Azolla fern is invasive in Mwea Irrigation Scheme in Kenya and its management in paddy rice fields is a challenge to farmers. A survey was undertaken to establish farmers’ knowledge and potential nitrogen contribution by Azolla in the paddies. The Scheme was stratified into seven sections and a questionnaire administered to 250 farmers. Data were collected on awareness levels, source, trend of infestation, abundance, fertilizer regimes and management practices. Five farms from each of the sections were also sampled for Azolla coverage and tissue N levels analyzed. Survey data were analyzed using SPSS software and interpreted using descriptive statistics. Biomass sampling data were analyzed using SAS software and means separated using the least significant differences at P ≤ 0.05. The results demonstrated that Azolla has infested nearly all the paddy farms in Mwea. Azolla invasion occurred more than 10 years ago and coverage per unit area was on a decline and stood at 25%. Water shortage and herbicide use were the main reasons associated with this trend. Azolla is conspicuously noticed at transplanting and weeding times. The presence of Azolla in Mwea is enhanced by widespread use of P and K fertilizers and continuous paddy cropping, thus providing a suitable environment for Azolla growth. Azolla was reported to enhance soil fertility, rice yield and yield components. The maximum Azolla biomass coverage was 14.92 t/ha, with a potential nitrogen contribution of 37.6 kg N/ha. Azolla is invasive in Mwea, widespread, beneficial to paddies and with a high potential N contribution.
Azolla tissue contains 5% N, which is slowly released into the soil upon decomposition. Timing of incorporation is therefore important for maximum benefit to a crop. The effect of time to incorporate Azolla biomass on growth and yield of rice was investigated in Mwea-Kenya. Treatments consisted of 7.5 t ha-1 Azolla biomass applied at transplanting, 7.5 t ha-1 Azolla applied at 21 days after transplanting (DAT) and 30 kg N ha-1 inorganic N applied in splits at O, 21 and at 55 DAT. There were control treatments without Azolla and without inorganic N application. The treatments were laid out in a Randomized Complete Block Design (RCBD) with three replications. Phosphorus and potassium were applied at 50 Kg ha-1 each as P 2 O 5 and K 2 O. Plant height and tiller numbers were recorded at 21 (rooting/tillering), 32 (tillering), 42 (maximum tillering), 60 (flowering) and 75 DAT (heading) while yield parameters were determined at physiological maturity (120 DAT). Data were analysed using SAS software and means separated using the least significant difference test (p≤0.05). Azolla incorporation at transplanting significantly enhanced panicle m-2 , grain weight and grain yield while incorporating it at 21 DAT only significantly enhanced panicle m-2. Higher environmental temperatures enhanced Azolla effect. The effect of Inorganic N significantly increased plant height, tiller number, grain weight and spikelets panicle-1. However, percentage grain filling was reduced. The effect of interaction between Azolla application and inorganic N was significant on spikelets panicle-1 and grain weight. Observations therefore indicate that the effect of Azolla on yield and yield components was more when incorporated at transplanting.
<p><em>Azolla</em> is a floating pteridophyte, which forms an association with an endosymbiont, the nitrogen-fixing cyanobacterium <em>Anabaena azollae</em>. In Mwea Irrigation Scheme paddies, <em>Azolla</em> biomass coverage ranges from 25 to 50 % with a high biomass growth rate and this has caused a challenge in its management. Knowledge on the effect of <em>Azolla</em> biomass on rice tillering, root development and grain yield are important in order to exploit its potential benefits in Mwea Irrigation Scheme, where nearly 60 % of the total rice in Kenya is produced. The effect of <em>Azolla</em> on tillering, plant biomass, adventitious roots development, basal internode growth and yield of rice, was studied during 2015/2016 short and long rains. <em>Azolla</em> was inoculated in 30 cm x 30 cm plastic pots planted with rice variety Basmati 370. Controls where no <em>Azolla</em> was inoculated were included. Tiller number, plant height, flood water temperature and pH were determined at 21, 32, 42, 60 and 75 days after transplanting (DAT). At 120 DAT, grain yield and yield components were determined. Length of basal node and adventitious root were measured and dry biomass weights of, root and above ground biomass determined. Water temperature in <em>Azolla</em> inoculated pots were significantly lower than in controls by 0.8 °C and 1.3 °C in the second and first seasons respectively with a daily fluctuation of 2 °C. The pH of flood water in potted rice inoculated with <em>Azolla</em> was significantly lower than in control. <em>Azolla</em> inoculated potted rice had significantly higher number of tillers/m<sup>2</sup>, spikelets per panicle<sup>-1</sup>, panicle size m<sup>-2</sup>, 1000 grain weight and plant biomass than in non-inoculated controls. Adventitious roots were significantly longer and more per unit area in all treatments than in controls. The basal stem node length was significantly shorter while root biomass was less for the <em>Azolla</em> inoculated potted rice than in controls. In all treatments, <em>Azolla</em> doubled its biomass within an average of 5 days.</p><p> </p><p> </p>
<p><strong>Background. </strong><em>Azolla </em>Lam<em>.</em>, a mosquito fern, is invasive in major rice growing Schemes in Kenya, where it clogs irrigation canals and forms dense mats in paddy fields. However, the species of <em>Azolla</em> has not been established. <strong>Objective. </strong> to characterize <em>Azolla</em> accessions collected from six major rice Irrigation Schemes in Kenya: Mwea, Ahero, West Kano, Bunyala, Taveta and TARDA. <strong>Methodology. </strong><em>Azolla</em> accessions were collected, grown for 10 days at Mwea Irrigation Agricultural Development Centre (MIAD) and their vegetative traits examined microscopically using 13 Pereira’s morphological characters. The vegetative characteristics were evaluated on a binary 0/1 system, pairwise similarity was estimated using Jaccard’s coefficient (S1)and a dendrogram generated. Genomic DNA was extracted from each of the<em> </em>accessions, amplified with SCAR primers and amplified products resolved and scored using agarose gels. Polymorphic SCAR markers were identified and correlated to the accessions. <strong>Results. </strong>Nine vegetative characters useful for distinguishing between the two <em>Azolla</em> sub-genera (<em>Euazolla </em>and <em>Rhizosperma</em>) and the seven <em>Azolla</em> species were examined. Possession of hook-like, septate glochidia suggested the presence of <em>Azolla filiculoides</em> in TARDA1 accession. The presence of pinnate sporophyte with septate rhizome papillae and fronts measuring 2-4 cm with 2-4 cm long roots and lack of anthocyanin suggested the presence of <em>Azolla nilotica</em> for TARDA 2 and Taveta 2 accessions. SCAR marker based 490 bp primers that identify with <em>A. filiculoides </em>also amplified Mwea and Taveta 1 accessions to give a distinct band. <strong>Implications.</strong> Results suggest the existence of <em>Azolla nilotica</em> and <em>Azolla</em> <em>filiculoides</em> among the Kenyan accessions. <strong>Conclusion.</strong> <em>Azolla filiculoides</em> and <em>Azolla nilotica</em> are the two main <em>Azolla</em> species characterized in the major Irrigation Schemes in Kenya. Of the two species, <em>Azolla filiculoides</em> has infested four of the Kenya irrigation schemes (Mwea, Ahero, Bunyala, Tana River and West Kano), while <em>Azolla nilotica</em> exists only in Taveta and TARDA.</p>
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