We examined factors of soil nitrogen mineralization in the middle and later part of rice growth (after July), and obtained the following results. 1. For Gray Lowland soil, coefficient of determination in a simple regression analysis was about 0.7. This analysis was between the cumulative effective temperature and the soil liberalization in the middle and later part of rice growth, but the coefficients of determinations for the other soils were below 0.55.2. In strong Gley soils and Ando soils, more soil nitrogen was released in the middle and later part of rice growth than in the early growth stages. In strong Gley soils and Gray Lowland soils, the soil nitrogen released in the middle and later part of rice growth was almost the same as the soil nitrogen released in the earlier growth stages. In Peat soils and Muck soils, far more soil nitrogen was released in the earlier growth stages. 3. The annual fluctuation of nitrogen released in the middle and later stages of growth was lower than the estimated soil nitrogen in the earlier stages. However the annual fluctuation of soil nitrogen in the middle and later stages is relatively greater between the maximum tiller number stage and reduction division stage ; this might be influenced by the length of the rainy season and so on. 4. The nitrogen mineralization in the middle and later stages of rice growth was estimated using cumulative effective temperatures and soil moisture. With rainfall details from March and April, temperature and moisture levels were estimated using a multiple regression method.

View full abstract

Fertilizers coated with polyolefin resin are characterized by controlled release rates of nutrients, and are leading to improved fertilizer-use efficiency and reduced labor. However, the coating material remains as a residue in the soil after the release of nutrients. In the present study, a new coating material was developed by adding polyolefin resin (SGS) including 2% Feacethylacetonate and 0.2% Ni-dibutyldithiocarbamate in order to promote light oxidation of the coating material and its biodegradation. The patterns of release of nutrients into water from fertilizer coated with SGS-polyolefin, were similar to the nutrient release patterns from coated fertilizer without SGS addition. Similar nutrient release patterns from the coated fertilizers with and without SGS were also observed when fertilizers were either applied to the surface of soil with or without 50% shading, or embedded in soil. These results indicated that addition of SGS did not affect the patterns of release of nutrients. The fertilizer coated with SGS-polyolefin was found to be broken down easily after a one-year exposure to natural light and the proportion of compounds having less than 3,000 molecular weight was increased to 38%, which was twice that of the fertilizer without SGS. During a 39-month exposure to natural light, the peak molecular weight of polyolefin with SGS decreased from 35,500 to 1,700,indicating strongly that addition of SGS polyolefin promoted the light oxidation and subsequent decomposition of polyolefin. Bacteria were screened from Japanese soils using 34-month exposed SGS-polyolefin resin as a sole carbon source. Nine species of bacteria were isolated and identified as Pseudomonas sp., Sphingomonas sp. and Acinetobacter sp. Only the compounds with molecular weights less than 3,000 in SGS polyolefin were utilized by these bacteria as a sole carbon source. From these results, the maximum concentration of residual coating material with SGS polyolefin in soil was estimated to converge to 0.63 kg m^<-3> after 120y, under the typical condition of cultivation.

View full abstract

We found the phenomenon that insolubilized polymer accumulated as an impermeable layer in a soil, when an aqueous solution of the polymer with carboxyl groups such as polyacrylic acid percolated into the soil. We conducted the layer formation in a soil column with various compositions of the polymer solution, and studied the effects of the preparation condition of polymer solution on the formative phenomenon of the impermeable layer. The results are as follows.1. An impermeable layer was formed deeper in a soil as the polymer concentration of the solution decreased or the neutralization ratio of the carboxyl groups of the polymer increased. We can use these results to control the depth of the impermeable layer in a soil from soil surface to 100cm.2. The amount of the polymer solution needed to form an impermeable layer increased as the polymer concentration decreased or the neutralization ratio of the carboxyl groups increased. The amount of the polymer solution varied in proportion to the depth of the impermeable layer in a soil.3. It was suggested that 0.7-1.0 kg m^<-2> of the polymer in the solution reached to the depth of the impermeable layer and 0.3 kg m^<-2> of the polymer became the element of the impermeable layer.4. Addition of salts to the polymer solution made the impermeable layer form at a more shallow level in a soil.5. Polyacrylic acid with an average molecular weight over 100,000 was able to form the impermeable layer in a soil, but that with an average molecular weight below 20,000 was not able to form it.

View full abstract

We found a phenomenon that, when an aqueous solution of a polymer having carboxyl groups such as polyacrylic acid is percolated into soil from its surface, insolubilized matter of the polymer accumulates as a membrane in the soil resulting in an impermeable layer. We carried out experiments of the layer formation in soil columns on various soil conditions, and investigated effects of soil codition on the formative phenomenon of the impermeable layer. The results are as follows. 1. The impermeable layer was formed deeper in a soil as the packing density of the soil decreased, and the layer did not form in soil with a bulk density below a certain value.2. Regardless of the water content of a soil, the impermeable layer was formed at the same depth in the soil.3. Formation of the impermeable layer seems to require the following two conditions : one is that the amount of exchangeable calcium ion of the soil is 1 cmol(+) kg^<-1> or more and the other is that permeability of the soil is not too low.4. The less exchangeable calcium there was in a soil, the deeper the impermeable layer formed in the soil ; when the amount of exchangeable calcium was less than 1 cmol(+) kg^<-1>, the layer was not formed in the soil.5. The impermeable layer was not formed in Tottori sand dune soil because of a small amount of exchangeable calcium in it, 0.3 cmol(+) kg^<-1>. When calcium ion was added to Tottori sand dune soil to the extent of 0.9 cmol(+) kg^<-1>, the impermeable layer came to be formed in the soil.6. When the polymer solution was fed into a hollow of a soil surface and it percolated into the soil without the effect of a wall of a soil column, a hemispheric impermeable layer was formed in the soil.7. In a layered soil having a lower layer of fine soil particles, the impermeable layer was formed at the depth in the soil above or just at the boundary of layers, and it was not formed below the boundary. This result shows that the impermeable layer is formed by filtrating the solution with insolubilized polymer.8. The impermeable layer seems similar to the spodic horizon formed in nature. In both phenomena, an aqueous solution of organic substances infiltrates or percolates into a soil from its surface, the organic substances accumulate in a soil with polyvalent cations, and the organic substances have carboxyl groups.

View full abstract

The spatial distribution of soil solution chemistry was investigated in a 40 years-old Japanesecedar stand of 0.25 ha with a slop of 20°. This area was divided into 25 systematic plots of 10m×10m, and at each plot soil solutions were sampled from depths of 10cm and 100cm with ceramicsuction lysimeters on three dates in August, September and October 2000. The solutions wereanalysed for major cations and anions.The results obtained were follows : 1) The dominant ion species for soil solutions at the depth of 10cm (referred to as 10cm samples) and 100cm (referred to as 100cm samples) were NO_3^- and Ca^<2+>. NO_3^- concentration for 10cm samples was always higher than the sum of NO_3^- and NH_4^+ concentration for throughfall. This suggests that mineralization of organic nitrogen followed by nitrification occurred in all plots within the slope. High NO_3^- concentration for 100cm samples would be caused by insufficient uptake of NO_3^- generated in surface soil.2) Highest variations were observed for H^+ and HCO_3^- for 10cm samples, and for K^+ and SO_4^<2-> for 100cm samples. For 10cm samples, higher H^+ and lower HCO_3^- concentration was observed at plots located in the upper slope. On the other hand, K^+ and SO_4^<2-> concentration for 100cm samples had random distribution within the slope.3) In most plots, ion concentration for 10cm samples was the most lowest in September when heavy rain occurred. In contrast, the temporal variation of ion concentration for 100cm samples was smaller than that for 10cm samples. In the concave plots, however, a larger temporal variation of NO_3^-, Cl^- , Ca^<2+> and Mg^<2+> concentration was observed. This must have been mainly because the ratio of verticalflow and throughflow coming into the concave plots was changed by precipitation strength.

View full abstract

Mounitoring of water quality and trihalomethane formation potential (THMFP) of ground waters (30m for No.1 well, 25m for No.2 well) of an agricultural area of humic volcanic soil on Shirasu plateau where livestock wastes have been applied, was carried out with twelve monthly samplings for one year to ascertain the characteristics of water quality and THMFP. For a comparison, water of a mountain stream running out from the neighboring hillside was also analyzed for both water quality and THMFP. 1) Concentration of some inorganic ions, particularly of NO_3^- , suggested that the ground water of both wells was contaminated with inorganic solutes by the agricultural activities, though the origin of the contamination was not clearly ascertained by this study. Furthermore, the seasonal changes in concentration of Cl^- and Na^+ in No.1 well, which were synchronized with that of NO_3^- , suggested that the ground water of No.1 well was more strongly affected by livestock waste application than No.2 well. As a whole, from the ionic composition, particularly from the key-diagram analysis for water quality understanding, it was inferred that the ground water of both wells was affected by agricultural activities on the ground surface. 2) Concentration of the precursor of trihalomethane (THM), i.e. DOC, were 0.59mg L^<-1> as mean value for ground water of the No.1 well, 0.69mg L^<-1> for the No.2 well, and 0.73mg L<-1> for mountain stream water, implying that the ground waters seemed to be not contaminated with organic matter, as contrasted to some contamination with inorganic materials, even though the organic livestock wastes had been applied on the ground surface. 3) The optical density of water at 1cm pass length of 260nm (OD_<260>) for unit weight of DOC(mg) was much smaller for the ground water than for the mountain stream water, suggesting that the organic matter in the ground water was less humificated than that of the mountain stream water. 4) THMFP of ground water was 4.11μg L^<-1> as mean value for well No.1,and 4.76μg L^<-1> for well No.2,and never exceeded the governmental guideline for drinking water of 100μg L^<-1> as the total. The value for mountain stream water was 10.7μg L^<-1>, indicating that the ground water has much smaller formation potential for trihalomethanes. 5) THMFP of unit weight of DOC (mg) was 7.1,6,9 and 14.7μg for well No.1,well No.2 and mountain stream water, respectively, indicating that organic matter of the ground water had much smaller potential than that of the mountain stream water. The difference between the ground water and the surface water was supposed to be the difference in the degree of humification of organic matter as described above. 6) However, the THMFP for these samples, including the mountain stream water, for unit of optical density measured at 260nm (OD_<260>) by 10mm optical path length was quite similar. Moreover, THMFP (Yμg L^<-1>) was well correlated to the OD_<260> (X) as follows : Y=1038.5 X (r=0.916,n=36) 7) The composition of THM produced from the ground water was characterized by a relatively higher proportion of Br containing species, particularly of CHBr_2Cl and CHBr_3 than the mountain stream water. It was reasoned that the ground water had smaller ratio of DOC/ Br^- than the mountain stream water.

View full abstract

The citric- and water-solubilities and mineral composition of fused potassium silicate fertilizer produced in the steelmaking process were examined by chemical and X-ray diffraction methods. The formation of K_2Ca_2Si_2O_7 was analyzed in terms of the reaction of potassium carbonate with the slag, whose CaO/SiO_2 mole ratio was about 0.8. The amount of K_2Ca_2Si_2O_7 formed reached a maximum, when the K_2O/SiO_2 mole ratio was about 0.4,resulting in minimization of water-solubility of potassium to about 13%. In the case of using slag whose CaO/SiO_2 mole ratio was about 1,the water-solubility increased to 17%. The citric-solubility of potassium was higher than 90% for any K_2O/SiO_2 mole ratio. In the experiment with the K_2O-CaO-SiO_2 system reacting at 1,150℃, the amount of K_2Ca_2Si_2O_7 formed was maximum when the K_2O/SiO_2 mole ratio was about 0.5 and the CaO/SiO_2 mole ratio was about 1. The water-solubility of potassium decreased to a minimum of 10%. A higher CaO/SiO_2 mole ratio caused the formation of β-Ca_2SiO_4 and water-soluble amorphous potassium silicate in part, and a lower CaO/SiO_2 mole ratio caused the formation of K_2SiO_3 in part, resulting in an increase in water-solubility. The citric-solubility of potassium was higher than 90%, and a part of potassium was adsorbed into gelatinous silica formed during the weakly acidic dissolution experiment. On substituting magnesium for a part of calcium in K_2Ca_2Si_2O_7,the water-solubility increased because of the formation of K_2MgSiO_4. In the case of adding manganese instead of magnesium, the water-solubility did not increase as mentioned above, because of forming a solid solution substituted manganese for at most about 10% of the calcium in K_2Ca_2Si_2O_7.

View full abstract