Lowland Paddy Soils Research Articles

Properties of non-humic substances of fulvic acids fractionated by ethanol precipitation

Abstract The PVP-non-adsorbed fulvic acids (FAs), which are non-humic substance fractions of FAs, were fractionated by precipitation from an aqueous solution upon gradual addition of ethanol. The amount of precipitate increased exponentially with the increase of the ethanol concentration, and one-third of these fractions was soluble in a 90 × 10-2 L L-1 ethanol solution. The characteristics of the fractions suggested that the non-humic substances of FAs consisted of a variety of materials differing in their chemical composition and molecular size. Saccharide contents, elementary composition and IR spectra indicated that the contents of aliphatic chains and carboxyl groups as well as the degree of unsaturation were higher in the fractions precipitated at a higher ethanol concentration. The reverse was true for the contents of saccharides and peptides as well as the molecular size distribution. Differences in the saccharide contents and IR spectra among the sub-fractions were most conspicuous in the samples obtained from the brown forest soil, while they were attenuated in the samples from the lowland paddy soil. However, the elementary composition and molecular size distribution were also clearly different in the sub-fractions from the lowland paddy soil.

Ethanol-soluble and insoluble fractions of humic substances in soil fulvic acids

Abstract Humic substances in fulvic acids (FAs) obtained as polyvinylpyrrolidone (PVP)-adsorbed fractions were further fractionated based on their solubility in ethanol. Elementary composition, IR spectra, UV-Vis spectra, saccharide contents, molecular size distribution, and 13C-NMR spectra were clearly different between the ethanol-soluble and the insoluble fractions. The yield of the ethanol-soluble fractions exceeded 80%. These fractions showed higher aromatic-and carbonyl-C contents than the insoluble fractions. The differences in the signal intensities of phenol or aryl ether C1 and methoxyl groups in the 13C-NMR spectra (lowland paddy soil > brown forest soil > ando soil) as well as the aromatic-C contents (lowland paddy soil > ando soil > brown forest soil) of these fractions among the three soils suggested that the content and composition of the aromatic components varied depending on the soil types. Saccharides and nitrogen compounds were mainly distributed in the ethanol-insoluble fractions and ...

Ethanol-soluble and insoluble fractions of non-humic substances in soil fulvic acids

Abstract The non-humic substances in fulvic acids (FAs) of three Japanese soils were obtained as the non-adsorbed fraction through a column of insoluble polyvinyl-pyrrolidone (PVP), and this fraction was further fractionated based on the solubility in ethanol. Although the yield of the ethanol-soluble fractions from the PVP-non-adsorbed FAs was 5–7%, the analytical data indicated that their chemical structure was clearly different from that of the ethanol-insoluble fractions. The ethanol-soluble fractions were characterized by low average molecular weights, low saccharide contents and strong peaks for aliphatic C-H, alcoholic C-O, and carboxyl groups in the IR spectra. The 13C-NMR spectrum of this fraction in the ando soil that was determined quantitatively also showed strong peaks for the long alkyl chain, secondary alcohol or aliphatic ether, and carboxyl groups. The main constituents of the ethanol-insoluble fractions consisted of polysaccharides. Contents and composition of saccharides, however, varied depending on the soil types. Pentose content of the insoluble fraction was very high in the lowland paddy soil, and the uronic acid content was higher in the ando soil than in the other two soils. The carbohydrate-C content of the insoluble fractions estimated from 13C-NMK spectra was in the order of lowland paddy soil, ando soil, and brown forest soil. The aliphatic-C content was in the opposite order. These findings suggested that abundant plant components remained in the FA of the lowland paddy soil while many aliphatic components were incorporated into the FA of the brown forest soil.

Fractionation of soil fulvic acids using polyvinyl -pyrrolidone and their lonization difference spectra

Abstract Fulvic acids were divided into adsorbed brown fractions and non-adsorbed. pale-yellow fractions using insoluble polyvinylpyrrolidone (PVP) as an adsorbent. The distribution pattern of the two fractions varied with the types of soils. The yield of the PVP-adsorbed fraction was higher in the order of brown forest soils, ando soils, and lowland paddy soils and red-yellow soils. The difference spectra between pH 12 and pH 7 (ΔE 7-12 spectra) and those between pH 7 and pH 3 (ΔE 3-7 spectra) of the PVP-adsorbed fractions were classified into three types corresponding to the types of soils. The ΔE 7-12 spectra of the PVP-adsorbed fractions and humic acids obtained from the same soil were similar. In the PVP-non-adsorbed fractions, both the ΔE 7-12 and ΔE 3-7 spectra did not clearly differ among all soils.

Variability in growth and nutrient accumulation in sorghum grown in waterlogged soils

Abstract Sorghum [Sorghum bicolor (L.) Moench] is a potential crop for use in lowland paddy soils following rice in the Philippines. Little is known about the variability in sorghum germplasm with respect to yield potential in these soils, or the alterations in mineral uptake which might occur if late season rains resulted in waterlogging. Eight sorghum cultivars including the most widely used Philippine cultivar were grown after rice under flooded or non‐flooded conditions. Flooding was initiated 30 days after seeding and terminated when most cultivars were at or near the boot growth stage. Flooding markedly reduced dry matter production, and delayed bloom date on the average of 5.5 days. Grain yield was reduced about 57% over all cultivars. Early maturing cultivars were not reduced in days to bloom as much as the late maturing types, and there was a significant cultivar x treatment interaction for both bloom date and grain yield. Later maturing cultivars outyielded the other cultivars at physiological maturity in both flooded and non‐flooded conditions. Concentrations of the major nutrients N, P, K, Ca, Mg, and S were decreased in foliage at the boot stage due to flooding. The only nutrient to fall below published “critical” levels in leaf tissue, however, was N, and plants growing in these conditions showed classical N deficiency symptoms. Iron and Mn concentrations were significantly higher in foliage at the boot stage with flooding, but not high enough to be considered toxic. Most differences observed at boot still existed at maturity, but of less magnitude. Marked variability existed in the response among cultivars to waterlogging. It would appear that flooding tolerant genotypes could be selected which would improve existing cultivar choices for use in these difficult soils.

Chloritization in lowland paddy soils

Abstract This paper is concerned with the alteration of clay minerals which takes place when well-aerated lowland soils (Brown lowland soils) are cultivated for growing rice. For this purpose the clay mineral compositions of paddy soils were compared with those of adjacent arable soils at four locations. In the case of arable soils a larger part of the 14Å spacings collapsed to 10Å on treatment with NH4NO3 solution, or on drying at about 100°C, whereas in paddy soils the spacings were more stable to thelie treatments. Cation exchange capacities of clays were always smaller In paddy soils than in arable soils. Alternate treatments of reduction and oxidation somewhat increased the stability of the 14Å spacings to heat treatment. These results indicate that chloritization is a very common process occurring in lowland paddy sons. Chloritization In paddy soils appears to be closely associated with the seasonal cycle of reduction and oxidation.

On the two kind of soil sequence, i.e. hydro-catena and permeability of the solum, in paddy soils of lowland area. : in relation to the genesis and classification of lowland paddy soils

On the two kind of soil sequence, i.e. hydro-catena and permeability of the solum, in paddy soils of lowland area. : in relation to the genesis and classification of lowland paddy soils