| The oxidation-reduction, complexation-dissociation and dissolution-precipitation of iron effect the conversion and migration of iron in the soil profile and play an important role on evolution of soil development and plant availability of iron. The morphology and distribution of soil iron and plant type, planting system and water conditions and other factors are closely related. In the experiment, the fourth stage terrace of Sichuan Mingshan bleached paddy soil was been used as the research object, as a reference to forest yellow, by the research methods that combine outside observations and laboratory analysis, researched the effects of the conversion and migration characteristics of different forms of Bleached paddy soil in the land use types from paddy soil into tea garden, provide the basis for the rational use and management of soil resources. The results showed that:(1) The changes of distribution and migration of the Bleached paddy soil iron profiles when the paddy field changed into tea garden:With the increase of years of tea, tea on iron absorption and total iron in soil decreased year by year, total iron content (28.31 g/kg) of the six year's tea garden was lower significantly than the three year's tea garden (33.78 g/kg) and paddy field (33.90 g/kg). After flooding, paddy soil reductive enhanced, Eh decreased, early year, drainage to enhance soil oxidation, Eh increased, with the tea time extended, soil aeration deteriorated, Oxidation decreased, Eh decreased, coupled with increased organic matter, soil total increase in reducing substances, the soil reducing increased, overall changes in soil characteristics of various forms iron:Ferrous iron content and BFe/TFe% decreased significantly after the first slight increase, paddy field soil the ferrous iron content (0.23 g/kg) and BFe/TFe%(0.73%) of paddy soils were higher significantly than the three year's tea garden soil (0.08 g/kg,0.25%), but there were no significant differences of ferrous iron content (0.16 g/kg) and BFe/TFe%(0.51%) between the six year's tea garden and three year's tea garden; The free iron content and free degrees of the three year's tea garden soil changed little, however, there was a significant decline in six years later, It's also had relations with solubility of iron passivation reduced and soil total iron content decreased after drainage, The free iron content (7.56 g/kg) and free degrees (0.25) of the six year's tea garden was lower significantly than the three year's tea garden (10.81 g/kg,0.32) and the paddy field (10.63 g/kg,0.31); Active iron content in the soil decreased significantly after the first increased slightly, but still lower than the rice fields, The active iron content of the three year's tea garden (2.10 g/kg) was lower significantly than the six year's (2.40 g/kg) and the paddy field's (2.54 g/kg); Also affected by soil organic matter, total amount of reducing substances, the activation degree of soil iron, chelated iron content and complex degree showed the trend that first decreased and then increased.(2) The characteristics of the soil profile distribution of iron of the Bleached paddy when the paddy field changed into tea garden:The paddy field soil was in an inundated and reducted condition over a long period of time, with decreasing of soil profil's Eh, soil reducing environment was been increased and the ferrous iron content had been increased. with the increasing of inundated time, the ferrous iron content was increased, of which it's content belowed 70 cm soil layer was increased to maximum value,0-20 cm soil layer has a large amplitude compared than the 40-70 cm layer, the total ferrous iron content and BFe/TFe% of tea garden 0-20 cm layer and 70-110 cm was higher than the middle layer.The total iron, free iron, active iron, chelated iron concentrate at soil surface at the beginning, With the increase of years of tea,, it was reduced. the free iron content in 40-70 cm soil layer was:the paddy field> the three year's tea garden> the six year's tea garden,the content in the 70-110 cm soil layer was:the paddy field> the six year's tea garden> the three year's tea garden; The active iron content of the 0-20 cm layer was rising when the paddy field changed into tea garden in the early years. The content of active iron in tea garden soil was reduced after 6 years, and it was opposite with the 0-20 cm layer in soil profile below the plow layer. The chelated iron of 0-20 cm soil layer was: the three year's tea garden> the paddy field> the six year's tea garden, it in the 20-40 cm,70-110 cm soil layer was tneded to:the six year's tea garden> the paddy field>the three year's tea garden, the 40-70 cm soil layer was:the paddy field>the six year's tea garden> the three year's tea garden.(3) The seasonal changes of migration of iron profile in bleached paddy soil was follow:because of the the cropping system in the bleached paddy soil, the ferrous iron content and percentage in total iron in every soil layers was highest in March, and the 0-70 cm soil layer of the tea garden soil appeared in September, paddy field and tea garden generally lowest in January. The active iron content and the iron activation degree had a little change and the highest values generally appeared in may. The higher chelated iron content and complex degree of 0-70 cm layer of the paddy soil and the three year's tea garden soil appeared in September, but the 70-110 cm layer of paddy soil and the six year's tea garden soil appeared in March and may, the complex degree of chelated degree of paddy field and tea garden soil layer were the lowest values in July. |
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