Azolla Biomass Research Articles

Nutrient Starvation Enhances the Phenolic Compounds and Antioxidant Activity in Azolla caroliniana Plant

THE AIM of this study is evaluating the effects of nutrients deprivation in growth media of Azolla caroliniana plant on growth and production of various phenolic components and antioxidant activity. Nutrient-deficient cultures (0.2, 0.1, 0.05 strength Hoagland solution) of Azolla plants resulted in a significant reduction in Azolla biomass, particularly with 0.05 strength compared to those grown on nutrient-sufficient culture (control). The doubling time (DT) and relative growth rate (RGR) were significantly affected with different Hoagland strength and that was accompanied with a significant accumulation of H2O2 and MDA. Anthocyanins, total flavonoids and total phenolics were enhanced in starved-Azolla. HPLC analysis of phenolic acids revealed a significant increase in caffeic, o-coumaric and t-cinnamic acids in Azolla grown on 0.2 strength Hoagland culture, whereas coumaric acid was markedly accumulated in Azolla plants grown on 0.1 strength media. There was a significant increase in phenylalanine ammonia lyase (PAL) and antioxidant activities in starved Azolla. The results indicated that, the antioxidant activity might depend mainly on phenolic compounds

Azolla-derived hierarchical nanoporous carbons: From environmental concerns to industrial opportunities

Abstract Azolla biomass as a very fast growing fern was utilized to prepare hierarchically nanoporous activated carbons with high surface area and crystallinity. As-prepared activated carbons were characterized using powder X-ray diffraction (PXRD), Raman, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), N2 sorption, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). XRD and FTIR results confirmed that CaCO3 which is naturally present in azolla biomass is responsible for crystallinity of the final materials and in collaboration with NaOH as activation agent led to high surface area nanoporous carbons. Activation process increased the specific surface area of the initial char from about 3 m2 g−1 to 2680 m2 g−1. Large ordered atomic layers domains of carbon were observed in HR-TEM. CO2 adsorption capacity was investigated for the azolla-derived carbons which proved the high room temperature capture ability of near 7.18 mmol g−1 at 1 bar and 12.5 mmol g−1 at 20 bar. More significantly, extraordinary capacity of methylene blue uptake by about 4448 mg g−1 has been observed in azolla-derived porous carbon which is the highest ever reported for water cleaning.

Phytofiltration of anaerobically digested sugarcane ethanol stillage using a macrophyte with high potential for biofuel production

ABSTRACTAnaerobically digested stillage (ADS) requires treatment before being discharged into water bodies or soils to avoid adverse effects. Phytofiltration systems are eco-friendly technologies for wastewater treatment, and they simultaneously serve as a source of biomass for biofuel production. The aim of the present study was to investigate the phytofiltration of ADS using Azolla sp. The effects of the ADS strength (dilutions 1: 50 and 1 : 25 v/v) and initial biomass density (IBD) [15.44 (IBD1) and 23.16 (IBD2) g dry weight (dw) m−2] on plant growth and pollutant removal were assessed. Productivities obtained at ADS 1: 50 (2.93 and 3.04 g m−2 d−1 for IBD1 and IBD2, respectively) were not significantly different from those of a synthetic medium (2.56 and 3.15 g m−2 for IBD1 and IBD2, respectively). Higher organic matter removal was found using ADS at 1: 25 than that obtained using ADS 1: 50 (52.16–53.34 vs 32.29–38.16%), while no IBD effect was observed. The nutrient concentrations in ADS were reduced significantly, especially the concentrations of NH4-N (75.11–82.54%), PO4-P (88.72–92.90%) and SO4-S (55.95–66.61%). The conversion of nutrients from ADS into Azolla biomass may result in an effective way to produce an attractive feedstock for biofuel production.

Impact of climate on biomass production of Azolla in Bihar

Widely cultivated in the Asian regions, Azolla is either incorporated into the soil before rice transplanting or grown as a dual crop along with rice. To examine the feasibility of its use in flooded rice fields, the study was conducted during 2011-13 with 9 different species/ strains of Azolla at BAU Sabour, to study the growth-development dynamics and the resistance/tolerance to extreme temperature which generally occurs in the area. Azolla biomass increased during February- April but suddenly decreased during May-June and again increased during July-September thereafter, biomass decreased during October-January. The correlation coefficient between biomass growth rate of strains A. faliculoides, A. microphylla and BAUAS-1 of Azolla and maximum temperature was found significantly positive. Significant positive correlation between biomass production of species A. faliculoides and strain BAUAS-1 with minimum temperature was found 0.70 and 0.62 respectively, which indicates that increase in minimum temperature up to limit, may increase the growth rate in these strain/spp. There was significant negative correlation (0.70, 0.63 and 0.68) between biomass production rate and relative humidity measured at morning, in the species/strain A. rubra, BAUAS-1, BAUAS-2 respectively. Biomass production rate of azolla species A. pinnata showed significant negative correlation with relative humidity at evening. Significant positive correlation between biomass production and rainfall during the growth period in species A. faliculoides was found, which indicates rainfall or sufficient water increases the growth in Azolla.

Kajian Peningkatan Peran Azolla Sebagai Pupuk Organik Kaya Nitrogen pada Padi Sawah

The study aims to get an optimum dose of Azolla organic fertilizer that provides maximum growth and yield of rice crops. The experiments are arranged in complettely randomized block design with 5 treatments and 4 replications. The treatments tested were fresh Azolla biomass dose embedded in the ground to accompany the provision of Azolla that left to grow on the surface of the water of the rice fields. Treatments dose of fresh Azolla biomass awere M0 = control (without organic fertilizer Azolla); M1 = 100 g.pot-1 ; M2 = 200 g. pot-1; M3 = 300 g. pot-1 ; and M4 = 400 g. pot-1. The experimental results show that: (1) organic fertilizer Azolla improve the growth and yield of rice paddy fields, and (2) Results of maximum 56.35 grams of dry grain per plant with an optimal dose of organic fertilizer as much as 48.102 ton.ha -1. Keywords: Organic fertilizers, Fresh Azolla, growth, yield, rice paddy.

Nitrogen and Ammonia Mitigation on Laying Hen Farms: Effects of Low-protein Diet and Manure Filtering

Background: Lowering dietary Crude Protein (CP) has been widely reported as a method to reduce nitrogen (N) excretion, but information on its effect in combination with filtering by Azolla pinnata to further mitigate N or ammonia (NH3) volatilization from laying hen manure is limited. Materials and Methods: Two experimental diets containing 17% (control) and 15% (low) crude protein were assigned to 2 groups of 22 weeks old ISA Brown hens, so each treatment had 20 replicates with 6-7 birds each. The manure from each group was flushed into two terraced ponds, in which Azolla pinnata was grown in the lowest terrace to filter the N in the sludge. Fresh manure was collected when the hens were 29 weeks old to analyze the N and NH3 contents and perform microbial counts and analyses of pond water quality (total dissolved solubles, temperature and pH), Azolla N and egg quality were conducted. Data were subjected to either a one or two-way ANOVA. Results: Lowering dietary crude protein to 15% resulted in a 21.83% (p<0.05) decrease in manure NH3, but it did not alter the microbial counts or N content. Additionally, pond water quality was not affected by dietary CP, the presence of Azolla in the pond or the dietary crude protein× Azolla interaction and there was no difference in the N content of the Azolla biomass among dietary groups. Eggs laid by hens given the low-CP diet had comparable quality to those laid by the control hens. Conclusion: Reducing dietary crude protein to 15% lowered NH3 volatilization and did not negatively affect egg quality. However, growing Azolla in a terraced pond failed to elicit an N-filtering effect. Key words: Ammonia mitigation, nitrogen, low protein, manure filtering, laying hen

Aquatic plant Azolla as the universal feedstock for biofuel production.

BackgroundThe quest for sustainable production of renewable and cheap biofuels has triggered an intensive search for domestication of the next generation of bioenergy crops. Aquatic plants which can rapidly colonize wetlands are attracting attention because of their ability to grow in wastewaters and produce large amounts of biomass. Representatives of Azolla species are some of the fastest growing plants, producing substantial biomass when growing in contaminated water and natural ecosystems. Together with their evolutional symbiont, the cyanobacterium Anabaena azollae, Azolla biomass has a unique chemical composition accumulating in each leaf including three major types of bioenergy molecules: cellulose/hemicellulose, starch and lipids, resembling combinations of terrestrial bioenergy crops and microalgae.ResultsThe growth of Azolla filiculoides in synthetic wastewater led up to 25, 69, 24 and 40 % reduction of NH4–N, NO3–N, PO4–P and selenium, respectively, after 5 days of treatment. This led to a 2.6-fold reduction in toxicity of the treated wastewater to shrimps, common inhabitants of wetlands. Two Azolla species, Azolla filiculoides and Azolla pinnata, were used as feedstock for the production of a range of functional hydrocarbons through hydrothermal liquefaction, bio-hydrogen and bio-ethanol. Given the high annual productivity of Azolla, hydrothermal liquefaction can lead to the theoretical production of 20.2 t/ha-year of bio-oil and 48 t/ha-year of bio-char. The ethanol production from Azolla filiculoides, 11.7 × 103 L/ha-year, is close to that from corn stover (13.3 × 103 L/ha-year), but higher than from miscanthus (2.3 × 103 L/ha-year) and woody plants, such as willow (0.3 × 103 L/ha-year) and poplar (1.3 × 103 L/ha-year). With a high C/N ratio, fermentation of Azolla biomass generates 2.2 mol/mol glucose/xylose of hydrogen, making this species a competitive feedstock for hydrogen production compared with other bioenergy crops.ConclusionsThe high productivity, the ability to grow on wastewaters and unique chemical composition make Azolla species the most attractive, sustainable and universal feedstock for low cost, low energy demanding, near zero maintenance system for the production of a wide spectrum of renewable biofuels.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0628-5) contains supplementary material, which is available to authorized users.

From phytoaccumulation to post-harvest use of water fern for landfill management

We examined the potential of Azolla japonica as a remediating plant for leachate channels and post-accumulation use as fertilizer for landfill slope. The harvested biomass of Azolla after one month grown in leachate was 254% that of the initial biomass and the predicted annual harvestable biomass of Azolla using a growth model was 32 times that of the initial biomass. Na, Fe, Mn, Mg, and P were accumulated in Azolla at very high concentrations. Such rapid increase of biomass and high accumulation rates suggest that this plant could be an excellent remediating plant. The post-harvest use of Azolla as compost was studied for the management and use of phytoaccumulating Azolla. Metal contents of Azolla compost were below permissible limits for co-composting material. Nitrogen, organic matter, P, and Mg content of the Azolla compost improved the soil condition of the landfill and enhanced ecophysiological responses of the plants. The application of Azolla compost can improve management of sanitary landfills, including the restoration of vegetation. Considering its ease of harvesting, high accumulation rates, harvestable biomass and suitability for composting, Azolla can provide a suitable solution for sustainable management of leachate channels and landfill slopes.

Experimental and Kinetic Studies on Acid Red 88 Dye (AR88) Adsorption by Azolla filiculoides

The use of Azolla filiculoides (AF) for the removal of Acid Red 88 dye (AR88) from aqueous solutions at different contact times, temperatures, pH, adsorbent doses and initial dye concentration was investigated. The extent of dye removal decreased with increasing adsorbent dosage and AR88 concentration, also increased with increasing contact time and temperature. The adsorption isotherms are described by means of the Langmuir, Freundlich, Tempkin and Sips isotherms. It was found that the Langmuir equation fit better than the other equation. Maximum adsorption capacity (qm) was calculated at different temperatures (20, 30, 40 and 50°C) 22.45, 23.95, 25.29 and 26.17 mg/g, respectively. The adsorption kinetics of Acid Red 88 could be described by the pseudo-second-order reaction model. The obtained results are: (1) high levels of color removal (>98%) were achieved with low contact times adsorbent/dye (less than 90 min contact); and (2) the whole Azolla filiculoides can be successfully used as adsorbent of AR88 in aqueous solutions. Azolla biomass, an inexpensive and easily available material, can be alternative for more costly adsorbents used for dye removal in wastewater treatment processes.

Selenium invoked antioxidant defense system in Azolla caroliniana plant

Plants of Azolla caroliniana were treated with differentselenium concentrations (0, 1, 2, 5, 7, 10 ppm) for seven days.Selenium (Se) content in Azolla plants increased significantly withincreasing Se concentrations in the culture media up to 5 ppm. Thisindicated that Azolla plants were a good accumulator for Se. Seleniumaccumulation determined changes in Azolla biomass, doublingtime and relative growth rates. Treatment of Azolla plants with lowconcentrations of Se (1 ppm) resulted in a significant increase in biomass.This was accompanied by a reduction in hydrogen peroxide andmalondialdehyde (MDA) contents; the decrease percentages were78% and 60%, respectively at 1 ppm Se in comparison with the control.At higher Se concentrations (>5 ppm), there was a significantincrease in H2O2 and MDA contents, these increases were 3.2- and2.8-fold at 10 ppm Se in comparison to controls, respectively. Comparedto that in controls, total ascorbate as well as total glutathionecontents, were significantly increased. The activity of the GR enzymewas significantly increased in Azolla plants with addition of differentconcentrations of Se. The increase was 2.2- and 3.4-fold at 2 and7 ppm Se, respectively. The addition of high concentrations of Se(>5 ppm) to the growth media resulted in a significant increase inthe GSH-PX and APX activities in Azolla plants. Thus, addition ofSe affects Azolla plants, and these effects change from beneficial totoxic, as reflected in the metabolism and growth of the plants.

PENGARUH DOSIS P DALAM FOSFAT ALAM PADA PENINGKATAN BIOMASA Azolla microphylla Kaulfuss

Azolla microphylla is one of the green resources fertilizer, adding natural P respectively will increase the biomass including. The on time embedding of azolla are able to provide nutrition to the plants such as rice especially N. The experiment was conducted in Desember 2nd , 2006 - April 5th , 2007 in Tegalgondo, Karangploso, Malang, East Java ( 550 m up sea level). The experiment applied Randomized Block Design (RBD) under two factors, dose and embedding time with three replications. The doses were applied are P0 = 0 kg ha-1; P1 = 25 kg P ha-1; P2 = 50 kg P ha-1; and P3 = 75 kg P ha-1 . The embedding times were a day before planting, 50 % azolla in 14, 28 and 24 days after planting, 50 % azolla in 21 and 49 days after planting, and 50 % azolla in 35 day after planting. The parameters of observation were wet weigh of azolla; N, P , K contents before and after treatments and azolla decompositions. The result showed 75 kg P ha-1 with interaction of azolla embedding, was the most effective dose to increased azolla biomass.

Effect of Azolla pinnata on Seed Germination, Vigour Index, Biomass and Yield of French Bean (Phaseolus vulgaris)

A study was conducted to know the effect of Azolla pinnata collected from Hampapura of K.R. Nagar in Mysore district on seed germination, vigour index, biomass and yield of French bean. A total of four different treatments of earthen pots containing soil: sand: farmyard manure (2:1:1) amended with 10g (T1), 25g (T2), 50g (T3) and 100g (T4) of fresh Azolla biomass and pots amended with 10g (T0) of Factamphos served as positive control. Pots without any supplement served as negative control. 10 seeds of French bean variety ‘S 9’ were sown in each pot and normal agronomic practices were followed. Seed germination was determined after eight days of sowing, and after every 15, 30, 60 and 90 days of sowing, vigour index, biomass and pod yield were determined. The results of the study showed that, high percentage seed germination (81.66%) was recorded with the treatment incorporated with 25g (T2) of Azolla biomass followed by 10g (76.33%), 100g (76.00%) and 50g (72.66%) of Azolla biomass respectively. Minimum seed germination percentage of 64.66% and 65.66 % were recorded in respective negative and positive controls. Significant increase in seedling vigour (VI) was recorded in all the treatments compared to controls. Pod yield increased in T2 followed by T0, T1, T3, T4 and untreated respectively after 90 days of sowing. The study showed that Azolla could be used as a supplement for other pulse crops for increased biomass and overall yield of French bean.

Application of AzollaFiliculoides Biomass in Acid Black 1 Dye Adsorption from Aqueous Solution

Background and purpose: The textile dyes are considered as important pollut ants due to the toxicity on human and environment. Therefore, the d ye removal from industrial effluents is necessary. This study evaluates the ability of Azol la for the adsorption of acid black 1 (AB1) dye from aqueous solution. Materials and Methods: This was an experimental-laboratory study. The Azol la biomass was sun dried, crushed and sieved to particle sizes in the range of 1-2 mm. Then, it treated with 0.1 M HCl for 5 h, followed by washing with distilled wat er, and it used as an adsorbent. The effect of study parameter was investigated, and the residues AB1 concentration was measured by DR2800 spectrophotometer at in λmax = 622 nm . Results: The results indicated that the efficiency of AB1 ad sorption decreased with increased initial dye concentration. It increased with increa sed contact time and adsorbent. The highest adsorption efficiency was occurred at pH = 2. The e quilibrium data were the best fitted on Langmuir isotherm and pseudo-second-order kinetic model. Conclusion: The Azolla could present high ability in dye remov al. Therefore, it can be used as inexpensive and effective adsorbent in textile effl uent treatment. [Zazouli MA, Yousefi Z, Yazdani-Charati J, *Mahdavi Y. Application of Azolla filiculoides Biomass for Acid Black 1 Dye Adsorption from Aqueous Solution . IJHS 2014; 2(3): 24-32] http://jhs.mazums.ac.ir

Integrated effects of organic, inorganic and biological amendments on methane emission, soil quality and rice productivity in irrigated paddy ecosystem of Bangladesh: field study of two consecutive rice growing seasons

Effects of different soil amendments were investigated on methane (CH4) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh. The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha−1) + rice straw compost (2 t ha−1) as a control, urea (170 kg ha−1) + rice straw compost (2 t ha−1) + silicate fertilizer, urea (170 kg ha−1) + sesbania biomass (2 t ha−1 ) + silicate fertilizer, urea (170 kg ha−1) + azolla biomass (2 t ha−1) + cyanobacterial mixture 15 kg ha−1 silicate fertilizer, urea (170 kg ha−1) + cattle manure compost (2 t ha−1) + silicate fertilizer. The average of two growing seasons CH4 flux 132 kg ha−1 was recorded from the conventional urea (220 kg ha−1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH4 flux ha−1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha−1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha−1) in paddy field. Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH4 emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh.

Serapan dan Ketahanan Azolla terhadap Kromium pada Vertisols dan Entisols Dengan Berbagai Tinggi Genangan Air

Title : The Uptake and Tolerance of Azolla to Chromium on Vertisols and Entisols at Various Water Levels. This research aims to study the effect of water level, soil kind, chromium concentration (Cr), and their interactions on uptake and tolerance of azolla to Cr. The research was done in March to May 2009 in the green house of Faculty of Agriculture, Sebelas Maret University, Surakarta. The research used completely randomized design (CRD) factorial with three treatment factors, they were: soil kind (Vertisols of Jatikuwung and Entisols Colomadu, Karanganyar), water levels (0; 2; and 7 cm) and Cr concentrations (0; 5; 10; 15; and 20 ppm). There were 191 g of Vertisols and 200 g of Entisols pass to 2 mm sieve put into plastic pot and watering at various levels according to the treatments. A gram of fresh azolla was spread on each pot and incubated for three weeks. Each treatment combinations were replicated three times. Sampling was taken at 1, 2, and 3 weeks after planting for azolla biomass, Cr uptake of azolla, available Cr, and Cr toxicities symptoms of azolla. The data analyzed statistically by Kruskal Wallis test at 95% level significant, followed with Mood Median test. The result shows that soil kind has no significant effect, while water level, Cr concentration, and treatment interaction contribute highly significant influence on uptake and tolerance of azolla to Cr. The highest uptake of Cr at the Vertisols was taken at 7 cm water level and 15 ppm Cr concentration, while at the Entisols was in 2 cm of water level and 15 ppm Cr concentration. Azolla most tolerance to Cr at treatment combination of 2 cm water level and 10 ppm Cr concentration in Vertisols, and at 2 cm water level and 5 ppm Cr concentration at Entisols. Keywords: A. mycrophylla, chromium, Cr uptake and tolerance, water level

Nitrogen and Phosphorus Storage in Contrasting Reaches of a Sub-tropical River System

This study investigated the storage of nitrogen (N) and phosphorus (P) in the biomass, bed sediments and water column of representative reaches of a sub-tropical river, the upper Brisbane River (UBR), Queensland, Australia, and contrasted instream storage with total wet season exports. In reaches which contained accumulated fine sediments, more than 87% of total P and between 50% and 92% of total N were stored in the surface sediments. The lower proportion of N in sediment at some sites was attributed to substantial differences in the N/P ratios of sediments and macrophytes. At one site, the riverbed was dominated by cobbles and boulders and total nutrient stocks were comparatively low and dominated by the biomass. In reaches with a narrow channel and intact riparian cover, biomass N and P were stored predominately in leaf litter, while in wider unshaded reaches, macrophytes dominated. Total instream storage in the mid to lower reaches of the UBR was ∼50.9 T for N and ∼18.1 T for P. This was considerably higher than total wet season N (∼15.6 T) and P (∼2.7 T) exports from the UBR. The first flow event in the river after a prolonged period of no flow resulted in the export of free-floating, emergent species Azolla. The estimated biomass of Azolla in the mid to lower reaches of the river was equivalent to approximately 24% and 9% of the total N and P flux, indicating that this may be a significant, previously unaccounted for, source at peak flow.

Ability of the aquatic fern &lt;i&gt;Azolla&lt;/i&gt; to remove chemical oxygen demand and polyphenols from olive mill wastewater

We investigated the biofiltration ability of the aquatic fern Azolla to remove polyphenols and chemical oxygen demand (COD) from olive mill wastewater (OMWw) collected from the traditional (TS) and continuous (CS) extraction systems. Azolla biomass was packed into five sequential Imhoff cones and five sequential columns. In both experiments, the filtrates collected from the 5 th biofilter showed a decrease in polyphenol contents: from 7650 mg l –1 to 3610 mg l –1 in TS OMWw and from 3852 mg l –1 to 1351 mg l –1 in CS OMWw. The COD contents decreased from 110200 mg L –1 to 52400 mg L –1 in TS OMWw and from 41600 mg L –1 to 2300 mg L –1 in CS OMWw. A 5:1 OMWw to Azolla -fresh-weight ratio was optimal for both polyphenol and COD removal. The biofiltration ability of alfalfa was compared with that of Azolla , but the treatment with alfalfa did not result in the reduction of COD or polyphenols.

Cultivation of Azolla microphylla biomass on secondary-treated Delhi municipal effluents

Abstract Study was conducted on recycling municipal wastewaters for cultivation of Azolla microphylla biomass, which is used for inoculation into paddy fields as N biofertiliser and has other applications as green manure, animal feed and biofilter. Secondary-treated municipal wastewaters were collected from Wazirabad sewage treatment plant in New Delhi during all four seasons and tested for reactive P and heavy metal content. The reactive P levels in effluents ranged between 1–2 ppm and levels of heavy metals like Cd, Pb, Ni, Zn, Fe and Mn were well below permissible limits. A. microphylla was grown in sewage effluents and its dilutions prepared with tapwater. It showed good growth potential on sewage effluents. Doubling times during September and December months compared well with those on Espinase and Watanabe (E and W) medium and tapwater. Dried Azolla biomass produced on sewage waters did not show presence of toxic heavy metals Cd, Cr and Pb. However, levels of P in dried biomass cultivated on sewage effluents were lower as compared to those from E and W medium and tapwater. The biomass produced can be used for inoculating paddy fields or for other applications and polished wastewaters can be recycled for irrigation purposes.

Conservation of urea-N by immobilization-remobilization in a rice-Azolla intercrop

Nitrogen losses are notoriously high in flooded rice fertilized with urea. An Azolla intercrop can reduce such losses by immobilizing urea-N during periods of potentially high N-loss. The reduction in N loss linked with the absorption and remobilization of urea-N by Azolla, was studied in two greenhouse experiments conducted in Goettingen (Germany). Grain yield and N recovery were positively influenced by Azolla more than doubling grain yield and N uptake as compared to the split application of 300 mg N pot−1 alone (Exp. 1). In the second experiment, the yield increase was 78.3% with single applications of 97.5 and 68.4% after a split-application of a total of 195 mg N pot−1. In both years the effect of urea and Azolla combined exceeded that of the sum of the factors alone, a clear positive synergistic effect on yield and N uptake by rice. Azolla effectively competed with the young rice plants for applied urea, capturing nearly twice the urea-N than the rice plants up to tillering in experiment 1. In the second experiment, 64.6 mg N of the 97.5 mg applied early in the season was immobilized by Azolla within 2 weeks. This represented 63.1% of the total N accumulated in the Azolla. The fraction of Azolla-N derived from urea sank to 36.4 mg within 4 weeks and only 27.2 mg at maximum tillering as a result of Azolla senescence and N-release. Of this 64.6 mg urea N immobilized 28.7% is eventually taken up by the standing rice plant, representing 43.1% of the remineralized, urea-derived Azolla N. Following the second urea application, only 17.9 mg N were immobilized in the Azolla biomass during the 2 weeks, of which 6.9 mg pot−1 were still retained in the Azolla at maturity. At this stage, rice is the more effective competitor for applied N. As much as 42.1% of this immobilized N finds its way into the rice by maturity. Thus, Azolla contributed to the conservation of N in the system, particularly of the urea applied early in the season. Loss of N from the system amounted to no more than 15%. Although the early-applied N directly recovered by the rice plant was low (20%), 2/3 of the N captured by Azolla following this first urea application was released to the system by the time of rice harvest, over 40% of which was available to the rice plant. Azolla thus appears to act as a slow release fertilizer.

EFFECT OF SOME METABOLIC INHIBITORS AND GROWTH HORMONES ON THE SPORULATION AND GROWTH OF AZOLLA MICROPHYLLA

Foliar sprays of 25–100 mg L−1 dinitrophenol, sodium azide (NaN3) and thiourea solution applied to Azolla microphylla (strains 202 and 203) at seven days after inoculation significantly increased the sporulation frequency and number of micro- and mega-sporocarps per plant. Azolla biomass production was decreased by the application of NaN3 at 50–100 mg L−1 and dinitrophenol or thiourea at 75 and 100 mg L−1. Both the sporulation frequency and sporocarp number were maximal with dinitrophenol and NaN3 at 100 mg L−1 and thiourea at 75 mg L−1. At this concentration, NaN3 was more effective than dinitrophenol and thiourea in enhancing sporulation in A. microphylla (strain 203). The sporulation frequency and micro-sporocarp number were significantly higher with gibberellic acid (2.5 mg L−1) than with indole acetic acid (6 mg L−1) application, while the effects of NaN3 were comparable with those of gibberellic acid. The mega-sporocarp numbers in these treatments were comparable. The combined application of any two of the metabolic inhibitors had antagonistic effects and decreased the sporulation frequency and sporocarp number over their individual applications. Combined applications also substantially reduced the biomass production. The application of gibberellic acid or indole acetic acid along with one of the metabolic inhibitors had synergistic effects on the formation of sporocarps and significantly increased the biomass production, irrespective of the metabolic inhibitor treatment. The number of both micro- and mega-sporocarps in the gibberellic acid + NaN3 and indole acetic acid + NaN3 treatments, and micro-sporocarps in the gibberellic acid + dinitrophenol, indole acetic acid + dinitrophenol and indole acetic acid + thiourea treatments was significantly higher than when each of these chemicals was applied alone. Of the different combinations of gibberellic acid, indole acetic acid and NaN3, gibberellic acid + NaN3 recorded the highest sporulation frequency and micro-sporocarp number, and indole acetic acid + NaN3 the highest mega-sporocarp number. Application of all three chemicals together had no extra advantage.