| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1994: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1993: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1992: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
In this investigation, we have newly developed a rhizobox system to study the behavior of nutrients in rhizosphere. The rhizobox is a box which consist of several compartments of 1mm thickness and each compartment was filled with soil of 40g (dry soil) mixed with nutrients. Nylon cloth of 25 mum mesh was used to separate the soil compartments of rhizobox and this nylon cloth was successfully used to limit the root growth to the central compartment where the plants were grown. Thus, we succeeded to sample the soil from each compartment of certain distance from root without root contamination and to determine the distribution of total and soluble fraction of the nutrients (Ca, Mg, K,Na, SO4, NO3, Cl, Zn, Cu, Mn and Fe) in the rhizosphere. The following results were obtained.
1) The concentrations of total fraction of the nutrients were not affected by the root and only soluble fraction of them changed in the rhizosphere. Soil pH of rhizosphere sometimes in creased and other times decreased due to cation/anion balances in the soil solution.
2) Soluble Ca, Mg, Na, SO4 and Cl were increased in the rhizosphere due to the greater amount of massflow than the plant uptake.
3) Soluble K and NO3 were decreased in rhizospere due to the greater amount of plant uptake than massflow.
4) Changes in soil pH in rhizosphere affected the solubility of Zn and Cu but not the solubility of Fe and Mn. Soluble fractions of Fe and Mn always increased in rhizosphere in spite of soil pH change.
5) Tracer studies using ^<59>Fe and ^<54>Mn were carried out and these experiments showed that massflow and/or diffusion of Mn and Fe were very slow. The tracer experiments also showed that rhizosphere soil and root exudates increased the solubilities of MnO2 and Fe2O3. Thus, in the rhizosphere, some compounds exuded from the plant root dissolved insoluble Mn and Fe in the soil.
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