The nitrogen transformative capacities of three kinds of composted wastes, prepared from city refuse (CRC), swine feces-sawdust mixture (SSC), and cow feces (CM), differing in the composting period, were estimated according to the levels of inorganic nitrogen during air-drying, or incubating with or without soil. By air-drying, ammonium volatilization and/or immobilization of inorganic nitrogen were estimated in the immature samples, but ammonification and nitrification were done as an exception. However, the mature samples did not show any nitrogen transformations. The changes of nitrogen transformative capacities estimated by incubation without soil differed according to whether or not the samples contained sawdust. For the CRC and CM which did not contain sawdust, ammonium volatilization, denitrification and/or immobilization of inorganic nitrogen predominated in the most immature samples, and ammonification and nitrification predominated in the most mature samples. Accumulation of nitrite was estimated together with the nitrogen transformations recognized in the medium-mature samples. For the SSC which contained sawdust, ammonification, denitrification and immobilization of inorganic nitrogen were estimated even after 30 weeks of piling. By incubating the samples which did not contain sawdust, with soil, the peculiar nitrogen transformations estimated by incubating without soil were shown until 2 weeks of incubation, and then ammonification and nitrification predominated. For the SSC which contained sawdust, immobilization of inorganic nitrogen predominated after 4 weeks of incubation in the sample before composting, and it was shown until 4 weeks of incubation even in the sample piled for 30 weeks. According to whether or not composts contained woody material, the changes of nitrogen transformative capacities with the progress of maturity were assumed as follows: For the composts which did not contain woody material, ammonification and ammonium volatilization were principal reactions at the most immature stage. With the progress of maturity, ammonification decreased and accumulation of nitrite, nitrification and denitrification increased. At the most mature stage, ammonification and nitrification predominated. For the composts which contained woody material, ammonification and ammonium volatilization were principal at the immature stage and accumulation of nitrite, nitrification and denitrification were shown at the secondary stage. After the two stages, immobilization of inorganic nitrogen due to the decomposition of woody material was dominant. At the most mature stage, ammonification and nitrification predominated.

View full abstract

Three kinds of composts differing in the raw material and the period of piling were air-dried at 25℃ or 50℃, or incubated without soil at 30℃. Inorganic nitrogen contents were measured periodically on four replicate samples. The results obtained were as follows: 1) Some of the compost samples were preserved for 5 months at 4℃. During the preservation inorganic nitrogen contents were changed, but the maturities did not proceed. 2) The nitrogen transformations estimated by air-drying did not greatly differ between the temperatures utilized, and the principal reactions were estimated within 24 h of air-drying. More nitrogen transformations were estimated when ammonium nitrate was added. 3) The nitrogen transformations estimated by incubation without soil changed periodically, and the peculiar transformations occurred within 2 weeks. 4) The coefficients of variations of inorganic nitrogen contents measured during air-drying or incubating without soil were less than 35%, and the variations did not affect the estimation of nitrogen transformative capacities. 5) From the above results, the experimental conditions of air-drying or incubation without soil for estimating nitrogen transformative capacities were concluded to be as follows: air-drying, for 24 h at 25℃; incubation, for 2 weeks at 30℃. In addition, both the experiments should be carried out on the duplicate samples by adding ammonium nitrate.

View full abstract

Winter barley has often been observed to show such peculiar symptoms of magnesium deficiency that the chlorosis emerges in winter or early spring but is recovered naturally after mid-spring. In order to examine our presumption that the magnesium deficiency of this type should be induced by ammonium-nitrogen applied as basal fertilizer and the recovery could be brought about through the nitrification of the ammonium, barley plants were pot-cultured from early in December on an andosol low in exchangeable magnesium under the application of ammonium-nitrogen or nitrate-nitrogen, with and without magnesium addition. In the plants which received ammonium and no magnesium, chlorosis appeared early in February and became severer toward the end of March. together with these changes, the retardation of growth also proceeded. The chlorotic plants, however, began to be green early in April; then they became dark green and also showed rapid restoration of growth. In contrast, the plants which received nitrate and no magnesium did not show either chlorosis or retardation of growth substantially, the same as in the case of the plants which received ammonium and magnesium. At the end of March, magnesium content in the above-ground parts was lower in the plants which received ammonium and no magnesium than in those which received nitrate and no magnesium, though at the matured stage the relative magnesium content was reversed between them. At the end of March, in the soil to which ammonium and no magnesium had been applied, an amount of nitrogen corresponding to 65% of the initially added amount was found as nitrate-nitrogen and the ammonium-nitrogen content was reduced to the level as low as that in the soil under the application of nitrate-nitrogen. All these results support the above presumption.

View full abstract

Relationship between leaf nitrogen and the limiting factors for the photosynthetic rate under ambient air conditions wee examined in soybean leaves. The results obtained here were compared with data from wheat and rice leaves. The rate of CO_2 assimilation for a given leaf-nitrogen content in soybean was about 15% lower than that in wheat and rice. This was mainly due to the smallest conductance and ribulose-1, 5-bisphosphate carboxylase/oxygenase (RubisCO) content per leaf-nitrogen in soybean. Although the RubisCO activity per enzyme protein from soybean was comparable to that from rice, it was appreciably lower than that from wheat. The factors described above caused the smallest rate of CO_2 assimilation for a given leaf-nitrogen content in soybean leaves.

View full abstract

A short-season rice variety, Fujihikari, was transplanted from April to July under the same fertilizing conditions. Variations in the growth of panicle and the mineral content in hull, rachis-branch, and grain due to shifting of the cultivation season were investigated. 1. The dry weight of rice grains transplanted in June reached the maximum most rapidly at about 20 days after the heading, depending on higher temperature of the ripening period than other plots; that of rice grains transplanted in April, which showed the slowest growth rate, reached the maximum weight at about 30 days after the heading. The dry weight of rice grains at harvest transplanted in June and July were higher than that of those transplanted in April and May. 2. The water content in unhulled rice decreased rapidly during the maximum grain filling rate. In contrast to this, the water content of rachis-branch decreased suddenly after the near completion of ripening in all plots of the cultivation seasons. 3. The content of N, P, and Mg in rachis-branch and hull decreased markedly until 20-25 days after the heading, while that of K increased until about 20 days after the heading. The concentrations of N, P, and Mg in rice grain were relatively constant through the ripening period but that of K was decreased from the heading to about 20 days after the heading and then became constant. Although no clear differences were found in the content of N, P, and Mg in rachis-branch and hull by shifting of the cultivation season, the different patterns in the accumulation of K were dependent on the ripening stages. 4. The content of N in rice grains at harvest was higher in plots transplanted in the later seasons, while the accumulating patterns of K varied with the seasons. The ratio of Mg/K in rice grain, which might be one of the characteristics of rice grain in relation to taste, was higher with the delay of the cultivation season.

View full abstract

To clarify the characteristics of soils in tea gardens with root-rot disorder, the following two types of soils were taken from four tea gardens which had various extents of damage of root-rot disorder in the western part of Shizuoka Prefecture: (1) root zone soils with root-rotted plants which were sporadically found in the tea gardens (Rs); (2) the soils with health plants which were found in the same tea gardens as above (Hs). 1) The gaseous phase ratio of Rs was lower than that of Hs. The Rs in which root-rot disorder was severe showed higher sand and lower clay contents, and gravitational water content higher than those of Hs. 2) The EC of Rs was lower than that of Hs. The ratio of permanent charge (CECp) was lower in Rs than in Hs and was lowest in Rs in which root-rot disorder was severe. 3) The main clay minerals identified were illite and aluminum-vermiculite (chlorite). The content of aluminum-vermiculite was higher in Rs than in Hs. The correlation coefficient between CECp (%) and aluminum-vermiculite (%) was -0.71. 4) The oxygen consumption was great in Rs in which the percent of root-rot disorder was high.

View full abstract

Inoculated Azolla japonica was multiplied in flooded rice field for 38 days before transplanting and incorporated into the soil at pudding. We investigated effects of Azolla application on rice yield, amount of nitrogen uptake by rice plant and nitrogen content in soil. The following results were obtained. 1) The Azolla biomass in flooded field attained 6.0-6.3 t fresh weight/10 a and it was considered to be maximum yield when A. japonica was multiplied in field condition. The amount of nitrogen incorporated into soil as Azolla was estimated to be 6-11 kg N/10 a. 2) Application of Azolla increased rice yield and amount of nitrogen uptake by rice plant. The results suggested that Azolla was effective as green manure for rice plant. 3) In the panicle formation stage (in mid-August), total nitrogen content and amount of mineralized nitrogen in the surface soil layer were higher in Azolla-incorporated plot than in non-incorporated one. These results indicated that application of Azolla increased the nitrogen content in the surface layer of paddy field soil.

View full abstract

We examined the validity of the soil respiration rate as a simple indicator of the soil biomass in upland soil. The results were summarized as follows: 1) There was a high positive correlation between the ATP content in soil and the rate of soil respiration measured in situ (r=0.076, n=36, p<0.001). 2) There was a positive correlation between the ATP content and the rate of soil respiration measured in the laboratory (25℃). However, the correlation coefficient of this (r=0.46, n=36, p<0.01) was lower than that between the ATP content and the rate of soil respiration measured in situ. No significant correlation was found between the soil respiration rate measured in situ and that measured in the laboratory. These results seem to be due to a unique change in the soil respiration rate measured in the laboratory when organic matter was applied and to the effect of soil moisture on the rate of soil respiration measured in the laboratory. From the results mentioned above, we suggest that the rate of soil respiration measured in situ is a simple indicator of the soil biomass.

View full abstract

[in Japanese]

View full abstract