Adsorção e dessorção aniônicas individuais por gibbsita pedogenética Individual anionic adsorption and desorption by pedogenic gibbsite

<abstract language="eng">Anion adsorption/desorption dynamics was studied as individual processes on surface of particles of a gibbsitic clay. The data suggest a remarkable gibbsite role as nitrate leaching retardant in soil. The opposite behavior of gibbsite towards adsorption/desorption of silicate and phosphate suggests the need of an adequate compromise solution regarding interval and rate applications of anions in cultivated gibbsitic soils. The high P adsorption verified in pH values lower than that reported for the point of zero charge of synthetic Al-hydroxides implies that this process takes place in pedogenic gibbsites through inner sphere complexation

Suprimento do silicato de cálcio e a eficiência nutricional de variedades de cafeeiro Effect of calcium silicate suplly and the nutritional efficiency of coffee cultivars

Embora não seja considerado nutriente essencial às plantas, o Si é classificado como elemento benéfico ou útil, mas pode alterar a dinâmica nutricional das plantas. Objetivando comparar a eficiência nutricional de variedades de cafeeiro (Catuaí, Mundo Novo e Icatu) em resposta à adubação silicatada, realizou-se um experimento em blocos casualizados, com as três variedades de mudas em tubetes combinadas com seis doses de CaSiO3 (T0 = 0, T1 = 0,063, T2 = 0,125, T3 = 0,25, T4 = 0,5 e T5 = 1,0 g dm-3 de substrato). A variedade Icatu teve a maior eficiência de absorção (EA) de Cu, Zn, Fe e Si, maior eficiência de uso (EU) de N, K, Ca, B e Mn, não diferindo da Mundo Novo com relação aos nutrientes N, Ca e Mn, e maior eficiência de translocação (ET) de N, S, Zn e de Fe. A Catuaí teve maior EA de P, K, B e Mn, não diferindo da Mundo Novo com relação aos nutrientes P, K e Mn, maior EU para Mg, S, Cu, Zn, Fe e Si, provavelmente devido à melhor ET desses nutrientes, exceto para Fe e Si. A Mundo Novo foi mais eficiente na absorção de N, K, Ca, Mg, Mn e Si, teve maior EU de P e Mn e maior ET de K, Ca, B, Mn e Si.<br>Silicon is classified as a beneficial nutrient and can improve the nutritional dynamics of plants, although it is not considered an essential nutrient for plants. In an experiment in a randomized block design, three coffee cultivars (Catuaí, Mundo Novo and Icatu) were planted in plastic tubes, combined with six doses of calcium silicate (T0=0, T1=0.063, T2=0.125, T3=0.25, T4=0.5 and T5=1.0 g dm-3 substrate), to compare the nutritional efficiency of the cultivars in response to silicon fertilization. Cultivar Icatu showed the higher uptake efficiency (UE) of Cu, Zn, Fe, and Si, and efficiency of use (EU) of N, K, Ca, B, and Mn, but the later did not differ from Mundo Novo cultivar (N, Ca, and Mn). The efficiency of translocation (ET) was higher for N, S, Zn, and Fe. For Catuaí the uptake efficiency of P, K, B, and Mn was higher, but did not differ from Mundo Novo for P, K, and Mn. The Catuai's s efficiency of use for Mg, S, Cu, Zn, Fe, and Si was higher, probably because of a better ET of these nutrients, with exception of Fe and Si. The cultivar Mundo Novo was the most efficient in N, K, Ca, Mg, Mn and Si uptake, had the higher EU of P and Mn, and the highest ET of K, Ca, B, Mn, and Si