Abstract
The chemical speciation of the soil solution is an important tool for evaluating nutrient availability and aluminum phytotoxicity. The effect of liming in the composition of the soil solution under the no-till (NT) system is still not well known. We evaluated the chemical speciation of Al and nutrients in the soil solution (water extract 1:1), five years after liming at the moment of the establishment of NT in a native pasture, in Ponta Grossa, Paraná State, Brazil. Dolomitic lime was applied at a rate of 4.5 t ha-1 (either incorporated or surface-applied), or split in three annual rates of 1.5 t ha-1. Soil samples from a dystrophic clayey Rhodic Hapludox were collected at the 0 - 0.05; 0.05 - 0.1; 0.1 - 0.2; 0.2 - 0.4; 0.4 - 0.6; and 0.6 - 0.8 m layers, in May, 2003. Aluminum was mainly complexed to dissolved organic carbon (DOC) and fluoride, while the free form Al3+ was present in fewer amounts even under acidic conditions. Calcium and magnesium were found as free forms (Ca2+, Mg2+) and complexed by organic anions. Phosphorus was found as free forms (HPO4(2-), H2PO4-) and complexed with aluminum (ionic pair Al-HxPO4x) up to 0.1 m. Complexation of Al by DOC was not influenced by surface-applied or incorporated liming. Liming did not change Ca and Mg speciation in the soil solution under NT system. The presence of free forms HPO4(2-) and H2PO4-, however, was influenced by liming, because of the increase in cation associated forms.
Highlights
The no-till (NT) system is an efficient soil conservation practice, there is a lack of information on soil fertility and crop management for this system (Rheinheimer et al, 2000)
Samples from a dystrophic clayey Rhodic Hapludox were collected in a field experiment set up in 1998, in a native pasture area located in Ponta Grossa, Paraná State, Brazil (25o10’ S, 50o05’ W)
The soil chemical analyses performed before the beginning of the experiment, following the methodology described by Pavan et al (1992), indicated the following results, for the 0 - 0.2 and 0.2 - 0.4 m soil layers, respectively: pH CaCl2 of 4.6 and 4.2; organic matter (OM) content of 31 and 21 g dm-3; P (Mehlich-1) of 0.3 and 0.1 mg dm-3; K+ of 3.6 and 2.2; Ca2+ of 25 and 7; Mg2+ of 20 and 8; Al3+ of 3 and 8; H + Al of 77.6 and 97.0 mmolc dm-3; base saturation (V) of 38 and 15%; aluminum saturation (m) of 6 and 32%
Summary
The no-till (NT) system is an efficient soil conservation practice, there is a lack of information on soil fertility and crop management for this system (Rheinheimer et al, 2000). There has been an increase in studies about liming in NT, focusing on forms and rates of application and correction of soil acidity (Alleoni et al, 2003, 2005; Amaral & Anghinoni, 2001; Caires et al, 1998, 1999, 2000, 2004; Kaminski et al, 2005). Studies that focus on the soil solution under NT, especially through chemical speciation, are scarce. In a recent study with samples of an Oxisol collected in areas of distinct acidity conditions, and later placed in columns with several rates of phosphorus, Nolla & Anghinoni (2006) pointed out the importance of chemical speciation in the evaluation of the phytotoxic potential of aluminum in soils cultivated under the NT system
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