Masahiko Saigusa

The Nature, Properties and Management of Volcanic Soils

Abstract Soils formed in volcanic ejecta have many distinctive physical, chemical, and mineralogical properties that are rarely found in soils derived from other parent materials. These distinctive properties are largely attributable to the formation of noncrystalline materials (e.g., allophane, imogolite, ferrihydrite) containing variable charge surfaces, and the accumulation of organic matter. Formation of noncrystalline materials is directly related to the properties of volcanic ejecta as a parent material, namely the rapid weathering of glassy particles. The composition of the colloidal fraction forms a continuum between pure Al–humus complexes and pure allophane/imogolite, depending on the pH and organic matter characteristics of the weathering environment. For soil management purposes, volcanic soils are often divided into two groups based on the colloidal composition of the surface horizons: allophanic soils dominated by allophane and imogolite, and nonallophanic soils dominated by Al–humus complexes and 2:1 layer silicates. Volcanic soils exhibit a wide range of agricultural productivity, depending on the degree or intensity of pedogenic development and the colloidal composition of the rooting zone. The different charge characteristics of allophanic and nonallophanic soils is the most important factor regulating chemical fertility attributes. Phosphorus fixation, strong acidity, and aluminum toxicity are the primary chemical limitations to agricultural productivity. Volcanic soils generally have high physical fertility (tilth) and mature soils are relatively resilient to erosion and compaction. To maximize the productivity of volcanic soils, proper management based on an understanding of the unique physical, chemical, and mineralogical properties of these soils must be practiced.

CHEMISTRY AND CLAY MINERALOGY OF ANDO SOILS, BROWN FOREST SOILS, AND PODZOLIC SOILS FORMED FROM RECENT TOWADA ASHES, NORTHEASTERN JAPAN

We conducted chemical and clay mineralogical studies on Ando soils, Brown forest soils, and Podzolic soils that had been formed mainly from felsic Towada-a (1000 B.P.) and Chuseri (4000 B.P.) ashes under different climates and vegetation. Organic carbon accumulated remarkably in the humus horizons of all the soils and contributed to the high CEC of the soils. Soil acidity was observed to be in the order of Ando soils < Brown forest soils < Podzolic soils, reflecting the differences in base saturation and clay mineralogy of these soils, and to have a tendency to decrease with depth within the same profiles. Diagnostic properties of soil samples, such as pH(NaF), phosphate absorption, pyrophosphate-soluble Fe(Fep)/dithionite-citrate-soluble Fe(Fed), pyrophosphate-soluble Al(Alp)/dithionite-citrate-soluble Al(Ald), Fep + Alp/percent clay, Fep + Alp/Fed + Ald, etc., were studied in detail. None of these chemical criteria, however, could distinguish satisfactorily among Ando soils, Brown forest soils, and Podzolic soils formed from Towada ashes. It was noted that both Fep/Fed and Alp/Ald ratios increase with decrease in the soil pH(H2O). Notable differences in clay mineralogy were observed between soil groups. Ando soils had mostly clay fractions dominated by amorphous materials consisting mainly of allophane and imogolite. Nonexpansible chloritized 2:1 mineral, which was major among the crystalline clay minerals, was present in relatively large amounts only in the surface horizons. Brown forest soils showed a diversity in clay mineralogy within the same soil profiles. The clay fractions of the surface soils showed an abundance of chloritized 2:1 mineral with high expansibility and an absence of allophane and imogolite. The subsoils showed major amorphous and paracrystalline materials with minor 2:1 layer silicates. The clay fractions of the Podzolic soils, except those of IIB horizon soils, were characterized by the abundance of chloritized 2:1 mineral varying widely in expansibility and by the absence of allophane and imogolite. The IIB horizons from Chuseri ash had clay fractions dominated by amorphous materials consisting mainly of free iron and alumina. Laminar opaline silica was found in almost all the humus horizons and was relatively abundant in the modern humus horizons of Brown forest soils. We concluded that formation of allophane and imogolite, as well as chloritization of 2:1 layer silicates, is related primarily to soil acidity. Allophane and imogolite formed only in the soils having pH(H2O) >4.9, irrespective of differences in soil groups and soil horizons. The 2:1 layer silicates were considered to have formed largely by alteration of volcanic glass. Chloritization of 2:1 layer silicates was observed to proceed with formation of allophane and imogolite. The formation of laminar opaline silica in the surface soil was considered to be suppressed not only in the Ando soils containing large amounts of allophane and imogolite, but also in the Podzolic soils, which are subject to strong leaching.

Properties Of Nonallophanic Andosols From Japan

We studied various properties of nonallophanic Andosols in Japan. Our results showed that, despite many similarities between nonallophanic and allophanic Andosols, significant dissimilarities also exist between the two groups of soils. The nonallophanic Andosols used for our study formed from rhyolitic, dacitic, or andesitic volcanic ash in a humid temperature climate. They had distinctive morphological properties common to allophanic Andosols in Japan: (1) very dark, thick humus horizons, (2) granular structure in the humus horizons, (3) friable to very friable consistence, and (4) abrupt or clear smooth boundaries between humus and nonhumus horizons. The clay mineralogy of the nonallophanic Andosols was very different from that of the allophanic Andosols. In nonallophanic Andosols the clay fractions are mostly dominated by chloritized 2:1 minerals and the active Al (acid-oxalate-ex-tractable Al) consists largely or wholly of Al complexed with humus (pyrophosphate-extractable Al). The nonallophanic Andosols had mostly medium to fine textures and considerable high water retention at 15 bars. We noted that these soils have characteristically low bulk density, which is closely correlated with the organic carbon content. A remarkable accumulation of humus took place in the nonallophanic Andosols and was closely correlated with the formation of Al-humus complex. The high CEC of these soils was ascribed to the high humus content. We noted that nonallophanic Andosols are strongly acid to very strongly acid, reflecting the abundance of chloritized 2:1 minerals and the very low base saturation. Therefore, they had high Al saturation and large amounts of KCl-exchangeable Al, which is a major deterrent to plant growth in the soils. The average values of Al saturation and KC1-ex-changeable Al were 74.4% and 5.51 meq/ 100 g for humus horizon soils and 59.8% and 3.50 meq/100 g for nonhumus horizon soils, respectively. Almost all the nonallophanic Andosol samples had pH (NaF) >10 and phosphate retention > 85%. These values were significantly correlated with the acid-oxalate-extractable Al (Alo). Soils containing > 1% Alo have pH (NaF) > 9.4 and phosphate retention >85%. Therefore, we noted that Al complexed with humus has a significant amount of OH groups and is highly reactive. The analysis of pyro-phosphate-soluble components indicated that the humus associating with Al and Fe consists largely or wholly of humic acid with the highest degree of humification.

Relationship between chlorophyll content in leaves of sorghum and pigeonpea determined by extraction method and by chlorophyll meter (SPAD-502)

ABSTRACT The estimation of chlorophyll content in leaves by the chlorophyll meter (SPAD 502) is more convenient than by the extraction method for studies on photosynthesis or senescence where the total chlorophyll is estimated on the same leaf over time. This study was to test hypothesis that specific leaf weight (SLW) appears to be one of the factors determining SPAD index under different conditions. The influence of SLW on SPAD index and an improved simple method to determine chlorophyll content of sorghum and pigeonpea by a chlorophyll meter was studied. The results indicated that regression lines were significantly different between sorghum and pigeonpea, and at the vegetative and physiological maturity stages in each crop. Residuals of simple regressions calculated from all data of each crop were correlated with SLW. Multiple-regression with SPAD index as the dependent variable, and chlorophyll content and SLW as the independent variables gave the best estimation of chlorophyll content in leaves of sorghum and pigeonpea. These results suggest that SLW is an important factor affecting SPAD index and the influence of SLW on SPAD index can vary with crop species. Devices for estimating SLW could be incorporated into the chlorophyll meter to provide SPAD values adjusted for SLW. Further investigation is required on the influence of SLW on SPAD index for other crops.

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.

PLANT ROOT GROWTH IN ACID ANDOSOLS FROM NORTHEASTERN JAPAN: 2. EXCHANGE ACIDITY Y1 AS A REALISTIC MEASURE OF ALUMINUM TOXICITY POTENTIAL

Chemical and greenhouse studies were conducted to show that exchange acidity Y1, determined by titration of 125 ml of N KC1 soil extract (soil:N KC1 = 100:250) with 0.1 N NaOH, was a useful, realistic measure of aluminum toxicity potential in acid Andosols from northeastern Japan. Twenty-eight soil samples consisted of allophane-imogolite soils (11 samples; pH(H2O) 4.6 to 5.9, Y1 0.4 to 3.1 ml/100g), chloritized 2:1 mineral soils (13 samples; pH(H2O) 3.9 to 5.0, Y1 6.8 to 38.2 ml/100g), and allophane-imogolite-chloritized 2:1 mineral soils (4 samples; pH(H2O) 4.6 to 5.3, Y1 3.3 to 5.0 ml/100g). Three test plants, burdock cv. Takinogawa (Arctium lappa), barley cv. Norin-24 (Hordeum vulgare), and dent corn cv. Choko-1 (Zea mays), were grown on these soils in a greenhouse, and their root length and acid-injury were observed. Root length of all the test plants had a significant relationship with exchange acidity Y1, shown by exponential equations. Degrees of acid-injury determined by root length and root morphology were also closely related to exchange acidity Y1. Chloritized 2:1 mineral Andosols had “critical” pH(H2O) of about 5.0 and “critical” pH(KCl) of about 4.5, whereas allophane-imogolite Andosols did not have these “critical” pHs and did not restrict the root growth greatly even at low pH(H2O), such as 4.6. Acid substances relating to exchange acidity Y1 were found to consist mainly of Al3+ ions whose amount was closely correlated with total exchangeable Al. A comparative study of exchange acidity Y1, pH(H2O), pH(KCl), fluoride-reactive Al, etc., showed that exchange acidity Y1 was a useful realistic measure of aluminum toxicity in the acid Andosols.

Transgenic rice lines that include barley genes have increased tolerance to low iron availability in a calcareous paddy soil

Abstract Iron (Fe) deficiency stress is a widespread problem in agriculture and must be overcome to increase crop yields, particularly in calcareous soils. Unlike barley, rice, one of the three major crops in the world, is very susceptible to low Fe availability because of a low capacity to secrete mugineic acid family phytosiderophores (MAs), which are Fe chelators secreted by graminaceous plants. We tested three transgenic rice lines possessing three barley genes involved in MAs synthesis in a field experiment on a calcareous soil under paddy conditions. Two rice lines, one with a barley gene encoding nicotianamine synthase (NAS) and the other with a barley gene encoding a dioxygenase, referred to as Fe-deficiency specific clone no. 3 (IDS3), showed higher tolerance to low Fe availability under these conditions. The rice line with the IDS3 gene also had increased concentrations of Fe and zinc (Zn) in the grains. These results show that introducing barley genes involved in the synthesis of MAs into rice is an effective and practical method to improve agricultural productivity in calcareous soils.

Properties of Spodosols and Andisols showing climosequential and biosequential relations in southern Hakkoda, northeastern Japan

We conducted comparative studies on the chemical and mineralogical properties of selected pedons of Spodosols (Placorthods) and Andisols (Fulviudands and Melanudands) derived from Towada-a ash of 1000 B.P. and Chuseri ash of 5000 B.P., Spodosols and Fulviudands of the climosequence showed most remarkable differences in such chemical properties as soil acidity, fluoride and phosphate reactivity, humus accumulation and composition, and clay mineralogy, chiefly in noncrystalline aluminosilicates. Fulviudands and Melanudands, however, having a biosequential relation, showed contrasting differences mainly in the properties of soil humus. Spodosols showed remarkable accumulations of Fe and Al and also displayed the existence of placic horizon. Nevertheless, one of the two Spodosols did not meet the chemical criteria for a spodic horizon. Both Andisols and Spodosols satisfied the andic properties. In this paper we also discuss Spodosol-Andisol transition problems and propose some solutions.

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.

Aluminum release rates from allophanic and nonallophanic Andosols

Abstract Aluminum release rates were studied for subsoil horizons of allophanic and nonallophanic Andosols and for imogolite gel films. Release rates were determined using a stirred, flow-through reaction vessel with a 10−3 M acetate buffer adjusted to pH 3.3, 3.8, or 4.2. To determine the sources of dissolved AI, soils were pretreated with Kel, Na-pyrophosphate, citrate-bicarbonate-dithionite, and acid oxalate to remove various solid-phase pools of active AI. Rates of Al release for imogolite gel films during the first minute of reaction ranged from 74.8 nmol/gls at pH 4.2 to 113.3 nmol/g/s at pH 3.3. Rates of AI release for nonallophanic Andosols were greater than for allophanic Andosols due to the rapid release of exchangeable Al from nonallophanic Andosols. Aluminum release rates showed fractional order H+ -dependence ranging from 0.23 to 0.54. The primary source of dissolved Al in allophanic Andosols was from AI-humus complexes and allophane/imogolite. In nonallophanic Andosols, exchangeable Al and A...