phosphate fertilizers during 33 years in the vineyard soil increased the levels of organic and inorganic P until the 20 cm layer in all P fractions. The highest levels of P in the vineyard soil were found mainly in the labile fractions extracted with anion exchange resin and NaHCO3, which indicates high nutrient availability to plants, but also indicates the potential of transfer of solution from soil to surface run-off or percolated through the soil profile, which represents greater potential for contamination of surface and subsurface waters.

Effects of Pig Slurry Application and Crops on Phosphorus Content in Soil and the Chemical Species in Solution

“…In the surface layer in the 2 nd sampling, the P concentration in the solution of soil treated with 80 m 3 ha -1 was higher than 0.15 mg L -1 down to the 20-30 cm layer, confirming the interpretation of the critical limits of environmental contamination, which are above the critical limit (59 mg dm -3 P extracted by Mehlich-1 for soils with clay content ≤20 %) (Gatiboni et al, 2014) down to this depth, evidencing the risk of contamination of subsurface waters by applications of high PS rates to sandy soils for long periods.…”

“…But on the other hand, part of the P accumulated in the upper soil layers can be transferred in soluble form in the runoff solution or adsorbed to particles, to surface waters adjacent to the cultivated area, increasing the risk of water eutrophication, which is undesirable (Ceretta et al, 2010b;Wang et al, 2013;Schmitt et al, 2014).…”

“…In addition, according to Gatiboni et al (2014), 59 mg P dm -3 in the 0-10 cm layer in soils containing ≤20 % clay is regarded as the critical limit, which is the safe level which can be achieved in soil and, consequently, levels above this value can cause water contamination. In this study, in the 0-10 cm layer at all PS rates, the P concentrations extracted by Mehlich-1 exceeded the safety threshold.…”

“…However, when P is added successively and at high rates to the soil, for example by PS application in crop conservation systems such as no-tillage (NT), where the soil is not tilled, the total P content may increase (Berwanger et al, 2008;Lourenzi et al, 2014), and especially the content available to plants, which can be diagnosed by the method of Mehlich-1 (Gatiboni et al, 2008;Guardini et al, 2012). Thus, the saturation of the most avid adsorption sites and a reduction in adsorption energy between phosphate oxygen and functional groups of the surface of oxides and clay minerals are expected, increasing the P concentration in the solution (Guardini et al, 2012;Schmitt et al, 2014); consequently, the P transfer in surface runoff solution to surface waters increases, but also migration in the soil profile by water flow, raising the risk of contamination of subsurface waters, especially in soils with sandy surface texture (Berwanger et al, 2008;Ceretta et al, 2010b;Wang et al, 2013).…”

Phosphorus fractions in soil with a long history of organic waste and mineral fertilizer addition

“…However, when compared with the use of mineral fertilizers, the increases in depth are restricted up to the 0.04 m layer, when the extraction was carried out with NaOH 0.5 mol•L −1 , i.e. both sources were more effective in accumulating in the soil considering the fraction of P physically protected within micro aggregates (Guardini et al 2012;Schmitt et al 2014) (Table 3).…”