e increasing land use intensity without adequate and balanced use of chemical fertilizers and with little or no use of organic manure have caused severe fertility deterioration of our soils resulting in stagnating or even declining of crop productivity in Assam. e need of the hour is to achieve substantially higher crop yield than the present yield levels from our limited land resources on a sustainable basis. A study was carried out in the paddy �elds of tea garden belts namely, Rungagora, Balijan, Banwaripur, Khomtai, Rungajaun, Lattakoojan, Borjan, Behora, Negheriting, and Borsapori of Golaghat district of Assam to investigate the fertility status of soil during 2008-2010. Results of the present study showed that soil solutions were acidic in nature in all seasons. Medium-tohigh BD, medium SOM, medium-to-high available N and available phosphorous, and low availability of potash showed that soils were not sufficiently fertile for crop production. Depending on the SOM, available N, available P, and exchangeable K in soil, the study areas were grouped in to six fertility classes as MMML, MMHL, MMMM, MHHL, MHHM, and MMHM. Student t-test values of all the parameters with control sample showed statistically signi�cant results for SOM, available N, and available P in both seasons (dry and wet) and EC in wet seasons and bulk density in dry season only.
The use of appropriate level of theories for studying weak interactions such as stacking of aromatic molecules has been an important aspect, since the high level methods have limitations for application to large molecules. The differences in the stacking energies of various structures are found significant for identifying the most favored stacked benzene rings and the pyridine rings. The most favored structure of benzene rings obtained from various methods are similar, and also comparable with that of reported accurate CCSD(T) method. The effect of basis set in the stacking energies of MP2 calculations is small. Thus the moderately accurate methods may be feasible for studying the stacking interactions as demonstrated for benzene and pyridine molecules.
Acid-base properties of drugs are important in understanding the behaviour of these compounds under physiological condition. In order to understand such behaviour the proton affinities of acridine 4-carboxamides with substitution (R) at the 9-position are theoretically studied, and considered for the basic sites of both the heterocyclic ring as well as side chain nitrogens. In 9-amino acridine 4-carboxamide, the-NH 2 group is observed to be an additional basic site. The heterocyclic nitrogen of substituted carboxamides (R =-NH 2 ,-O-methyl,-O-ethyl, and-O-phenyl) is more basic than the side chain nitrogen, however, side chain nitrogen corresponds to more basic site for some carboxamides (R =-OH and-Cl) and the-NH 2 group represents the least basic site of 9-amino acridine 4-carboxamide. In addition to presenting the basicities of these drugs an indication of another hydrogen-bond between heterocyclic ring N and carboxamide chain O is observed. The difference of basicities with substituents at 9-position are very narrow and carboxamides with substituents at 9-position are found to be suitable for studying intramolecular H-bonds between the heterocyclic N and carboxamide O. The resultant stabilization of a configuration due to such H-bonding is determined.
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