Zinc levels in vineyard soils from the Alt Penedès-Anoia region (NE Spain) after compost application

Abstract

The mechanization of fields that is taking place in some Mediterranean areas is generating soils with poor structure and lack of nutrients. The application of organic wastes for improving soil properties is becoming a frequent practice, but with the risk of producing a negative impact, because of the presence of metals. This application is carried out without any additional checks using the same rates in disturbed and in non-disturbed soils. In the present study, the influence of composted cattle manure application in vineyard soils from the NE of Spain was evaluated. The study focuses on the changes of soil total Zn content in both disturbed and undisturbed soils. The same treatments and practices were applied in both plots. The area has a Mediterranean climate and the main type of soil is Typic Calcixerept. Total levels (digestion with aqua regia) and plant available fractions (extraction with (NH 4)OAc-EDTA and CaCl 2-DTPA) of Zn, the main metal component of the applied organic wastes, were analysed and compared with those existing in the untreated soils. Zinc levels rose to 130 mg kg −1, which implies increases ranging between 60 and 100% in some parts of the plots. Significant increases were observed in the treated soil samples. The available fraction represents, on average, 30% for Zn extracted with EDTA and 10.8% when it was extracted using DTPA. Significant differences were found between disturbed and undisturbed soils. The organic matter content was the soil characteristic that showed a higher influence on the Zn total levels and on the available fraction, although it was different for the two methods used. The analysis points out the importance of an analysis previous to the application of any waste at general scale. This practice, which is common in the area and repeated in each plot every 3 or 4 years implies a risk of soil pollution in a very short time period.