effect of municipal compost and sewage sludge on soil chemical characteristics, quality and quantity of sugar beet in rudasht - esfahan

the study was conducted during 2002- 2007 in the first and last stage of a four-year rotation (sugar beet, forage maize, onion, wheat and sugar beet) at research station of irrigation and drainage rudasht. in each year, four treatments of organic fertilizers (25 and 50 t/ha urban compost and 15 and 30 t/ha sewage sludge) with a control (no organic fertilizer) were studied in a randomized complete block design with three replications. it was revealed that the maximum organic carbon content, available potassium and lead in the soil was observed in the 50 t/ha urban compost, treatment whereas the maximum available phosphorous and copper in the soil was associated with the application of 30 t/ha sewage sludge. as time elapsed, the available zinc in the soil was enhanced significantly by application of urban compost. utilization of urban compost as well as sewage sludge significantly enhanced the sugar beet root yield. however, the sugar content was decreased. the decrease in sugar content was greater for the sewage sludge treatment than for the urban compost treatment. in the last year of the rotation, the effect of application of the organic fertilizer on sugar yield was not significant. however, due to the increase in the root impurities resulted from the application of urban compost as well as sewage sludge, the white sugar yield in the last year showed a significant decrease in comparison with that of the first year of the rotation. it follows that continuous application of the types of organic fertilizers, particularly the sewage sludge, to the rudasht district of esfahan as well as regions with a fine textured soil is not recommended.