Adsorption of Cd, Cu, Ni and Zn in tropical soils under competitive and non-competitive systems

The adsorption of heavy metals in soils affects their behavior in the environment and their bioavailability to plants. The knowledge of the adsorption mechanisms in competitive systems allows a more realistic evaluation of the metals' behavior in the soil than the single metal adsorption. The objectives of this study were (i) to evaluate Cd, Cu, Ni, and Zn adsorption in 14 surface samples (0-0.2 m) of representative soils of the Brazilian humid-tropical region, in competitive and non-competitive systems, and (ii) to establish metal affinity sequences for each soil, based in the maximum adsorption capacity (MAC) estimated by the Langmuir model. The Rhodic Eutrudox, the Kandiudalf Eutrudox, the Arenic Hapludalf, the Arenic Hapludult and the Typic Argiudoll had the highest metals' adsorption capacity, whereas the Typic Quartzipsamment and the sandy-textured Arenic Hapludult had the lowest values. In general, the MAC values for metals were lower in the competitive than in the non-competitive system. In the non-competitive system, the most common affinity sequence was Cu > Zn > Ni > Cd, whereas the most common sequence was Cu > Cd > Zn > Ni in the competitive system. In general, the Langmuir model fitted well the adsorption data of metals on the studied soils.A adsorção de metais pesados em solos afeta seu comportamento e biodisponibilidade às plantas. O conhecimento dos mecanismos de adsorção em sistemas competitivos permite uma avaliação mais realista do comportamento dos metais no solo do que estudos com adsorção de cada metal, isoladamente. Os objetivos desse trabalho foram: (i) avaliar a adsorção de Cd, Cu, Ni e Zn em amostras superficiais (0-0,2 m) de 14 solos representativos da região tropical úmida, em sistema competitivo e não-competitivo, e (ii) estabelecer sequências de afinidade metálica para cada solo, com base nos valores de capacidade máxima de adsorção (CMA) dos metais estimados por meio do modelo de Langmuir. O Rhodic Eutrudox, o Kandiudalfic Eutrudox, o Arenic Hapludalf (Alf2), o Arenic Hapludult (Ult2) e o Typic Argiudoll apresentaram elevadas capacidades de adsorção dos metais, ocorrendo o inverso para o Typic Quartzipsamment e para o Arenic Hapludult textura arenosa. No geral, a CMA dos metais aos solos foi menor no sistema competitivo. A sequência de afinidade mais comumente encontrada no sistema não-competitivo foi Cu > Zn > Ni > Cd. No sistema competitivo, a sequência foi Cu > Cd > Zn > Ni. Em geral, o modelo de Langmuir simulou de maneira satisfatória a adsorção dos metais nas amostras de solo

Incidencia del chañar en la producción bovina en San Luis

The aim of this issue was to quantify the loss of productivity of bovine meat caused by the chañar (Geoffroea decorticans) invasion in the most affected region of this specie in the San Luis province. A digital map of its spatial disposition in 1998 was used as a base for calculations. It was assumed that the bovine productivity in the invaded areas was nule due to the lack of fodder, and that the losses were equal to the productivities quoted in the bibliography for areas in which the Animal Health Provincial Commitee of San Luis divided the province. The studied surface consisted of 996.148 ha, of which 101.866 ha were invaded by chañar, and the estimated loss was of 4.040,8 tn of meat.year-1.El objetivo del presente trabajo fue cuantificar la pérdida de productividad de carne bovina causada por la invasión del chañar, Geoffroea decorticans, en la región más afectada por esta especie en la provincia de San Luis. Se utilizó como base de cálculo el mapa digital de la disposición espacial en 1998. Se asumió que la productividad ganadera en las áreas invadidas era nula debido a la carencia de forraje, y que las pérdidas eran iguales a las productividades citadas en la bibliografía para las áreas en que la Comisión Provincial de Sanidad Animal de San Luis dividió la provincia. La superficie estudiada fue de 996.148 ha, de las cuales 101.866 se encontraron invadidas por chañar y la pérdida calculada fue de 4.040,8 tn de carne.año-1