Reddy, P.M.

Roger, Pierre-Armand

Ventura, W.

Watanabe, I.

Horizon / Pleins textes

PHiL. AGRI. 69: 629-632 
SPECIAL BGA ISSUE 
:198fiJ 
JSSN 0031-7454 
BLUE-GREEN ALGAL TREATMENT AND INOCULATION HAD NO 
’SIGNIFICANT EFFECT ON RICE YIELD IN AN 
ACIDIC WETLAND SOIL 
P.M. REDDY, P.A. ROGER*, W. VENTURA, and I. WATANABE 
The International Rice Research Institute Los Bahos, Laguna, Philippines 
Key words: Blue-green algae; inoculation; rice fields; acidic soil 
A field experiment on an acidic soil poor in availahle phosphorus 
showed .that a pretreatment of rice seedlings with a blue-green algal 
culture and/or inoculation of the field with a composite iaaculum of 
N,-fixing blue-green algae had no significant effect on rice yield. 
INTRODUCTION 
Over the past three decades, there have been reports on the use of blue- 
green algae (BGA) inoculants (algalization) to enhance biological N, fixation 
(BNF) and grain yield in wetland rice fields. The reports conflict in both the 
success of inoculation and the inoculation’s effect on rice yield (Roger and 
Kulasooriya, 198 O). 
When successful, algalization increased yield by an average 14% (field 
experiments). The increase was attributed to N, fixation and the production 
of growth-promoting substances by BGA. This so-called “auxinic effect’’ was 
studied mostly in uitro- or in pot experiments, hardly representative of field 
conditions (Roger and Kulasooriya, 1980). 
Possible reasons for algalization failure include soil properties, climatic 
factors, biotic factors, and the quality of the inoculum. Studies of the 
relationship hetween the physicochemical propertie’s of the soil and response 
to algalization indicate that low pH limits BGA growth (Okuda and Yama- 
guchi, 1952; Subrahmanian et al., 1965). A negative correlation between pH 
and the abundance of soil BGA was also reported in several ecologic@ studies 
of rice soils (see Roger et al., this issue). 
This note reports a field experiment conducted to study tlw effect of 
algal inoculation in an acidic soil and to test if the pretreatment of rice seed- 
lings with BGA culture could increase rice yield in such a soil. 
./ 
MATERIALS AND METHODS 
. Experimental Design 
-The experiment was conducted in an acidic soil poor in available 
The indigenous algal population in the upper one centimeter of the so& 
evaluated by plating on B G l l  agarized medium, was 1.3 x lo5 colony 
forming units (CFU)/cm2, among which 17% (1.5 x lo4 CFU/cm2) were 
- ‘-phosphorus, located in Luisiana (Laguna Province, Philippines) (Table 1). . 
630 THE PHILIPPINE AGRICULTURIST VOL. 69 
Table 1. Chemical and algological characteristics of Luisiana soil. 
Chemical properties Algal flora (O-lcm soil layer) 
pH (water) 
Organic C (%) 
Total N (%) 
CEC (meq/lOOg) 
Na 7 7  
K Y >  
Mg 7 )  ’ 
Ca 7 7  . ’ 
Avail. p (ppm) 
5.7 Total (CFU/cm2) 1.3 105 
1.42 BGA (CFU/cm2) 2.2 104 
0.156 
27.70 Nostoc spp. 94% 
2.47 Calothrix spp. 5% 
0.75 Others - 1% 
6.36 
11.60 
5.8 
N2-fiiing BGA (CFU/cm2) 1.6 x lo4 
N,-fixing BGA, mostly Nostoc spp. The methods of analysis are described 
elsewhere (Roger et al. 1986). 
The field experiment layodt was a randomized design with six replica- 
ted plots (4 x 5 m) per treatment. Treatments were 1) control, 2) presoaking 
rice seedlings4h a BGA culture, and 3) presoaking rice seedlings in a BGA 
culture and field inoculation with$GA. 
Pretreatment of the Seedlings 
Seeds of IR58 were soaked in a dense culture of Nostoc sp. (about 1.5 
g dw/litre) for 48 h and spread on a seedbed sat IRR1 for germination. Nostoc 
culture used for soaking was evenly spread on the surface of the seedbed. 
Seeds soaked in water and grown on a seedbed where no BGA culture was 
applied served as control. After 1 4  days, BGA-treated seedlings and control 
seedlings were dipped in 1% zinc oxide solution for half an hour to prevent 
zinc deficiency. Seedlings were then transplanted in the field at  20 x 20 cm 
spächg on August 14,1984. 
BGA Inoculum 
Inoculation at one week after transplanting, used simultaneously 
composite fresh and dry inocula to increase the chances of establishment of 
inoculated strains. 
The fresh inoculum was a mixture of Nostoc sp. (Strain SL of IRRI’s 
collection), Anabaena variabilis, Aulosira fertilissima, and Tolypothrix 
tenuis. The inoculum, obtained by decantation of liquid cultures in BG El 
medium without mineral nitrogen, contained about 4 g dw algal material per 
liter. It was applied at 250 ml/plot, equivaleni to 500 g dw/ha. 
at 20 kg/ha, was a mixture of 24 mono- 
strain soil-based inocula produced on Maahas soil according to the method 
described by Venkataraman (1981). Nostoc wzs the dominant gems in the 
mixture. 
The dry inoculum, applied 
Density of colony-forming units (CFU) in the dry inoculum was 2 x 
106/g. Assum~g an average density of 1.7 x 10’ CFU/g dw in dried, pow- 
dered cultures of BGA (unpublished data), ihe applied inocula (fresh + dry) 
were equivalent together to 1.25 x 103 CFU/cm2. The number of CFU of 
SPECIAL ISSUE ALGAL INOCULATION IN AN ACIDIC SOIL 631 
BGA applied per hectare was therefore about 10 times less than the number 
of CFU already present in the soil. However, the quantity of inoculum 
applied (fresh + dry) was equivalent, on a CFU basis, to 70 kg of soil-based 
inoculum /ha, or seven times the recommended dose (Venkataraman, 1981). 
Agronomic Practices 
Plots were kept flooded (2-7 cm water depth) throughout the experi- 
mental period. Phosphorus and potassium were applied at 30 kg/ha. No 
nitrogen fertilizer was applied. Plots were hand weeded at 28 and 45. days 
after transplanting (DT). Insecticide carbofuran (Furadan G) was applied 
at 1.0 kg ai/ha after transplanting and at 1 4  and 35 DT. Insecticide mono- 
crotophos was sprayed at 0.4 kg ai/ha at flowering. No herbicide was 
applied. A t  maturity (November 16), yield was estimated by harvesting 
plants at ground level from two 6-m2 areas in each plot. 
RESULTS AND DISCUSSION 
The seedbeds showed no earlier germination of treated seeds nor 
difference in size or color of the seedlings. RGA material applied on the 
treated seedbed periisted for a few days but did not develop into a bloom. 
In the field, large freshwater snails (Ampullaria sp.), predators of algae, 
were present in all the plots before transplanting. Furadan application 
reduced their number. During the crop cycle, a few csbnies of mucilaginous 
BGA, mostly of the unicellular type, were obseived, but no algal bloom 
developed in the inoculated or control plots. The density of BGA colonies at 
the beginning of the cultivation cycle was not higher in the inoculated plots. 
Yield measurements (Table 2) were in agreement with the visual 
observations, showing no statistically significant differences between treat- 
ments. 
Table 2. Straw and grain yielda. 
Control 1916 k 315 208 & 68 4142 2 587 6267 f 830 17.2 k 2.4 
Seedling 2016 f 213 197 k 84 4304 k 409 6517 -I- 571 17.8 f 1.6 
treated 
Seedling 1973 & 277 197 f 50 4336 k 349 6506 & 552 18.0 ? 1.48 
treated and 
soil inoculated 
F value (4.20 ns 0.05 ns 0.30 ns 0.27 ns 0.32 ns 
cv % 14 34 11 10 11 
~~ 
value is the average of six replications. Values are followed by the 5% confidence 
interval of the mean. 
, 
632 THE PHILIPPINE AGRICULTURIST VOL. 69 
Our results confirm the earlier observation Gy Okuda and Yamaguchi 
(1952) and Subrahmanian et al. (1965) that algal inoculation might be 
ineffective in acidic soils. Despite a very high level of inoculation (seven 
times the recommended dose) and the utilization of a composite inoculum 
containing fresh and dry material, no BGA bloom was established. The 
presence of a fairly high level of propagules of indigenous N,-fixing BGA in 
the field confirms that the absence of blooms in the field is due to un- 
favorable environmental conditions rather than the absence of BGA. 
Pretreatment of rice seedlings with a BGA culture was reported to 
enhance rice growth in in vitro and pot experiments (see Roger and Kulasoo- 
riya, 1980) but did not significantly increase yield in the field. 
ACKNOWLEDGMENTS 
- This research was conducted under a scientific agre,ement between IRR1 
and ORSTOM (France) and was supported by the United Nations Develop- 
ment Programme. 
References Cited 
OKUDA A, YAMAGUCI-II M. 1952. Algae and atmospheric nitrogen fixation in paddy 
soils: II relation between the growth of blue-green algae and physical or chemical 
properties of soil and effect of soil treatments and inoculation on the nitrogen 
fixation. Mem Res Inst Food Sci 4: 1-11. 
ROGER PA, KULASOORIYA SA. 1980. Blue-green algae and rice. The International 
ROGER PA, SANTIAGO-ARDALES S. WATANABE I. 1986. Nitrogen-fiuing blue-green 
! 
Rice Research Institute, PO Box 933, Manila, Philippines, 112 p. 
algae in rice soils of northern Luzon (Philippines). Phil Agric this issue. 
SUBRAHMANIAN R, MANNA GB, PATNAIK S. 1965. Preliminary observations on the 
interaction of different soil types to  inoculation of blue-green algae in relation to 
rice culture. Proc Indian Acad Sci Sec B 62 (4) 171-175. 
VENKATARAMAN GS. 1981. Blue-green algae for rice production. A manual for its 
promotion. FAO Soil Bull. no 46. 102p. 


Blue-green algal treatment and inoculation had no significant effect on rice yield in an acidic wetland soil

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