Effect of long-term cultivation on zinc and copper contents in soils from the Bahia Blanca horticultural belt (Argentina)

The objectives of this work were to quantify the total and available copper (Cu) and zinc (Zn) contents in soils which have been used for intensive ag ricultural production and to investigate the influence of the soil's proper ties on the absorption and migration of these metals. Total and available Z n and Cu contents in the topsoil and their variation with depth in Mollisol s from the Bahia Blanca (Argentina) horticultural belt have been studied. T otal contents of Cu and Zn were extracted by means of acid digestion in Tef lon bombs placed in a microwave oven. The available Cu and Zn contents were extracted using the DTPA method and the analysis of Cu and Zn was carried out by atomic absorption spectrophotometry. High contents of Cu and Zn were found in the surface layers of all the plots studied and lower contents we re noted in plots recently used for horticulture. The lowest contents were found in control farms. The results showed that 70% of the Zn in the surfac e layers were found in unavailable form, whereas almost 50% of the Cu was i n available form. No relationship was noted between each kind of cultivatio n and Cu content. Most of the Zn in the different plots was adsorbed or com plexed by organic ligands and clay. The variation of Cu and Zn content with the depth indicated a greater mobility of Cu. Most of the Zn was detected in the surface soil, whereas no differences were noted in Cu content betwee n surface and subsoil. The results obtained confirmed the anthropic origin of these metals in the cultivated plots, The correlation found between the different forms of Zn and Cu as well as between their total and available c ontents suggested that these metals have been applied together via agrochem icals and waste.