Rice yield varies among different types and fields. To understand why, researchers studied 23 rice varieties in 236 fields in Zhejiang Province. They found that the number of grains per panicle and panicles per plant had the biggest impact on yield differences. Varieties with more grains per panicle tended to have higher yields. They also discovered that the best planting density for high yields varied depending on the rice type. For single-season indica hybrid rice, the best density was between 1.00-1.20×104 per 667m2, while for late-season indica hybrid rice, it was between 1.10-1.40×104 per 667m2. Increasing planting density initially boosted yield, but too high a density led to lower yields.