It is a study of the ecological, physiological and agronomic aspects of blue-green algae in rice fields and is the result of the compilation and analysis of 369 references. LITERATURE RECORD OF BLUE-GREENALGAE AND RICE 5. Analysis of the literature on blue-green algae and rice.
2 ECOLOGY OF
BLUE-GREEN ALGAE IN PADDY FIELDS
DESCRIPTIVE ECOLOGY
- Occurrence of blue-green algae in paddy fields
- Record of dpecies and taxonomic studies
- Quantitative estimations 1, Methodology
- Evolution of the algal flora along the cultivation cycle 1. Quantitative variations of the total flora
- Light
- Temperature
- Other factors
These difficulties may explain the lack of quantitative ecological studies of algal flora in paddy fields. Studies on the qualitative development of the algal flora were carried out by Roger and Reynaud in the rice fields of Senegal.
BIOTIC FACTORS
- Pathogens
- Antagonisms
- Grazers
In Philippine paddy fields, the colonization of the water by submerged weeds suppressed the algal blooms that developed after transplanting (239). The introduction to the rice paddies of the freshwater fish Tilapiu mozambicu, which feeds on algal grazers such as chironomial larvae, had a beneficial effect on the growth of the Nostoc community (151).
SOIL PROPERTIES
- Other properties
- Inorganic fertilizers
- Organic manure
- Pesticides I . Methodology
In saline soils in the Soviet Union, N-fixing PGI was reportedly observed less frequently than non-fixing PGI. Magnesium sulfate also had a depressant effect on algal growth when used in the absence of phosphate (5 1).
CONCLUSION
The effect of STAM F-34 on Nostoc muscorum was similar to that of E M U, which inhibits both growth and heterocyst differentiation (308). By repeatedly growing and removing BGA from a BHC-containing medium, Das and Singh (46) observed a gradual loss in the toxicity of the pesticide and suggested detoxification by BGA. Insecticides are generally less toxic to BGA than other pesticides and have the secondary beneficial effect of suppressing the pasture population.
Field experiments are much needed to more accurately demonstrate pesticide effects and determine in situ toxicity levels.
BLUE-GREEN ALGAE
PHOTOSYNTHESIS
The direct use of HCOj and even COi2 by the other algae, including BGA, is controversial, but it appears that BGA extracts dissolved inorganic C at high pH values more competently than other algae (232). This was demonstrated by Shapiro (see 232) who manipulated pH, nutrient concentration and amount of free CO2 in isolated lake zones. The addition of free CO2 resulted in a large dominance of green algae; lowering the pH had a similar effect.
Based on these results, it was suggested that high CO2 production in the paddy field, either after soil rewetting (priming effect) or organic matter uptake, might be more beneficial for green algae than for BGA (232). Some reports support the hypothesis that organic matter uptake promotes green algae growth (34, 120), but dense BGA growth was also reported two weeks after applying straw to the surface (1, 62). Photosynthetic activity of the algal biomass in the paddy field influences the balance of the ecosystem by increasing the O2 concentration and the pH of the flood water during the day.
The primary productivity of the f l d w a w community (including submerged weeds) was reported to be high and equal to that of eutrophic lakes, and corresponded to 10 and 15% of that of rice plants in fertilized and unfertilized plots (239). Implications of BGA photosynthetic activity for the aboveground microflora (0, increase) and N losses through volatilization (pH increase) are certainly of agronomic significance, but there is little information on this aspect.
NITROGEN FIXATION 1. Methodology of measurements
- Daily variations of algal NFA
Another difficulty is the slow dissolution and diffusion of acetylene and ethylene in flood waters. Curves of the second form result from a transient inhibitory effect of high light intensity in the middle of the day. The high temperature during the day can have an inhibitory effect, but in flooded fields the floodwater is a relatively good temperature buffer.
On unfertilized fields, the highest ARA appeared late in the growth cycle, in both the dry and wet seasons, when PGI activity in the flood water was highest (353). Most results regarding the relative contribution of photosynthetic nitrogen fixers have been obtained by comparing soil samples incubated in the dark and in the light. In situ ARA measurements performed at the International Rice Research Institute assessed the contribution of BGA and the rice root zone to nitrogen fixation in the submerged rice soils (the method failed to detect NFA occurring in most of the anaerobic soil).
Nitrogenase activity in the root zone of rice was at a nearly constant but low rate (353,355). From the results it appears that the relative contribution of BGA as a percentage of the total N fixed in the sand field varies greatly.
BLUE-GREEN ALGAE
I AND THE RICE PLANT
- GROWTH-PROMOTING EFFECTS OF BGA
- DETRIMENTAL EFFECTS OF ALGAE
- EPIPHYTISM
- OTHER EFFECTS
Nutrient release through microbial decomposition after algal death appears to be the primary means by which N is made available to crops (232). In the fourth and fifth years, the yields in the presence of algae were much higher than the yields in their absence, as well as those at the beginning of the experiment. Field experiments conducted with Tolypothrix tenuis for 4 consecutive years showed that only one third of the field algae decomposed in the first year.
Recently, Wilson et a1 (361) recovered from a rice crop 39% of the nitrogen from lSN labeled Aulosira spp. Subsequent algal decomposition during the growth of the crop can result in a slow release of nitrogen and a more efficient utilization of the crop. Another harmful action develops when the water dries up and the algae form a layer at the bottom of the field.
Field inoculation (6) and pre-soaking of rice seeds (108) reduced rice crop sulphide injury. This has been associated with oxygenation of the medium unfavorable for sulfate-reducing bacteria (6) and with a growth-promoting effect that improves seedling development, which increases sulfide resistance (108).
ALGALIZATION
METHODOLOGY
- Comparison between pot and field experiments
- Duration of the experiments
- Assessment of the effects of algalization
- Effect on grain yield 1. Global effect
Standard deviations are higher than the mean in pot experiments and lower than in field experiments, which also indicates a greater variability of the results in pot experiments (Table 16). The better growth of BGA in pot experiments than in the field is probably due to less climatic or mechanical disturbances than in the field (rain, wind, water movements), better control of the experimental conditions and better care than in the field. It can also be a mechanical effect of the wall of the pot, where algae often seem to grow preferentially and abundantly.
On a practical basis, grain yield is certainly the most important outcome for evaluating the effects of algalization. However, experiments conducted on this basis alone will not explain the mode of action of BGA in rice, nor will they allow for improvements in algalization technology. Unfortunately, most experiments were conducted on a "black box" basis where only grain yield was measured; There is very little information available on the qualitative and quantitative evolution of the Nz-fixing algal flora, the evolution of the phototrophic activity of nitrogen fixation and the nitrogen balance in a sandy polluted field.
In addition, basic information such as soil physico-chemical characteristics and climate data are generally not provided. Algalization, when effective, is said to increase plant size; its nitrogen content; and the number of rosettes, ears, panicles and filled grains per panicle (see Section 5.2.2).
0 India
Effects of algalization on rice other than grain yield
In pot experiments, nitrogen deficiency symptoms such as leaf color, poor tillering and poor seed development disappeared in treatments inoculated with Tolypothrix tenuis, although there was no other nitrogen source (62). In the absence of N fertilizer, the same algae increased yield and nitrogen content of the grain and the straw; but in the presence of ammonium sulphate it only gave a significant increase in yield, and not in nitrogen content. This result was considered as evidence of the effects of growth promoting substances on rice yield (292).
Soaking the rice seeds with BGA cultures or extracts improved germination and growth, extended the period of cultivation, promoted the growth of roots and increased the weight and protein content of the grain (see section 4.2). Several reports indicate an increase in the nitrogen content of inoculated soil in both pot and field experiments. These results are consistent with the reported cumulative effect of algal inoculation which was partly attributed to the accumulation of algal material and a build-up of the organic N content of the soil (see section 5.2.1.5).
However, in the state of Kerala, after four consecutive crops, algal inoculation had no significant effect on the level of organic matter and nitrogen content of the soil, but significantly reduced the content of reduced compounds. Laboratory experiments carried out in beakers (237) showed that algal growth initially caused an increase in soil pH, which later dropped to the original value in some of the soils.
SIGNIFICANCE OF ALGALIZATION AND STRAIN SELECTION
- Climatic factors
- Biotic factors
- Inoculum production and conservation
- Methods of inoculation
- Economics
In most reports on the effect of algalization and soil treatments on wheat yield, soil physicochemical properties (even pH) are not reported. Among the biotic factors capable of suppressing the growth of algal inoculum, grazing by zooplankton has been observed in the field, see also Sect. Knowing the relationships between soil properties and algal inoculum establishment is certainly a major gap.
Some of the reports placed more emphasis on the practical aspects (99,330) and others contained more complete reviews of research findings (1 3, 326). After the soil has settled in the tray, sprinkle the starter culture on the surface of the standing water. In hot summer months the growth of the algae in the hills will be rapid and in about 7 days they form a thick mat on the soil surface and sometimes float up.
The efficacy of various methods has been tested by Venkataraman (Table 23) who concluded that soil application and seed inoculation are preferable (326). Knowing the relationship between soil properties and algal inoculum establishment is certainly a major gap.
Blue-green algae of rice fields in Skadovsk district (Kerson region) [Russian, English summary].
ANALYTICAL
LISTING OF REFERENCES
Daily changes in algae NFA. Changes along the cultivation cycle Assessment of algal NFA during cultivation.
