بررسي آثار استفاده از علف كش ها بر شاخص هاي توليد و دوام آنزيم اوره آز خاك

چكيده انگليسي :

129 Effects of Herbicides on Soil Urease Production and Persistence Hassan Fallah h fallah66@gmail com January 8 2014 Department of Soil Science Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Prof F Nourbakhsh Email farshid@cc iut ac ir Abstract The activities of soil microorganisms are central to soil sustainability and resilience Soil microbial populations and the enzymes synthesized by the microorganisms play vital roles in soil organic matter decomposition and nutrient cycling and hence the sustainability of agroecosystems is directly related to soil biodiversity and functional biodiversity Application of pesticides is a common management practice in most of the agroecosystems Exceptionally in organic farming systems the entrance of whole chemicals is exclusively restricted Other agricultural ecosystems receive pesticides to different extents Herbicides are widely used in order to control or eradicate the weeds and therefore have attracted increasing attention due to environmental concerns It has been suggested that they not only influence the target plants but also negatively affect other biological performance in soils Urease is among amidohydrolases which contribute to nitrogen mineralization in soils and consequently plays an important role in providing inorganic nitrogen to plants and soil microorganisms Urease catalyzes the hydrolysis of urea to ammonia and carbon dioxide Generally speaking it is thought that enzyme activities are sensitive soil biological sensors and that is why they have been widely used as indicators of soil biological quality We hypothesized that i the effect of herbicides on soil urease activity is a function of type and concentration of the herbicide and ii herbicides limit either the production and the persistence of urease in soil The later hypothesis was made on the basis that in a preliminary experiment we showed that the herbicides adversely influence the rate of soil microbial respiration Therefore the objective of this study were to identify first the effect of Oxyfluorfen Butachlor Trifluralin Glyphosate Metribuzin Nicosulfuron and Haloxyfop R methyl at different concentration levels on soil urease activity and second the effect of two most inhibitory herbicides on the production and persistence of the urease Two soil samples were collected from calcareous soils of Isfahan province The soils were crushed and passed through 2 mm sieve A 5 g soil sample was treated with the herbicide at 0 10 20 30 40 and 50 mg kg 1 soil After 30 minutes of equilibration the activity of urease was assayed according to the standard method In order to evaluate the effect of herbicides on the production and persistence of urease in soils the soils were first amended with adequate amounts of carbon and nitrogen and then treated with different levels of the selected herbicides Urease activity was assayed at 1 2 3 4 5 7 9 12 15 20 25 30 days of incubation The respired CO2 C was also determined in a parallel experiment Results indicated that soil urease was consistently insensitive to all herbicides at the concentration of 10 mg kg 1 In greater concentration herbicides inhibited soil urease to different extents so that Oxyfluorfen and Trifluralin were detected as the most toxic herbicides Therefore the production and the persistence of soil urease were assayed in soils treated with the two herbicides In most of the cases urease production was not limited at the 0 5 mg kg 1 Both herbicides showed to restrict urease production in soils Interestingly the ideal pattern of enzyme production was changed when soils were first treated with the herbicides We could not find a clear description for the pattern shift The similar pattern of the urease activity and soil respiration in soils treated with the herbicides support the hypothesis suggesting that herbicides may influence the soil enzyme activities either by affecting the enzyme protein molecules or affecting the micro

فلاح، حسن

بررسي آثار استفاده از علف كش ها بر شاخص هاي توليد و دوام آنزيم اوره آز خاك

فعاليت اوره آز , معدني شدن كربن , تنفس ميكروبي