SAID SHEHATA

The possible interaction of four nematicides (Terbufos, Carbofuran, Fenamiphos, and Aldicarb) with Azospirillum lipoferum and growth of two Zea maize cultivars was studied in a greenhouse experiment. Application of nematicides, Fenamiphos in particular, resulted in higher plant length, dry matter production and N yield over the nematicide‐untreated plants. Azospirillum spp. inoculation stimulated the growth of nematicide‐treated Z. maize. Among the nematicides used, Carbofuran and Aldicarb inhibited the nitrogenase activity on plant roots more seriously than Fenamiphos and Terbufos. Generally, the inhibition percentages in acetylene reducing activity in soil of inoculated treatments were lower (14.4 ‐ 61.8%) than those reported for the uninoculated ones (21.4 ‐ 73.9%). Soil, irrespective of treatment, regained a part of its normal N2‐ase activity with time. Field concentrations of all nematicides showed different inhibitory effects on N2‐ase activity of Azospirillum spp. in culture medium, such effects increased with increased doses (10‐ and 100‐ fold) and incubation periods (10 days). The contribution of Azospirillum spp. to the N economy of soil treated with nematicides is discussed. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim

Differential scanning calorimetry (DSC) curves and electrical conductivity α were measured for three forms of zeolite-Y, namely NaY, HY and dealuminated HY (DAY). The DSC curves gave dehydration endotherms for all the forms, whereas the σ values have a number of breaks indicating higher mobilities of the charge carriers. NaY exhibited by far the highest conductivity values, mainly resulting from a large number of Na + ions in the presence of freely diffusing water molecules. DSC indicated a lower free diffusion of water molecules in the HY form which, together with a relatively weaker acidity, contributes to its lower σ values despite its high water content. The production of a relatively large percentage of Al 3+ ions in DAY by dealuminating the mother zeolite HY, together with the presence of freely diffusing water in the zeolitic channels (despite the low water content of DAY), results in its σ values being higher than those of HY. © 1990.

The screening of 27 isolates grown on nitrogen-free medium for nitrogen-fixing ability resulted in the isolation of five organisms belonging to Bacillaceae, Enterobacteriaceae and Pseudomonadaceae. Estimates of N2-fixation efficiencies of these isolates indicated that they may be responsible for low rates of N2-fixation in soil. The possible association of these isolates as well as of Azotobacter and Azospirillum with wheat and barley was investigated in a greenhouse experiment. The highest values of nitrogenase activity on plant root were recorded in treatments inoculated with composite inocula of the isolated N2-fixers, particularly when Azotobacter and/or Azospirillum were added in combination. Inoculation with single inoculum of each of the N2-fixing isolates had no significant influence on plant growth, except with Pseudomonas and Bacillus for wheat and barley, respectively. Highly significant increases in growth of both plants were recorded in all cases of multistrain inoculation. © 1990 ACADEMIA, Publishing House of the Czechoslovak Academy of Sciences.