investigate the causes of the decline in agricultural production after a period of cultivation of saffron

iran is a major producer of saffron in the world. about 255 tons of saffron is produced on 70 thousands hectares of land, of which 125 tons are exported. production is practiced on small holding, using traditional cultivation practices. one of the major problems associated with saffron cultivation is soil fertility depletion during the first cultivation period, the effects of which extends for a time period equivalent to three times of the first cultivation period. this will adversely affects the sustainability of saffron production in areas most suited to saffron three hypotheses have been proposed as the possible causes of this phenomenon: 1) changes in soil physico-chemical properties, 2) changes in biochemical conditions of the soil and 3) major changes in the population of the soil microorganisms. a few researches dealt with this problem suggest that soil morphological, physico-chemical and genetic properties do not change after one period of saffron cultivation. in addition, no micronutrient limitations were observed in the soil after harvesting the crop. production of allelopatic compounds is probably the main reason for soil familiar to satisfy crop needs. one study evaluated soil leaching after harvesting the crop saffron cultivation, with the hypothesis that allelopatic compounds may have been produced, and that it is possible to remove them by leaching. the results were relatively successful.