Effects of Sowing Dates on Japonica Rice Yields in Northeast : Field Experiment and Climatic Understanding

Juqi Duan1, 3，Xin-Zhong Liang2, 3，Shengyang Sun4，Yan Wang4，Qingyu Jia5，Yufeng He3，Yaoming Liao1

1. National Climate Center, China Meteorological Administration, 100081, China 2. Climate, Environment and Sustainability Center, University of Information Science and Technology, Nanjing, 210044, China 3. University of Maryland, Earth System Science Interdisciplinary Center, College Park 20740, USA 4. Meteorological Bureau, Fujin 156100, China 5. Institute of Atmospheric Environment, China Meteorological Administration, 110016, China Abstract: Adjusting crop sowing dates to take full advantage of climatic resources in the growing season is an important strategy for agricultural adaptation to climate change. This study investigates the climate characteristics of different sowing dates for temperate paddy rice and their effects on annual yields. Field experiments with four sowing dates (April 18, April 28, May 8, and May 18) for Japonica rice were conducted in Northeast China, where the climatic factors during the growth period were recorded and the biomass accumulation, yield and its components were measured. We found that the second sowing date (April 28) led to the most stable and highest yield of rice. This resulted from the favorable climate characteristics during the growing season, including low daily average temperature in the early stage, high daily maximum temperature and suitable daily minimum temperature in the late stage, and generally high solar radiation. The average temperature between sowing and elongation and between heading and maturity as well as the solar radiation between heading and maturity and whole growth period mainly affect crop growth rate, grains per spike and biomass. Meanwhile the solar radiation from the sowing to elongation period and effective temperature accumulated（GDD10, accumulated growing degree days greater than 10℃）after flowering also significantly affect grain number per spike and weight of biomass. Adjusting sowing dates can reduce the GDD10 at the early stage, increase the GDD10 and grain filling time after flowering and receiving sufficient solar radiation during the whole growth period, all of which form the suitable climatic conditions favorable for rice growth in Northeast China.