Effects Of Dryland Soil Being Reclaimed Into Paddy Soil And Of Various Rice-Based Cropping Systems On Chemical Fractions And Availablity Of Manganese In Soils

Total Mn, available Mn and its chemical fractions and their profile distributions of dryland soils and paddy soils derived from several major parent materials in Hunan province were studied with field investigation, sampling in situ and laboratory determination; The effects of various rice-based cropping systems, application rates of organic manure and different groundwater levels on total Mn, available Mn and its chemical fractions of the paddy soil reclaimed from cultivated red soil, dynamic variation of exchangeable Mn and easily reducible Mn contents and Mn uptake by early and late rice at different growth stages after dryland red soil being reclaimed into paddy soil were also studied based on the long-term stationary experiment of Hunan agriculture university. The main results are as follows:1. The contents and profile distributions of total Mn and available Mn of the dryland soil and paddy soil derived from the identical parent material were remarkably different. In paddy soil, continuous flooding stimuted 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; but in profiles of dryland soil, Mn leaching was much weak and Mn only accumulated in the second layer (20-40cm). Distribution models of the contents of total Mn and available Mn in profiles of dryland soils and paddy soils were remarkably different: dryland 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. Oxide Mn and readily soluble Mn were major chemical fractions of available Mn(the respective relative proportion of the two chemical fractions in total available Mn reached 86.4% and 7.7%). For the tested calacious spils, available Mn was divided into readily soluble Mn> weakly absorbed Mn> carbonate-bound Mn and oxide Mn, and oxide Mn and carbonate-bound Mn were major chemical fractions of available Mn, relative proportion 95%, contents of readily soluble Mn and weakly absorbed Mn were both less than 2%. For different chemical fractions of available Mn, only readily soluble Mn content in plough horizon of paddy soils was higher than dryland soils, and other chemical fractions of available Mn were lower than in the plough horizon of dryland soils. The contents and profile distributions ofinvarious chemical fractions of available Mn were remarkably different. For the tested dryland soils, contents of various chemical fractions accumulated in the second layer(20-40cm). For the tested paddy soils beyond content of readily soluble Mn decreased with increasing depth in the profiles, contents of various chemical fractions of available Mn increased with increasing depth in the profiles.3. The results of long-term stationary experiments showed that Compared to the original dryland soil, the contents of total Mn, oxide Mn and available Mn in the plough layer of paddy soil reclaimed from red earth were significally decreased, but contents of readily soluble Mn increased evidently. For various rice-based cropping systems, application rates of organic manure and groundwater levels, various rice-based cropping systems had strongest effects on chemical actions and availability of Mn in soils, the contents of total Mn and various chemical fractions of available Mn of the soil with "early rice- late rice- flooded follow in winter" treatment were higher than that of the soil with two treatments of "early rice- late rice- green manure crop in winter" and "early rice- late rice- oilseed rape in winter". Analysis of variance showed that the difference in contents of various chemical fractions of available Mn between different treatments reached the signific...