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Modifications of Phosphorus in Latosol As a Function of Humic Acids and Acidity Márcia H

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Modifications of Phosphorus in Latosol As a Function of Humic Acids and Acidity Márcia H ISSN 1807-1929 Revista Brasileira de Engenharia Agrícola e Ambiental v.22, n.7, p.488-492, 2018 Campina Grande, PB, UAEA/UFCG – http://www.agriambi.com.br DOI: http://dx.doi.org/10.1590/1807-1929/agriambi.v22n7p488-492 Modifications of phosphorus in Latosol as a function of humic acids and acidity Márcia H. Beck1, Pedro A. V. Escosteguy2 & Deborah P. Dick3 1 Instituto Federal do Paraná. Foz do Iguaçu, PR. E-mail: [email protected] (Corresponding author) - ORCID: 0000-0002-4458-0751 2 Universidade de Passo Fundo/Faculdade de Agronomia e Medicina Veterinária/Programa de Pós-graduação em Agronomia. Passo Fundo, RS. E-mail: [email protected] - ORCID: 0000-0001-8212-387X 3 Universidade Federal do Rio Grande do Sul/Instituto de Química/Departamento de Físico-Química. Porto Alegre, RS. E-mail: [email protected] - ORCID: 0000-0002-5615-8611 Key words: A B S T R A C T phosphate The effect of humic acids (HA) on phosphorus (P) availability is still contradictory; thus, sorption it is necessary to identify the conditions that play a crucial role in this effect. The aim of humic substances this study was to investigate the effect of HA application, combined with doses of P, on the content of this nutrient in a Latosol with and without acidity correction. Two experiments were carried out, one with HA from peat and another with HA from mineral charcoal (leonardite). Doses of these acids (0; 1.12 and 5.62 mg C g-1 of soil) and P (26.2 and 104.7 mg P g-1 of soil, 1 and 4-fold higher than recommended, respectively) were tested at soil pH 4.5 and 7.0, in a three-factorial design. The soil was incubated for 20 days and the soil-P content was measured by Mehlich-1 and remaining-P tests. The effect of HAs on P availability varied with the P doses and soil acidity. Humic acids application increases P content in Latosol when P dose is higher than recommended and there is no acidity correction (pH 4.5). However, there is no effect of HAs application on soil-P content when applying the recommended amount of this nutrient, irrespective of the pH value. Palavras-chave: Modificações de fósforo em Latossolo fosfato sorção em função de ácidos húmicos e acidez substâncias húmicas R E S U M O O efeito de ácidos húmicos (AH) na disponibilidade de fósforo (P) ainda é contraditório. Assim, é necessário identificar as principais condições que podem influenciar esse efeito. Com o trabalho, objetivou-se investigar o efeito da aplicação de AH, combinada com doses de P, no teor desse nutriente em Latossolo com e sem correção de acidez. Foram conduzidos dois experimentos, um com AH extraído de turfa e outro com AH extraído de carvão mineral (leonardita). Doses desses ácidos (0; 1,12 e 5,62 mg C g-1 de solo) e de P (26,2 e 104,7 mg P g-1 de solo, 1 e 4 vezes maior que o recomendado, respectivamente) foram testadas, em dois valores de pH do solo (4,5 e 7,0), em esquema trifatorial. O solo foi incubado por 20 dias e os teores de P foram extraídos com os métodos Mehlich-1 e P remanescente. O efeito dos AHs na disponibilidade desse nutriente variou com as doses de P e o pH do solo. A adição desses ácidos aumenta o teor desse nutriente em latossolo somente quando a dose de correção de P for maior que a recomendada e a acidez (pH 4,5) não for corrigida. Por outro lado, os AHs não influenciam o teor desse nutriente quando a dose de correção aplicada corresponder à quantidade recomendada, independentemente do pH do solo. Ref. 185317 – Received 14 Sept, 2017 • Accepted 24 Jan, 2018 • Published 28 May, 2018 Modifications of phosphorus in Latosol as a function of humic acids and acidity 489 Introduction Analysis of total contents of elements in the soil, determined by X-ray fluorescence (Bruker Ranger S2 EDFRX), Phosphorus (P) is one of the most important nutrients indicated 0.14% (P2O5), 24.51% (Al3O3) and 11.68% (Fe2O3). to plants but it limits agricultural yield in tropical soils. Oxides and mineral composition were analyzed in an aliquot Amorphous iron (Fe) oxides in these soils form low-solubility of soil, ground (agate mortar) and sieved (0.50 mm). Fe oxide complexes with phosphate, reducing the availability of this content extracted with dithionite-citrate-sodium bicarbonate anion (Devau et al., 2011; Fink et al., 2014), which can also (Mehra & Jackson, 1960) was 57.9 g kg-1, whereas Fe oxide be influenced by humic acids (HAs) (Gerke, 2010). These content extracted with ammonium oxalate (Camargo et al., interactions are surface phenomena which are influenced by 2009) was 1.6 g kg-1. various factors (Weng et al., 2012; Fink et al., 2014; Kleber et Soil analysis by X-ray diffractometry (Bruker D2 Phaser al., 2015). diffractometer) with CuKα radiation, angle range from 3 to Among the mechanisms of action of HAs, some of 60°, speed of 0.03° at 1 s per step, and operation and voltage them reduce P reaction with oxides, such as the blocking of 30 v and 15 mA, respectively, identified the following of adsorption sites (Kleber et al., 2015) and pores of the minerals (MINDAT, 2017): kaolinite (7.27 Å), hematite (3.62; adsorbent (Kaiser & Guggenberger, 2003), exchange of 2.71; 2.51 and 2.20 Å), goethite (3.37 and 4.49 Å) and quartz binders (Fu et al., 2013) and increase of negative charge (1.84 Å). Maximum P adsorption capacity in the Latosol was density (Antelo et al., 2007). On the other hand, HAs can determined at pH 4.5 (0.64 mg P g-1) and 7.0 (0.58 mg P g-1), increase phosphate adsorption (Fu et al., 2013), dissolving Fe using the Langmuir equation. oxides and complexing this anion combined with this cation Peat HA was extracted in a peat bog in Arroio do Silva, (Gerke, 2010). These mechanisms vary according to the type Santa Catarina (29° 1’ 3.95” S; 49° 30’ 12.32” W). Leonardite of HA and physical-chemical conditions of the medium, such HA was obtained from the International Humic Substances as pH, among other factors (Weng et al., 2012). Society (Lot 1S104H; IHSS, 2016). Total contents of carbon, In general, the effect of HAs on P content have been hydrogen and nitrogen in the peat HA was determined in an reported in studies that use larger amounts than the Thermo Fisher Scientific elemental analyzer (Flash EA1112). recommended one to correct P deficiency in agricultural P, S, Fe and Mn contents were extracted by nitric-perchloric soils (Hua et al., 2008; Cessa et al., 2010). Besides being digestion and determined by inductively coupled plasma- uneconomic, high P doses reduce the adsorption sites that optical emission spectrometry (Perkin Elmer Optima® 8300 retain this nutrient with greater energy (Guppy et al., 2005), ICP-OES) (Table 1). The HAs used were selected for having which may lead to overestimation of the observed effects. different origins and chemical compositions, and also because The effects of HAs on P content have also been evaluated in leonardite is the most used HA in agriculture. simple systems (solutions with Fe, HA and P oxides, without Treatments consisted of HA doses (0, 1.12 and 5.62 mg C g-1 soil) (Antelo et al., 2007; Weng et al., 2012; Fu et al., 2013; of soil) and P doses (26.2 and 104.7 μg g-1) in Latosol at two Yan et al., 2016). Thus, there are uncertainties in relation to pH values (4.5 and 7.0). The lowest value corresponded to the effect of HAs addition on P availability, considering the the pH of the soil collected in the field, whereas the highest conditions of application in soil and recommended doses of value was obtained by applying calcium carbonate (analytical P. This study aimed to investigate the effect of HA application, reagent, A.R.), three months before the experiment. In combined with P doses, on the content of this nutrient in addition to these treatments, two controls were used (soil Latosol with and without acidity correction. without and with pH correction and without HA application) HA doses were 0, 2.37 and 11.87 mg g-1 (Peat HA) and -1 Material and Methods 0, 1.76 and 8.82 mg g (Leonardite HA). The lowest P dose -1 is equivalent to the application of 120 kg P2O5 ha (0-20 cm), Two experiments were simultaneously conducted at the recommended for this soil based on the contents of P and Laboratory of Soil Chemistry and Fertility of the University clay. The highest P dose was tested to evaluate whether the of Passo Fundo (UPF), Passo Fundo, Rio Grande do Sul, application of an amount larger than recommended can over- -1 Brazil (28° 23’ 8.97” S; 52° 32’ 16.70” W), in 2016. HA was estimate the effect of HAs and is equivalent to 480 kg P2O5 ha . extracted from peat in one experiment and from mineral charcoal (leonardite) in the other. Table 1. Total contents of some chemical elements of HAs were tested in a humic dystrophic Red Latosol the peat and leonardite humic acids (HA) used in the collected in the 0-20 cm layer, in the UPF’s experimental field. experiments The soil had not been cultivated for the last 8 years (fallow) prior to the experiment. Before the experiment, the soil was analyzed according to Tedesco et al.
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