Changes in Physical Properties of Chernozems under the Impact of No-Till Technology

Eurasian Soil Science - This article presents the results of research on the impact of no-till technology on the natural bulk density and macro- and microaggregate composition of the topsoil...     

Chemical equilibria and quantity—Intensity relationship of zinc in some acid soils of India

Laboratory studies were conducted to investigate the nature of chemical equilibria of zinc in some acid soils of Himachal Pradesh (India). The results indicated that one of the chemical reactions controlling zinc ion activity in the ambient soil solution may be represented by the equation:

$\text{Si(OH)}{}_4\text{+ 2H}{}_2\text{O ? Zn(OH)}{}_2\text{(}\text{crys.}\text{) + SiO}{}_2\text{(}\text{amorph.}\text{) + 2H}{}_3\text{O}{}^{\mathrm{+}}$

Sequential extraction of ⁶⁵Zn-equilibrated soils provided a measure of the intensity of its different forms and their relative contribution to the pool of potentially available zinc in such soils. Adsorption-desorption parameters have been derived from a quattitative treatment of these phenomena as defined by the Langmuir equation. A supply parameter, $\text{√}\text{cq}\text{√K}{}_1\text{K}{}_2$, integrating the combined effects of quantity, intensity and buffering capacity has been derived from the adsorption studies. A linear relationship between the supply parameter and cumulative desorption of applied zind in these soils has been noted. The desorption of zinc from these soils is an exponential process. The solubility relationship of zinc is expressed in terms of the theory of simultaneous equilibria of competitive chemical reactions which obviates the necessity of assuming a single physico-chemical model in predicting and relating the activity of zinc in the ambient soil solution and its surface reactivity on solid phases in the immediate vicinity of plant roots to its ultimate transport and uptake by plants.     

Detection of tricresyl phosphates and determination of tri-o-cresyl phosphate in edible oils

Tricresyl phosphate (TCP) in contaminated edible oils was extracted using acetonitrile and detected by thin layer chromatography as well as gas chromatography (GC). The chromatoplate was developed with isooctane-ethyl acetate (90 + 10) and visualized by spraying with 2,6-dichloroquinone chloroimide. TCP gives a characteristic blue-violet spot when heated at 100 degrees C for 15 min. The method is direct and sensitive and can be used to detect as low as 2.5 micrograms TCP or TOCP (tri-o-cresyl phosphate). GC was carried out using 10% OV-101 as the stationary phase and flame ionization detection for confirmation and quantitation of TOCP in oils.     

Synthesis and Inhibitory Activities against Colon Cancer Cell Growth and Proteasome of Alkylresorcinols

We have identified alkylresorcinols (ARs) as the major active components in wheat bran against human colon cancer cell growth (HCT-116 and HT-29) using a bioassay-guided approach. To further study the structure-activity relationships, 15 ARs and their intermediates (1-15) were synthesized expediently by the modified Wittig reaction in aqueous media, and six 5-alkylpyrogallols and their analogues (16-21) were prepared by the general Grignard reaction. The synthetic AR analogues were evaluated for activities against the growth of human colon cancer cells HCT-116 and HT-29 and the chymotrypsin-like activity of the human 20S proteasome. Our results found that (1) AR C13:0 and C15:0 (13 and 14) had the greatest inhibitory effects in human colon cancer cells HCT-116 and HT-29, while decreasing or increasing the side chain lengths diminished the activities; (2) two free meta-hydroxyl groups at C-1 and C-3 on the aromatic ring of the AR analogues greatly contributed to their antitumor activity; (3) the introduction of a third hydroxyl group at C-2 (20 and 21) into the aromatic ring of the AR analogues yielded no significant enhancement in activity against HCT-116 cells and decimated the effects against HT-29 cells, but dramatically increased the activity against the chymotrypsin-like activity of the human 20S proteasome; and (4) AR C11:0 (12) was found to have the greatest effect in a series of AR C9:0-C17:0 against the chymotrypsin-like activity of the human 20S proteasome.     

Compatibility of crosses between gene pools and evolutionary classes in the common bean (Phaseolus vulgaris L.)

The extent of genetic divergence between the Mesoamerican and Andean gene pools and between evolutionary classes (wild, landrace and bred) in Phaseolus vulgaris was explored. The compatibility of crosses was assessed by the frequency with which pollination was successful and the number of seeds in the resulting pod. Mesoamerican genotypes were more effective as pollinators than Andean genotypes, regardless of the gene pool of the female parent. Though certain individual genotypes were more easily pollinated by genotypes of one or other of the gene pools, there was no consistent tendency for pollinations between genotypes within a gene pool to be more successful than those between gene pools. In crosses among wild and landrace genotypes, the landrace genotypes were more easily pollinated. In those among wild and bred genotypes, the bred genotypes were more effective as pollinators, and the number of seeds per pod was greater in crosses between the evolutionary classes than in those within classes. In crosses among landrace and bred genotypes, those within evolutionary classes had higher success rates than those between classes (47.2% vs. 38.9%), and produced more seeds per pod. However, these results do not represent a major barrier between the evolutionary classes. The hypothesis that dwarf-lethal incompatibility in inter-gene pool crosses is controlled by two complementary dominant genes (the DL-gene hypothesis) was tested by comparing the numbers of normal and abnormal plants in the progeny of three-way crosses, and the ratios obtained were consistent with the hypothesis. It is concluded that there is no biological barrier between the two gene pools and that they are distinct because, by accident of ancestry, they are located in geographically isolated and ecologically distinct areas, with different cultural practices and preferences. Research programmes aimed at transferring desirable traits between the gene pools should therefore be encouraged.     

Time-course of dinitrogen fixation of promiscuous soybean cultivars measured by the isotope dilution method

 Soybean cultivars capable of nodulating with indigenous Bradyrhizobium spp. have been developed by the International Institute of Tropical Agriculture (IITA) and national programs in Africa in order to avoid artificial inoculation by resource-poor farmers in Africa. The current selection procedure for enhanced N₂ fixation is based on an assessment of nodule formation which does not directly quantify the proportions of crop N derived from the atmosphere. We have monitored N accumulation patterns and N₂ fixation in nine promiscuous soybean cultivars with different maturity periods, using the ¹⁵N dilution technique. Nodule development generally peaked at the early podfill stage for all cultivars except Tgx 1519-1D and Tgx 1447-2D in which it continued to increase. The proportion of crop N derived from fixation (%NDFA) ranged between 51% and 67%, 77% and 84%, and 66% and 73% at full bloom, early podfill, and physiological maturity stages, respectively. Total N accumulation increased in all soybean genotypes with increasing plant age. Significant correlations (P<0.001) were established between nodule weight and %NDFA, even though this did not explain the relationship between nodule development and N₂ fixation in cultivars such as Tgx 1519-1D. Promiscuous soybean cultivars retained between 10% and 19% of total N accumulated at the final harvest, in belowground biomass. Our results indicated that these soybean cultivars can derive substantial proportions of plant N from N₂ fixation in soils where compatible indigenous bradyrhizobia populations are adequate and effective. Also, we have substantiated the claims that qualitative nodulation parameters currently used to select varieties with a high N₂ fixation capacity need to be validated with other measurements of N₂ fixation. Received: 5 November 1998     

Estimation of the diffusion coefficients of adsorbed and non-adsorbed solutes in soil

A method is proposed which follows Darrah's experimental procedure and takes advantage of a mathematical solution provided by Carslaw & Jaeger to estimate the diffusion coefficients of adsorbed and non-adsorbed solutes in soil. The method requires only the values of the concentration of the solute at the input face of a uniform column of soil, C^s, and of the total amount, Q_t, that has entered the soil after a specified time during which the surface of the block is in contact with a thin porous pad containing a known initial amount of solute, Q₀, at concentration C₀, expressed in the same units as C^s. In the C^s/C₀ vs. Q_t/Q₀ space there is a unique relationship between the effective diffusion coefficient, D_e, of the solute in the soil and the contact conductance for this solute, h, between the pad and the soil surface. The proposed procedure is firstly to determine D_e, and h for a non-adsorbed solute in the experimental soil using the experimental values of C^s/C₀ and Q/_Q for that solute. This value of D_e, gives the diffusion impedance factor for the solute in the soil, f, which is assumed also to apply to adsorbed solutes. A first estimate of the effective diffusion coefficient of an adsorbed solute, ¹D_ea, is then made using f and the diffusion coefficient of the free solute in water, D_L, obtained from the literature (i.e. ¹D_ea= D_Lf). Only if the solute is weakly adsorbed will the values of C^s/C₀, and Q_t/Q₀ lie in C^s/C₀, vs. Q_t/Q₀, space as defined by ¹D_ea and the contact conductance, h. Instead a second space relating C^s/C₀ and Q_t/Q₀, is now constructed from nominated values of h and D_e, where D_e, is defined in terms of ¹D_ea, the adsorption coefficient, F , and the volumetric moisture content of the soil, θ. The position of the experimental values of C^s/C₀, and Q_t/Q₀ within this new space defines h and the actual D_e, and F of the solute as it diffuses and is adsorbed in the soil. The advantages and limitations of the method are discussed. In particular, the method assumes that the adsorption process is linear and reversible.