Rapid, Micro-Methods to Estimate Plant Silicon Content by Dilute Hydrofluoric Acid Extraction and Spectrometric Molybdenum Method

By treating 0.5 g DW of a plant sample directly with 10 ml of a dilute hydrofluoric acid solution (HF solution, 1.5 M HF—0.6 M HCl), all the silica in plant (as much as 150 mg SiO₂) was dissolved within 1 h. After dilution of the extract with 40 mL of distilled water, the silica in the extract was measured by the spectrometric molybdenum yellow method. The molybdenum yellow method, in which silica in 0.1 mL of the diluted extract can be determined in 8 min, is well suited to rapid, micro-estimations of the silica content in plants. In the micro-modification, the size of the plant sample was reduced to 100 mg DW. The analytical procedure was simple, and the analytical time was less than 2 h. The method can save much labor and time, compared with the gravimetric analysis. The dissolution with HF solution and the molybdenum yellow method were also applied to the measurement of the content of silica separated by acid digestion of rice plants. Excellent agreement in the silica measurement of rice plants was confirmed among the direct extraction method, the gravimetric method and the digestion-separation-dissolution method. In the molybdenum yellow method, the addition of boric acid enabled to mask the interference of hydrofluoric acid, and the least amount of citric acid required for the elimination of phosphorus interference was proposed. In conclusion in this report, recommended methods for the rapid estimation of the silica content in rice plants were presented.     

Effect of Application of Acidified Porous Hydrate Calcium Silicate and Porous Hydrated Calcium Silicate on the Growth of Rice Plants (Oryza sativa L.)

The effect of the application of acidified porous hydrate calcium silicate (APS) in nursery bed soil and porous hydrate calcium silicate (PS) in paddy fields on the growth of rice plants ( Oryza sativa L. cv. Hitomebore) was examined in 2002 and 2003. The results revealed the following: 1) Shoot dry weight of rice seedlings increased by APS treatment in nursery bed soil. The tiller number of rice plants after transplanting in both years also increased by APS treatment in nursery bed soil, and in 2003, the tiller number in the treatment with a combination of APS in nursery bed soil and PS in paddy fields was significantly higher than that in the other treatments until the maximum tiller number stage. Furthermore, the root length of rice plants 14 d after transplanting increased by APS treatment in nursery bed soil. 2) Silicon concentration in the soil solution significantly increased by PS treatment in paddy fields, and the concentration of dissolved carbon oxide increased by APS treatment in nursery bed soil. 3) Only in the APS treatment the rice yield was 341 g m⁻², while 400 and 450 g m⁻² in the PS and both APS and PS treatments, respectively, in 2003. Percentages of ripened grains in the plots without PS treatment ranged from 57 to 63%, respectively, while, those in the PS treated plots were 82%. The numbers of panicles and ripened grains in both APS and PS treatments were the highest among the treatments. Based on the above results, we concluded that both APS in nursery bed soil and PS in paddy field treatments were effective in improving the silicon nutrition and growth of rice plants, and that this effect was enhanced by a combination of treatments with the two.     

Co-situs application of controlled-release fertilizers to alleviate iron chlorosis of paddy rice grown in calcareous soil

Abstract

Co-situs is the placement with one application of a sufficient amount of controlled-release fertilizer for an entire growing season at any site, together with seeds or seedlings, without causing fertilizer salt injury. An experiment was conducted to find an efficient method for ameliorating Fe deficiency in two rice cultivars (cv. Tsukinohikari and cv. Sasanishiki) grown in a calcareous soil (pH 9.2, CaCO₃ 384 g kg^?1), which was poor in organic matter (0.1 g kg^?1) and available Fe (3.0 μg g^?1 soil). The field treatments consisted of co-situs application of the following fertilizers: 1) controlled-release NPK fertilizer (CRF-NPK) containing no micronutrients; 2) controlled-release NPK fertilizer containing micronutrients (CRF-M1); and 3) controlled-release NPK fertilizer containing micronutrients (CRF-M2). The main difference between CRF-M1 and CRF-M2 was that the former had larger granules than the latter. All the fertilizers were placed in contact with the roots of rice seedlings at transplanting time. Plants in the CRF-M1 and CRF-M2 treatments had similar lengths, number of stems, leaf age, and leaf color (SPAR value) during the cultivation period. By contrast, plants from the CRF-NPK treatments grew poorly, showed severe chlorosis symptoms of Fe deficiency, and all died on 30 DAT. Plants of both cultivars accumulated more macroand micronutrients with the CRF-M2 treatment than with the CRF-M1 treatment. The grain yield of cv. Tsukinohikari was 0.0, 1,910, and 2,160 kg ha^?1 for the CRF-NPK, CRF-M1, and CRF-M2 treatments, respectively, and 0.0, 2,490, and 2,860 kg ha^?1 for the same treatments for cv. Nihonbare. Chlorosis due to iron deficiency was successfully ameliorated and world-average grain yields were obtained with the co-sites application of both controlled-release fertilizers.     

Effects of polyolefin‐coated fertilizer on nutritional quality of spinach plants

Pot experiments were conducted in order to evaluate the effects of four different urea or ammonium containing polyolefin‐coated fertilizers (POCFs) on the nutritional quality of spinach (Spinacia olèracea L.) and to investigate the mechanisms of these effects in comparison with conventional, rapidly available fertilizer. Compared to the conventional fertilization method yield was decreased in all the four POCF treatments due to less available fertilizer nitrogen (N) and/or realized ammonium nutrition. However, application of POCFs decreased oxalate and nitrate contents and increased ascorbate concent in spinach. Decreased oxalate and nitrate contents were attributed to lower nitrate availability in the soil having caused by the controlled‐released characteristic of POCFs and/or ammonium nutrition. Increased ascorbate content was due to both decreased oxalate and decreased nitrogen contents of the spinach plants. It was concluded that band applications of urea or ammonium containing POCFs improved the nutritional quality of spinach due to realized ammonium nutrition and/or less amount of available fertilizer N.     

Occurrence of laminar opaline silica in some Oregon Andosols

Laminar opaline silica was first found in the 0.2 to 5 μ fraction and most abundant in the 0.4 to 2 μ fractions of young Japanese Andosols by Shoji and Masui (1969a, b). It was noted that the A horizon of a profile tends to be relatively rich in opaline silica whereas the B or C horizon, in allophane (Shoji and Masui, 1972a, b). They (I972a) distinguished four types of opaline silica particles such as circular, elliptical, rectangular, and rhombic, of which the circular and elliptical types predominate. It has been suggested that the formation of opaline silica is favored by a plentiful supply of soluble silica in the early weathering stage of Andosols, the supersaturation of silica by surface evaporation of soil solution, and the suppression of aluminum activity in the soil solution by the accumulation of soil organic matter (Shoji and Masui, 1972b; Wada and Harward, 1974). The purpose of the present short communication is to describe the occurrence of laminar opaline silica particles in some Oregon Andosols, U.S.A.     

Chemical and morphological changes of porous hydrated calcium silicate in paddy soil

The chemical and morphological changes of porous hydrated calcium silicate material (PS) during the dissolution process in paddy soil were investigated by using both a scanning electron microscope (SEM) and an energy dispersive X-ray (EDX) analysis. The results showed that original PS consisted of agglomerate of various sizes with almost the same elemental composition. The SEM images at a high magnification showed that the original PS consisted of agglomerates of small platelike crystals (≦ μm) of tobermorite [Ca₅(Si₆O₁₈-H₂)·4H₂O]. On the other hand, elemental composition showed that the PS agglomerates in paddy soil altered to Si- and Ca-rich agglomerates after incubation for 53 d. The morphological differences between the two types of agglomerates were observed by SEM at a high magnification. The Si-rich agglomerates were similar to the original PS in morphology, whereas the Ca-rich agglomerate appeared as a large crystal. The X-ray diffraction patterns obtained in a previous study suggested the presence of quartz and calcite in PS after incubation for 53 d (Saigusa et al. 2000: Soil Sci. Plant Nutr., 46, 89–95). Si- and Ca-rich agglomerates were identified as silica skeletons of PS and calcite, respectively. It was suggested that the silica skeletons of PS remained as a silicon source for rice plants even after the disappearance of tobermorite revealed by the X-ray diffractogram.     

Increase in Iron and Zinc Concentrations in Rice Grains Via the Introduction of Barley Genes Involved in Phytosiderophore Synthesis

Increasing the iron (Fe) and zinc (Zn) concentrations of staple foods, such as rice, could solve Fe and Zn deficiencies, which are two of the most serious nutritional problems affecting humans. Mugineic acid family phytosiderophores (MAs) play a very important role in the uptake of Fe from the soil and Fe transport within the plant in graminaceous plants. To explore the possibility of MAs increasing the Fe concentration in grains, we cultivated three transgenic rice lines possessing barley genome fragments containing genes for MAs synthesis (i.e., HvNAS1, HvNAS1, and HvNAAT-A and HvNAAT-B or IDS3) in a paddy field with Andosol soils. Polished rice seeds with IDS3 inserts had up to 1.40 and 1.35 times higher Fe and Zn concentrations, respectively, compared to non-transgenic rice seeds. Enhanced MAs production due to the introduced barley genes is suggested to be effective for increasing Fe and Zn concentrations in rice grains.     

Evaluation and improvement of MODIS gross primary productivity in typical forest ecosystems of East Asia based on eddy covariance measurements

Gross primary productivity (GPP) is a major component of carbon exchange between the atmosphere and terrestrial ecosystems and a key component of the terrestrial carbon cycle. Because of the large spatial heterogeneity and temporal dynamics of ecosystems, it is a challenge to estimate GPP accurately at global or regional scales. The 8-day MODerate resolution Imaging Spectroradiometer (MODIS) GPP product provides a near real time estimate of global GPP. However, previous studies indicated that MODIS GPP has large uncertainties, partly caused by biases in parameterization and forcing data. In this study, MODIS GPP was validated using GPP derived from the eddy covariance flux measurements at five typical forest sites in East Asia. The validation indicated that MODIS GPP was seriously underestimated in these forest ecosystems of East Asia, especially at northern sites. With observed meteorological data, fraction of photosynthetically active radiation absorbed by the plant canopy (fPAR) calculated using smoothed MODIS leaf area index, and optimized maximum light use efficiency (ε _max) to force the MOD17 algorithm, the agreement between predicted GPP and tower-based GPP was significantly improved. The errors of MODIS GPP in these forest ecosystems of East Asia were mainly caused by uncertainties in ε _max, followed by those in fPAR and meteorological data. The separation of canopy into sunlit and shaded leaves, for which GPP is individually calculated, can improve GPP simulation significantly.     

Amelioration of Cadmium Polluted Paddy Soils by Porous Hydrated Calcium Silicate

Porous hydrated calcium silicate (PS) is a by-product of autoclave light weight concrete and is being used as a silicon fertilizer in Japan. The impacts of this amendment on the yield and cadmium content of rice (Orzya sativa L. var. Kokoromachi), soil pH and the extractability of soil cadmium assessed by 1 M NH₄OAc were compared with those of silica gel and CaCO₃ by pot experiments. The application of PS at the rate of 2.0% and silica gel at the rate of 1.0% in Andosol and PS at the rate of 0.75% in Alluvial soil significantly increased the grain weight of rice. PS and CaCO₃ treatment significantly increased soil pH, decreased the 1 M NH₄OAc extractability of cadmium and reduced cadmium content in straw and brown rice in the two soils. However, cadmium content of rice of PS treatments was not significantly different from that of CaCO₃ treatments in Andosol, while was significantly lower than that of CaCO₃ treatments in Alluvial soil. Soil analysis showed that it was less effective in increasing soil pH and decreasing the extractability of cadmium by 1 M NH₄OAc than CaCO₃ at the same application rate in Andosol. Soil pH and 1 M NH₄OAc extractability of cadmium were not significantly different between 2.0% of PS and CaCO₃ treatments in Alluvial soil. The application of silica gel did not improve soil pH nor decrease the extractability of soil cadmium, but resulted in a significant decline of cadmium content in brown rice. These results demonstrate that the supply of silicon together with an increase in soil pH, as obtained by PS application, shows potential to reduce the cadmium content of rice.