the development of new varieties to replace the existing traditional ones, which up to now have been widely cultivated in Asia. Initially, these new varieties were known as 'High Yielding Varieties' (HYVs) due to their significantly higher grain harvest compared to the traditional varieties. Then as they evolved, they were named the modern varieties (MVs) as not only did they have a high yield, but also improved taste and greater resistance to disease and insects.
Various factors including good irrigation conditions and increased fertilization are necessary to realize the Green Revolution, but it would not exist at all without the development of these modem varieties. So, reconfirmation of the nature of these modem varieties, which deserve to be called revolutionary, may be needed. First of all, the changes in the modem varieties will be clarified after summarizing the general character of the ordinary varieties.
1. The Character of the Traditional Varieties (2)
The traditional varieties of rice which were previously wide-spread over Asia in the tropical regions were tall, but didn't grow very well and their leaves were often yellow due to malnourishment as there was insufficient nutrition (especially nitrogen) in the soil. The yield was quite low per hectare, compared to the average in the temperate zone of 5.6 tons (of hulls) in Japan, and even in Indonesia, the country with the highest yield, the average was only 1.8 tons, and there were some countries whose yield was less than one ton on average in the 1960's. However, three tons were the maximum in Asia, although the yields in the test area in the agricultural test fields was higher.
The understanding in those days was that the same yield as the temperate zone couldn't be expected because of high temperatures in the tropical zone, soil productivity was low as the soil had suffered strong weathering, and disease and insects thrive in these weather conditions. It was thought that Indica Varieties could not improve the yield even with increased use of fertilizers as it's ability to assimilate nitrogen was considered weak, and it apparently couldn't produce protein through assimilation of nitrogen rich fertilizer well. To use an analogy, the traditional varieties in the tropical zones were like rice that has
