1) Rates of nutrient release from 4 different kinds of resin-coated compound fertilizers were measured under varying soil conditions: 40,20,10 and 5% of the maximum water holding capacity (MWHC), which corresponded to -0.1, -3.0, -40, -100MPa of the matric potential, respectively. From the nutrient release data, the release constant (k) was calculated. The k values for different coated fertilizers at 40% MWHC were similar to those previously obtained in the dissolution test, but were decreased with decreasing moisture contents. The release rate coefficient (α) was defined as the ratio of the k values of the different coated fertilizers. 2) Release rate coefficient α was expresses as a function of soil moisture potential, and incorporated into a new simulation model which successfully estimated nutrient release under different soil moisture conditions. 3) Two different kinds of coated fertilizers were embedded in the spring and autumn in soil layers at 1 and 10 cm depths in a field. The fertilizers were collected intermittently for several months, and the residual nutrients were determined. When the fertilizers were embedded at 10 cm, the release rates were influenced little by the soil moisture variation, but the release rate from the fertilizers embedded at 1 cm was delayed. The delay was marked particularly in the dry period with little rainfall. The release rates simulated with the temperature and moisture variation agreed well with the measured values, and we confirmed the validity of the simulation model.

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It is well known that stemflow of the Japanese cedar tree is strongly acidic, which causes severe acidification of soils close to the trunk of the tree. However, the possible effects of this acidification on aluminum species distribution in soil solutions is virtually unknown. Thus, in order to conduct aluminum speciation, soil solutions were collected for one year from the Ah horizon at plots close to (-10 cm) and far from (>100 cm) the trunk of a Japanese cedar tree in Gunma Prefecture, Japan. Throughfall and stemflow samples were also collected to elucidate the dominant process that controls soil solution chemistry. The results obtained are summarized below: 1) The pH of soil solutions close to the trunk (referred to as C samples) and far from the trunk (referred to as F samples) ranged from 4.40 to 4.65 and 5.65 to 6.15, respectively. The difference between the two was 1.3 pH units on average. 2) The speciation of monomeric aluminum was conducted using HPLC with fluorescence detection of the Al-lumogallion complex in combination with equilibrium calculations. For F samples, only organic aluminum was detected, with a low level (1.2μmol L^<-1> on average). For C samples, however, Al^<3+> was dominant throughout the year, having an average concentration of 27.1μmol L^<-1>. 3) The dominant ion species for F samples were calcium and nitrate, showing that the chemistry of the samples was governed primarily by nitrification. During the dry winter season, the total ion concentration became two- or three-fold due to evaporation. 4) For C samples, the concentrations of calcium and nitrate fell to 38 and 56%, respectively, of those of F samples, because internal nitrate production was suppressed due to acidification. In the winter, the Al^<3+> level rose to 75.8μmol L<-1>, probably because the increases in calcium and hydrogen ion concentrations caused by evaporation enhanced the ion exchange with exchangeable aluminum in the soil.

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Amounts of nutritional constituents accumulated in komatsuna, which were grown under the application of chemical fertilizers (CF) or organic fertilizers (OF, rice bran+okara) in virgin soils (VS) and soils in which composts had been applied for 12 y (CAS), were measured. The amount of fertilizer applied was adjusted to give the same growth range of komatsuna for all treatments. 1) Nitrate concentrations of komatsuna grown in CAS were higher, and 0.8 m^3 m^<-3> ethanol soluble total sugar (TS) concentrations tend to be lower than those grown in VS. In the case of VS, nitrate concentrations of komatsuna grown under OF applications tended to be higher than those grown under CF applications, but in case of CAS, those grown under OF applications tend to be lower than CF applications. After 6 d of preservation, nitrate concentrations of komatsuna grown in CAS were higher, and total ascorbic acid (AS) and TS concentrations tended to be lower than those grown in VS. 2) Strong negative correlations were found in between nitrate concentrations and both AS and TS concentrations. 3) The nitrate concentrations of komatsuna were determined by the nitrate concentrations in the soils, but in VS, they were also influenced by chloride concentration. Relatively high nitrate concentrations of the OF-applied komatsuna in VS is due to the low concentration of chloride in VS and OF. 4) There results indicate that the application of organic fertilizers and composts does not always improve the nutritional constituents of komatsuna, and the concentration of chloride in organic fertilizers and composts as well as soils may need to be considered in organic farming.

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Soil samples with a wide range of copper contents (32 to 11,700 mg kg<-1>), classified as Dystric cambisol and Lithic leptosola (FAO-UNESCO), were investigated for Cu speciation in soil solutions in order to clarify the forms of Cu adversely affecting soil bacteria. The speciation of the metal was estimated using an equilibrium thermodynamic computer model, SOILCHEM. The copper effects on soil bacteria were evaluated by an indicator: Cu tolerance level of the bacterial community, shown as IC_<50>. The simulated free ion of Cu in the soil solutions ranged from 18 to 98% of total Cu, and organic complexes of Cu from <1 to 56%. The estimated Cu speciation in the soil solution was dependent on a variety of soil properties. The copper metal tolerance levels of the bacterial community were dependent on copper ion activities with a high square of correlation coefficients (R^2=0.735, P<0.01), but had no relationship with the total concentration of Cu in the soils. The results proved that the high ion activities in the soil solutions led to the development of the heavy metal tolerance levels in the bacterial community. IC_<50> was also correlated with chloride, nitrate and sulfate complexes of Cu in the soil solutions, respectively. The organic-Cu complexes in the soil solutions did not affect the IC_<50> of the bacterial community. Toxicity of the Cu ion was somewhat reduced with the low pH of the soil solutions, implying that protons competed with Cu ions for soil bacterial uptake sites, but accelerated solubilities of the metals from the soil particles.

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Methane emission from rice paddy fields (with or without rice straw application) was measured in Yamagata, a cold district of Japan, from 1992 to 1994. The characteristics of methane emission and influence of rice plant growth and mid-summer drainage on methane emission are as follows. 1) Methane emission from the rice paddy fields in the cold district was less than that of warm districts during the early growth stage of rice in June. Methane emission increased in July and August as (soil) temperature rose. 2) In years when rice plants grew briskly in the early growth stage, complete mid-summer drainage was needed to control plant growth, which in turn suppressed methane emission. In the case that weather in July and August was unusually cool, the rise in soil temperature was held down and the emission rate of methane was decreased. 3) In the case of poor rice plant growth and high soil temperature after mid-summer drainage, the emission rate of methane increased. 4) As the result of multiple regression analysis, the influences of soil reduction and temperature were different before and the mid-summer drainage. 5) These results suggested the importance of cultivation management for the suppression of methane emission and the maintenance of rice yield as follows. (1) Sufficient rice plant growth must be kept by appropriate ponding to keep soil temperature high, which enables strong mid-summer drainage. (2)After mid-summer drainage, soil oxidation and a drop in soil temperature would be anticipated by appropriate intermittent irrigation.

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The responses of vegetable plug seedlings were examined to determine the suitable physical and chemical properties for their growth under substrates mixed with different ratios of soil, peat and calcined vermiculite. 1) Mixed substrates covered wide ranges of bulk density (0.12-0.75g mL^<-1>), vapor phase ratios (13-31%), porosity (75-96%) and cation exchange capacity (7-21 cmol(+)L^<-1>). 2) Air porosity lower than 20% suppressed the growth of seedlings of Chinese cabbage (Brassica Pekinensis Rupr), cabbage (Brassica oleracea L.), cucumber (Cucumis sativus L.) and tomato (Lycopersicon esculentum Mill.) growth were suppressed at an air porosity lower than 16%. 3) Higher porosity of the substrates raised the ratio of root ball formed in the plugs for all of the vegetables. Satisfactory root balls (over 90% of the seedlings) were formed at 85% porosity for Chinese cabbage, cucumber and tomato ,and at 90% for lettuce (Lacutuca sativa L.) and cabbage. The air porosity values were 21 and 26%, respectively, under these conditions. 4) Cation exchange capacity affected leaching losses and plant absorption of nitrogen during the seedling raising period. However, cation exchange capacity did not affect the growth of tomato much during the seedling raising period and after transplanting. It was concluded that the cation exchange capacity of the growing substrates be maintained at a level of not less than 11 cmol(+)L^<-1> to ensure nomal plant growth.

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Nitrous oxide (N_2O) flux from a gray lowland soil cultivated for onion in Hokkaido, Japan, was measured during the growing season (from April to October) in 1995,1996 and 1997. The range of N_20 flux was from 0.03 to 20.9 mg Nm^<-2> d^<-1>. N_2O flux increased after summer when precipitation was high. The amount of N_2O flux and its ratio to fertilizer nitrogen were O.78 g N m^<-2> and 2.9% in 1995, 0.38g N m^<-2> and 1.1% in 1996 and 0.53g N m^<-2> and 1.9% in 1997. The maximum value of amount of N_2O flux and its ratio to fertilizer nitrogen was more than two times than the minimum value. The amounts of N_2O flux were in the high class category of published studies, which may be due to the lowland soil having a heavy texture. The contribution of nitrification to the N_2O emitted after mid-summer is considered to be relatively low.

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Soil maturation, the process of improving soil fertility and sustainability for crop production, is not fully understood in spite its importance. Hence, in order to elucidate the factors regulating soil maturation, the physicochemical properties of surface soils collected from reclaimed and ordinary farmlands were investigated in the Tango District, the northern part of Kyoto Prefecture, in 1996. Based on the results of the physicochemical properties of the soils, reclaimed farmland soils had higher EC and base content when compared with ordinary farmland soils. Ordinary farmland soils, on the other hand, had higher total C, biomass N and available P, indicating the storage of soil organic matter. As for the change in properties over time, organic matter content increased vehemently and became stable at a high level after a few decades. EC and base content increased during a couple of years, then varied depending on the soil management. C/N ratio remained around 10 regardless of the cultivation years. A multivariate analysis was carried out in order to determine the factors regulating soil maturation quantitatively. Firstly, a principal component analysis of 14 soil properties was carried out and 4 principal components were obtained. The first component was named 'organic matter factor (OMF)' based on its high factor loadings of total C, total N, available P, biomass N, degree of softness and cultivation years. The second component was named 'soluble nutrient factor (SNF)' for its high factor loadings of exchangeable Na, K and EC. The third and forth components were named 'nutrient holding factor (NHF)'and 'magnesium factor (MF)' for their high factor loadings of pH, exchangeable Ca, C/N ratio and CEC, and exchangeable Mg, respectively. Secondly, a stepwise multiple regression analysis was carried out using the scores of 4 factors as independent variables, with the degree of soil maturity (DM) determined on the field observation as a dependent variable. As a result, the following equation was obtained: (DM)=1.38×(OMF)-0,24×(SNF)+0.58×(NHF)-0.35×(MF)+2.83(R^2=0.80). In conclusion, high organic matter content, low soluble nutrient level and high nutrient holding capacity corresponded to a high degree of soil maturity.

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The effects of single basal co-situs application of polyolefin-coated urea (POCU) and ammonium sulfate (AS) on the yield and nutrient uptake of dent corn (Zea mays L.) in no-tillage (NT) and tillage (CT) cultivation were studied for four years (1995-1998) in Andisol. Yields of dent corn in the NT-POCU plot were the same or higher than those in conventional fertilization and CT-POCU plots. Yields in the NT-POCU plot were stable and high, while yields in the NT-AS plot changed under different climatic conditions. Under dry conditions, corn density in the AS plot decreased because of salt damage. Nitrogen uptake of dent corn in the NT-POCU plot was the same as that for the conventional fertilization and CT-POCU plots. Nitrogen uptake from soil in the NT-POCU plot was lower than that in the CT plot. However, nitrogen uptake from fertilizer in the NT-POCU plot was higher than that in the conventional fertilization and CT-POCU plots. In the no-tillage system, fertilizer nitrogen uptake in POCU plot was higher than that in the AS plot under dry and wet conditions. Nitrogen fertilizer recovery in dent corn of the NT-POCU plot ranged from 50 to 60%. In contrast, nitrogen fertilizer recovery in dent corn of the conventional fertilization and NT-AS plots ranged from 27 to 30% and 26 to 51%, respectively. Low recovery of fertilizer nitrogen in these plots was attributed to nitrogen leaching by rain. Accordingly, single basal co-situs application of POCU is a suitable fertilization method for the no-tillage cultivation of dent corn.

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In a no-tillage system, the application rate of herbicides increases more than the conventional tillage system. To lower environmental pollution, the application rate of herbicides needs to be reduced. The objective of this study was to investigate the effects of the co-situs application of controlled availability fertilizer and row app1liation of herbicides on the yield of dent corn (Zea mays L.) in comparison with the surface application of readily available fertilizer and whole or no herbicide application in no-tillage cultivation. Field experiments were conducted for two years (1998-1999) in Andisol. No herbicide application increased the biomass and nutrient uptake of weeds and decreased those of dent corn compared with the whole application of herbicides. In co-situs application plots, yield and nutrient uptake of dent corn tended to be higher than those in surface application plots. In the case of no application of herbicides, biomass and nutrient uptake of weeds in the row of co-situs application plots were increased more than those of the surface plots. Row application of herbicides reduced biomass and nutrient uptake of weeds per row compared with no herbicide application. A combination of co-situs fertilization and row application of herbicides increased the nutrient uptake of dent corn and yield compared with the no herbicide application or surface fertilization. As stated above, a combination of co-situs fertilization using controlled availability fertilizer and row application of herbicides is feasible to reduce the application rate of herbicides and to restrain reduced yields in no-tillage dent corn cultivation. However, the yield of this combination is less than that of the full application of herbicide because of the increase in weed biomass inter-row. This needs to be solved in the future.

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Three experimental plots were set up: 1. A conventional plot, where conventional plowing and piddling were practiced with the application of conventional doses of N-P-K as the basal and two top-dressings. 2. No-piddling plot, where conventional plowing without piddling was practiced before transplanting and all the N was applied to a nursery box in the form of a coated fertilizer (containing 30% N and 10% K_2O), with P and K supplemented as the basal dressing before plowing. 3. No-fertilizer plot, where plowing and piddling were practiced but neither fertilizers nor pesticides was applied. The leaf length, tillering number and yield of rice plants of the no-piddling plot were less than those of the conventional plot, but palatability was improved. The nutrient concentrations of surface, subsurface, irrigation and rainwater were measured in three plots. After cultivation, the contents of nitrogen and phosphate in the unhulled rice of three plots were measured. The nutrient loads of irrigation water, rainwater and fertilizer were counted as incoming factors into the paddy fields. The nutrient loads of surface water, subsurface water and unhulled rice yield were taken into account of the outgoing factors from the paddy fields. In the conventional plot, the incoming factors of nitrogen and phosphate were greater than their outgoing factors because of too much fertilizer. In the no-piddling plot, the incoming and outgoing factors of nitrogen were balanced because of a smaller amount of fertilizers than the conventional plot. In the no-fertilizer plot, outgoing factors were greater than the incoming factors, thus the nutrients in the soil were transferred into the unhulled rice.

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[in Japanese]

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