Les apports des métaux traces par les fertilisants chimiques phosphatés dans les sols libanais PDF Download

Author: Valérie Azzi
Publisher:
ISBN:
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Languages : en
Pages : 242

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Book Description
Soil compaction and contamination with heavy metals were the response of the use of heavy machinery and phosphate fertilization to improve and expand agricultural productivity. The Eastern Mediterranean emerging countries suffer from lack in legislations and regulations organizing the chemical fertilizers use. This is due to the insufficient data on soil characteristics and agricultural practices. Thus, excessive fertilization can be considered as potential sources of soil contamination by trace metals susceptible to be transferred to the different food chains. One of the main occupations of the Lebanese Agriculture Research Institute (LARI) was to evaluate the associated risks to the trace metals inputs coming from phosphate fertilizers. The investigation of phosphate fertilizers used in Lebanon and neighboring countries showed that cadmium is well bonded to sulfate-phase when sulfate is present in the fertilizers. The annual average of the deposition of Cd, Cu, Pb and Zn in soil was found lower than the recommended limits in some countries like Brazil and Britain but such contribution is relatively high when considering the alkaline nature of the soil. Thus, norms and legislations for acidic soil cannot be necessarily adaptable and used for alkaline soil knowing that such soil is the best environment to stabilize the metals and limit their bioavailability. Lactuca sativa (lettuce), widely consumed specie in Mediterranean countries, has been chosen as target specie to be studied in order to follow cadmium in different parts of the plants and its partition between water, soil and plants. The effects of the compaction, cadmium and phosphate fertilizers were evaluated on morphological and physiological characteristics of Lactuca sativa cultivated in columns. Cadmium mobility in soil and its transfer to lettuce, the microbial population (the number of total bacteria, total fungi, cadmium resistant bacteria CRB and phosphate solubilizing microorganisms PSM) and the enzymatic activities of alkaline phosphatase (ALP), acid phosphatase and dehydrogenase activity (DHA) were also studied. Cadmium mobility was decreased in the soil amended with cadmium and phosphorus and compaction increased the Cd accumulation in the lettuce's aerial part and the nitrate infiltration. A decrease of the number of total bacteria, fungi, ALP and an increase in the number of PSM, CRB and acid phosphatase activity were observed in the treatment where the soil was compacted and amended with cadmium and phosphate fertilizers. In absence of any interactive matrix with the metals and the phosphate fertilizers other than the lettuces, the effects of cadmium and phosphate fertilizer were evaluated on morphological and physiological characteristics of lettuces grown in hydroponic culture. Cadmium absorption and transfer to aerial part was also studied. The lettuces development's was important in the hydroponic culture more than in soil cultivation in presence of phosphate fertilizer. Despite the rapid growth of lettuces in hydroponic culture, this system is a potential source of bioavailable cadmium that is absorbed by lettuces and transferred to roots and aerial parts conducting to morphological changes.