Disponibilidade de potássio para as plantas em solos do sul do Brasil estimada por métodos multielementares

Abstract

RESUMOA avaliação da disponibilidade de K para as plantas é feita pela estimativa de seus teores na forma trocável. Métodos multielementares aumentam a eficiência nos laboratórios de análises de solo, porém a capacidade de troca de cátions (CTC) do solo pode alterar a predição do K disponível. O objetivo deste trabalho foi estimar o K disponível para o milho e para a soja em solos representativos do Estado do RS, pelos métodos Mehlich-1 (M 1 ), Mehlich-3 (M 3 ), resina de troca iônica (resina) e Acetato de Amônio pH 7,0 (AcNH 4 ), bem como verificar se a CTC influencia a estimativa da disponibilidade de K no solo para as plantas. O experimento foi conduzido em microparcelas a céu aberto e, após 45 dias de cultivo, quantificou-se a matéria seca da parte aérea das plantas e determinou-se o o teor de K no tecido. Foram feitas as correlações entre os teores de K extraídos pelos métodos e a relação com a absorção de K pelas plantas em todos os solos e separando os solos em classes de CTC. As quantidades de K extraídas pela resina foram aproximadamente 50 % menores que as das soluções de M 1 , M 3 e AcNH 4 . Os coeficientes de correlação entre os teores de K extraído pelos métodos tiveram alto grau de associação. A relação entre os teores de K acumuladas pelas culturas e os teores extraídos pelos métodos não diferiram, independentemente da separação por classes de CTC. A disponibilidade de K para as plantas em solos do RS pode ser feita pelos métodos testados no presente trabalho. Não houve diferença entre os métodos na avaliação da disponibilidade de K nas classes de CTC. O método da resina, embora não diferindo dos demais na predição do teor de K disponível, apresenta desvantagem em relação aos demais pela menor capacidade extrativa, o que resulta em classes de disponibilidade menores e propicia o erro analítico.Termos de indexação: métodos de análise de solo, correlação, adubação potássica, soja, milho.

Ammonium Chloride Solution as an Alternative Laboratory Procedure for Exchangeable Cations in Southern Brazilian Soils

“…The slope of the regression, however, differed significantly from "1", at both times of shaking, possibly due to some systematic difference. However, for the 60-min shaking time, the "a" (intercept) and "b" (slope) values were not different from "0" and "1", respectively (Table 2, also as shown in Figure 1F), indicating that the two solutions extract equivalent amounts of exchangeable K. Similar results are reported in the literature by several authors (Shuman and Duncan 1990; Boeira et al 2004;Bortolon et al 2010). …”

“…Despite the high correlation coefficient (r=0.95), it is evident that Mehlich-1 extracts smaller amounts of K compared to standard 1.0 M NH 4 OAc, mainly in soils with high level of K. Similar amounts of K, however, were extracted up to 0.30 cmol c kg -1(Figures 1A, 1B and 1C). These results are in agreement with those of several other studies(Zbíral and Nemec 2005;Hosseinpur and Samavati 2008;Bortolon et al 2010). It can be speculated that the higher extraction capacity of NH 4 OAc is due to the ability of the NH 4 + to replace K in the 2:1 mineral interlayer.…”

“…Improvements in instrumentation and analytical techniques have significantly favored the use of universal extractants, which allow for measuring a higher number of elements with a single extraction. Example of the universal extract is Mehlich-3 (Bortolon et al 2010), which can be utilized to test for up to 13 elements, including Al, Mn, boron (B) and sulphur (S). Since Mehlich-3 is not yet routinely used in soil testing in Brazil, most soil testing laboratories tend to use 1.0 M KCl as standard method for Ca, Mg, Al and Mn determination and Mehlich-1, or ionic resin, for K and P. In a standard procedure, determination of Mehlich-1 method for P and K entails the use of a colorimeter and a flame photometer, while determinations of Ca, Mg, and Mn are carried out by atomic absorption (AA), and Al is determined by back-titration.…”

Extraction Methods and Potassium Availability for Soybean in the Parana State’s Soils, Brazil

“…Slaton et al (2010) compared Mehlich-3 and 1 mol L -1 HNO 3 and found that Mehlich-3-extractable K is an excellent predictor of soil K availability for soybean grown on silt loams in eastern Arkansas. Bortolon et al (2010) found that Mehlich-1, Mehlich-3, and ion exchange resin extractants were good indices for available K estimation for soybean and wheat in soils of southern Brazil. On the other hand, Hosseinpur and Zarenia (2012) showed that 1 mol L -1 NH4OAc, 0.1 mol L -1 BaCl 2 , 0.1 mol L -1 HCl, and boiling 1 mol L -1 HNO 3 can not be used as available K extractants, whereas 0.1 mol L -1 HNO 3 , Mehlich-1, and 0.01 mol L -1 CaCl 2 extractants would be suitable as soil testing methods for determining available K for common bean in Iran soils.…”

Does Ferralsol Clay Mineralogy Maintain Potassium Long-Term Supply to Plants?

“…However, available K to plants is controlled by a complex exchange phenomenon between the solid and solution phases (Martin and Sparks, 1985). The most commonly used methods for estimating the content of available K for plants are those that determine exchangeable K, such as the ammonium acetate (NH 4 OAc 1 mol L -1 ), Mehlich-1 (HCl 0.05 mol L -1 + H 2 SO 4 0.0125 mol L -1 ) and cation exchange resin methods (Bortolon et al, 2010). However, assessing the exchangeable K form alone is not sufficient for estimating the total K uptake by crops, because some non-exchangeable K can be released from K-bearing clay minerals (Meurer and Anghinoni, 1993;Bortoluzzi et al, 2005;Darunsontaya et al, 2012;Moterle et al, 2016).…”