[Passive nighttime warming (PNW) system, its design and warming effect].

Based on the technique of passive nighttime warming (PNW), a convenient and energy-saving PNW facility was designed for a rice-wheat cropping system in Danyang, Jiangsu Province. The facility could guarantee 15.75 m2 effective sampling area, with a homogeneous amplitude of increased temperature, and making the nighttime canopy temperature during whole rice growth season increased averagely by 1.1 degrees C and the nighttime canopy temperature and 5 cm soil temperature during whole winter wheat growth period increased averagely by 1.3 degrees C and 0.8 degrees C, respectively. During the operation period of the facility, the variation trends of the canopy temperature and 5 cm soil temperature during the whole growth periods of rice and winter wheat in the warming plots were similar to those of the control. Though the facility slightly decreased the soil moisture content during winter wheat growth period, wheat growth was less impacted. The application of this facility in our main production areas of rice and winter wheat showed that the facility could advance the initial blossoming stages of rice and winter wheat averagely by 3 d and 5 d, respectively. In despite of the discrepancy in the warming effect among different regions and seasons, this energy-saving facility was reliable for the field research on crop responses to climate warming, when the homogeneity of increased temperature, the effective area, and the effects on crop growth period were taken into comprehensive consideration.