The Study On Chemical Fractions And Availability Of Manganese In Upland Soil And Paddy Soil, Hunan Province Of China

Total Mn, available Mn and its chemical fractions and their profile distributions of upland soil and paddy soils derived from several major parent materials in Hunan Province, China, were studied with field investigation and sampling in situ and laboratory determination. The main results showed as follows:1. The contents and profile distributions of total Mn and available Mn of the upland soils and paddy soils derived from the identical parent material were remarkably different. In paddy soil, continuous flooding stimulated Mn leaching. As a result, Mn in the profile of paddy soil were significantly different, Mn accumulated in the lower soil layers, while contents of Mn in plough layer of paddy soil decreased evidently. Content of Mn increased with increasing depth in the profiles: Mn leaching but in profiles of upland soil was much weaker and Mn only accumulated in the second layer (20-40cm). Distribution models of the contents of total Mn and available Mn in profiles of upland soils and paddy soils were remarkably different, i.e., upland soil: the second layer (20-40cm)>the first layer(0-20cm)>the third layer(40-75cm);paddy soil: the third layer(40-75cm)> the second layer(20-40cm)> the first layer(0-20cm).2. For the tested acid soils, available Mn was divided into four chemical fractions, which were readily soluble Mn, weakly absorbed Mn, specifically absorbed Mn and oxide Mn and readily soluble Mn were main fractions of available Mn, and the relative proportion of the two fractions in total available Mn accounted for 86.4% and 7.7% respectively. For the tested calcareous soils, available Mn was divided into readily soluble Mn, weakly absorbed Mn, oxide Mn and carbonate-bound Mn were amounted to fractions of available Mn, the sum of relative proportion of both them in total available Mn more than 95%. The contents of readily soluble Mn and weakly absorbed Mn Were both less than 2%. For different chemical fractions of available Mn, only readily solubleMn content in plough horizon of paddy soils was higher than upland soils and other 3 fractions of available Mn in plough horizon of paddy soils were all lower than in the plough horizon of upland soils. The contents and profile distributions of various fractions of available Mn in the soils were remarkably different .For the tested upland soils, various chemical fractions of available Mn accumulated in the second layer (20-40cm). For the tested paddy soils, only the content of readily soluble Mn decreased with increasing depth in the profiles, and the other 3 fractions of available Mn increased with increasing depth in the profiles.