Effect of accumulated temperature before overwintering on wheat seedling growth status in north winter wheat area of China.

To explore the impacts of global climate change on the suitable sowing date for winter wheat in north winter wheat area of China, we carried out a wheat sowing date experiment during growing seasons of 2019-2021 at the Beijing Experimental Base of the Institute of Crop Sciences, CAAS. Two winter wheat cultivars with different tillering powers were selected as experimental materials. Four different sowing dates were set: September 25th (J), October 5th (S0), October 15th (S1) and October 25th (S2), to examine the responses of population quality, individual characters, and stem and tiller physiology to the accumulated temperature difference before overwintering. The results showed that with the delay of sowing date, the accumulated temperature before winter and their difference between the adjacent sowing dates decreased gradually. The accumulative temperature at the sowing J and S0 both exceeded 550 ℃, which met the basic condition for the formation of strong wheat seedlings before winter. The average accumulated temperature at sowing S1 and S2 was 148.0 and 282.4 ℃ lower than that of S0, which was not conducive to the establishment of strong wheat seedlings before winter. The average accumulated temperature decreased by 204.0, 148.0 and 134.4 ℃, when the sowing date was delayed by 10 days under the four different sowing dates, respectively. The days from sowing to emergence were affected by the average daily temperature. The days from sowing to emergence gradually increased with the delay of sowing date when the daily average temperature was lower than 15 ℃, while the days from sowing to emergence were constant when the daily average temperature was higher than 15 ℃. The total stem number, leaf area index, dry matter weight, nitrogen accumulation and tiller number per plant of wheat also decreased with the decreases of pre-winter accumulated temperature. The soluble sugar content and nitrate reductase activity at the seedling increased first and then decreased with the decreases of accumulated temperature before winter, while the soluble protein content and glutamine synthetase activity to accumulated temperature performed differently among varieties. According to the population quality and individual traits of wheat before winter, among the four different sowing dates, the total stem number and tiller number per plant of wheat before sowing on October 5 were the closest to the standard of strong seedlings before winter in north winter wheat area. The accumulated temperature before winter is conducive to the formation of strong seedlings. When the daily average temperature is 15-17 ℃, it is the best sowing time for winter wheat in Beijing.

[Effects of tillage mode and nitrogen application rate on nitrogen use efficiency of wheat in a farming-pasture zone of North China].

A field experiment was conducted in a farming-pasture zone in Chifeng City of Inner Mongolia Autonomous Region, North China to investigate the effects of different tillage modes and nitrogen (N) application rates on the grain yield and nitrogen use efficiency (NUE) of winter wheat. The results showed that long term conservation tillage increased the wheat NUE by 3% -4%, and decreased the environmental pollution by fertilizer N. Conservation tillage promoted the N absorption by wheat, and increased the grain yield. When the N application rate increased from 120 kg hm-2 to 360 kg . hm-2, the NUE decreased from 36. 5% to 26% , fertilizer N loss increased by about 5% , i. e. , the corresponding N loss was increased from 60 kg hm-2 to 200 kg hm-2, and the environmental N pollution increased markedly. The wheat NUE of the residual N in last season was less affected by tillage mode, but more affected by the N application rate in last season, with an overall tendency of the higher the N application rate in last season, the lower the NUE and the more the fertilizer N loss. After two seasons' wheat planting, the proportion of the total nitrogen recovery by the wheat-soil system was about 44% -50%, among which, the residual N in soil occupied about 13% -18% of applied N.