Fate and interaction with native soil N of ammonium N applied to wetland rice (Oryza sativa L.) grown under saline and non-saline conditions

Summary The effect of salts on the balance of fertilizer N applied as ¹⁵N-labelled ammonium sulphate and its interaction with native soil N was studied in a pot experiment using rice (Oryza sativa L.) as a test crop. The rice crop used 26%–40% of the applied N, the level of applied N and salts showing no significant bearing on the uptake of fertilizer N. Losses of fertilizer N ranged between 54% and 68% and only 5%–8% of the N was immobilized in soil organic matter. Neither the salts nor the rate of N application had any significant effect on fertilizer N immobilization. The effective use of fertilizer N (fertilizer N in grain/fertilizer N in whole plant) was, however, better in the non-saline soil. The uptake of unlabelled N (N mineralized from soil organic matter and that originating from biological N₂ fixation in thes rhizosphere) was inhibited in the presence of the salts. However, in fertilized soil, the uptake of unlabelled N was significantly enhanced, leading to increased A values [(1-% Ndff/% Ndff)x N fertilizer applied, where Ndff is N derived from fertilizer], an index of interaction with the added N. This added N interaction increased with increasing levels of added N. Since the extra unlabelled N taken up by fertilized plants was greater than the fertilizer N immobilized, and the root biomass increased with increasing levels of added N, a greater part of the added N interaction was considered to be real, any contribution by an apparent N interaction (pool substitution or isotopic displacement) to the total calculated N interaction being fairly small. Under saline conditions, for the same level of fertilizer N addition, the added N interaction was lower, and this was attributed to a lower level of microbial activity, including mineralization of native soil N, rootdriven immobilization of applied N, and N₂ fixation.     

Effect of Baythroid on nitrogen transformations in soil

Laboratory incubation experiments were conducted in soil to study the influence of the insecticide Baythroid on immobilization-remineralization of added inorganic N, mineralization of organic N, and nitrification of added NH _inf4 ^su+ -N. Baythroid was applied at 0, 0.4, 0.8, 1.6, 3.2, and 6.4 g g^-1 soil (active ingredient basis). The treated soils were incubated at 30°C for different time intervals depending upon the experiment. The immobilization and mineralization of N were significantly increased in the presence of Baythroid, the effect being greater with higher doses of the insecticide. Conversely, nitrification was retarded at lower doses of Baythroid and significantly inhibited at higher doses. The results of these studies suggest that excessive amonts of insecticide residues affect different microbial populations differently, leading to changes in nutrient cycling.     

Comparative effects of applying leguminous and non-leguminous green manures and inorganic N on biomass yield and nitrogen uptake in flooded rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

The beneficial role of green manures in rice production is generally ascribed to their potential of supplying plant nutrients, particularly nitrogen (N). However, the mechanisms through which green manures enhance the crop productivity are poorly understood. Pot experiments were conducted using a ¹⁵N-tracer technique: (1) to compare the biomass production potential of sesbania (Sesbania aculeata Pers.) and maize (Zea mays L.) as green manuring crops for lowland rice and (2) to compare the effect of the two types of green manure and inorganic N on the dry matter accumulation and N uptake by two rice (Oryza sativa L.) cultivars, viz. IR-6 and Bas-370. Although maize produced three times higher shoot biomass compared with sesbania, the latter showed higher N concentration; and thus the total N yield was similar in the two types of plants. Applying the shoot material of the two plants to flooded rice significantly enhanced the dry matter yield and N uptake by the two rice cultivars, the positive effects generally being more pronounced with sesbania than with maize amendment. The difference in the growth-promoting potential of the two plant residues was related more to an increased uptake of the native soil N rather than to their direct role as a source of plant-available N. A positive added nitrogen interaction (ANI) was observed due to both plant residues, the effect was much more pronounced with the application of sesbania than with maize residues. In both rice cultivars, inorganic N also caused a substantial ANI, particularly at higher application rate. Losses from the applied N were 2–3 times lower from sesbania, compared with maize treatment. Green manuring with sesbania also caused much lower N losses than the inorganic N applied at equivalent or higher rates. The overall benefit of green manuring to rice plants was higher than inorganic N applied at comparable rates. The two rice cultivars differed in their response to green manuring, IR-6 generally being more responsive than Bas-370.     

Release, movement and recovery of 3,4-dimethylpyrazole phosphate (DMPP), ammonium, and nitrate from stabilized nitrogen fertilizer granules in a silty clay soil under laboratory conditions

 The composition of soil microbiota in four heated (350  °C, 1 h) soils (one Ortic Podsol over sandstone and three Humic Cambisol over granite, schist or limestone) inoculated (1.5 μg chlorophyll a g^–1 soil or 3.0 μg chlorophyll a g^–1 soil) with cyanobacteria (Oscillatoria PCC9014, Nostoc PCC9025, Nostoc PCC9104, Scytonema CCC9801, and a mixture of the four) was studied by cultural methods. The aims of the work were to investigate the potential value of cyanobacteria as biofertilizers for accelerating soil recolonization after fire as well as promoting microbiotic crust formation and to determine the microbial composition of such a crust. The inoculated cyanobacteria proliferated by 5 logarithmic units in the heated soils which were colonized very quickly and, after 2 months of incubation, the cyanobacterial filaments and associated fungal hyphae made up a matrix in which surface soil particles were gathered into crusts of up to 1.0 cm in thickness. These crusts were composed, on average, of 2.5×10¹⁰ cyanobacteria, 2.8×10⁶ algae, 6.1×10¹⁰ heterotrophic bacteria (of which 1.2×10⁸ were acidophilic, 1.3×10⁶ were Bacillus spp. and 1.5×10⁸ were actinomycetes) and 77.8 m fungal mycelium (1.4×10⁶ were fungal propagules) g^–1 crust. Counts of most microbial groups were positively correlated to cyanobacterial numbers. The efficacy of treatment depended on both the class of inoculum and the type of soil. The best inoculum was the mixture of the four strains and, whatever the inoculum used, the soil over lime showed the most developed crust followed by the soils over schist, granite and sandstone; however, the latter was comparatively the most favoured by the amendment. In the medium term there were no significant differences between the two inocula rates used. Biofertilization increased counts of cyanobacteria by 8 logarithmic units while heterotrophic bacteria, actinomycetes, algae and fungal propagules rose by >4 logarithmic units, acidophilic bacteria and Bacillus spp. by around 3 logarithmic units and fungal mycelia showed an 80-fold increase. The results showed that inoculation of burned soils with particle-binding diazotrophic cyanobacteria may be a means of both improving crust formation and restoring microbial populations. Received: 8 March 2000     

Denitrification losses from an Inceptisol field treated with mineral fertilizer or sewage sludge

In order to evaluate the climatic and soil variables which control the denitrification processes in the field, measurements of N₂O-losses using the C₂H₂ inhibition technique were carried out in an Inceptisol cropped with spring wheat. The silty sand was amended with mineral fertilizer (120 kg N ha^?1) or additionally with sewage sludge (620 kg total N ha^?1). Soil temperature, moisture, nitrate and available carbon, the release of nitrous oxide (N₂O) from the soil surface as well as the N₂O concentrations along the soil profile were measured from March until November 1985 The N₂O surface fluxes from the inorganically fertilized field were well correlated with those from the sewage sludge amended plots (r = 0.76). Multivariate correlation analyses show that particularly soil moisture and nitrate content had a significant effect on the nitrate respiration. The correlation with the soil water content was more clearly expressed by the N₂O surface fluxes than by the N₂O concentrations of the soil air. The N₂O surface fluxes during 1985 totalled about 3 kg N ha^?1 in the minerally fertilized field. Sewage sludge amendments increased the N₂O evolution by 5 times. Spatial variability was high and the N₂O surface fluxes were not well correlated (r = 0.4) with the N₂O concentrations in the soil atmosphere. These experiments provide the background data for a denitrification model and better knowledge about the variables which have to be considered for its validation.     

Antimicrobial and cellular activity of poly(L-lactide)/chitosan/Imipenem antibiotic composite nanofibers

Synthesis of biocompatible polymer nanofibers is valuable, due to their use as a cover for burns and as a replacement for bandage because of their antimicrobial properties. In this study, electrospinning of chitosan(Ch) and nanofibers synthesis with antibacterial properties was investigated. Nanofibers with antibacterial properties were synthesized by electrospun of Ch/poly(L-lactide)(PLA)/Imipenem(Imi) polymer solution. The results showed that the optimized ratio of Ch/PLA polymer solution was ratio of 50:50 and Ch 2 wt% and PLA 10 wt% polymer solution was the best weight percentage for nanofiber preparation. Also, the average diameter of Ch/PLA/Imi nanofibers was 143 nm and measured with ImageJ software. Afterwards, the antibacterial properties of Imi as additives (with different percentages) was studied in the polymer solution. The scanning electron microscopy (SEM) images and antibacterial tests were showed that the electrospun of Ch/PLA/Imi polymeric nanofibers were effective against Gram negative bacteria Escherichia coli (E. coli) and inhibited growth of E. coli. The growth and viability percentage of fibroblast cells with nanofibers in αMEM culture are at desirable levels after 6 days.     

Rice Pi-ta gene Confers Resistance to the Major Pathotypes of the Rice Blast Fungus in the United States

ABSTRACT The Pi-ta gene in rice prevents the infection by Magnaporthe grisea strains containing the AVR-Pita avirulence gene. The presence of Pi-ta in rice cultivars was correlated completely with resistance to two major pathotypes, IB-49 and IC-17, common in the U.S. blast pathogen population. The inheritance of resistance to IC-17 was investigated further using a marker for the resistant Pi-ta allele in an F(2) population of 1,345 progeny from a cross of cv. Katy with experimental line RU9101001 possessing and lacking, respectively, the Pi-ta resistance gene. Resistance to IC-17 was conferred by a single dominant gene and Pi-ta was not detected in susceptible individuals. A second F(2) population of 377 individuals from a reciprocal cross between Katy and RU9101001 was used to verify the conclusion that resistance to IC-17 was conferred by a single dominant gene. In this cross, individuals resistant to IC-17 also were resistant to IB-49. The presence of Pi-ta and resistance to IB-49 also was correlated with additional crosses between 'Kaybonnet' and 'M-204', which also possess and lack Pi-ta, respectively. A pair of primers that specifically amplified a susceptible pi-ta allele was developed to verify the absence of Pi-ta. We suggest that Pi-ta is responsible for resistance to IB-49 and IC-17 and that both races contain AVR-Pita genes.