Abstract
The inhibition of nutrient uptake by rice plant was studied by increasing concentrations of butyric acid or respiration inhibtors such as H_2S, NaCN and NaN_3. Rice plants were grown by customary water culture technique and treated for 28 hours in the green-house with various concentration of these inhibitors in the basic nutrient solution as shown in Table 1. The nutrients uptake was calculated from the concentration difference of the respective elements. The results are shown in Fig. 1 : (1)〜(10). In general, the relationship between the nutrient uptake and the concentration of inhibtors can be represented by y_i = a_i + b_ie^<-cjxj> where y_i represents nutrient uptake, x_j the concentration of inhibitors, i and j being variables according to the kind of elements and inhibitors respectively. a_i respresents y_i at x_j →∞ and was designated as Ultimate-absorption, the approximate values of which are shown in Table 2. Further, the Inhibition Coeffieients of nutrient uptake were calculated by ((y_<i(xj→0)>-y_<i(xj→∞)>))/(y_<i(xj→0)>)×100 as shown in Table 3. The Ultimate Absorption a_i seems to be almost independent of the kind of inhibitors but primarily dependent on the kind of elements. The Inhibition Coefficients decreased according to K_2O・P_2O_5>SiO_2・SO_3・Br>MnO・NH_4-N・H_2O>MgO・CaO. The outstanding depression of P_2O_5 uptake was doubtless as repeatedly revealed in Fig. 2. The result was discussed on the basis of the essential mechanism of aerobic respiration, K_2O and P_2O_5 probably linking more directly in the metabolic cycle and MgO and CaO standing more indirectly or far apart from the cycle. Practically, this will give important suggestion to the improvement of the nutritional status of the crop plants in such cases as the metabolic activity of their roots are inhibited by toxic substances (for example H_2S and butyric acid to rice plant), cold climate, draught or bad drainage.
