Phka Rumduol cultivar is one of the main rice cultivars in Battambang province of Cambodia. Lower rates of seedling establishment are observed when Phka Rumduol is directly sown in paddy fields under flooded conditions. In our previous report, lack of dissolved oxygen (DO) in flood water was considered to be the main cause of the low seedling establishment. In the present report, the relation between the DO quantity and establishment of seedlings was verified. When the number of seeds sown in the water in pots increased, the DO quantity in the water decreased and resulted in the lack of seedling establishment. When the pots were supplied with air, seedling establishment was improved, and hence the relationship between dissolved oxygen quantity and growth of Phka Rumduol cultivar was verified. The coleoptile grew in any quantity of DO, while the foliage leaf and roots did not grow with less than 2 mgl
-1 of DO. The Phka Rumduol cultivar required more than 3 mgl
-1 of DO for normal growth. Decrease in DO levels in paddy soil may be caused by microorganisms. When seeds treated with Kosaide and Kasmin Bordeaux mixture were sown into paddy soil under flooded conditions, the rates of seedling establishment for both treatments increased. Addition of Bordeaux mixture to the paddy soil inhibited the decrease of DO and Eh, suggesting that the Bordeaux mixture controlled the activity of microorganisms in the paddy soil. Hence improved seedling establishment can be expected when rice seedlings are treated with the Bordeaux mixture.
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