A kinetic analysis for nitrogen mineralization was investigated in the well-drained paddy field and ill-drained paddy field. 1) It was found that the nitrogen mineralization patterns of paddy soils in both soil types can be approximated by the first-order reaction model irrespective of the soil sampling time. 2) The accurate nitrogen mineralization patterns of soils were made by binding of each nitrogen mineralization pattern of soils which are sampled after transplanting. In the well-drained paddy field, the nitrogen mineralization patterns of soils sampled after one, and two months after transplanting were close to the patterns of soils sampled after one, and two months after transplanting were close to the patterns of soils sampled just before flooding; the nitrogen mineralization pattern of soils sampled after three months after transplanting had a sharper curve than the pattern of soils sampled just before flooding. In the ill-drained paddy field, the nitrogen mineralization patterns of soils sampled after transplanting had a more moderate curve than the pattern of soils sampled just before flooding. 3) The amounts of nitrogen mineralized in both soil types, estimated from the soil sampled just before flooding, were closer to the amounts of nitrogen absorption of paddy rice, except in the initial stage and the late stage of rice growth in the well-drained paddy field. 4) Coefficient of variation of the N_0 was close to the amounts of nitrogen absorption of paddy rice. It was suggested that the coefficient of variation of the N_0 was a good index of the source of mineralized nitrogen in soils. It is concluded that the nitrogen mineralization patterns of paddy soils can be estimated by using a kinetic analysis for nitrogen mineralization of soils sampled just before flooding.

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Dry matter production and the amount of phosphorus absorbed were compared among 25 field-grown plant species, including some weeds, under low and high P conditions. 1) In summer croppings, few species showed significant differences in top dry matter between high and low P conditions, and there was no difference in the response to P application among most species. 2) Relatively high amounts of P were accumulated in summer croppings: alfalfa and Brassica campestris in winter croppings. No weed species tested accumulated a higher amount of P than those species.

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To obtain high yields of rice plant, it is important to hasten its uptake of silica. To clarify factors affecting silica uptake by rice plant in northern Japan, where there are often cool summers, the influence of temperature on silica uptake by rice plant was investigated. From panicle initiation stage to full heading stage, the period at which rice plant absorbs silica most actively, silica uptake by rice plant and supply of silica from a paddy soil (fine-textured Gray Lowland soil) were examined under greenhouse conditions at various temperature levels and on field conditions over seven years. Results are as follows: Greenhouse experiments: Both the silica content in rice plant and the amount of silica uptake by rice plant per pot were higher at high temperature than at low temperature, i.e., 30℃>25℃>20℃. The silica content in soil solution of unplanted pots was also 30℃>25℃>20℃. The application of calcium silicates (10 g/pot) increased the silica content in soil solution by about 10 ppm, and also increased the silica content in rice plant by about 1.5% at any temperature. Field experiments: The uptake rate of silica by rice plant correlated with the soil temperature in paddy field from panicle initiation stage to full heading stage. The increase in silica uptake per the increase in dry weight of rice plant correlated with the soil temperature until meiosis stage. After that , the negative correlation between them was formed until full heading stage. The silica content in soil solution in the plot of paddy field where rice plant had been removed became higher at high soil temperature than at low. It is concluded that both the supply of silica from paddy soil and the silica uptake by rice plant depend on temperature, and that the application of calcium silicates in a cool summer is effective for hastening silica uptake by rice plant.

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The experiments were carried out to establish an adequate method, which can be recommended to the farmer, for raising healthy seedlings of tomato plants by rockwool culture. The following factors, which will affect not only the seedling but the yields of the fruits, are examined: fertilization in the seed bed, the date of temporary planting, and the space in the bottom of the nursery pot. 1. The addition of nutrients to the seed bed promoted the growth of seedlings and shortened the duration of maturity. 2. Early temporary planting produced higher yield. Late temporary planting resulted in low yield, especially in the case of no fertilization to the seed bed. 3. Water requirement by seedlings greatly depended on the space in the bottom of the nursery pot. From these facts, the following are proposed for the raising of seedlings in rockwool culture of tomato plants. 1. Addition of nutrient solution (EC=1) to the seed bed. 2. Early temporary planting. 3. Small space in the bottom of he nursery pot.

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To explore the effectiveness of nitrogen mineralization parameters (NMP) in studies of nitrogen dynamics in soil, characteristics of NMP values and their relation to soil nitrogen availability indices (NAVI) were examine. 1) Soils were collected from a plow layer of experimental fields located in Tohoku district, in the northern part of Japan . NMP of the soils were determined by the kinetic analysis of the mineralization curves at some temperature levels. the nitrogen mineralization curves corresponded to a first-order reaction equation. The ranges of NMP obtained were as follows: nitrogen mineralization potential, N_0, 4.7-30.6 (mg N/100g soil) ; rate constant, k, 0.0015-0.0077 (/d, 25℃); activation energy, E_a, 9900-23,000 (cal/mol). Some humus-rich Andosols showed a tendency of higher N_0, lower k and higher E_a values than non-volcanic ash soils. 2) To predict NMP without incubating soils, various NAVI were measured and their relation to NMP was examined. Several NAVI, such as autoclaving extractable nitrogen, correlated with N_0. On the other hand, no NAVI showed a significant correlation with k and E_a. Therefore, it was impossible to predict NMP without incubating soils. 3) Annual variation in soil nitrogen mineralization was estimated based on NMP and soil temperature. The amount of nitrogen mineralized during the summer growing season of 1983, a cool summer, was lower than of 1984, a hot summer, by approximately 10kg N/ha. 4) The estimated amounts of nitrogen mineralization during a summer growing season highly correlated with the amounts of nitrogen mineralized by incubating air-dry soil at 30℃ for 4 weeks, and also correlated well with UV absorbance of soil extracts by 1-hour autoclaving.

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This report describes two model equations obtained by a kinetic study and an appropriate method of calculating nitrogen mineralization parameters. The estimation procedure is as follows: 1) Raw and air-dried samples of paddy soil are cultured by long-term indoor culture at 20, 25, and 30℃ to determine the nitrogen mineralization of each. 2) The data on raw soil are subjected to the single exponential model: N=N_<01>{1-exp(-k×t)}+B. The parameters with the least variance are adopted as most appropriate, and basic k and E_a are calculated. Then, the culture data on the mixtures of air-dried soil and raw soil are subjected to the double exponential model: N=N_<0q>{1-exp(-k_1t_1)}+N_<0s> {1-exp(-k_2×t_2)}+B. In this case, the parameters (k_2 and E_<a2>) in the member N_<0s> of the model are fixed with the k and E_a of raw soil to determine the rest of the parameters. 3) Nitrogen mineralization potential (N_0) is defined as the sum of a fraction resulting from air-drying of soil and that resulting from a rise in soil temperature. N_0 can be calculated as the sum of N_<0q> (the potential of the total effect of soil-drying) and N<0s> (the potential of the total effect of a rise in soil temperature) by subjecting the culture data an air-dried soil to the double exponential model.

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Fly ash from coal was blended with potassium sulfate and small amounts of magnesium hydroxide and powdered coal and was calcined in a reducing atmosphere at 950℃ for 30 min to produce citric-soluble potassium silicate fertilizer. A fly ash from a domestic coal rich in CaO readily reacted to form soluble K_2O・Al_2O_3・sSiO_2(KAS_2) and 2CaO・2SiO_2 (C_2MS_2), etc., while CaO lean fly ash from an imported coal gave considerable amounts of insoluble K_2O・Al_2O_3・4SiO_2 and K_2O・MgO・3SiO_2. Addition of CaO to the CaO-lean ash helped the formation of KAS_2 and C_2MS_2. An amorphous phase was also present in the calcined products. Tests with synthetic K_2O-Al_2O_3-SiO_2 glass indicated that the glass lean in K_2O was less soluble and the solubility increased with K_2O content of the glass.

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Each microbial species is thought to be adapted to its chemical environment. In other words, each microbial species is expected to be adversely affected by substances to which it has never been exposed. To test the supposition, we examined effects of Mn^<2+> on nitrification in two soils (Konosu paddy soil and Saitama upland soil) and growth of several species of Pseudomonas, because these bacteria were considered to be rarely exposed to Mn^<2+>. Nitrification was really inhibited when added with 50ppm Mn^<2+>. This inhibitory effect of Mn^<2+> was more remarkable for Konosu paddy soil than for Saitama upland soil and was intensified at low soil pH. Mg^<2+> was found to alleviate the inhibitory effect of Mn^<2+>. Furthermore, Mn^<2+> (10ppm or 100ppm) inhibited growth of most of the Pseudomonas in two cultural solutions (the ordinary solution and its diluted counterpart). The effect was more clearly recognized in the dilute cultural solution than in the ordinary cultural solution, suggesting that cultural solution itself weakened the inhibitory effect of Mn^<2+>. Mg^<2+> alleviated this inhibitory effect of Mn^<2+> for only two species.

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