Effect of Seasonal Variation on Growth and Nutritive Value of Azolla pinnata under Agro Climatic Condition of Assam

Azolla, a free floating aquatic fern fixes atmospheric nitrogen in association with nitrogen fixing blue green algae (Kannaiyan, 2002), making it an excellent source of protein for livestock and is very popular as an unconventional source of feed because of its capability to grow on artificial water pools, fast growth in nitrogen deficient habitats and production of enormous green and dry fodder with high nutrient content (Shukla et al., 2018; Rex Immanuel, 2019). Fresh Azolla pinnata alla pinnata can act as best protein replacement source for protein in Sahiwal calves ration up to 30% level (Bhatt et al., 2020) as well as has no impact on growth of calves (Bhatt et al., 2022). Besides, it has no significant impact on haematological parameters like PCV, Hb, RBC and WBC (Singh et al., 2023). It is rich in protein, essential amino acids (Kantwa et al., 2022), vitamins, growth promoter intermediaries and minerals. It is recognized as the cheapest and most abundant source of protein because of their ability to synthesize amino acids from a wide range of virtually unlimited and readily available primary materials.
       
It can be cultivated in nursery plots, ponds, cemented tanks, polythene sheets and readymade Azolla growing beds etc depending on requirement and availability. Azolla grows in full to partial shade (100-50 per cent sunlight) with growth decreasing quickly under heavy shade (Ferentinos et al., 2002). The biomass production greatly decreases at a light intensity lower than 1500 lux (Liu et al., 2008). The most favourable relative humidity for Azolla growth is between 85-90 per cent. Rate of plant growth and biomass production is dependent upon the temperature adjacent to the plant and each species has a specific temperature range represented by a minimum, maximum and optimum. Extreme weather events occurring during the summer period would have the most dramatic impact on plant productivity.
       
Under optimal conditions, Azolla species has a rapid vegetative multiplication with biomass doubling time of two to five days (Sadeghi et al., 2013). The mean air temperature ranging from 30-35°C which varies according to species and growth conditions (Uheda et al., 1999). There have been some studies about the influence of differences in temperature on responses of Azolla species and their eco-physiological strains indicated that a very high (above 30°C) or very low temperature (below -4°C) could play an inhibitory role in the growth of Azolla (Fernandez-Zamudio et al., 2010; Liu et al., 2008; Sadeghi et al., 2013). At higher temperatures (38±1°C/25±1°C) Azolla consistently showed a superior growth rate (Kannaiyan and Somporn, 1989). Accordingly, the information about the effects of seasonal temperature during hot weather period on the green and dry biomass production of Azolla is necessary for its year round cultivation and management in artificial water bodies.
       
Hence, keeping in view of these facts, an experiment has been designed to evaluate the effect of seasonal variation on growth and nutritive value of Azolla pinneta under the agro climatic conditions of Assam.

The experiment was conducted in the AAU-Zonal Livestock Research Station (LRS), under Assam Agricultural University, which is located at Mandira, Kamrup district of Assam. The latitude and longitude of this area is 26.51465°N and 91.1017°E respectively. The station is situated at medium low and low land, of which, 90% area submerges under water during last week of May to September, in each calendar year. The weather at the location of the experimental site was moderately warm with high relative humidity in hot summer months. The mean annual rainfall of the experimental farm was 1950mm distributed over 300 days. The potential evapotranspiration varies from 2.5 mm to 3.5 resulting in an annual water deficit of 705 mm year^-1. Temperature prevailed during the period is shown in Table 1. The maximum temperature ranged from 18.5 to 38.5°C with a mean of 28.5°C while the minimum temperature varied from 10.0 to 34.7°C with a mean of 22.0°C. The highest relative humidity was 85.50% (August) and lowest was 62.65% in the month of February. The rainfall was highest (158 mm) during the month of July. The experiment was conducted for one year, from 2^nd January, 2021 to 2^nd January, 2022.
       

 
Azolla beds were used to cultivate Azolla pinnata with three replications and the size of the individual beds were (10.0 m × 4.0 m). Deep bore well was the source of water for growing with pH 5.8. The fresh Azolla pinnata was collected from the nearby pond of the farm and further cultured in artificial water bodies in concrete tanks under homogenous conditions. Before the beginning of experiment, samples were washed thoroughly with tap water and rinsed with distilled water. Organic cultivation was practiced. As the Azolla plant is a N₂ fixer, it has a competitive advantage over other floating plants for its production in water without added nitrogen fertilizer. Cow dung was added @ 100 g per bed and MOP and DAP were applied @ 200 g each per bed. First harvesting was done on 15^th day after inoculation and the subsequent harvesting was done at fortnightly interval. The fresh weights were determined and recorded.
       
Two samples of fresh Azolla pinneta were collected and analysed for its nutritive value (AOAC, 2007) during the month of January and June 2021 in order to evaluate the difference of nutritive value due to seasonal temperature difference.
       
The observations recorded on the various parameters were computed with the help of MS Office Excel Worksheet. Statistical analyses were done as per Snedecor and Cochran (2000).

Fresh weight of Azolla was recorded at every fortnight under three bed conditions. Highest fresh Azolla was recorded in bed 2 (9.5 kg) in the month of May and lowest being recorded as 2.0kg during January (in bed 2). The increased Azolla production (Fig 1 and 2) during May to June was related with the rise of temperature prevailed in the surrounding area of ZLRS, Mandira. Similar finding was also recorded by Kannaiyan and Somporn (1989). But, during the month of July, despite of higher environmental temperature, due to the higher rainfall (Fig 3), the night temperature in the surrounding area was found to be low compared to May and June. The relative humidity was also highest during this period (Fig 4). Due to that fact, the Azolla could be grown well in these two months (viz May and June) only comparing to the other months.


 

 

 

       
The mean temperature of 26°C to 30°C was recorded at ZLRS, Mandira and gradual increase production of Azolla was observed during the period of mid April to mid July. Thereafter, although the temperature was higher from July to August, its growth was retarded due to huge quantities of rainfall during this period (Fig 3). Thus it may be confirmed that, the biomass production of Azolla was also dependant on particular specific growing period. This is in conformity with the findings of Rex Immanual (2019). Low temperature occurs during winter period; while highest production was recorded during the period of summer and pre monsoon having higher temperature of more than 30°C. Similar findings were also reported by Speelman et al., (2009) and Aziz (2012).
       
The values of dry matter, crude protein, crude fat, ether extract, total ash and nitrogen free extract of Azolla cultivated in both summer and winter season has been presented in Table 2. It has been observed that, there were no significant differences between the two seasons regarding the nutrient content of Azolla. The values of nutrient content are similar with the values that reported by Bhatt et al., (2020).
 

It can be concluded from the study that, growth of Azolla is affected by seasonal variations viz., maximum and minimum temperature, rainfall and humidity. Under the agro climatic condition of Assam, it grows well during April to May. From the nutritional value point of view, there is no significant differences occur between summer and winter production of Azolla.

All authors declare that they have no conflict of interest.