| The rice area in our country belongs to the monsoon weather, so the low temperature was unavoidable during seed production of Two-Line Hybrid rice. Then, the data of day by day and hour by hour in August from 1971 to 2001 in China southern rice area of 35 cities, the biologic data of Pei'ai64S measured during fertility sensitive period, the data of temperature, humidity, radiation and wind speed etc, measured by agrometeorology and ecology monitoring system and infrared thermometer, and the multi-model for water and heat transfer in irrigated rice field, were analyzed. At last, the techniques by irrigation for defending against damaging by low temperature were proved up.(1)Analyze the weather data in southern rice area, it was showed that the low temperature risk of summer lay in the Changjiang river valley and the Huaihe river valley rice area, the average strength was 22~23℃, the duration was about 3~5 days. Therefore, the target of irrigation depending against low temperature was definitely as 2℃. The air temperature at 11:00-18:00 was ≥24℃, when the irrigation could be stopped; while the air temperature at 00:00-06:00 was ≥22℃, when the irrigation quantity should be increased.(2)During Pei'ai64S fertility sensitive period, the average plant height was 78.5cm, the active layer of canopy was at 45cm, the average spike length was 4.19cm, and the spike peak was 11.0cm from ground. During the latter fertility sensitive period, the average spike peak was 15.23cm from ground, and the tallest spike was 20.3cm highly.(3)By analyzing the measured data, the irrigated and checked fields, because of different hot source and remit, led to different meteorological environments. The valid incalescence height of the irrigation was 40cm, the effect of incalescence at 20cm obviously amounted to 2.3 ℃, which completely satisfied the target of defending against low temperature.(4)The data showed that TinS and Tq150 were the key factors of air and temperature. RH20 was positive correlated with TJ20 and Tq20. The advection of V200 could reduce TJ20 and Tq20. And the stepwise regression by Tq150, TinS and V200 was fitting well.(5)The calculated results from multi-layer model in irrigated paddy field showed: the trends were that along with the irrigation depth, the water temperature at infall and at export and the surrounding temperature went up, air temperature at 20cm gradually went up. But the extent of incalescence was comprehensively affected by the factors above, which interact each other.(6)Based on the analysis above, the irrigation depth was better for 15-20cm, the watertemperature at infalls was not less than 26.0℃, the water temperature at exports was not lower than 24.5℃ etc. The results of self-fertility rate and pollens fertility rate approved that the irrigation could lower self-setting percentage, and TQ20 and TJ20 availably indicated the regulation of fertility transfer better than screen temperature.
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