Problems to be solved

Seedling establishment in DIPPS

Seedling establishment is sometimes poor

Although calcium peroxide which promotes seedling establishment is coated to seeds, poor seedling establishment is sometimes observed. This is one of the most important problems to be solved in DIIPS.
Other problems are;

further enhancement of lodging resistance
further enhancement of yield (5-10% lower than transplanting method)

We are carrying out research on the problems in relation to seedling establishment in DIPPS.

Why seedling establishment becomes poor?

Step 1: How CaO2 promotes seedling emergence?

We developed a new research method named "Methylene blue soil method" to investigate soil conditions around germinating seed. As methylene blue changes its color according to redox potential (blue when oxidized and colorless when reduced), redox potential of soil around germinating seed is easily and visually investigated by the color reaction of methylene blue added to soil.

Comparison of redox potential around CaO2-coated and non-coated seeds
by using Methylene blue soil method

Soil around a seed is reduced from the beginning. Black parts (iron sulfate) around a seed appears within a few days after seeding.

Seeds not coated with CaO2 germinating
in submerged soil.

Soil around a seed is oxidized (blue) by the oxygen generated from CaO2. Soil around a seed is kept oxidized for about a few days after seeding. Then (around a time of germination), reduced parts appears around a seed, and the reduced area enlarges as days after seeding increases.

Seeds coated with CaO2 germinating in
submerged soil.

These observation revealed that

poor seedling emergence in non-coated seed is attributed to soil reduction around a seed from just after seeding,
and that

improved seedling emergence in coated seed is attributed to soil oxidation around a seed until germination.

Step 2: Relation between soil reduction and seedling emergence percentage

1. Degree of soil reduction around a seed was evaluated by reduction index as shown below.
2. Reduction index and seedling emergence percentage was investigated.
3. Seedling emergence percentage decreased with increasing reduction index.

However, the seedling emergence percentage was kept high when reduction index was maintained within a certain value.

Calcium peroxide promotes seedling emergence by oxidizing soil around a seed, but the soil oxidizing effect is not long or strong enough to secure high and stable seedling emergence percentage.

Possible approaches to much improved seedling emergence in DIPPS

would be;

Reinforcement of soil oxidizing effect of CaO2
and

Screening and breeding of new varieties resistant to soil reduction

But, what is making the problem difficult is that germination and soil reduction around a seed are linked. Germination promotes local soil reduction around a seed. Intensive research into the interaction among a seed, soil and soil microbes occurring in spermosphere is still a challenge.

For more detailed and related information, please refer to;

Hagiwara, M., M. Imura and S. Mitsuishi, 1987. Oxidation-reduction State of Soil in the icinity of the Paddy Rice Seed Sown into Flooded Siol., Jpn. J. Crop Sci.56: 356-362. (in Japanese with English summary)
Hagiwara, M., M. Imura and S. Mitsuishi, 1990. Local Soil Reduction in the Vicinity the Paddy Rice Seed Coated with Oxygen Generating Chemicals in Relation to Germination and Emergence., Jpn. J. Crop Sci.59: 56-62. (in Japanese with English summary)
Hagiwara, M. and M. Imura, 1991. Promotion of Seedling Emergence of Paddy Rice from Flooded Soil by Coating Seed with Potassium Nitrate., Jpn. J. Crop Sci.60: 441-446.
Hagiwara, M. and M. Imura, 1993. Varietal Difference and Temperature Response of Local Soil-Reduction around Germinating Rice Seed., Jpn. J. Crop Sci.62: 105-110.
Hagiwara, M. and M. Imura, 1993. Local Soil Environment around Seed Influencing Seedling Emergence in Direct Seeding of Rice. In Crop Production and Improvement Technology in Asia, Proceedings of the First Asian Crop Science Conference, September 24-28, 1992, Seoul, Korea.: 123-131.
Hagiwara, M. and M. Imura, 1993. Seedling Emergence and Establishment of Direct-sown Paddy Rice in Soils Incorporated with Substances Produced in Reductive Paddy Soil., Jpn. J. Crop Sci.62: 609-613.
Hagiwara, M. and M. Imura, 1996, Interaction between Germinating Rice Seed and Soil Influences Seedling Emergence in Direct Seeding into Flooded Soil., In Crop Research in Asia: Achievements and Perspective, Proceedings of the 2nd Asian Crop Science Conference: 224-227.

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