Final answer:
The rise in population in Song China during the eleventh century was primarily due to innovative rice cultivation practices, leading to significant agricultural yields and demographic expansion.
Explanation:
The major increase in population in half of China during the Song era can be attributed to the use of strains of rice that ripened quickly enough to allow two harvests in a single year. This agricultural innovation significantly boosted food production, leading to a rise in population. As a result, Northern Song presided over 100 million people by 980, showcasing a substantial population growth.
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