Study On The Dynamic Changes Characteristics Of Soil Active Mn And The Responese On Rape In The Main Acid Soils

The dynamic change characteristics of active manganese and the biological response of oilseed rape were studied through pot experiment and indoor incubation experiment with three acid soils under the contrast of calcareous alluvial soil in Hubei province. Meanwhile, the effect of several organic compounds to adsorption-desorption characteristics of manganese in soils was also studied by flow displacement method. Through the experiments, the main results were obtained as follows:1. In pot experiment the soil pH decreased while the Eh increased; the ERO-Mn converted to CARB-Mn; the increase of EXC-Mn was clearly hysteretic to CARB-Mn after soil acidification. Through regression analysis among soil Eh, pH and Mn2+, electrical pairs MnO2/Mn2+ was the main mode to describe the dynamic changes of Mn oxides to Mn2+ in the brown-red soil while electrical pairs MnOOH/MnO was the probable mechanism in the yellow-brown soil.2. In the incubation experiment, the soil pe + pH decreased more clearly in the flooded condition than that in the water saturation, and the EXC-Mn and ERO-Mn changed in the reverse direction. The EXC-Mn increased in this order: brown-red soil, yellow-brown soil > calcareous alluvial soil > red soil originated from granite, with the increase of soil ERO-Mn content, which indicated that the increase of soil EXC-Mn was closely related with the soil ERO-Mn concentration. Parabolic diffusion equation could better reflect the transformation process of soil Mn, This suggests that diffusion processes control the rate of Mn transformations.3. The adsorption of added Mn by soil was related to soil pH, so calcareous alluvial soil had better fit in presenting the capacity of Mn adsorption-fixation. Power function equation could better describe the adsorption dynamics of soil Mn in different soil types. Among the organic compounds, citric acid had a better capacity in dissolving soil Mn. On the basis of added Mn and organic compound coexistence, there existed two competitive mechanisms, adsorption and complex reaction, which reaction preponderated depended on the ERO-Mn content. In brown-red soil and yellow-brown soil, the complex reaction was the dominant process.4. The oilseed rape leaves turned yellow and curved from the edge; foxinessemerged in old leaves and the florescence was delayed with less flower, more twig, growth period prolonged and seed yield decreased. The Mn concentration and Mn/Fe ratio in the rape plant had a positive correlation with the soil EXC-Mn. The soil available Fe, Mn, Cu and Zn increased after acidification treatment. During the flowering stage, the Mn uptake had a significant effect on the uptake of Ca and Mg between the treatment of strong acidification and calcium carbonate application in brown-red and yellow-brown soil, and Mn in the plant distributed unevenly in this order: leave>flower>stem.